Audio September 1953
for the
FINEST
in recorded
sound
IIAOt _ _
America's leading phonograph record manufacturers use
Gudiotap-e for the original sound
and a.uclicrcliscSjor the master recording
o ONE listens to recorded sound with a more critical ear
than the professional recordists who make America's finest
phonograph records. Here there can be no compromise with
quality.
That's why it's significant that so many of them repeatedly
specify Audiotape and Audiodiscs to meet their most exacting
requirements. For example, it was found that 29 of the 30
best selling records of 1952 were made from Audiodisc
masters. And over 43 % were first recorded on Audiotape
before being transferred to the master discs.
Remember - you get this same superlative sound by using
Audiotape and Audiodiscs in your recording work.
N
@) Th e txclUJiut trade.mark 0/ Columbia Lont PJayiliX Records - Re,. U.S . Pal. og.
*
Trade Mark. AltdiodisC8 are manufactured in the U.S.A.
under exclu8i've license from PYRAL. S.A.R.L., Pari.
AUDIO DEYICES, Inc.
444 MADISON AVE ., NEW YORK 22, N. Y.
Export Dept.: 13 Ea.t 40th St., New York 16, N. Y.
Cables "ARLAS"
Successor to
!RADIOI -Established 1917
INCLUDINCi
IVilIo\
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C. G. McProud, Editor and Publisher
Henry A. Schober, Business Manager
Harrie K. Richardson, Associate Editor
Edgar M. Villchur, Contributing Editor
Robin Melton, Production Manager
S. L. Cahn , Advertising Director
.
H. N. Reizes, Advertising Manager
Edgar E. Newman, Circulation Director
Representatives
H. Thorpe Covington. Special Representative
7530 North Sheridan Road. Chicago 26. III.
Sanford R. Cowan, Mid-West Representative
67 W. 44th St., New York 18, N. Y.
Editorial Advisory Board
.Howard A. Chinn
John D. , Colvin
West Coast
Jame, C. Galloway
J. W. Harbison
/. p. Maxfield
816 W. 5th St., Los Angeles 17, Calif.
CONTENTS
SEPTEMBER, 1953 '
Vol. 37, No. 9
Audio Patents-Rl:chard H. Do?·f .... .. ..... . ... .. ... : . .. . . .... ... .... .
Letters ....... . ..... ... ... . . .. . . . ........ . ................ . ... . .. .. .
Coming Events ..... . ..... ...... . . ... ...... . ..... .... .. .. .. .. .... . .... .
Book Review . ...... ......... . . ... ...... .......... ... ... .. .. .. .. . .>
:.
Audiology-W. R. Ayres ..... ..... .. ...... . ... . .... ... ........ . . . .. .
Editor's Report ........... .. ................ . . . . ........ .. ........ . .
Organ for One-Finger Artists-Richard H. Dorf ........ .. . ... . . . ... ... .
Horn EnClosure for Custom I11stallations-A. f. Gassan .... ... .......... .
The Dictating Machine-Part II-R. M. Somers
Flexible Tone-Control Circuit-Basil T. Barber
A New Volume Vi sualizer-Norman Prisament .......... . ...... . ..... .
The Case for Mus ic-fohn H. Thompson ............................ ..
D.C. Pack for H eaters and Bias-Alla1v M. Penes . ......... . . . . :' . ... . . .
Twin-Triple Resistance Decader and Bridge-L. B. Keim . . ... .. . . .. .. .. .
Handbook of Sound Reproduction-Chap. 12, Part III-Edgar M. Villchu,r
Industry Vievirs The Aud io Fair-Har-rie K. Richardson. . . . . . . . . . . . . . . ..
Equipment R ep9rt-Bogen R714 T1-mer, Lorenz Speaker System . .. .. .....
Im!'Jrovements on the 'Universal Tape Recorder Amplifier-C. G. McPro1{,d
Record Revue-Edward Tatnabl Canby . .. ...... . .. . .. ..... .... _ . . . . . . ..
New Products .. .... ...... . . .. . ....... . ............ .. .......... ... ..
New Literature ......................................... , .......... .
Employment Register ....................... .... ... . ..... . . ........ .. .
Radio's Master Reports . .... . ....... . .... . . . .. ... ~ ................. . .
Industry Notes and People ..... . .. ......... . ....... .... . . ....... . . .. .
Advertising Index ....................... . ... .. .. .......... . ........ .
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29
30
tcrTRIAD
Designed by Triad to meet
ng
military requirements
airborne
telemetering equipm
tinyelectric wave filter shown
actually
contains eleven pr
components: 2 toroidal ind
rs, 5 JAN-C-5
capacitors, and
recision wirewound resistors.
resulting attenuation
50 decibels per
octave.
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40
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46
52
57
73
82
83
84
COVER
Since phonograph records provide such a large part of the source material for
home music systems, this cover is in the nature of a tribute to a new device
which offers a means for determining the condition of the all-important
stylus tip-a means which does not involve expensive laboratory
equipment (doubtful in effectiveness anyhow except in the
hands of an expert ) but which may be used at any time
with a minimum of trouble and which will give reliable results to even the novice in the hi-fi art.
RADIO MAGAZINES, INC., P. O. BOX 629, MINEOLA, N. Y.
AUDIO ENGINEERING (title registered U. S. Pat. Ol!.) Is published monthly at 10 McGovern Avenue, Lancaster, Pa, by
Jladlo Magazines, Inc., Henry A. Schober, President: C. G. McProud, Secretary. Executive and Editorial Omces:
204 Front St., Mlneola, N. Y. Subscription rates-United States, U. B. PossessioDJ and Canada, $3. 00 for 1 year,
$5.00 for 2 years; elsewhere $4.00 per year. Single copies 35c. Printed in U. S. A. All rights reserved. Entire contents
.copyright 1953 hy Radio Magazines, Inc. Entered as Second Class Matter February 9, 1950, at the Post omc., Lancaster, P,,- under the Act of March 3. 1879.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
For specifications and prices on
Triad's general line of transformers,
write for Catalog TR-53F.
,
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Engineering
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EN GINEERS, E. E. or PHY SICS
GRADUATES, f or pre parati on
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HUGHES RESEARCH AND
DEVELOPMENT LABORATORIES'
expanding pt'ogr arn fot· production of radar, electt'onic
digital cornpu ters, gu.ided
rnissi les and other rnilitat·y
advanced electt'onic syste11ts
and devices t'equires the
following:
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to prepare
operating, servicing and overhauling instructions for complex
electronic equipment, Those
with previous maintenance
experience on military equip- ,
ment preferred. Writers will
participate in a three-month
program in our technical
, training school to become
familiar with the latest Hughes
equipment prior to writing
assignments.
PHYSI CS GRADUATE S
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ENGINEERS EXPE RIENCED
maintenance manuals for
electronic equipment or guided
missiles. These specialists will
work step-by-step with the
people designing, developing
and manufacturing the products
involved. Experience in the
writing of engineering reports
is of value.
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of you r qualifications to
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of te chni cal manuals .. .
: D ELECTR ICAL ENGINEERING AND
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Research and Developrnent
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LalJoratories
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points on which magnetic recording loses the argument to
disc recording is the matter of cost.
Using ordinary tape methods, the cost of
tape for a recording of given length is much
higher than the cost of a record blank for
the same program content. This does not
matter particularly when the taped material
is kept only temporarily, but when one is
building a library or retaining tape for r ecord purposes, the cost is high. For that
very r eason the writer keeps high-quality
. disc recording equipment in addition to a
magnetic recorder ; once taped, the music
is divided up appropriately and put on LP
discs, after which the expensive tape is
free for the next session.
Inventor Robert H . Dicke of Princeton,
N. J., has come up with Patent No. 2,641,656; which covers a method of cutting down
tape speed drastically and still retaining
the wide frequency capabilities of conventional speeds. According to the specification,
one typical embodiment of the invention
will allow a tape speed of only 1 ips to
r ecord frequencies up to 9000 cps, for which
.conventional techniques require at least the
standard 7.5 ips. While the system has certain apparent disadvantages such as a
lower signal-to-noise ratio, the complications it adds do not seem great and the
principle is most interesting.
The system is basically a method of converting all aud~o. frequencies to lower frequencies by beatmg and then r econvertmg
them in playback to their original values.
The low beat fr equencies can be recorded on
the slow-moving tape. Unlike some other
schemes, however, the action of this one is
mechanical. It is both simpler and less susceptible to error than other similar ideas.
Figure 1 shows the assembly that does
the job, consisting of a magnetic recording
head of very special design including the
rotating modulator. The U-shaped section
of the head is more or less standard, made
up of core laminations with a coil wound
around the closed end. The pole pieces are
O
N E OF THE FEW
*255
W . 84th St., New York 24, N. Y.
separated from the U -core by nonmagnetic
spacers which create auxiliary air' gaps.
The pole pieces themselves are made of
laminations, each separated from the rest by
a nonmagnetic spacer. Thus when the tape
passes over the portion of the pole pieces
shown, a number of. separate tracks are r ecorded on the tape equal to the number of
pole-piece lami nations, which is nine. The
gap over which the tape passes is very
small, as is customary.
The lower gap between the pole pieces is
comparatively large. A special modulator
cylinder is mounted as shown in Fig. 1.
Fig~tre 2 shows how the modulator is
built. It consists of three groups of toothed
wheels, each gr oup containing three identical wheels. The first three wheels have
four teeth each, the second three have eight,
and the last group 16. All are on a ,co'11mon
shaft, and each wheel is separated from its
neighbors by a lamination of nonmagnetic
substance. The separations between wheels
are so arranged that when the mo<j.ulator is
in position as shown in Fig. 1 each wheel
coincides with a pair of pole-piece laminations. When a tooth of any wheel is in the
correct position, it completes the magnetic
circuit through the lower pole-piece gap
between a pole-piece lamination on the left
and one on the right.
Notice in Fig; 2 that the wheels in each
group are so oriented that each wheel is
displaced one-third of a tooth spacing-120
deg.-from the next one.
The two gaps in the pole pieces-one over
which the tape passes and the other occupied
by the modulator- are in paralle1. For a
given tape track (defined, you will recall, by
one set of pole-piece laminations) the tape
will be magnetized most strongly when the
bottom gap' of that set of laminations is not
completed by a wheel tooth; it is magnetized least when the lower gap is filled with
a wheel tooth, since the lowered reluctance
of the lower gap bypasses more of the available field strength. The nonmagnetic laminations separating the pole pieces from the
U-core emphasize this effect.
Now assume that the system is turped
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SCIENTIFIC AN D E N GINEERING S T AFF
Culver Ci ty . Los Angeles County
California
Assu rance is requi re d that relocati on
of th e ap pli cant wil l not cause dis rupt ion
of an urge nt mili tary proj ec t.
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Fig. 2.
Fig. 1.
AUDIO ENGINEERING
/
•
SEPTEMBER, 1953
FAN
World's finest record chang·
ers and record players. See
the new Model RC90, the
greatest Garrard changer ever
built, and the 301 transcrip'
tion turntables, plus other
new models.
"Point One" amplifiers. See
the new "Varislope" pre·
amplifier .• . the only pre·
amp with this feature.
Cloth · suspended loudspeakers. Single speakers with the
range and brilliance of multispeaker combinations.
Maximum bass • • . minimum
space! Finest performance
from any loudspeaker.
-- ------ ------ -- ---------IF YOU CANNOT COME TO EITHER AUDIO FAIR . • . Send in the
coupon for FREE literature especially prepared for these events. Our
24-page booklet, "Sound Craftsmanship" will bring the British Industr-ies
exhibits to you! Limited edition . • • write today.
Please send my FREE copy of "Sound Craftsmanship."
Name ................................................................................................... .
Address .........................._.................................................................. ..
8RITISH INDUSTRIES CORP. 164 DUANE STREET. NEW YORK 13. N. Y.
City........................................_...... _.~ .............State...... ,............~;~.:~ ..
Above, Fig. 3; below, Fig. 4.
Meet the Redheads •••
tops for tape recording
See how the latest additions to the Brush family of magnetic
recording components can improve your tape recorders!
The BK-I090 record-reproduce head has the standard track
width designed for dual track recording on l4 inch tape. It provides unusually high resolution and uniformity over an extended
frequency range. Cast resin construction assures dimensional
stability, minimizes moisture absorption, and affords freedom from
micro phonics. Its balanced magnetic construction, precision
lapped gap, Mu-metal housing, and single-hole mounting provide
importallt design advantages.
The BK-1110 erase head has the same basic construction as the
companion record-reproduce unit. Its outstanding feature is its
efficient erasing at low power consumption-less than Y, voltampere.
Investigate these new "Redheads" for your magnetic recording.
Your inquiries will receive the attention of capable engineers. Write
Brush Electronics Company, Department 22-9, 3465 Perkins A venue,
Cleveland 14, Ohio.
BRUSH ELECTRONICS
INDUSTRIA~ AND RESEARCH" INSTRUMENTS
PIEIO·ELECTRIC MATERIALS
ACOUSTIC DEVICES
MAGNETIC RECORDING EQUIPMENT
ULTRASONIC EQUIPMENT
4
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COMPANY
formerl,
The Brush Development Co.
Brush Elutrollics Compnn'1
is an operating uTlit of
Clevite Corporation.
on and a constant (d.c.) current applied to
the head coil. On anyone tape track the
magnetism left on the tape will vary from
maximum to mirnmum every time a tooth
of the cor responding rotating modulator
wheel passes through the lower gap. If we
assume that the modulator is so geared to
the capstan motor that it rotates at a speed
of 9000 r.p.m. or ISO r.p.s., magnetism of
the three tracks coinciding with the fourtoothed wheels will vary 600 times per second, of those opposite the 8-toothed wh~els
1200 times per second, and of those agamst
the 16-toothed wheels 2400 times each second.
The wheel teeth are so shaped that the
variations are of sine form. Thus we have
nine tracks, each now containing tones; the
first three of 600, the second three of 1200,
and the third three of 2400 cps. However,
if the tape is now played back, either with
an ordinary head or with this head minus
the modulator the total output will be zero
at each frequ~ncy. The reason is that the
outputs of all tracks combine. And because
of the 120-deg. displacement of the wheels
in each group the three recorded tones for
each frequency are of identical level and
120 deg. apa rt in phase. They cancel exactly, leaving nothing in the output.
Let us suppose, however, that instead of
d.c. in the coil we have a tone of 1500 cps.
This tone is modulated by the 600-cps
wheels to produce 900- and 2100-cps beats,
by the 1200-cps wheels to produce 300 and
2700-cps beats, and by the 2400-cps whee!s
to produce 900 and 3900-cps beat~. It ~s
these beats which are recorded on the vanous tracks. Specifically the differen~e ra~h~r
than the sum beats are recorded, smce It IS
assumed 1200 cps is the top frequency
limit of the tape because of its slow speed.
N ow suppose we play back the tape, with
the modul ator still running. The 900-cps
recorded tone will combine with the 600cps-wheel modulating frequency to prod~ce
either 300 or 1500 cps; the 300-cps tone With
the 1200-cps wheel will produce 900 or 1500
cps; and the 900-cps tone with the 2400-cps
wheel will produce 3300 or 1500 cP.s. In
each case the original 15OO-cps tone IS reproduced. I n addition, a second tone would
be produced for each modulator frequency
-if th.ere were only one wh.eel for each ~re­
quency. That is because, the playba~k bemg
a re-beating process, sum and difference
frequencies would both appear.
How the presence of three wheels per
g roup corrects this ambigui.ty is not e~sy
to understand, but the followmg explanatIOn
may clarify the operation. Each modulator
frequency appears in three different phase
relationships because of the thre~ 120-deg.displaced wheels. A frequency hlgher than
the modulatino- frequency represents a case
of advancing phase with respect to a constant-phase sine wave at the modulator frequency. A lower frequency is a case of continually lag ging phase.
During the first third of the signal cycle
it will produce the most magnetism on that
one of the three tracks with whose modulation waveform it is most nearly in phase.
Fig1lt'e 3, for instance represents a piece
(Contimled on page 74)
AUDIO ENGINEERING
•
SEPTEMBER, 1953
,
,...-
f
r
Improvements on the Universal
Tape Recorder Amplifier
c. G.
McPROUD
Description of the second model of the unit first presented in these pages
iast year. Minor refinements provide slightly improved performance.
•
Fig. 2. View of the
chassis removed from
the case to show new
transformers and
new mounting of the
selector switch.
•
in building
only one of a piece of equipment is
that there is no opportunity to im'prove on layout, circuit, or mechanical
design in the same fashion that a manufacturer would before introducing the
instrument or equipment to the market.
The Universal Amplifier described in the
earlier article1 was no exception to
NE OF THE DIFFICULTIES
O
1 JE,
May- July, 1952. This article
adapted from the original material describing the second model which appeared
in the 211d audio anthology, but which has
not appeared in JE heretofore.
this difficulty, as was mentioned. Certain
changes and improvements were indicated as desirable if a second unit were
to be built. Not that the unit was unsatisfactory as it was-but although it performed well and turned out good
recorded tapes, there were a few slight
deficiencies.
In the first place, the transformers
used for inputs were relatively old, and
while their frequency response was adequate for most applications, there was
a 4-db peak at 10,500 cps which caused
a higher hiss level than was considered
desirable on playback. Also, there was
some loss in the circuit for direct monitoring of the incoming signal, as compared to the NOR position of SW1, necessitating an increase in the gain setting
of the amplifier which followed. Furthermore, it was felt that the difficulty of
changing the volume controls-in case
they became noisy-was too great.
Modifications
Accordingly, the entire amplifier was
rebuilt. The same outside case was used,
as well as the same panel, VU meter, and
switching arrangements. The input
transformers were changed to Triad
HS-S and the output transformer was
changed to Triad HS-S2. The Triad
HS-5 transformers were designed \ to
work from a 30/ S0-ohm microphone into
a grid; frequency response is extended,
and the amplifier is now free of the hiss
level which accompanied the first model.
This was not considered too troublesome
at the time of the first articles on this
amplifier, because it was felt that very
few who might wish to duplicate the unit
would go to the expense or trouble of
obtaining the Western Electric transformers specified for the input circuits.
A ll three of the Triad transformers
are mounted in the same size of case, and
the total chassis space required was
somewhat less than with the three previ(Contim~ed on p'age 71)
sw 10
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R37 820
05 O.f M
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D--REC
°AtJ P
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ERASE
elAS
SW5
Fig. l. Revised schematic for the second model of the Universal Amplifier. Principal changes a re in equalizing circuits and in monitor output
circuit for playback channel.
44
AUDIO ENGINEERING
•
SEPTEMBER, 1953
the controls are smooth, and are adequate
fo r all practical requirements.
A lthough the vohllne control is uncompensated, a Loudness Contro~ Sel~ctor is
available as an accessory. This umt plugs
into the rear apron, and functions as a loudness control with 10-db steps. Thus it
is set by the user fo r the approximate
loudness level desired ( in db belo\v normal
maximum room level), and the volume
control is th en used for minor variations in
output. The curves for the selector follow
the Fletcher-Munson curves approx imately.
When a crystal pickup is used, the preamplifier is disconnected from tlie circuit
by a switch on the rear apron, and any
required compensation may be introduced
by the tone controls. Fo r magnetic pickups,
however an accessor y R eco rd Compensator
is plugg~d into the rear apron. This. unit
is marked with six position s, and adj usts
turnover and roll-off in accordance with
the required characteristics. Both accessory units are eq ui pped with similar
PROFESSIONAL DISC RECORDER
PLAYBACK PHONOGRAPH
and
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''''',.... £OUt:... Cl'
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The outstanding advantage of a permanent disc recording is theif it
can be played on any phonograph. Most tapes, in fact, ultimately end up
on discs.
Naturally, the quality of the results greatly depends upon the quality
of the equipment used. The Rek-O-Kut Challenger is the only portable disc
recorder designed expressly for professional recordists, musicians, educators, and recording enthusiasts, who desire the kind of quality normally
associated with costly professional installations. The Rek-O-Kut Challenger
is, in fact, the only portable, 12-inch recorder capable of handling professional 13 V4" masters.
-
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Fig. 3. Performance data for Bogen R701 tuner.
brushed brass dial plates which match the
appearance of the main face plate of the
tuner. They may be attached to the sides of
the chassis, in holes al ready provided, or
they may be placed at any convenient location adjacent to the tuner.
The complete unit employs 14 tubes, including rectifier, and is 15 by Sy, by 9
inches in size. Output impedance is 6000
ohms, which permits operation at a reasonable distance from the main amplifier. An
additional input is available for TV, tape
recorder, or any similar source. The Bogen
R701, with a good power amplifier, would
provide a satisfactory tuner and preamplifier-control unit for any high-quality home
system.
(Co1ftim~ed
AUDIO ENGINEERING
•
(JII
page 64)
SEPTEMBER, 1953
Every feature has been embodied to assure the highest quality of
recorded sound. It is the only portable, 12-inch recorder driven by a constant speed, hysteresis synchronous motor. This means recordings with virtually no noise, wow, or flutter. Moreover, it is the only portable recorder
with a professional overhead recording lathe and with interchangeable
leadscrews for standard as well as microgroove recordings, whether at 78
or 33 % rpm (an accessory idler is available for 45 rpm).
The Challenger amplifier was designed for the utmost fidelity. It has
a frequency response ± 1 db from 30 to 20,000 cycles, with independent
equalizer controls for bass and treble response. Recordings can be made
from microphones, from radio tuners, tape recorders, and other signal
sources. Recording level is visually indicated by means of a meter.
For playback,the Challenger is a complete high fidelity phonograph
with dual-stylus magnetic pickup, and a wide range 10-inch PM loudspeaker.
Rek-O-Kut Challenger for 78 and 33 % rpm, with Standard
Groove Leadscrew - _ _ _ _ __
. .$459.95
_.-._--------------------------------THE
REK-O-KUT
COMPANY
38·01 Queens Boulevard, Long Island City I, New York
Export Division. 458 Broadway, New York 13, U.S.A. Cables. Morhanex
In Canada. Attas Radio Corp., btd., 560 King Street. W., Toronto 2B
43
/
Equipment Report
BOGEN R701 AM -FM TUNER
W
music lovers obtain most
of their entertainment from records,
it must be remembered that still
many others use radio as the principal
source of program material. There are two
recognized trends in equipm ent arrangement
-one involves the use of a stripped tuner,
without tone or volume controls, and without any means of providing for phonograph
pickups and therefor e requiring a preamp/control unit; the other involves th e
use of a tuner with all of the necessary
control facil ities . In many instances, the
tone controls and other circuit refi nements
incorporated in tuners have not been as
well designed as they mi ght be, causing
HILE MANY
.
the use r to employ a more flexible "front
end" to provide the necessary compensation
for magneti c pickups, and thus increasing
over-all cost.
Thi s does not a ppear to be the case in
the new Bogen R701 tuner shown in Fig.
1, for-with two accessory items which are
available for use with the tuner-a great
degree of fle xibility is available. Considering first, however, the specific characteri stics of th e radio section of th e tuner, the
new model is extr emely satisfactory. I t has
a sensitivity of 3 microvolts for 30 db of
quieting in the FM section, and a sensitivity
of 5 microvolts fb r the AM section. FM
drift is stated to be ± 3 kc with the aJ.c.
•
Fig. 1. The Boge n
R701 AM- FM tuner,
with bu il t-in preampl ifier.
•
circUlt 111 operation, and only ± 20 kc w ith
the a.f.c. defeated. However, it is not practicable to operate the tuner with the a.I.c.
defeated since the control is a push button
-the circuit being desi gned so th e use,'
depresses th e push button t6 defe-at the a.tc.
circuit while tuning a station in, then releasing th e button for norma l operation. Critical tests on the performance of the tuner indicate that when the set is turned off after
several hours of operation and allowed to
cool overnight, the same station is tuned in
quite accurately when th e set is turned 0 11
again. Thus for practical purposes, there
is no drift. Frequency r esponse on FM is
within ± 0.5 db from 20 to 20,000 cps.
Two positions a re provided for AM
reception-the hi-fi position is flat from 20
to 7500 cps, wh ile the normal position is
flat from 20 to approximately 4000 cps.
Hum and noise a re more than 60 db below
100 per cent modulation, and distortion at
3 volts output is less than 0.5 per cent.
Tone controls provide boos t and cut for
both bass and treble, as shown in the curves
of Fig. 3. It will be noted that the r esponse
shows r esonance at around 60 cps for both
cut and boost, the effect being apparent at
the extremes. It is undoubtedly the result
of the tone-control circuit employed, th e
choke and capacitor serving as a resonant
circuit at maximum settings. Subjectively,
. -..
~~-'M'
~
,
1/lM_fIIUoI.
,
/oIOT( ~ ...~ ~[!otS1"'"
TO K .,,_,r,t I O'l,.
utoUUO IIC_P'CC.CO .
....... ~~.l(ITOII'I""M DlC .. AL_VlE.
AIIC . "O_"'" 'U(R eANelTCI'''.
400DC .... ; ..... lnO'"[IIW1S(II"(UI(O.
) . ..... L C:U",,'0101 ' .,,"W>o..t ..uotM~
... u . . . . . . . .
_O .OIO
all(t;(IIIAtoIC'
CANO'_ ......1.l 1I OTICII""SI ..... ~.D.
Fig. 2. Complete schematic of th e Bogen R701 tuner. Circuit deta ils for the Loudness Con trol Se lector and fo r the Reco rd Com pensator are no t
shown.
42
AUD IO ENGIN EERING
•
SEPTEMBER, 1953
'"
!
EVERYBODY
HAS BEEN
WAITING FOR IT!
5th Anniversary of
••••••••••••• ••
THE AUDIO FAIR
NOW. • •
You and over 20,000 other Broadcast Engineers, Government and Military Agencies, Recordists, Sound-OnFilm Men, Hobbyists, High Fidelity Enthusiasts, and
Distributors and Dealers of quality audio and high ,
fidelity equipment as well as just plain lovers of good
music reproduction will be treated to the most exciting experience in sight and sound.
IT'S HERE!
YOU WILL SEE AND HEAR
for the first time, units representing the latest up-to the-minute developments in sound reproduction .
•••••••••••••••
YOU WILL SEE AND HEAR
more equipment devoted to quality sound reproduction than has ever before been assembled under one
roof.
THE BIGGEST
A UDIO anti HI - FI
YOU WILL SEE AND HEAR
the remarkable components which are giving lIew
meaning to music enjoyment in the American home
which has set a new standard in American qJlture .
EVENT OF THE YEAR!
.... ...... .....
-
A new popular interest has arisen . . . and it is
spreading like wildfire across the face of the land!
Hi-Fi is rapidly becoming the most talked-about
pleasure in human experience.
SPONSORED BY
This Is Your Show . . . it is run for your benefit
. . . for you to see and to hear . . . for you to experience, appraise and pass judgement . . . therefore, you pay
IN CONJUNCTION
WITH ITS
NO ADMISSION CHARGE
FIFTH ANNUAL
CONVENTION
••••••••••••• •
WHEN~OTE THE TIME
WHE . October 14 15
ANO PLA
RE: Hotel N
' ,16, 17, 1953
ew Yorke N
egistration
7 r, ew York C·
on th 6th
Ity
E
' a n d 5th FI
R
AUDIOBAMA
is presented by
THE AUDIO FAIR
HARRY N. REIZES
Managing Director
67 W. 44 St., N. Y. C.
Wednesday, o
Thllrsday 0 ct.
,
;riday,
ct IS
.
XHIBIT HOURS
CE
oors
14 . .
'" ".
. . . .. " . . . .. . . . II :00 A
8anq~~i~~ '7' " 10:00A.·~·:: 9:00P.M.
Oct. 16 (AES
atllrday, Oct. 17 ·· ·· · · .... .. ..
.30 P. M.)
6 :00 P. M
" . 10 :0 0A
P.M. . .
~~""""~"".' ~'~"~'.'~10~:~00~~'M~.~t~O~'0~::00~P::
An Audio Fair - Video Fair, Inc. , Project~
AUDIO ENGINEERING
•
SEPTEMBER, 1953
A.M. to S · M.
:00
41
I
Industry View ~
Th~' Audio Fair
What the Audio Fairs mean
the audio ind Istry as a whole is highlighted by these representati ~ comments fn m a few of its members.
M
ORE TH AN
000
20,-
:M U S IC
LOVERS, audio
hobbyists, broadcast
technicians, and recording and sound
engineers will pour
throug h the entrance
of Manhattan's H otel
N ew Yorker' October 14, 15, 16, and
17 to make the 1953
Audi o F air th e g reates t public ex hibit in
audio history. Using
the attendance at
previous Fairs as a
basis of comparison, the twenty thousand
figure is distinctly on the conse rvative side,
according to a recent announcement of
Harry N. Reizes, Fair manager.
Paralleling a new high in attendance will
be a record-breaking number of exhibitors,
many of whom are maj or manufacturers
entering the high-fidelity field for the fir st
time this year, and who have chosen th e
Audio Fair as the most effective means of
introducing publicly their audio products.
Indicative of industry g rowth and th e acceptance of the N ew York Audio F air as
the official meeting place of manufacturers.
engineers, and hobbyists a like, is th e fact
that the Fair this year will occupy three
floors 'Of the N ew Yorker in comparison
with the two floors which have suffi ced in
previous years.
Joining with the Fair management in
announcing completion of plans for the
country's foremost audio event were officials of fhe Audio Engineering Society,
whose annual convention is scheduled to
coincide with the Audio Fair. Jerry B.
Minter, convention chairman, stated that
this year the AES will entertain a greater
array of technical papers on audio subjects
than has ever before been presented at a
single meeting.
Shortly before press time, th e editors' of
}E approached a number of industry' leaders
in an effort to measure the enthusiasm
which wou ld welcome the Fair of '53. Considering that six weeks are yet to lapse
before the opening day, we believe you' ll
agree that the opinions which follow point
to a Fair which will really be something to
write home about.
LEONARD CARDUNER, president,
British Industries Corporation: "My
company has exhibited at every Audio Fair
held to date.
"We have found the Fairs invaluable for
a reason which is not, perhaps, self-evident. That is, that we not only have the
opportunity to display and demonstrate our
new equipment but, what is even more
valuable, we have the opportunity to talk
40
to our past c
future customer
"The insight
high-fidelity e
and looking fq
proved to be
believe that 0
future so long :
the industry ni
integrity in ke~
by producing
and standing fi,
ity of product.
"The A udio
to be a mos t v,
and a wonderft
customers on c(
that it will con'
omers and our potential
concerned. The results speak for themselves."
us gained as to what the
usiasts are hoping for,
in new equipment, has
invaluable guide to us. I
industry has a brilliant
the manufacturers within
tain the highest possible
ing faith with the public
uly first-rate equipment,
on the question of qual-
HERMAN HOLSTEIN, advertising
manager, Hudson Radio and Television
Corporation: "We look forward to the
Audio Fair each year because it is a stimulant for our business and for the entire
high-fidelity industry. It enables us to
present our wares and our services directly
to the public under the most competitive
conditions. Thus, our people are a lerted to
keep abreast or ahead of competition. The
Audio Fair also permits us to meet large
numbers of interested people, and to observe their tastes, prefer ences and reactions.
By so doing we can guide our buying and
merchandising in the right direction."
ir has in the past proved
able meeting place fo r us
opportunity to greet our
mon ground. Vif e are sure
ue to be just that."
LA WRENC ' E P STEIN, sales manager, Univen y Loudspeakers, Inc:
"The concept , an Audio Fair must be
marked as one f the prime contributing
factor s toward ~UbliC acceptance of highfidelity equipm, t. It has been an invaluable aid in eXI ing the lay public to the
virtues of high uality music systems considered heretof( Ie exclusively in the realm
of the theater and laboratory; and has
done much to ! 'mulate greater interest in
audio on the p: t of hobbyists and experimenters. Exec ion of the Audio Fair has,
in my opini ,been highly satisfactory and
I add my vote of thanks to th e ori ginator."
F . SUMNER HALL, president, The
Audio Engineering Society. "As one
whose interest in audio is basically professional, I rega rd the Audio Fair, together
with the AES Convention with which the
Fair coincides each year, as a literal necessity to th e audio equipment industry. Convening under one roof and at the same time,
they offer the professional engineer an un equalled opportunity for keeping well in formed on the technica l and commercia l
aspects of audio. Everyone with a sincere
interes t in the betterm ent of reproduced
sound should attend both th e Convention
and the F air."
BRYCE HAYNES, vice-president
and sales manager, Audio Devices, Inc:
"We at Aud io Devices are again looking
forward to participati on in the Audio Fair,
for at this annual convocation of audio experts one can, at first hand, feel the pulse
of the entire industry. A nd by reviewing
the pas t and evaluating the present, fu ture
trends become readily discernibl e.
" \lYe feel that th e Audi o Fair has done
much to further the development and
growth of the recording industry. By
bringing together the finest, modern modern eq uipment and material s, as well as the
best engineering ta,lent, it has helped to
stimulate the interest and enthusiasm of a ll
CHARLES RAY, Arrow Electronics'
Audio Center: "We at Arrow Audio Center are certain that the high-fidelity industry has now passed through its critical
infancy and is making vigorous strides as it
becomes of age. Public acceptance has been
marked by ever increasing attendance at
the annua l Audio Fair with which Audio
Center has been proudly associated from
the beginning . Audio fans wait in anticipation of the new wonders to be unveiled at
each show: and always come away with a
personal feeli ng of pride in the accomplishments of 'their' industry."
GEORGE SILBER, president, The
Rek-O-Kut Company, Inc: "It must be
recognized that the Audio Fair is a powerful medium for bringing the ex perience of
high-quality sound to the general public.
As a manufacturer of high-fid~ lity equipment, we are vitally interested in this
market. Therefore, it is important that 'we
be able to reach this market with our story
of product quality.
"Naturally we employ advertising to do
this for us. But nowhere can we hope to
achiev e th e advantage of direct personal
contact as it is offered at the Audio Fair.
" \i\Thatever may have been the expectation when the idea was born, the Audio
Fair in practice is a dynamic' ma rketing
aid. It suppl ements and reinforces our efforts to make high quality sound a part
ot the Ameri ca n way of life."
. R efl ectin g the penetration of reproduced
sound an d music into all phases of home
and industry, th e 1953 Fair will be built
around a theme of "Audiorama," a word
coined to dramatize th e extent to which
a udio has gained acceptance as a prime
amenity in the panorama of American life.
In keeping with the policy establi shed
with the fir st A udio Fai r five years ago,
the 1953 conclave will be open to a ll interested parti es, professional and amateur,
free of charge.
Remember , the A udi o Fair is YOUR
affair! Plan NOW to be th ere !-H.ICR.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
~
NEVER SUCH EXTRAVAGANT MUSIC
SO MISERLY IN SPACE AND COST
WITH THE NEW JENSEN ~
Here's a spec iall y designed unit, coord in ating speakers and small
enc los ure .... "presence" yo u never dreamed you'd get in suc h a
compact, inexpe nsive unit. , , two speakers in a true '2-way systym
for real high fidelity performance. Ideal for small space hi-ti, as a second
or exten sion speaker, or in a pair for binaurel sound .
Use on table
bookshelves
or on floor standing on side or end
The "Duette" gives clean, smooth 'reproduction w ith the
unmi stakable "presence" of the 2-way hi -fi reprodu cer. Uses
special heavy duty 8" "woofer" and multicell horn
"tweeter" like expe nsive speaker systems. Impedances:
4 and 8 ohms. 20 watt power rating.
Only 11 " high, 23]1" wide, 10" deep . Mahogany
toned pigskin plastic ffnish with con trasting front.
Net price ... $69.50
Hear the H-520 Coaxial Louds.pei,lk~r.,;,._
(15") ... big brother to the famous H-222
(12") with all of the good listening qualities
of a finely balanced compression-driver
tweeter coaxial. Furnished with H-F
Balance Control. $79 .50 net
Listen to the new
H-530 Coaxial Loud
speaker (15") ... it is an
advanced design coaxial with
new compression-driver hornloaded " tweeter" with the smoothest
reproduction you've ever heard from a 2-way system!
Sets a totally new standard of coaxial performance. Furnished with H-F Balance Control. $129.50 net /
See us at the Audio Fair. Rooms 518·519
Hotel New Yorker· Oct. 14, 15, 16, 17.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
39
1 ••
I
I
)
I
I
I
I
I
_____L ____ ~------I
I
I
(AI
(B)
Fig. 12-22. (A) Transfer characteristics of two tubes in Class AB, push-pull. The two curves
effectively combine into the single curve of (B).
With a giveri pair of tubes, fixed bias
permits greater power output, at the
same distortion, than does bias which is
dependent on the average value of plate
current. This is because with fixed bias
the operating point of the tube is held
constant during increased signal amplitudes, rather than shifted downward
on the [p - Bu curve. The disadvantages
of fixed bias lie in greater cost and
circuit complexity, and in the fact that
the input impedance to the power amplifier stage must be of low value, almost always involving transformer
coupling between driver and output
stages.
The low value of impedance is required ·in order to protect the tube from
damage by surges of plate current. At
the moment that the signal grid is driven
positive-a possibility with high signal
input-current will flow from the C
supply tow(wds the .grid. If the gridcircuit impedance is high this flow of
current will create a large voltage drop,
and the protection given by the grid bias
supply against dangerously high plate
current flow is largely removed.
Cathode or self bias is secured from
the voltage drop across a resistor inserted in series between cathode and
ground, as at (B) of Fig. 12-23. The
current flow through this resistor, which
can only be in a direction from ground
to cathode, creates an IR drop which
makes the cathode po~itive with respect
to ground. Since there is no d.c. flow
through the grid resistor there is no
voltage drop across it (I = 0, hence
[ x R= 0), and the grid is at the same
d.c. potential as ground. The grid is
thus made negative with respect to the
cathode, in an amount determined by
the size of the cathode resistor and by
the amount of current flowing through it.
Cathode bias is much simpler and less
expensive than fixed bias. It has the
further advantage of protectively increasing the bias voltage, in a Class AB
circuit, when the signal amplitude becomes great enough to raise the average
value of plate current. The input impedance to such a stage can be a conventional grid resistor of several hundred thousand ohms.
38
The protective raising of the negative
grid voltage produced by cathode bias
also shifts the operating point, which
limits the power output at low distortion. However, in straight Class A
operation, cathode bias provides the
same operating characteristics as fixed
bias because the plate current flow r emains constant, resulting in a constant
value of IR drop across the bias resistor.
In Class AB, cathode bias remains constant when the signal amplitude is low.
Even with Class AB operation, therefore, cathode bias provides approximately the same operating performance
as fixed bias at lower power levels. For
example, tube manuals · list the Class
AB, power output of 6B4's as 10 watts
at 5 per cent distortion with cathode
bias, and 15 watts at 2.5 per cent distortion with fixed bias. It would be a
mistaken interpretation of this data,
howevel', to assume that the two circuits maintain the same relative quality
rating at low power output. Actually
their operating characteristics in the
latter circumstance are substantially
identical.
The cathode resistors of power amplifiers are normally bypassed by electrolytic capacitors of high value, to
keep the signal variations from the bias
voltage. These variations, as we have
seen, would introduce negative current
feedback, raising the' source impedance
of the output stage. The reactance of
the bypass capacitor at low frequencies
must be small {50 !J.f is a common val ue
of capacitance) I'elative to the value of
the parallel bias resistor, to avoid frequency selective feedback.
Often the two output tubes use a common bias resistor, halving its required
resistance and doubling its required
wattage rating. In such a case the sigHal currents from each half of the pushpull stage will combine out of phase and
oppose each other, removing the current
feedback to the extent of the symmetry
between the two signals. Unless the stage
is operated in Cla5"s A and the signals
are carefully balanced, however, the cancellation will not be complete. In an unbalanced amplifier, furthermore, there is
the danger that the distortion of one
half of the stage will be introduced in
phase into the grid circuit of the other
half. The residual signal from one tube
that appears across the cathode resistor
is applied as negative feedback to that
tube, and as positive feedback to the
other. While this improves balance and
would be a desirable feature in a voltage
amplifier circuit with low distortion, it
is not desirable for the output stage,
from which the greatest distortion is to
be expected.
Back bias taps the negative voltage
from a series resistance or choke in the
B minus line, as illustrated at (C) in
Fig. 12-23. This provides a compromise
between fixed and cathode bias . The
voltage drop across the bias resistor is
independent of signal amplitude to the
extent that the total B-supply current
contains current not used by the output
stage.
:An automatic bias control circuit has
been described.n and used commercially,
(see Fig. 12-24) in which the ampli fier
is biased for Class A operation up to
(COnJtit~1{ed
on page' 77)
11]. R. Edinger, "High-quality audio
amplifier with automatic bias control,"
AUDIO ENGINEERING, June, 1947, p. 7.
lie
+
(A)
(B)
Fig 12-23 Methods of providing grid bias voltage. (A) Fixed bias from separate power sUl!ply.
Th' oint ";arked X is sometimes used to supplv plate voltage for low-current voltage amplifiers.
e p
( B) Cathode or self-bias. (C) Back bias.
~
AUDIO ENGINEERING
•
SEPTEMBER, 1953
BRIDAL N E W .S
Tuner-Amplifier Wedding
arouses Hi-Fi interest
An event of country.wide interest
occurs with Stromberg. Carlson's
announcement of the "wedding"
of two popular components in its
"Custom 400" line.
The already·accepted features of
the High Fidelity "SR·401" Radio
Tuner and the " AR·410" 10·walt
Amplifier are now available in one
cha ssis-at a price considerably be·
low the cost of the separate com·
ponents.
An interesting advantage of the
new "SR-405" receiver.amplifier
combination is its easy application
to the modernization of existing
Radio.Phonograph s. Fine old
players-with cherished cabinetry
but lackin g true high fidelity-can
be brought to top performance by
substituting, for the old tuner and
amplifier, this compact 131,4 x 8 x
12·inch unit.
Further information and the
name of your nearest dealer gladly
furnished on request.
SR·401 FM·AM
Radio Tuner and
AR·410 10,watt
Amplifier now
combined in this
SR·405 chassis.
SPECIFICATIONS
volt. Crystal phono input and Magnetic Recorder
input sensitivity easi Iy changed to 2.0 volts.
Audio Power Output
Treble Control
10 watts at less than 1 % total harmonic content.
Control provides ... . .. . ...... . . 12 db. boost
20 db. droop at 10,000 cps.
Loudness control provides . . .... . 6 db . boost
Maximum Treble Boost . . .. • ....• 18 db.
4, 8, 16, 120 and 600 ohms. All 600 ohms at
+ 8 VU level.
Radio Sensitivity
Output Voltage Regulation
FM·3 microvolt signal produces 20 db. quieting.
AM·5 microvolt signal produces 1 watt output
using low·impedance antenna term inals; 15
microvolt signal using high·impedance
antenna terminals.
2 db.
Frequency Response
FM-20 to 20 ,000 cps. ±1.5 db.
AM-20 to 7,500 cps. ± 3 db. Interstation whistle
filter; Microphone, Television, Crystal Phono and
Magnetic Recorder inputs 20·20,000 cps. ± 1 db.
Radiation
Meets RTMA specification REC·129·C for mini·
mum radiation.
Base Control
Control provides .. ... . ... .. .. ... 12 db. boost
20 db . droop' at 40 cps.
Loudness control at 10 % rotation . . 10 db. boost
Maximum Base Boost ... ... ••. ... 22 db.
There is nothing finer than a
Input Sensitivity for Rated Output
Magnetic phono input·low level .008 volt, high
level .08 volt; Microphone .008 volt; Magnetic
Recorder, Television and crystal phono input .1
Output Impedances
Antenna
FM-72 to 300·ohm for use with dipole antenna.
AM - High impedance for short antennas, low
impedance for low impedance loop or long
antenna with coa xial cable lead·in.
Power Supply
117 volts, 50 to 60 cps., 138 watts.
Tube compliment-1S
Stromberg-Carlson®
Sound •
Division
1219 Clifford Ave., Rochester 3, N. Y.
Makers of famous XY dial equipment-telephones-television-radio-carillons and sound systems.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
37
•
Handbook of
Sound Reprodu ction
EDGAR M.
VILLCHUR '~
The Power Amplifier. Chapter 12, Part III.
The Output Stage and the LoudspeakerVariation in Value of Load Impedance
The selection of a value of load impedance to present to the output stage
involves, as we have seen, a compromise
between maximum ' power output and
minimum distortion. A special problem
is created when the load impedance
value varies with frequency, as is the
case with a loudspeaker. Low, internal
amplifier impedance can keep the voltage across the speaker constant, but
does not keep the actual speaker impedance constant.
Standard design procedure is to
match the amplifier to the rated impedance of the speaker, which is close in
value to its minimum impedance over
the frequency spectrum. In this way all
mismatching that occurs is in an upward direction; changes from the optimum value of load are always increases.
With triodes power is lost-no particular disadvantage in the bass-but the
increase of- load decreases distortion
where a decrease of load would hav~
had the opposite effect. Pentode dis~ortion may be increased by the load
1I1crease, but to a lesser degree than
would occur with a downward mis!TIatch, and more rather than less power
IS absorbed. Sufficient negative feedback
can bring pentodes to constant voltao-e
operation, and counteract the distortio~.
Classes of Operation
The /p - E y curve of Fig. 12-21 is
known as a transfer characteristic since
it indicates the plate current th~t will
flow (other circuit conditions having
been defined) when the voltage between
grid and cathode is at a specified value.
The input signal to the grid alternates
between positive and negative polarities;
for audio applications it is therefore
necessary to create circuit conditions
such that, with no signal input, the
plate current flow is somewhere between
zero and maximum. This is achieved by
providing a negative "bias" voltage on
the grid. The signal can then influence
the plate current in either direction, and
the accuracy of control can be read from
the linearity of that portion of the transfer curve over which current variations
take place.
It should be noted that the input signal
is a voltage variation, while the output
signal is plotted in terms of instantane-
* Contribu ting
NEERING.
36
Editor,
AUDIO
ENGI-
Fig. 12-21. Transfer characteristic illustrating Class A, operation. Plate current flows
during the entire cycle, and the input signal
is neither allowed to engage the curved lower
portion of the I. - E. curve, nor to drive the
grid positive.
ous current. The relative physical size
of the input and output wave forms as
they. appear on the diagram thus does
not represent either the voltage or power
gp.in of the stage. The output voltage is
the product of the current and the load
impedance, and is not shown here.
Figure 12-21 illustrates what is
known as class A, operation. The point
of no-signal current, or operating point,
is chosen (by determination of grid bias
in relation to other circuit conditions)
so that the input signal never causes the
plate current to cut off completely, and
plate current flows during the entire
signal cycle. In addition, the input signal is not allowed to engage the bottom
curved section of the transfer characteristic on its negative cycle peak, or to
cancel the grid bias on its positive peak,
an event that would create the undesirable flow of grid current. It may be
seen that the average value of plate
current over the cycle is not affected by
the amplitude of the signal.
elaS's Al operation provides the highest potential fidelity but lower power
output ·and efficiency from the same tube
or set of tubes. It is used in practically
all audio voltage amplifiers, and in output stages in which the power requirements, relative to the capabilities of the
tubes, are limited.
The subscript 1 used above refers, as
in other classes of operation, to the fact
that grid current is not allowed to flow.
Class A2 operation also keeps plate current flowing at all times, · but raises the
operating point and allows grid current
to flow on positive peaks. Class A.
allows greater power output but is
seldom used.
A class B amplifier has a lower
operating point, and allows plate current
to flow app roximately half of the cycle,
when the input signal is positive. It is
able to provide higher output and increased efficiency for power amplifier
stages, but the distortion in single-ended
use would be so great as to make the
circuit useless. Class B operation therefore must be used with push-pull circuitry, where the asymmetrical waveform distortion tend~ to cancel out. This
class of operation is useful for highpower, high-efficiency industrial amplifiers. Class B amplifiers are usually
of the type with subscript 2.
Class AB operation is midway between Class A and Class B. Plate current flows during appreciably more than
hali of the cycle. Since current does not
flow during the entire cycle, Class AB
amplification must, like Class B, use
push-pull circuitry. The combined effect
of the transfer characteristics of Class
ABI tubes in push-pull is illustrated in
Fig. 12-22. The stage is able to operate
in class A for weak signals, and increased signal amplitudes create a transition to Class AB. The ' average value
of the plate current is increased for
large signals with both Class AB and
Class B operation.
Class ABI operation is common in
high-quality power amplifiers where the
power available in pure Class A is not
considered sufficient, and where any
distortion generated is severely reduced
by negative feedback.
In Class C operation the grid bias is
greater than the cut-off point of the tube,
and plate current flows during appreciably less than half of the signal cycle.
This is the most efficient class of operation, but is entirely unsuitable for audio
service.
Crid Bias
Negative grid bias voltage may be
provided in several ways. Fixed bias, .
so called because it remains the same
under all signal conditions, is secured
from an independent voltage source.
The old "C" battery or bias cell was
such a source; nowadays a separate
power transformer winding, rectifier,
and filter are used. · (See A in Fig.
12-23.)
AUDIO ENGINEERING
•
SEPTEMBER, 1953
you want to know
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CITY_ _ _ _ _ _ _ _ _ _ _ _ _......1Z,ONL-STAT""E_ _ _ _ __
Twin-Triple Resistance Decader
and Bridge*
LLEWELLYN BATES KEIM e"e"
Development of tube circuits is simplified when accurate means are available
for measuring resistor values or for providing calibrated values of resistance.
O
components
comprising a vacuum tube cil-cuit,
none is more important than the
resistor. It establi shes operating parameter. , determines signal level, and it is
across this same component I that the
s ignal is developed. Because of its importance, a device which can serve as a
source of many res i -tance values which
can be qui ckly introduced into the circuit under study is a valuable tool in
the hands of the design enigneer.
Some idea of the importance of the
correct value of res istance in a particular circuit location is well known to
those who have made extensive studies
of intermodulation distorti on in audio
amplifiers and of methods of reducing it.
A slight change in the value of a
cathode resistot- or a n i~lcrease of perha,ps 20 per cent in a plate-load resistor
may cut 1M distortion to one quarte r its
previous value_ Hence, it is of paramoun t importance to have available
some means of making resistance measure'm ents and substituti ons if any really
worthwhile audio design work is to be
attempted. The widely publicized tables
of R-C values for resisfance-coupled
amplifi er design are cit-awn up for commercial standards, but their empirical
use is likely to lead to disappointment_
These tables can be taken as a sta rting
point from which desig n commences,
but improvement may be obtai ned by
careful selection of the " right" value of
F THE MANY DIFFERENT
* Author's copyright. Design patent applied for.
** 11
N. y_
Riverside Dr·ive, New Yor/~ 23,
3 DECADES OF 9 RESISTORS
OF VAWES SHOWN
,.:~
600
2700
~100
C
o
1------=-1-I\I\I\I\.,::+:..-.-----....J
3 DECADES OF 9 RESISTORS
OF VALUES SHOWN
Fig _ 2_ Schematic of the Twin-Triple Resistance Decader and Bridge.
resista nce in the circuit for slightly less
gain per stage, possibly, but with a materially lower distortion figure_ Cathode
followers are increasingly interesting as
the terminal stage of a preampli fier,
because their low output impedance will
permit a long line to the power stages
without frequency discrimination, and
also the possibility of feeding more than
one power stage without loss of response. A variable res istance box will
allow quick determination of the optimum load, at the same time keeping the
distortion at a minimum. Still a nother
source of trouble is the selection of the
proper decoupling resistor to prevent
motor-boating, without causing a n undes irable loss of supply voltage Other
uses wi ll suggest themselves to the researcher as hi s familiari ty with the convenience of this device becomes appar-
ent.
Some yea rs back it was poss ible to
buy a semi-calibrated 1.0-meg potentiometer which was capable of being
clipped into the circuit for ascertaining
the value of a defective resistor, and for
general circuit use in experimental
work. This unit was logarithmic in
scale, and permitted reasonable accuracy
in determining the valve. However,
these components seem to have disappeared fro m the market, the onl y similar
unit available now being a OJ-meg
linear potet{tiometer. Because of this,
the author determined to construct a
completely flexibl e decade resistance
'box. Study of the needs of audio circuitry reveals the fact that resistors
from 10 ohms to 10 megohms are used,
and this range of variables must be pro(Conlililled
011
page 60)
Fig. 1 (left) . Completed bridge and substitution resistor box_ Fig. 3
(below) . Internal appearance of the bridge showing simplicity of
construction _
34
AUDIO ENGINEERING
•
SEPTEMBER, 1953
D.C. Pack for Heaters and Bias
ALLAN M. FERRES':'
A simple and practical device which will provide hum-free he~ter power for I~w-Ievel amplifier stages, -thus making one further step toward . perfection In reproducing systems.
I
full advantage of the
excellent fidelity now available in
home radio-phonograph installations,
the hum level of the system must be reduced to a value much lower than that
required a few years ago. Moving toward improved realism, designers have
incorporated into the systems speakers
and amplifiers with better low-frequency
response and, at the same time, signal
sources'· . and circuit which requi re
greater voltage gain at these low frequencies. The magnetic cartridge, which
is the accepted standard for high-fidelity
record reproduction, and the increased
use of magnetic tape in the home, combined with "loudness" and separate bassboost controls, all contribute to the problem. A gain of 30 to 40 db at hum frequencies over the mid-frequency gain is
often encountered in most equipment.
The hum reduction problem centers
around the low-level stages where the
signal level may be as low as 100 microvolts. In order to keep the hum from exceeding the acceptable maximum, usually
considered to be 55 to 60 db below normal listening level, careful design is
essential.
After all possible precitutions are
taken to reduce the hum picked up by
the input source, the residual hum is
produced by the tube operating at the
lowest signal level. In good design, this
is the first tube in the circuit, that fed
by the input source. The hum produced
in this stage may be considered to come
from one or more of four' sources: magnetic fields, electrostatic fields, plate-supply ripple, and heater-supply ripple. As
the a.c. magnetic field is usually caused
by the power transformer, proper spacing between it and the input tube will
eliminate this source of trouble. The
effect of electrostatic fields may be minimized by completely enclosing the tube
and its associated parts in an aluminum
or copper shield can. As a resistancecoupled stage, customarily used in preamplifiers, requires plate current of the
order of one milliampere or less, the
plate voltage ripple can be reduced easily
by means of an R-C filter, and so may be
discounted as a "problem" ·in hum reduction. Therefore, the remaining factorheater-supply ripple-is the common
cause of the residual hum.
When a.c. is used to heat the cathode
of a tube, hum enters the signal circuits
by heater-cathode leakage, the a.c. magnetic field surrounding the heater, and
by capacitive coupling between the
N ORDER TO TAKE
* 267
W. 11th St., New Yark 14, N. Y.
AUDIO ENGINEERING
•
•
Fig. I. External view
of the author's d.c.
heater pack.
•
heater and the other tube elements and
circuit components. Although careful selection of tubes and arrangement of parts
can bring this hum down to a minimum,
a point is finally reached where the only
method of further reduction is the use
of d.c. as the heater supply. (Although
high-frequency heater current can be
used, it is not considered in this discussion due to its complications.)
Advantages of d.c. Supply
The use of a d.c. heater supply has
many advantages. As power-supply a.c.
does not have to enter the shield compartment of the low-level stages, shielding requirements of grid and plate leads
are not as stringent and better highfrequency res'ponse is easier to obtain.
Cathode followers and certain types of
phase inverters and feedback circuits
which require the cathode to be un-bypassed can be used at lower signal levels.
This, at times, simplifies design problems. The type of high-frequency oscillator often used in FM receivers in
which the .cathode is above ground potential is a stubborn source of modulation
hum until d.c. is used. More leeway is
permitted in the choice of the type of
tubes which can be used and the circuit
will be less cl-itical as to individual tube
selection.
In any given amplifier, the improvement to be expected 'by changing the
heater current from a.c. to d.c. is difficult to predict, as too many factors are
SEPTEMBER, 1953
involved. If the amplifier under discussion is still in the design stage, then d.c.
should be used if the lowest hum level is
required, depending only upon the cost
involved. If the amplifier has already
been built, then the improvement can be
readily measured by disconnecting the
heater leads from the transformer and
substituting a battery of the proper voltage. (This, incidentally, is a good way
of isolating the cause of hum in equipment when trouble-shooting.) It is possible that when the battery is used, the
hum will increase. This is due to hum
voltages from the heater having been
out of phase with hum caused by some
other source. It is usually due entirely to
coincidence and should not be depended
upon as a method of hum reduction, as
the other source often produces a voltage
which varies in amplitude and phase.
The other hum source can now be
tracked down and corrected.
If the d.c. heater supply used has a
ripple of 1 per cent or less, it may be
assumed to produce no more hum than
the battery, and the supply should be
designed with this in mind, unless experience has proven that in a particular
circuit a greater ripple can be tolerated.
Methods of Obtaining d.c.
In general, there are three sources of
d.c. which can be used. The first is to
connect the heaters in series in the negative side of the plate power supply, and
• I
33
The Case ·For Music
J.
H. THOMSON*
The author suggests that the installation of high-quality audio equipment is not, o'f i.tself,
the last step for full music enjoyment. Perhaps his opinions have considerable merit.
H
some of the phono- composers of his music, and he knew
graphs owned by music teachers? very little about the instruments in the
In schools and colleges, teachers orchestra. Furthermore, ke was not inof music literature, theory, instruments terested in those fields and made no efand voice usually have phonograplis, of fort to learn about them. When his phosome kind, for demonstration or study nograph was playing, it was a backpurposes. In general, the quality of the ground for other activities, usually conmusic reproduction is terrible. There are versation, and practically never, after
goal!! ones, and the number of good ones the first week of ownership did he really
is increasing, but in the decade between listen to the music that came out of the
1940 and 1950 most of them were very speaker. Consequently, his interest did
poor. They used heavy crystal pickups die. His music reproducing gear was
and replaceable needs which wore the considerably better than that of most
records badly, and after several years, professional musicians, but his musical
the sound that came out of the speakers knowledge was so limited that it could
was, in every .sense, terrible.
not long support enthusiasm.
These people live from day to day
This problem is a se·rious one and a
with music. They work with it, and with common one. The center of our friend's
people making it, and for the most part, musical activities was his phonograph.
they love it. The thought of losing inter- After he had acquired it, there was alest in it never seriously occurs to them. most no place to go. The center of a
The winters are spent teaching music, musician's musical activity is the music
going to concerts, singing in church itself, and his phonograph is simply a
choirs, or playing in ensembles or or- tool to help him enjoy his music. Conchestras. The summers are spent often sequently, after he gets his gear, there
at music camps, festivals or at summer is everywhere to go.
sessions of music schools. These people
know a great deal about music. They Listener's Imagination Nec;essary
know about the lives and times of the
Let us go one step deeper into the
composers, they know about the theory
and notation of music, and they know problem of listening to records. It is,
about instruments, .players, singers, ·a nd at present, impossible to reproduce muconductors 'involved in various composi- sic exactly as it sounded originally betions and performances. Most of them cause of a number of technical difficulhave studied music for ten years, and ties and differen.t listening conditions.
some for twenty or thirty or more. Their Since this is the case, it is always necenthusiasm for music would no more die essary to bring to a record-listening situthan the average person's enthusiasm for ation a certain kind of musical imagination, usually subconscious, which can
food.
Have you ever known of a situation add to or subtract from what is heard to
similar to the following one? An ac- make the "rea.! sound." This type of
quaintance, not trained in music, was imagination is similar to the imaginavisiting a friend where he heard a bril- . tion needed to turn words, sentences, and
liant recording played on a good qUjlJity paragraphs in a book into real people
reproducer. The acquaintance enquired and happenings, and the kind of imagiabout the cost and availability of the nation needed to change characters and
phonograph. His friend showed him his scenes in a play into believable people
collection of catalogues of audio gear, and vital situations. Of course, the worse
and within two months a corner of the the reproduction, the more the need for
living room was cluttered in typical fash- imagination.
Most musicians have this kind of muion with a corner baffle, cables, glowing
tubes, and a pasteboard box holding the sical imagination developed to a high
record-changer. The system worked very degree so they are able to listen to a
well. For a short time, his interest in ragged, distorted version of some composition, and immediately all of their old
the phonograph was intense.
It is only fair to say that his knowl- thoughts and feelings associated ' with
edge of music was very limited. H e did this composition crowd around them.
not play any instrument, nor did he sing Their knowledge of the composer and
in a church choir. His knowledge of the the forces that influenced his composiliterature was limited. He knew practi- tion and his life-and probably technically nothing about the lives .of the cal knowl edg e of the di·fficulties of performance a l ~ 0-c0ntribute to their ap* 1138 California A-.·e.. CiIl C;I/JWti. Ohio. preciation of the composition. So they
AVE YOU HEARD
I
32 .
get out of the situation, with comparatively little help from the phonograph,
a great deal of pleasure because of what
they knew about the music. If our musical novice heard the same performance,
all he would have heard was the poorquality sound, and the unfamiliar music
by an unknown composer. His attention
would probably have wandered and he
would have missed the recurrence of a
theme which might have been a key to
some enjoyment of the composition. So
he would have become bored and probably would have decided it was very dull
stuff and not worth listening to again.
He would have derived from the situation nothing but boredom, largely because of his lack of musica<l knowledge.
The quality of the sound reproduction
is important to both of .those people in
a variety of ways. The better phonog-raph, for the musician, cleans up the
inner parts, makes the instruments sound
more like themselves, and makes it much
less of a strain on his "musical imagination" to make "real" music out of the
sound. To the musical novice, the better
sound is generally more agreeable to
listen to. At worst, he has not had an
unpleasant experience l1stening to the
music, and at best he has really listened
to the music and enjoyed it.
Since .the increase in the quality of the
sound is nowhere near proportional to
the cost of the gear, especially past the
$250 to $300 region, ,and since the use
of "musical imagination" is necessary
anyway and not detrimental to anyone,
it appears to this writer that reasonably
good quality sound should be acceptable
to the most critical listener. The only
thing that a phonograph can be expected
to do is to reproduce the music on recordings reasonably well. Therefore th e
only way that the phonograph can give
lasting pleasure is for the listener to
learn as much as he can about the music
the phonograph plays for him. If he
doesn't, he is not doing his share by
meeting the phonograph and his records
half way, and the penalty is that he simply will not be satisfied with his phonograph or records.
How Does the Listener Learn
This process of learning' about music,
as with everything worth doing, is
fraught with additional trouble, expense
and disappointment, but the results are
so satisfying that once the process is
thoroughly begun there is usually no
question of stopping.
(C ontiwued ;111 page 51)
AUDIO ENGINEERING
•
SEPTEMBER, 1953
quarters of full screen area. Figur _ 1
shows three typical patterns.
If the instrument were to be used
solely for measuring steady~state signal
levels, nothing else would be required.
However, in recording opera tions, it is
desirable to have an indication which
is easily readable by the engineer and
the delay network makes this possible.
A five-position switch selects various
delay times so that the deflection can be
made to follow the instantaneous value
of the input voltage, or so that the pattern will expand quickly to max imum
size and then recede slowly.
One other feature of the instrument
is its ability to indicate pola rity or
phase of the signal. As is well known,
rpost program material is composed of
voltages which differ in magnitude on
the positive and nega tive halves of the
cycle. The signal is fed to two diode
rectifiers which can be switched so as to
control both amplifiers simultaneously,
thus making both indications equal and
proportional to the average of positive
and negative peaks, or so as to control
the two amplifiers independently. In
th is case, the pattern will appear as a
vertical rectangle, for example, if the
positive half cycle is the greater and as
a horizontal rectangle if the negative
half cycle is the greater. For certain
types of recording, this feature is of
considerable value, and it also offers
some advantages to broadcast program
monitoring.
In a more recent and simpler form,
the Visualizer provides an indication in
only one direction, being presented as
a half-inch band of light varying in
length in accordance with sig nal intensity. As a simple instrument fo r volume indication of only one cha nnel, thi s
permits the use of a rectangular-screen
cathode ray tube, mounted hori zontally
so as to give a conventional indication
fr~m left to right. For stereo recording,
usmg two or more channels, a number
of these rectangular-screen tubes may
be mounted side by side, as in Fig. 2,
to permit easy observation of the 'Ievel
in each channel. Although the simpler
system does not provide any indication
of polarity, operation of a switch can
select either positive or negative polarity, or the two may be averaged for
the indication.
•
SCOPE
Fig . 3. Block schematic of the Volume
Visualizer in its original form .
•
amplifier stages are fed to vertical. and
horizontal inputs of a conventional
'scope. Controls are provided fo r adiustment of operating conditions, such
as audio buss levd, pattern desired,
delay recession time, etc.
Figure 4 shows the complete schematic of the original instrument. The
input amplifier consists of two casca?ed
stages, using a 6SL7 and emploY111g
20 db of feedback. The output of the
second stage is transformer coupled to
the two diodes, and the switch Sf selects
the cathode res istors to control delay.
Switch S1 connects the two cathodes
together for symmetrical indication of
phase or signal polarity, being left open
for asymmetrical patterns. V 4 and Vs
are the two oscillators, arranged so as
to permit adj ustment of frequency so
they do not interlock and cause pattern
abnormalities. The outputs of the two
"oscillators are adjustable by Rg and
R 22 • Switch S 9 permits either oscillator
to be fed directly to the 'scope to provide a single-dimensioned pattern such
as those of (B) and (C) in Fig. 1.
Both oscillators are normally coupled
to the g rids of V 9' and the amplification of the two sections of V 3 are independently controlled by the diode voltage. Thus the signal fed to the 'scope is
proportional to the input voltage, g iving
the pattern described. The instrument is
powered by a conventional supply fo llowed by a voltage regulator tube, V 7 '
When used as a single-dimension
driver, the instrument is simplified by
the elimination of one of the control
circuits and by operating one of the
oscillators at a lower output level to
provide the half-inch band of the pattern.
When used w ith a stereo system, only
one pair of oscillators is required since
all the controlled amplifiers can be supplied by one and all the band-deflecting
circuits can be supplied by the other.
Thus the size and cost of a multichan nel indicator is not in direct proportion
to the number of channels. Figures 5
and 6 show the instrument from front
(C ontinued on page 7i)
Basic Circuitry
The circuit of the instrument is relatively simple. Referring to the block
schematic, Fig. 3, it will be seen that
the signal is fed through an a mplifier
to two diode rectifiers, with a control
voltage being developed ac ross cathodeto-ground resistors and charging up
two capacitors. The time constant of
this circuit is controlled by the value of
the resistors, which are adjustable.
The voltages developed across the
capacitors are fed to the grids of two
amplifier tubes through isolating resistors, and the outputs of two sinewave oscillators are fed to the grids
through capacitors. The oscillators operate in the vicinity of 50 kc, and differ
in fr equency by a slight amount to prevent interaction. The outputs of the two
AUDIO ENGINEERING
•
VERTICAL
HORIZONTAL
H. F. OSCILLATOR
H. F. OSCILLATOR
SEPTEMBER, 1953
POWER
SUPPLY
Fig. 4. Complete schematic of the cathode-ray Volume Visualizer.
. 31
A New Volume Visualizer
NORMAN PRISAMENT'"
Utilizing a conventional oscilloscope as the indicator, a new
driver unit provides instantaneous level readings which are
made useful by incorporating a controlla ble delay circuit.
•
Typical studio a pplication of t he new
volume
visualizer,
using a convent ional
'scope as the indi cator.
•
meter to fo llow the initial transients of
waveforms quickly but instead of r eturning to zero immediately, the pointer
" floated" back slowlj. With controllable
delay this circuit was useful for recording because the meter t ended to
float along the peaks of the signal. Such
instruments did not attain much popularity, and were generally displaced by
the standard VU meter which was
adopted by broadcast stations in an attempt to standardize level indications
throughout large and widespr ead network operations. For its purpose, the
VU meter is essentially satisfactory,
but fo r many recording operat ions a
fas ter indi cator is more desirable .
Use of The Oscilloscope
meters were needed the leads to them
were some 100 to 150 volts above d.c.
ground potential. The tube-type volume
indicator was superseded by the copperoxide rectifier type of meter, which
served quite well when used corr ectly.
Recognizing the need for faster movements, the manufacturers developed the
h i ~h-sp eed meter which responded to
the signal with a minimum of delay and
with low overshoot. The very speed of
the movement, however, defeated its
purpose to some extent, for the operator's eyes could hardly follow its movements.
A nother type of high-speed volume
indicator that was often used was an
a rrangement of neon lights, each being
actuated so that it flashed at a given
signal level. This instrument was somewhat complicated, difficult to maintain in
ad justment, although it was fast and
did provide an easily read indication.
In an attempt to give extremely high
speed with some means to enable the
operator to read the instrument easily,
circuits were developed to permit a
T
HE H I STORY OF THE RECORDING ART
port.ray.s a. wide variety of methods
fo r indicating the level at which the
recording is being made, each one attempting to give the engineer a more
reliable picture of the signal as it is fed
to the recording apparatus-whether it
be disc, fi lm, tape, or wire. \Vhile standard VU meters are now in general use
. in broadcasting studios- and even in
most recording plants-there is some
reason to believe that the familiar VU
meter is incapable of show ing the true
condition of the recording operation.
In the earliest days of broadcasting
and recording, the meter used as a volume indicator had little damping and
considerable overswing, but served quite
well in the absence of other methods for
indicating the signal intensity. One of
the principal disadvantages of the early
VI panel was that it occup ied considerable space, but in addition it r equired its
own power supply, and when extension
* R el'veso1JM.
Company, Inc., 35-54 36th
St., L.r.C., N.Y.
(A)
(8)
Ie)
Fig. 1. (A) Typical pattern obtained with the Visualizer at 100 per cent modulation and the
symmetrical presentation. The dotted line shows 50 per cent modulation, and the small dot
at the center of the pattern indicates zero modulation. (B) and (e) Asymmetrical presen tation for signals hoving differing polarities.
30
Obviously, the inertia of a beam of
electrons is considerably less than anythi ng attainable with a mechanical meter
movement. By its very speed, however,
it becomes difficult to read easily, especially when simply connected to a signal circuit. F urthermore, since beam deflection is linear with respect to voltage,
it does not g ive sati"sfactory scale with
respect to db. This problem has been
overcome in the new volume visualizer
which connects between any circuit being. monitore.d and a conventional oscilloscope. In the visuali zer, the instantaneous level is shown by a deflection
of the scope trace, and suitable delay
circuits give the " floating" action necessary to make the indication easily readable. In the first form in which the instrument was made, the intensity of the
signal is shown as a square pattern on
the screen, with both vertical and horizontal deflections being equal. A zero
signal is indicated by a spot in the
center of the screen, and 100 per >cent
modulation would be shown by a square
of light occupying the entire scr een
a.rea-th~ deflection being approximately
linea; WIth respect to db. However the
circuit is so arranged that SO per 'cent
modulati on can be indicated at any desi1"ed deflection from one haH to three
Fig. 2. Three rectangular c-r tubes arranged
for presentation of level information on three
channels simultaneously.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
Flexi-b'l-e Tone Control Circuit
BASIL T.
BARBER ~'
The advantages of variable inflection points in tone controls are well recognized, but
the circuit complications and additional expense does not always justify their use.
The author Americanizes a previously published circuit which is relatively simple.
Fig. 1. Simplified block diagram of the tone
control which employs negative feedback to
provide variable inflection points. Idealized
lead and log net.wo~ks ar.e...snown.
the subject of tone controls indicate ~he
desirability of having the transition frequencies variable, with the
amount and direction of variation determined by the degree of boost or attenuation required.
The analysis and determination of the
varying parameters and their range are
ably covered in Mr. Villchur's article. 1
Most tone-control circuits available at
present have a single transitjon frequency between 800 and 1000 cps, which
remains essentially constant at any position of the controls and their flexibility
and effectiveness is therefore limited.
A method of tone compensation is
presented in this article offering a con-
R
ECENT INVESTIGATIONS 011
* Research Eltgineer, Mass. Inst. of Technology, Cambridge 39, Mass.
1 "The seleetion of tone-control parameters," AUDm ENGINEERING, March, 1953.
tinuously variable transltlOn frequency
and a number of other advantages. The
original article was written by P . J.
Baxanda1l 2 and for a detailed explanation of the circuit the reader is referred
to his article.
One way of looking at this circuit is
to analyze it in terms of Laplace Transforms. Oversimplifying the original
schematic, the circuit can be broken
down into two lead and two lag networks, as shown in F ig . 1. The lead network (C), being inside a negative feedback loop, becomes a lag network and
similarly the -lag -network (B) becomes
a lead networR.3 The net curve will
theref.ore be either a boost or an attenuation, as shown in Fig. 2, depending on
the relative position of the time constants Ta, Tb, T c and T d . When T a>= Tb
and T c = T <1, the curves cancel each other
p.r oducing a fl-at.· fr-equency response.
Figure 3 presents the tone-control circuit in detail. It is similar to the original
circuit,· but with parameters slightly
modified to make the circuit adaptable
to American tubes and components.
Fig1lre 4 shows the actual frequency
response of the schematic of Fig. 3. The
low-frequency turnover is made variable
from 800 to about 100 cps, depending on
the degree of bass boost or attenuation
requi.red. The high-frequency turnover
varies similarly from 1000 to 8000 cps,
depending on the degree of treble boost
or attenuation requirea. These curves
2 Wireless World, October, 1952.
3See Ap.pendix.
4 Ref. 2, p. 404, Fig. 6.
-- '-IAI
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~
/
i
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T, T,
r-
//~.'"
~E
,
_._.-
. /.
-
"""
o·
1
1
Td
TO
trOd
.!..
. Inc.lTc
~
1
TO
[".. f 1
1
r; r;;
Fig. 2. Frequency response of the actual lead
and lag networks of Fig. 1. B' and C' are
curves Band C after feedback.
should therefore prove to be effective in
compensating certain deficiencies of an
audio system explained in Villchur's
article. Specifically, "partial" speaker
compensation can .be accomplished without any boominess (especially on male
voices) , and without high-frequency
distortion.
The circuit presented has, in addition,
a number of other advantages which are
equally important. In most tone-control
circuits at present, the apparent boost is
attained at the expense of an equal attenuation at the center frequency. An
additional gain equal to the boost attainable must therefore be provided. In a
"flat" position, there is unity gain plus.
all the distortion generated by the stage
of amplification. In the proposed circuit,
the loss is in the form of negative feedback with its associated advantages of
reduction of distortion, impedance, and
noise, and the increase of the linearity
and frequency response of the circuit.
For instance, if we assume that a boost
12AX7
+2 5
+20
+ i5
+ iO
-
r-:: f:::r-.
+5 L-
Hd>iO
-5
-5r-
-iO
-1
1..-
j....-i--' 10-
Io!:
~ r-.....
.... ~ k'"
I .~
~ ~ ~d:::
F=:::: l:::::
~~~
--=::::::::: t:::::: ~
-~~
i'-
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-20
IT-REBLEI
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r- t-
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V ...........
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•
100
FREOUENCY
J
.
f
1000
IN CYCLES PER SECOND
.,.
20000
Fig. 3 {left}. Over-all schematic of the circuit as modified for American tube types. Fig. 4 (right) . Response curves obtainable with the feedbacktype tone control.
AUD~O
ENCINEERINC
•
SEPTEMBER, 1953
29
parently does not impair the results. of the instrument. The ON-OFF-CARRY
An input range of some 60 db can be switch is located next to the air intake
obtained for a single setting of the vol- for the blower type cooling fan. This
ume control. This covers the range fan-more readily seen in Fig. 14-is
from a relatively low voice to a rather used in spite of its power consumption,
loud shout.
in order that. the instrument will never
The selation· of Sf}me of the prtlblems reach temperatures on its outer ca'Se
peculiar to portable equipment appar- high enough to interfere with the pack- \
ently improved the instrument for desk ing of the instrument into brief case or
use. Electronic instruments carried suitcase with other articles immediately
about sometimes must operate from odd after dictation has been concluded.
power sources through some type of
Mounting of the plastic di!>c is esconversion equipment, as for example sentially the same as on the Edison Telewhen recording machines are used in Voicewriter. The disc cover is raised,
the disc slipped in against a curved
automobiles. This is a common use for
portable dictation equipment-many stop, and the cover is lowered, bringing
salesmen and investigators dictate their down a cone which automatically centers
reports immediately upon returning to and clamps the disc.
A single knob called the 4-in-l contheir cars. Thus it is desirable that the
trol handles all recording and playback
power requirements should be as low as
possihle. By employing a low-powered operation. This includes positioning of
motor and increasing the efficiency of the styli, movement of the styli to any
the recorder (which permitted the use point on the disc, and changeover of
amplifier circuit fwm, r.e cord to reproof a Tow-power single-ended amplifier)
the required power consumption was duce in two different ways. An innovareduced from the previous minimum of t~on i.s the ~limination of a neutral posi60 down to a value of 25 watts .
. tIOn In whIch both styli are raised off
It is obvious that if the new instru- the disc by the user. Since a user will
ment employs the same disc as other be. ~ither recording ,Qr playing back, the
Edison instruments it can be much more abl!tty to move over the surface of the
disc has been combined with the playreadily integrated into existing systems.
This has been accomplished even back position.
With the control knob down, as shown
thou~h the disc now takes up 'a good
in Fig. 13, the VP is ready to record.
p~rtlOn of the total instrument area.
Both the diamond recording stylus and
F~gure 13 gives a good view of the instrument and its microphone. In addi- the sa~phire playback stylus are on the
tion, a floor switch and a stethoscope- disc with the reproducer head trailing
type hearing device are available to per- the recorder head by a few grooves.
mit operation of the instrument for The amplifier change-over switch, S1
transcribing purposes. This feature of in Fig. 15, is now set for recording. To
"combination" use is handy when travel- obtain playback of the last sentence or
so, the user turns the control knob to
ing if, by chance, the user should find
himself in an area where no Edison the right. This moves the S 1 to the r etranscribing equipment is available or produce position and the voice plays
if the instrument is used by doctors, back through the hand microphone.
lawyers, or others whose dictation pe- Since the recorder stylus is still on the
riods practically never correspond to disc during this recall playback, unmodulated grooves are embossed. The
transcription periods.
The new instrument is known as the control knob has a spring return bringVP Edison Voicewriter. Its low sil- ing it back to recording position when
houette permits all controls to be ap- released.
Lifting up the control knob fixes it
proached and operated from the top
Fig.
28
14.
in r.epmduce. position. This hfts. the recorder stylus from the disc and puts the
change-over switch in the reproduce
position. In playback position it is possible to scan the reproducer head
through any portion of the disc by rotat.i ng the control kflOb, This may be
done while the turntable is turning in
order to locate a particular part of the
dictation. The relatively light reproducer stylus pressure does not damage
the grooves.
Signal System
The signal system on the VP has
been refined to give positive warning
with minimum distraction. The ON light
glows continuously as long as the power
is on. The TALK light is on only when
the instrument is set up to record. If
the control knob is not in recording
position or a disc is not on the turntable or the disc compartment cover is
not closed, tHe T A'LK light is out.
The dictator is warned of the approaching end of the disc by a ticking
'sound. This starts during the last minute of recording, and gradually increases
in intensity until the end. This is accompl1shed by two little hammers alternately raised oy a pin on the recorder
carriage and dropped to hit the bottom
cover.
At the end of the disc a switch is
closed by the moving carriage, which
stops the turntable (during recording
only) and turns off the TALK light.
The indexing mechanism moves relative to the recorder-reproducer carriage
through a gear and rack arrangement.
The indexing mechanism and the CORRECTION and LENGTH buttons are driven
by a cord which is pulled by a wheel
attached to the gear rack, the other end
of the cord being reeled onto a springloaded wheel. A 4-to-l length amplification of the recorded band on the disc
is obtained on the index slip. Pressing
down on the "L" key for length of
letter or the "C" key to indicate a correction perforates the index slip in the
( Contin1ted on) page 66 )
The YP Yoicewriter, (left) with cove,r removed, and (right) with turntable and fro nt escutcheon removed to show drive and feed mechanism.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
the recorder is on the disc, one grid of
the multi vibrator is grounded causing
the light 14 to glow constantly. At the
same time, the warning relay K6 is deenergized. These actions are all accomplished by mechanically 0 per ate d
switches linked to the front control lever,
and the disc cover and centering cone.
As the recording arm and its associated control linkage is driven, it
carries with it a series of trips which
actu",te various switches. The first of
these switches, S 7 has no effect upon
operation until relay K 3 is de-energized
by depressing the cradle switch O l~ a
remote statiOil. It then completes a circuit through an - a.c. buzzer 13 which
warns the attendant at the recorder that
a disc exchange is necessary. The point
at which S 7 operates can be preset, depending on the average length of dictation, to cause an automatic exchange
insofar as the dictator is concerned. In
effect, the disc will seldom be recorded
tJ the end because anyone who hangs
up in the period between the closing of
S 7 and the end of the disc will automatically cause an exchange.
If, however, a dictator proceeds _
•through this portion- without hanging up
and approaches the end of the disc, a
second trip opens the grounded circuit
of the multivibrator causing it to
operate.
The pulses from this grid -are fed into
the audio system through an injection
transformer and serve as a "tick" to
signal the approaching end of the disc.
This ticking sound does not interfere
with the recording. Finally, if a dictator
proceeds all the way to the end of the
disc, the same trip closes the circuit to
the warning relay K6 which in turn injects the end tone (hum) into the audio
system to signal that the end has been
reached, sounds the warning buzzer 13
and cuts out the first t wo control relays
K3 and Ks.
The Amplifier
•
Fig. 13. The VP Edison Voicewriter.
•
from the remote audio lines or the
crystal reproducer directly.
.
Some a.v.c. action is necessary in thiS
amplifier to compensate £or v~riations in
signal strength due to varymg lengths
of line or to different voice an plitudes.
The 6BJ6 peniode connected as a diode
provides this action. The bias for the
a.v.c. circuit is preset by a voltage
divider network across the plate supply
to which the cathode of the a.v.c. tube
i3 connected.
L. order to prevent recoxder chatter
due to amplified noise when the eq';1ipment is in standby, a mute SWitch
grounds the signal at the grid of the
output tubes. This switch is mounted
on the clutch magnet and opens when
the clutch engages . This circuit is a refinement of an earlier model which provided muting by biasing the cathode
circuit of the output tubes to cutoff, but
the power output life of these tubes was
adversely affected due to cathode poisoning. This same problem has been encountered in computer circuits.
Thus it can be seen that the TeleVoice System provides simple, complete
dictation facilities wherever instruments
can be permanently set up. To complete
the line of dictation equipment it was
necesary to develop a more flexible instrument that could be readily moved
around within the office and easily carried for dictation anywhere at anytim e.
The audio amplifier in this instrument
is a straightforward dual-pprpose unit
employing three resistance-capacitance
coupled stages- a voltage . amplifier, a
phase inverter, and a push-pull output
stage. Since the carbon buttons approximate constant-voltage devices (output
voltage proportional to sound pressure,
equal at all frequencies within their
pass range), and since the magnetic reTHE VP EDISON VOICEWRITER
corder is a constant-velocity transducer
(stylus motion proportional to freAlthough a study .of business work
quency), the amplifier is designed with
pattern reveal.ed that 94 per cent of all
a substantial high boost. The result is _ instrument dictation took place within
a constant-amplitude recording. The the office rather than at home or on the
playback head employs a PN crystal, road, the public ' began to register its
which is amplitude operated. Therefore,
demand for one machine sturdy enough
the playback portion of the amplifier is for daily desk use and light enough for
fiat in response. As the whole amplifier comfortable carrying outside. In the
is used in both record and reproduce
long run, the customer gets what he
it is necessary to place the equalizing wants. Early in 1950 Edison engineers
networks in the input circuit.
-together with the eminent industrial
The output of this amplifier is coupled stylist, Carl Otto---began shaping plans
through a transformer either to a low- for the first truly portable di~tating inimpedance magnetic recorder or to the strument in the history of the business.
remote audio lines by the record-reproIn this matter the original thinking
duce switch, The high-impedance input seemed simple and sure. Since the one
i~ provided by a step-up transformer
extra piece of equipment a businessman
AUDIO ENGINEERING
•
SEPTEMBER, 1953
never seems to mind c~rrying with him
is his own brief case, the decision was
made to produce a machine which could
be slipped right into a standard lettertype case .
A large number of standard letter
cases were purchased and it was found
that a block of wood not greater than
20 in. in height would readily go into
all of them. The width and depth of the
cases gave considerable latitude to the
other two dimensions of the instrument.
An interesting bit of history is that, by
computing the average weight per cubic
inch of a number of standard dictating
machine components, such as motors,
amplifiers, drive systems and so on, a
weight expectation was arrived at which
turned out to be within 2 pounds of the
fina l machine.
With the important dimension determined, it was thought that the problem
was solved until it was realized that
there were a number of other items in
recording eguipment that determine
whether or not it is really portable.
Consider, for example, the recorder and
reproducer styli. Tests indicated that it
i3 not good common sense to have them
bouncing around on the record while the
instrument is being carried. This was
solved by adding a third position to the
ON -OFF switch-a CARRY position which
locks up the recorder and reproducer.
Another one that presented quite a
problem was that the loudness with
which most people talk is determined,
not only by their own natural habits,
but by the noise level surrounding them.
Thus, a man will talk rather low in a
quiet, soundproofed room, but the same
individual will practicaUy shout in a
noisy room. This meant that the recording levels can not be readily preset,
for one man in his travels will encounter
all variations of ambient noise levels.
To overcome this problem, a varistortype peak clipper was developed which
limits the recording level just below
that which would tend to cause cut-over
between grooves. Of course, when the
limiter is working hard, some distortion is introduced, but for all normal
ranges this is not noticeable and ap-
27
turn energize the "Busy" lights, start
the motor and permit this dictator to
seize the system.
When the dictator is ready to talk,
he presses the handset button thus placing the carbon button (d.c. resistance
approximately 50 ohms) in parallel
with the 680-ohm resistor. This increases the current in the network to
approximately 60 rna and energizes the
second control relay Ks which operates
the electro-magnet which engages the
clutch and thus starts the turntable.
The playback relay K~ operated by
the "listen" button on the station base is
energized by the same low-voltage
power supply, using one leg of the a.c.
lamp circuit in conjunction with one
leg of the audio circuit.
The playback relay operates the clutch
magnet K. and the record-reproduce
rotary solenoid K j • The discharge surge
of a 40-""f capacitor is used to overcome
the high inertia of this unit, while a
steady d.c. current keeps it energized.
The well shielded record-reproduce
switch operated by the solenoid transfers
both the input and the output circuits
of the amplifier- the input from the
transformer to the reproducer and the
output from recorder to the remote
audio lines.
When the equipment is set up for
operation, both the recorder and reproducer are On" the disc, although the
reproducer is displaced in such a way as
to trail the recorder by a preset number
of grooves. Therefore, when a dictator
listen' back, both the recorder and reproducer continue to track- the former
,x,0.15
.00047 :
AMP.
CHASSIS
I
I
I
I
embossing an un modulated groove while
the latter is picking up the last few
sentences of dictation. The dictator can
therefore stop listening back at any
time and proceed with his dictation
without the possibility of over-recording
or the loss of dictation.
.
The cuing or indexin~ system is composed of two small coils mechanically
coupled to the record-reproduce ar m
through a linkage which amplifies the
motion of the record-reproduce arm by
about 4 to 1, thus increasing the accuracy of the indexing system. The two
indexing coils with brass pointed
plungers are pulsed by the discharge of
an 80 microfarad capacitor through relay contact combinations. De-energizing
relay K3 pulses the "Length" index coil
L 3 (marking the end of the dictation)
while energizing K 2 , Ks and Ks at once
pulses the "Correction" or "Special Instruction" coil. The brass plungers in
turn punch holes in a paper index slip.
System Set- up
For practical purposes the limiting
factor on the number of stations per
recorder is the total dictation workload
emanating from these remote locations.
The 6,000 words per day average figure
which has been chosen as the result of
an extended field analysis of the nonobjectionable waiting and collisi.on times,
limits the number of stations in the
average installation to approximately
ten.
The technical factor limiting the number of remote stations which may be
connected to one central recorder, how-
ever, is the current available to light
the "Busy" lights and in many cases
this is the determining limit. This factor
is a function of the transformer design,
the requirements of a su fficiently bright,
long-lived lamp and the voltage drop in
the remote lines. The maximum secondary transformer rating- 16 volts open
circuit and 3 amps short-circuit- are
more or less set by the electrical code
requirements on low-voltage wiririg.
These factors result in the permissible
maximum of 20 stations connected to
one recorder.
In order to keep network wiring costs
at a minimum, standard telephone type
cables (#22 wire) may be employed
in most cases. If, however, an exceptionally large number of stations or exceptionally long runs are encountered, the
use of # 18 wire can eliminate the voltage drop in the lines from consideration
as a limiting factor in the installation.
Mechanically coupled to the drive system and the disc loading system of the
Tele Voicewriter itself are a ser ies of
warning devices which make incorrect
setup and operation of the equipment
practically impossible. A neon light in
the plate circuit of one-half of a 12AU7
used as a multivibrator, flashes if the
instrument is not correctly set up to
receive dictation. When the multivibrator is operating due to faulty set-up, a
warning relay K6 is energized which in
turn lights the remote "Busy" lights
and injects a 60-cps hum" rich in harmonics, from across one leg of the
bridge rectifier into the audio lines.
When a disc is on the turntable and
~7~
I
'V
I
I
'-- - ---l
t ill! r
'''0;1111
POWER SUPPLY
Fig. 12. Sche matic of the Te leVo icewriter, includ ing amp lifier, control circuits, a nd a re mot e station.
26
AUDIO ENGINEERING
•
SEPTEMBER, 1953
previously, a dictator ral·ely listens back
to his dicta.tion except when he has been
interrupted. Under these circumstances
he listens only to the last sentence or so
in ord~r to obtain his trend of thought
Therefore, a remote dictat ing system
must indude a means to obtain this
result. F urther, as the system is used
by many people, it is improper to permit
one dictator to listen back to a nother's
recorded dictation. A nother problem is
tha t whi le a dictator will indicate a
length mark after each letter during a
period of dictation, he usually fai ls to
indicate the length of his last letter.
This no doubt is due to the fact that he
mentally finishes his work at the end of
dictation and merely hangs up the
microphone. Hence, it is advisable to
make the last indication automatic.
A long study of dictating hab its indicated that the average length of letter
dictated was one and one-half minutes,
and that the average number of letters
dictated at anyone time II·as two.
Further, although the average dictation
takes place at the rate of 100 wo rds per
minute, S0 that a dictating machine
might ta ke some 40,000 to 50,000 words
a day, the actual numbel· that can be fed
into a system used by more than one individual is approximately 6,000-10,000
;words, beca use of the poss ibility of
collision between two dictators desiring
to use the system simultaneously and to
the large percentage of dictation time
employed for thinking . Of course these
figures do not hold for repo rt writing
and other special applications.
Early experience revealed that dictators were perfectly willing to wait one
or two minutes for a machine but obj~cted t~ longer waits. Although dictatIOn equipment has been on the market
for years, many people are still "mike
shy" and welcome the introduction of
a more fami liar type of microphon ethe standard telephone hand-set
The above are some of the factors
that determined the form of confie-uration of the system fina lly evolved. Fig. 9
shows the components of the T ele Voice
System, in which (A) is the recorder,
( B) the executive desk stat ion. (C) the
alternative executive wall station, (D)
the secretary's transcribing instrument
with (E) her start/stop and backspace
controls. The disc record is shown as
item (F) . (G) shows the internal appearance of the recorder, while Fig . 10
shows the underside and the control
base.
The recording is embossed on both
sides of the 7-in. Vinyl plastic disc
having a 10 -in center hole. A lthough
a band of only approximately 10 in.
is utilized on each side of the disc surface, one disc is sufficient for 36 minutes
of recording. The disc revolves a t 20
Lp.m. and is embossed at approximately
260 groves per inch. The inside recording is at the rate ·of about 4 in. per sec.
and the outside at 1.7 times this linear
speed. The disc is mounted simply by
raising the enclosure cover, slipping the
disc in as far as it will go and lowering
the cover. The turntable does not have
the customary spindle, but in its place a
centering cone is mounted on a shaft
AUDIO ENGINEERING
•
•
Fig. 11. Inside view
of the executive desk
station.
•
carried by the bridge over the turntable.
This cone is actuated by the enclosure
cover to center and clamp the disc to the
turntable. Centerin g is accurately reproducible to wi thin 0.001 inches-much
better than that obtained on phonograph
records.
The stations (F ig . 11 ) are modified
telephone sets, employing the standa rd
carbon button transmitter and magnetic
receiver. The dictator can perform. the
functions of ( 1) seize the system; (2)
start and stop; (3) signal correction ·;
(4 ) sig na l end of dictation ; and (5)
.play back a portion of the recording.
Seizure is accomplished by removing
the handset from the hanger. As basic
T eleVoice is a party line system, the
signal light is turned on in all stations
by this act Thus .another dictator need
not lift his handset to determine whether
the line is busy or free.
The handset button controls sta rt and
stop, while the button on the station
plays back the last 15 or 20 words.
P ressing both buttons at the same time
makes a correction hole in the index
slip on the recorder. Hanging up the
handset or momentari ly depressing the
hanger produces a nd end punch hole.
The controls and th e voice are transmitted over a 4-wire net work to the
centrally located recorder.
Usually the Transcribing and Recording instruments are placed close together so that one operator can handl e
both.
TeleVoicewriter Electrical Circuits
Fig'ure 12 is a .complete schematic of
the Tele Voice system whi ch can be
broken down into three units :
a. The remote-control circuits, lowvoltage power supply, and remote
telephone-type stations;
b. The mechanism-electro-mechanical devices to provide drive, start/
stop, indexing (cueing) , etc.; and
c. The amplifier- including recorder
and reproducer.
The telephone-type instruments which
comprise the "business end" of this dicta ting system are connected in par-allel
by -a four-wire network to the centrally
located, low-voltage power suppLy. One
pair carries the a.c. supply for the red
warning " Busy" light on each remote
station. Since the other pair carries the
audio, the pairs must be individually
twisted to maintain the hum below
audibility. A t the same time, the d.c.
supply for the carbon button transmitter
is used as the relay control current to
reduce the number of wires required
in the remote network.
The low-voltage d.c. supply of 45
volts is obtained through a step-down
transformer ·T 5 and a full-wave selenium
bridge recti fier C R, with associated
filter. The relays in this circuit add appreciably to the filter system. When the
handset is removed from the cradle at a
remote location, the circuit is completed
i ro111 th is low voltage supply through
l'il"} d.c. relays, [(3 and [( 5' the primary
of the in9ut tra nsfoi'mer Tl and a 680Oh111 res istor ac ross the transmitter and
··talk" switch.
The resulting current of approximacelv 45 ma is sufficient to energize
0111y ;·eJay [(" the contacts of which in
Fig. 10. Two views of t he Televoicewriter- ( A), und ersi de, showing ampl ifie r and motor; an d
(B), th e control base.
SEPTEMBER, 1953
25
The Dictatin-g Al\achin,~-
..
.,.,-
A Specialized Recording System
RICHARD M. SOMERS'"
In two parts-Part"
N TI L I'\O W, thi s report has been suffic,iently o bj e~ ti ve to cover th e d icta-
U
tIOn a rt as mterpreted by the fo ur
ma jor manufa cturers.
From here on in , di scussion is limited
to the E dison Voicewriters, but it shoul d
be possible to "obtain a 'good ' idea 'of the
general manner in which problems
peculiar to dictation r ecording a re
solved. At the present time, Ed ison is
concentrating its sales efforts on t wo
"Mana.ger af Eng ineering, Ediphone DiViS£OH,
T ho'm as A . Ediso'n, i nc.
di ffe rent types of di ctation systems, involving two recordin g un its and one
secreta l-ia l transcribing unit. Althoug h
both systems have been g iven considerabl e publicity, this is th e first time the
complete circuitry of each is bei ng exposed to the critical eye of the techn ical reader.
For many years it has been recognized that a centralized system of dictati on woul d be des irabk
There a r·e
many reasons why such a system was
so long delayed but hinds ight indicates
that only two were of any real importance; 1) lack of understanding of the
problem a nd 2) lack of equip;llent to
carrY out the prog ra m. The first was
overcome by Operation Guinea Pig,
wherein som e 60 insta llati ons were made
in one locality over a peri od of approximately 5 years. Each one differed from
all the other s and va ried fr om standard
telephones to pract ically compl ete recording machines at the dictator's desk.
From these evolved the simple system
in use fod ay.
In order ' to understand the operation
of the T eleVoice system, it is necessary
to deviate for a moment and discuss
some dict<lfti on habits. As mentioned
DISC CENTERING MECHANISM
-
---~---~.
:..
Fig, 9. The TeleVoicewriter ond related equipment: (A), recorder; (8) , executive desk station; (e), alternate wal.1 stat!on;. (El. secr~tarial ~t?rt­
stop-backspace control mounted on typewriter; (0), secretarial transcribing instrument;. an d (F), method of plaCing disc In recording pOSItion;
(G), the recorder with the outer case removed,
24
AU DIO ENGINEERING
•
SEPTEMBER, 1953
2
Fig. 7. Loudspeaker modifications: (1) Rad!al
slits; (2) Cemented area; (3) Rim, treated wIth
glycerol ; (4) Supporting ring of speaker frame .
Fig. 5. Detail of corner construction.
tempt to find the limits of accuracy and
design necessary in a straight horn, an
attempt which could be afforded because
the proposed structure made modifications comparatively simple. This would
not be true in a conventional horn.
Crossover Frequency
The reason for using a 600-cps crossover is rather complex. It is the writer's
opinion (and difficult to justify) that a
fo lded horn with an axis rotation
through 270 deg. should be used w ith a
crossover of 200 cps. Operation with a
crossover of 400 or 600 cps is not particularly good; there seem to be too Fig. 6. Rear view of horn during construction,
many resonances, unpleasing to the ear, showing details of the horn and of the speaker
and crossover network mounting.
which develop in the second octave. Now
whethel' these are due to the variations
of rigidity in the cabinet, the use of one create a loss of power. However, the
piece of wood as the wall of two sections adequate absorption of the back-wave
of the horn, or the organ pipe resonances removes the attendant difficulties imencouraged by the sharp bends neces- mediately apparent when one realizes
sary in a tightly folded horn, is not im- that in all horns using radiation from
mediately apparent .. One experimental - both the front and the rear of a single
horn the writer studied had definite or- speaker, two identical frequencies iss~e
gan-pipe resonance, wood resonance, from the same plane, and are not 111
and Helmholtz resonance. But, because phase. It would be interesting to see
the proposed horn would bend through some work done on the shifts in radiaonly 90 deg., and be simply constructed tion pattern and coincident reinforceand adequately back-loaded, it was felt ments and cancellations of such horns.
that a standard 600-cps crossover network could be used.
The theoretical cut-off of the horn
A
was set at 60 cps. The reasons are more
eas ily justifiable than those for the crossover. The curve of a 60-cps horn is easy
to plan; the horn can be of an effective
length (approximately 6 feet) without
'"v
having a mouth area the size of a wall.
G) -c:::::::J
Practically, there is good radiation to
40 cps, with audible sound to 17 cps.
OJ
'"
F inally, considering the loudspeakers
availabl e, it was doubtful if any frequency lower than 40 cps could be expected.
.~
Also the curves drawn of the 'frequency
resp~nse of the entire unit indicate that
the horn unit is quite efficient when
compared to the treble unit.
Rather than' try to hide the horn, considering it both as a prototype and-if it
performed satisfactor.ily-;-as a p~rma­
nent fixture in the wnter s home, It was
decided to make it an obvious piece of
furniture, generally rectilinear in shape.
The volume not used by either the horn
or the back-loading space was used as
a n enclosure fo r the treble unit, in this
case an E lectro-Voice SP-12B. At the
time" the plans were drawn it was decided that the framework holding the
grill clMh over the treble speaker would
be large enough and so placed that a
horn could be added later behind the
same grilL In other words, the basic design is fairly flexible. Because ?f the
position the horn would occupy 111 the
home, birch veneer ~ -in. plywood was
used for the outer surfaces. The corners
were left open, the plywood touching
corners as shown in Fig. 5, and ~ -in.
square maple strips were glued into
(Cont'il'llied on page 63)
f~~~l
t- I~~==I=HI
-t
--+'.,
Description of Horn
The horn structure itself is quite simple, as can be seen from Figs. 3 and 4.
It consists of two parallel walls, the
front and rear, 13 inches apart, and
slightly over six feet long; a long
straight narrow wall separating the
front and I'ear walls; and a fourth wall
which is an approximation of the curve
necessary to provide an increasing area
which is a function of an exponential
curve. The computations fo r determining this curve have been discu sed previously.l
The horn is back-loaded, which does
1
See
AUDIO
for March,
ENGINEERING
April, and October, 1952.
AUDIO ENGINEERING
•
'.,
-+.,
11-1----~Tf,',11
---t
@--+t--
~=1!==~~~~
SECTION
A - A
Fig. 3 (left). Construction of horn, viewed from the rear. Front and bock could be interchanged
to suit room shope and configuration, Fig. 4 (right>. Cross-section through A-A. The numbers
refer to the following parts : (1) Horn driver, an especially modified 12-in speaker. (2) Treble
unit; a tweeter can be mounted above or below it. (3) Crossover network. (4) Crossover network
control pad. (5) Reflecting baffle.
SEPTEMBER, 1953
23
A 'H orn Enclosu re for Custom
Installations
ARNOLD
J.
GASSAN ':'
Construction details for a built-i n horn-type lo udspeaker which is not
larger than the room in which it is to be used. T he a uthor covers the steps
involved in the original concept, and describes the installation fully.
I
the types of horn-loaded
presently
loudspeaker
enclosures
available, certain a-priori assumptions were considered. T he first of these
is that a horn should be so constructed
that it will radiate along an axis of 45
degrees from either ,of perpendicular
walls. The second is t hat a horn constructed in this way will produce an optimum sound pattern for listening. In
many cases the ass umptions are just ified.
However, if the room in which the enclosure is used is considerably longe'r
tha n it is wide, and the sound system is
designed to provide pl easure for a small
number of people, as it usually is, these
N EXAMINING
* 2176
Co lo.
S. ,Washington St., Denver 10,
assumptions are not necessarily valid. In
the w r iter's home the assumptions certainly are 1Vot valid, for he has tried
enclosures of the "corner" type, and they
did not produce the results desired, per- '
haps because the listeners us ually sat at
one end of the room, as indicated at (A)
in Fig. 1. From observation, it was decided that a horn radiating along the
major axis of the room was more satisfac tory, as indicated at (B). The same
circumstances have been noted in certain
custom install ati ons~that the optimum
radiation was along themajor (or in an
odd case, the minor) axis .
In certain cases there is a practical
objection to the use of a conventional
corner horn: it demands the availability
of two walls which are clear for a dis-
Fig. 2. Because of extending to the ceil ing, the e nclosure
does not appear to
be excessive ly large.
•
22
(AI
(B I
Fig. 1. Comparison between coverage of con ventional corner enclosure (Al and the a uthor's horn (8), which is ' designed to radiate
primarily over the major axis of the listening
room.
tance from the horn. In practice this is
quite often impossible to obtain.
F1'Om experiments in the writer's
home, and the observatiOl~s made above,
a decision was made to develop a horn
util izing one clear wall, and the j unction
of that wall with the floo r. There were
definite and pressing limitations on the
expense of the prototype horn and its
associated speakers, as well as limitations of the base area of the enclosure.
The general limiting parameters were:
1. \ Vidth- not in excess of fo ur feet.
2. Heig ht-not mo re than eight feet.
3. Depth-little more than one foot.
4. Speakers-limited by what was on
hand, or available at low cost.
5. Frequency- original design for
two-way system, with provision
for simple conversion to threeway.
6. Crossover-600 cps, for reasons
discussed in text.
7. Horn frequency- 60-cps theoretical cutoff.
The first two condi tions were those imposed by the max imum size of standard
plywood sheets. T he depth of the unit
was controlled by the proposed use of
similar models in custom installations in
new houses, where a horn could be built
into one wall, as an integral part of the
wall and a bookcase, where no floor
space was to be used for enclosures. Because this hClrn began as an experiment,
it seemed worthwhile to try certain other
innovations, such as using an inexpensive speaker, especially treated, for the
horn driver. Also, there was no attempt
to provide an elabo rate transition or
coupling chamber between the speaker
cone and the horn tiu oat proper. In
other words, there was a deliberate at-
AUDIO ENGINEERING
•
SEPTEMBER, 1953
trolled by a balancer potentiometer, the
arm of which goes to the main organ
preamplifier in common with outputs of
the other divisions.
'" 0s-'
...0
QW
"
....
'" S
Chard and Pedal Divisions
~~
~
Figure 6 shows the pedal and chord
divisions, as well as the amplifier section, which is simple.
There are six chord oscillators, each
tunable to two frequencies, making a
fu ll octave of twelve tones available.
No chord has more than four notes
and all use tones between F-174.6 and
E-329.6 cps. The chord oscillators also
supply the tones which pass through
frequency dividers and give the pedal
notes.
Each oscillator has four contacts, one
associated with each of four busbars.
When a contact is touched to the upper
bus bar the oscillator is moved down
one-half tone by connecting a capacitor
from the tap··on -the ·tuning ·inductor to
the grounded har. When 'a 'contact is
touched to the second bar the oscillator
plate output is connected to that .bar.
This second bus bar carries the chord
output signals.
The lower two busbars carry pedal
output signals taken "from the oscinators
in the same way.
The chord actuating system is a mechanical assembly which cannot well be
shown here. Each of the 96' buttons
selects the right three or four notes for
the chord .and the correct two notes for
the pedals. The notes are predetermined
by the positions of small projections
on 96 pivoted levers underneath the
buttons. The projections press actuators'
to operate the required contact springs.
Let us take an example, say the button which creates. the C-major chord
consisting of C-E-G. When the button is
pressed one lever projection actuates
the contacts connecting the B-C oscillator to the chord signal busbar. (This
oscillator need not be tuned since it is
normally running at the frequency of
( Co1'lt£nll ed on page 68)
o
i
CH ORD
BUTTONS
CHORD
GENERATING
SY STEM
Fig. 4. Simplified block diag·ram showing t he va rious sectio ns of the instrument.
tones and make them more pleasing.
The DPDT bass, tenor, and soprano
controls 'switch the three registers as
desi'r ed to the woodwind switch. With
the latter on, the grid of solo preamplifier V8 is connected to the woodwind
modifying networks; when the tab
switch is off, the more complex tone
goes to the preamplifier ,grid.
The preamplifier plate circuit feeds a
tone-color network containing five sections in series between the plate line
and ground. Each section is normally
shorted by a tab switch when the switch
is in the nominal OFF position--contacts closed on one side. When, for example, the 1ST VOICE tab is placed in the
ON position, the parallel combination of
L~o, C 511 and R68 is placed across the
signal line. This gives the tone a peak
near 750 cps, imparting to it a horn-like
quality. The 2ND VOICE section peaks at
around 1,000 cps. DEEP TONE places a
capacitor across the line to cut highs
and make the tone more "mellow,"
while FULL TONE has only a resistor
and gives fiat response. BRILLIANT
shunts the line with an inductor, reducin~ bass to give a rather piercing
quality.
The solo control stage V g-V 10 exists
to allow control of the tonal attack.
Normally the cathodes are at about plus
65 volts, obtained by voltage 'division
from the 270-volt point shown in the
diagram. This cuts off the stage. When
'any key is preS's ed, a solo control line
connected to point X is shorted to
ground QY the solo ,control busbar under
the keys and the key contact. This shorts
the bias voltage to ground. With the
switches in the position shown, C58
makes the attack fairly slow because a
sudden decrease in the cathode voltage
causes a negative surge through the
capacitor, charges C60 negatively, and
moves the grid in the negative direction,
which remains until the charge on C 6 0
leaks off through R rr . When the FAST
ATTACK tab is operated its switch opens,
disconnecting CS 8 ' With the solo accent
switch in the ON position, not only is
C5 8 disconnec,ted but C 6~ is connected
across R 8 0 ' For the sudden decrease in
cathode voltage caused by pressing a
key, C 6 2 effectively shorts the resistor
and reduces the bias for an instant,
causing the note to be loud at first and
giving a rather percussive effect.
Output from the solo division is con-
FROM SOLO OIV.- _ - " , " - A - FROM ORGAN DIV . ....V\I\r-+:,.....~-
+2~
.SOLO"ORGAH AND
'SUSTAINED CHOIlO SI GNALS
EXPRESSION
CONTROL
r-_..-IH - - - - - - f lDUD
TO
G-+ OUTPUT
~MNI.A/'....."""" SOFT
AMP.
CHORD
COOTACT 1
NUMBERS
CHORD SIGNAL
BUSBAR ........-0---'
L£rT PfOAI. SIGNAl
.. BUSSAR ...;j....!-<>J r .......- . .
PEDAl. CONTROL
RIGfT
PE,:~....I_ok>--' L---<~=::.:===-__Cl_RCUT_...JiC>.1j.ME'JG.UCi
ODlO SWITCH
Fig. 6. Simplified schematic of the chord section and the combining circuits.
AUDIO ENGINEERING
•
SEPTEMBER, ' 1953
21
pushing a cher.d button b-r~ing-s ~ in the
chord at moderate volume; when the
chord bar (see Fig. 1) is pressed at the
same time with the palm or thumb, the
chord gets louder. With the tab off the
chord will not sound at all unless the
chord bar is pressed. A MUTE tablet
makes, choras more "mellow".
The pedal division consists of the
two pedals and a FAST DECAY tab. When
the ldt pedal is pressed, a low-octave
tone similar to the lowest note of the
chord beiqg played is heard; when the
right pedal is played, the pedal tone is
a fifth higher; the two give variety.
The FAST DECAY tab makes the pedal
tone disappear almost at once; without
it, "the melody lingers on."
How The Organ Works
The block diagram of Fig. 4 gives an
idea of what is in the organ behind the
panelling, though the diagram is very
much simplified. There are three separate generating systems, all using
vacuum-tube oscillators. The solo and
organ generators are controlled by the
keyboard, after which too, selected tones
go to the tab controls, thence to a pair
of volume controls called balancers, the
amftli fier, the (!)Cp-ression control, and
finally to the bUilt-in speaker.
, Dt TO C6 EACH ,002
'TTTTTT
I~
BKl STEPs t
_ TUNINII swrTCH
SOlO OSCILLATOR
'Y
G.P.K
IOSCLLATllR
rv ru
V2
V2
' 9
P
SOLO
I
Solo Division
The solo division of the Chord Organ
is really a complete Solovox. It is shown
schematically in Fig. 5. V I-V! is the
oscillator, which is tuned over the range
from F-349.2 cps to F -2794 cps. The
tuning is done by the 37 tuning inductors, which are connected in series
between the grid of VI and ground.
When a key is pressed, a corresponding
key contact connected between two of
the series coils shorts the junction to
the solo tuning bar, which is g rounded.
This reduces the net inductance between
VI grid and ground, raising the oscillator frequency to that of the key, The
lowest F has no tuning contact, since
with all the inductors working the os6 llator tunes tq the. low F . C84 is the
main tuning capacitor, while the two
groups C I to Cs and C7 to C12 are for
coarse and fine tuning respectively.
They tune the entire range, of course,
RECTIfIER
I
SOlD
~
' 01
FREQUENCY
DIVIDER
I ~ -L I Y,3b 'VSb
I V3.
V3.
I G
P
I C, K
P
I
DRIVER
I
I
I
I
REGISTER
not the individual. notes. T he latte.r may
be tuned by sliding the cores in and out
of the inductors.
The oscillator rectifier V J(I creates
the sharp positive pulse necessary for
the driver, V ab • The latter drives an
aperiodic flip-flop circuit which reverses
its condition once per pulse--once per
oscillatof cycle. Output taken from one
side of the flip-flop is an almost square
wave of frequency half that of the oscillator, or one octave below. The output of the firs t flip-flop freq uency
divider is taken from the plate of V . a
through R 20 •
A second driver and flip-flop divider
is driven by the output from the first,
so that for each oscillator tone, there
are three octavely related frequencies
made available.
For each frequency there are two
tones, a woodwind tone and a complex
one. The highest-tone woodwind output
is the cathode of oscillator VI' a sine
wave. The next two are square waves
from the plates of one triode of each
divider. T he complex tones are taken
from the plates of the rectifiers and
driver sJages. Waveforms are shown in
The chord generators a re controlled
by the chord buttons, the chord bar,
and the pedals, as well as by the tabs.
Chord-button tones have no balancer
as they are fixed in relative level; pedal
tones can be balanced as desired. In
the following we shall describe the div~sions~ separately, which will clear the
cobwebs of complexity.
I
Fig. 5.
T he six outputs pass through modi·
fying networks of resistors and capacitors to take some of the "edge" off the
SOLO
2nd
FREQUENCY
I
~6bPi: V~
DIVIDER
BASS
1V5~ ""v"s
I
I
I
P
I
DRIVER
G
RECTIFI£R
TV7
P
I
I
I
CONTROLS
o
37 K~
~ ~___-+-~
1
SOLO CONTROL BUSBAR
I-
SOLO TUNING BUSBAR
37 OSCILLATOR TUNING COILS
Fig. 5. Simplified schemotic of the solo section showing t he tone-form ing circuit s which follow the oscillato r ond the frequency-dividers.
20
AUDIO ENGINEERING
•
SEPTEMBER, 1953
Organ for One~Finger
Artists
RICHARD 1rI. DORP
Design ingenuity provides a. wide variety of ton~s and ~o!"binatio~s in a r~la­
tively simple instrument which can be played wlth .a mlnlm.um ~f mstr~ctl?n
and practice. The author describes the Chord Organ CirCUit by circuit.
CONTROL
HAMMOND I NSTRUMENT COMTABLETS
PA NY has an interesting history
which not only includes being among
the first to popular ize the nonacoustic
musical instrument but also emphaSizes
the unconventional. The Hammond or- gan with its drawbars and the Solovox
with its original Idea of a melody 111strument for use with the piano are the
most outstanding items: and the N ovachord, with its ' complex combinations
of effects, though no longer manufactured, is remembered wi th pleasure by
many players and listeners.
The newest Hammond contribution
is the Chord Organ shown in Fig. 1. Fig. 1. The Ham Though it adds little to the art of music mond Chord Organ .
as ' ~ uch , it is des igned as an instrument
which can fulfill the dreams of many
innately ,musical people who have not
had the opportunity to learn to play
normal instruments. The Chord Organ
is primarily for one-finger a rtists and
it gives them, with small practice, the
ability to play full musical selections,
complete with harmonies. To do this it
resorts to more complexi ty than most
(which are
electronic in struments
usually c01npound---having many similar
circuits) but it is easy to understand
and is so ingeniously designed that the
Rube Goldberg aspect disappears after
thorough examination .
at the left with 96 buttons, a row of
button is pressed, a chord sounds. There
are 96 buttons; fo r each of the twelve
control tablets above the manual and
buttons, and a pair of pedals.
musical keys there are eight available
What The Chord Organ Does
There are four divisions. The solo
chords- from minor 7th to major plus
Examination of Fig. 1 shows that the division operates in the same manner 6th, as shown in F ig . 3. Movable button
organ has a 37 -note key manual, a board
as a Solovox: it is suitable for onecaps are provided so that before playing
note-at-a-time melody playing using the
a selection the chords which will be used
*A"/Idio COHsu.lta.nt, 255 West 84th keyl;>oard. Bass, tenor, and soprano tabmay be marked w ith the caps to make'
Street, New York 24, N. Y .
lets control the registers, somewhat as
recogni tion qu icker. In Fig . 3, for inthe 4-, 8-, and 16-ft. registers are sestance, a typical selection in the key of
lected in a normal organ . FAST ATTACK
C calls for F major (subdominant) , G
From the forthcoming book " Electronic Musical
and ACCENT tablets give the solo tones
seventh (dominant seventh), D seventh
Instruments," published by Howard ·W . Sams Ii
Co .• Inc.
(dominant seventh of dominant) and
a fast attack or a percussive quality.
so on .
A WOODWINDS tablet gives a symmetrical
waveform emphasizing odd harmonics.
A SUSTAIN CANCEL tab is provided for
A nd DEEP TONE, FULL TONE, FIRST
the chord division. With the switch on,
VOICE, SECOND VOICE, and BRILLIANT
tablets give various tone colors.
D~ At E~ B. F
eGO
A E B F. '
The organ division, played on the
~~~~ttt~b •• b.
same keyboard at the same time, g ives
MAJOR+6>h . . . . . . . 0 • • O .
0 •• 0 •
polyphonic music- several notes simulNINTH • • • .9 • • 0 • :
0 • • 0 ml
taneously. STRINGS and FLUTES tablets MAJOR_ • • 0 • G) ill • • 0 • • 0 "'
are provided to call forth either quality
MINOR- • • 0 • •
0 . , cl.·.o 1
or both together. Thus, when the manua l SEVENTH- • • 0 • • 0 G> @ 0 • • 0 _
DIMINiSHED . . . . . . . . 0 • •
0 • • 0 •• 0 +
alone is played with several notes s imulAUGMENTED...... •
0 • • 0 • : 0 • • 0 m1
taneously, the organ division is heard
MINOR 7,"_ • • 0 • • 0 •
on all notes and the solo division on th e
top note only.
Fig. 3, Numbered caps may be placed on the
The chord division is the main di sFig. 2. The chord section is operated by 96
buttons to aid the beginner in selecting t he
ting uishing feature. Figltr e 2 is a closebuttons, providing eight chords for each of
pro.per cords for the key in which he is
the twelve keys in an octave.
up of the button board. W hen a single
playing.
T
HE
•
•
AUDIO ENGINEERING
•
SEPTEMBER, 1953
19
THIS BOTTLE
TURNS
SEVEN YEARS
INTO
SEVEN MONTHS
~
Test blocks of pole wood are fed to destmctive fungi in
bottles like this at Bell Labomto1'ies. Wood rests on soil
which controls moisture condit-ions and promotes fungus
growth. Test speeds search for better preservatives.
This year the Bell System is putting 800,000 new
telephone poles into service. How eHectively are
they preserved against fungus attack and decay?
Once the only way to check a preservative was
to plant treated wood specimens outdoors, then
wait and see-for seven years at least. Now, with
a new test devised in Bell Telephone Laboratories
most of the answer can be obtained in seven months.
Cubes of wood are treated with preservatives,
then enclosed in bottles with fungus of the most
destructive kind, under temperature and humidity
conditions that accelerate fungus activity. Success
- or failure - of fungus attack on cubes soon reveals
the best ways to preserve poles.
A boring is taken from a pole section to
see how far preservaUve has penetr.ated.
For poles to last, it must penetrate deeply
and be retained for a long time.
The new test has helped sho,¥ how poles can
be economically preserved for many years. It is
another example of how Bell Telephone Laboratories works to -k eep down the cost of' your telephone
service.
BELL TELEPHONE
~ABORATORIES
Improving telephone service for America provides
careers for creative men in scientific and technical fields
PROFESSIONAL
AUDIO
EQUIPMENT
PICKERING CARTRIDGES •••
are the choice of audio engi""ers throughout the world . They are universally
acclaimed because of their "igh output, wide range performance and low distortion.
They are used wherever a fine cartridge is required in radio stations, recording studio.
and for purposes of quality control by leading record manufacturers.
••••••••••••••••••••••••••••
MODEL 410 AUDIO INPUT SYSTEM •••
is designed to provide a complete audio control center. Model 410 may be used
in any high quality playback system. Three input channel. are provided-one for
magnetic cartridgeF and 2 "fl~t~' channels -for other audio·, circuits. A 3-po·.ition
equalizer network is built into the magnetic cartridge channel. and provides accurat.
equalization for lP, AES and 78 rpm recording characteristics. Separate bass and
treble controls are also provided. These are of the step-type and permit bass and
treble adjustments in 2 db increments. The tone control circuits are intended to
compensate for record characteristics and for listener.. environment acoustical
conditions. They are no' intended
compensa'e for amplifier and/or loudspealrer
deficiencies. Model 410 i. intended for use with the highest quality professional type
playback equipment. The output of the Model 410 is fed from a cathode-follower
circuit and wiff work into any high quality audio or line amplifier having a high
impedance input. It may also be used with a transformer for the purpose of feeding
a 500 ohm line. Because of its flexibility, low noise and low distortion level, it is ideally
suited (or bridging and monitoring purposes and for critical listening applications.
'0
•
•
•
•
•
•
•
•
THE' MODE': 1'90' ARM •••
Is designed primarily for use with microgroove
records. Its design has been recognized by
leading audfo engineers as that which
incorporates all of the desirable' tracking
characteristics. Analysis has shown that for
maximum performance with lP records the
vertical mass of the moving arm element must
be held to a minimum and further, that the arm
must be counterbalanced about the vertical
axis. This Permits minimum stylus or tracking
force and provides maximum record life.
The Model 190 Arm embodies these all important
features necessary for proper microgroove
record playback.
•
•
•
• MODEL 132E RECORD
• MODEL 230H EQUALIZER-PREAMPliFIER...
COMPENSATOR •••
•
•
•
•
•
•
•
•
•
•
•
distortion is .2 per cent at normal ouljut level.
•
It is intended
use with high qua Ii'..,
•
amplifiers having gain and tone con' Jols.
is unique in its accuracy of equalizati . nand
frequency response. The intermodulati An
tOI
When used with the Pickering Model 132E
Record Compensator the 230H is ideal for
radio station and recording stUdio use and for
applications requiring accurate low noise
and distortion free playback,
~-~
•
•
•
•
•
is designed ttt be used in conjunction with a
magnetic cartridge preamplifier such as the
Pickering 230H or any preamplifier which
provides 6 db per octave bass boost. Six
playback positions are incorporated,
I-European 78 rpm Records
2-Victor 45 rpm and Decca 78 rpm Records
' J-No high frequency roll·off,
500 cycle turnover
4-Ati Capitol Records, new Victor 33l,/) .
Audio Engineering Society Curve
5-Columbia, London and most LP Records
6-To remove the hiss from old noisy records
Precision elements are used in its construction
to give accurate compensation. The 132E is
inherently a low distortion R·C device.
~~"'..~~~~~=_~~~.~ ....Jj"'""""""''' . ~::..,~,_.--::;m"'''...~,,,dl'__ ,i&£l_~,,
__~-"-'-"-'"-~.....:_
PICKERING PROFESSIONAL AUDIO EQUIPMENT
'2%daw ~mn~d:~'
• _. Demonstrated and, sold by Leading Radio Parts Distributors everywhere.
For the one nearest you and for detailed literature, write Dept. A-2.
PICKERING "nd eomp"nll ineo,.po,."ted •
AUDIO ENGINEERING
•
SEPTEMBER, 1953
Oee"n8ide, L.I.; New Yo,.k
17
EDITOR'S REPORT
"LET'S KEEP THE 'HIGH' IN 'HIGH FIDELITY'"
W
ITH THOSE WORDS as his opening statement, Leonard Carduner, President of British
Industries Corporation, begins a personal campaign in k~eping with the penultimate paragraph from
this page in the August issue. Weare heartily in accord, and th~ coincidence of Mr. Carduner's remark
with our own sentiments is not particularly surprising
in view of the offerings at the Music Industry Trade
Show in July. Charles Fowler, editor of High Fidelity,
comments similarly in the September-October issue of
his magazine. And today's mail brings a copy of a flyer
from The Dubbings Company of Long Island City decorated with a portrait of a Hyphithidiac--described as
"a person affected with hyphithiasis, a condition or
state of affairs developing among audiophiles when, in
spite of all efforts, hi s hi-fi equipment remains one step
short of perfection."
Now these three items are not particularly related,
but they do tend to show that the term "high fidelity"
is-to put it mildly-sweeping the ·country. Many of us
have been touting the term for years, always believing
it to mean a faitl~f~£l reproduction of music or speech
with a minimum of distortion, and with adequate fre- •
quency range to transmit all the necessary intelligence
required fo r true re-creation of the original program.
We beli'eve that if all home radio and music installations were of true high-fidelity characteristics, it would
no longer be necessary for announcers to be constrained
to spell such simple words as "whiz" or "vim." Perhaps, on hearing their transcribed messages on a $19.95
radio set, these announcers feel that they do not enunciate properly, and that the fault is theirs.
Returning to Mr. Carduner's statement, he says further that "a small part of the public has already heard
real hi-fi, with such enjoyment and enthusiasm that it
has spread and is becoming a national hobby. Naturally,
no one who has enjoyed high-fidelity sound could possibly be satisfied with less. Real high fidelity is what
people want-not ordinary equipment named for promotional reasons to take advantage of the public demand. " To which we say "Amen." Mr. Carduner concludes with: "The increased demand in the field (of
hi-fi) has naturally brought on a resurgence of interest
in home music listening equipment by commercial set
manufacturers. This can be fine, and I am heartily in
favor of it, if the sets produced are genuine. The phrase
"high fidelity" itself means nothing. If it is distorted by
poor product performance, people will lose interest and
·confidence in the entire field, to everyone's detriment."
The old timers in hi-fi will never be fooled-labeling
a poor piece of equipment with two magic words will
never keep it sold-although it may spur sales for a
16
time. Semi-hi-fi equipment may serve some purpose,
over a long period, in that it may whet people's tastes
for something better. But "ve do need definitions of
what actually constitutes high-fidelity-a yardstick by
which equipment can be measured accurately and conclusively.
A rose by any other name may smell as sweet, but
when one applies the name rose to a well known stripedback animal, the latter does not . thereafter affect the delightful scent of the American Beauty. We suggest,
therefore, that we fall into the habit of calling only
roses roses.
"THE REPRODUCTION OF SOUND"
That is the title of Edgar M. Villchur's fall course at
N. Y. U. commencing on September 23 and extending
to January 20, 1954. The material of the course is that
covered by hi s currently appearing "Handbook of Sound
Reproduction," augmented by his personal instruction.
The classes are to be held on Wednesday evenings from
7: .00 to 9: 45 at the Divi sion of General Education, New
York University, at Washington Square in New York
City. Registration for the course begins on September 9,
and further information may be obtained from the Registrar.
ELGI N SEEKS ENTERPRISES
In an unusual approach, the Elgin National \iVatch
Company recently announced that it is actively seeking
companies in the electronics and precision instrument
fields with a view of affiliation. At a recent press conference, J. G. Shennan, President, said that Elgin's
prime motives are the need for higher return on capital
and greater long-term stability. This does 110t presage a
deCt-ease in the demand for watches,~ but an expansion
of watchmaking techniques to a field where such facili·ties might well be in demand.
We would be' pleased to welcome Elgin into the electronics field-knowing full well that the company's integrity would soon develop it into a mainstay in the
industry.
LARGEST TAPE RECORDING JOB
The largest tape recording job to come to our attention was recently completed by Audio and Video Recording Company, in New York. The job consisted of
duplicating 10,769 copies of eleven different two-hour
recordings-12,922,800 feet of magnetic sound tape- .
for Jehovah's Witnesses, whose conclave in Yankee
Stadium was held during the week of July 20. To complete the massive recording operation, ten tape recorders
worked continuously 24 hours per day, for eight days,
turning out an average of 65 copies an hour, according
to Charles E . Rynd, President of the company.
AUDIO ENGINEERING .. • ..: SE.PTEMB.ER( .1953
Jrifain'5
GREAT
CONTRIBUTION
10
HI GH
fiDELITY
•
It is more than coincidence that Britain and the United
States both have gained distinction for accomplishment
in the field of sound recording and reproduction: More
likely, it is because of the common objectives and understanding shared by members of the great engineering
. fraternity on both sides of the Atlantic. Each has strived
to score over' the other, but with a characteristic sportsmanship in the interchange of know-how and experience.
Britain already has scored well with the Collaro record
changer. In England and on the European contin~nt.
the Collaro is more v:ideJy used than any other record
player in the world. Having won the acclaim of Europe's
most discrirpinating audio devotees, Collaro record
changers are now well on their way to repeating this
experience in America.
The new Collaro record changers are truly a great contribution to high fidelity. Rumble, wow and flutter have
been reduced to levels previously considered impossible
in changer design. In all respects, the Collaro establishes
a new standard of performance ... and brings high
fidelity reproduction a long way toward its ultimate goal
of perfection.
Model 3/532 Iniermixes
10 and 12 inch records.
list Price ........................................................$65.00
Model 3/531 Non·intermix.
list Price...................................................... 54.50
Model 3/534 Single record player.
list Price........................................................ 33.60
Available at radio parts iobbers,
distributors, and hi·fi dealers.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
Write for complete details to:
ROCKBAR
211
EAST
37th
(ORPORATI~N
STREET.
N!;W
YORK
16. N.Y,.
15
HEAR the difference, SEE the difference
Stability Testing
in the ~ model 1826
!Xl
)~
of Feedback Amplifiers
ultra-fidelity ensemble
00
0
The proof of unprecedented
""'io,i"
o"h,Ensemble
O~ ~U""D
Ultra-Fidelity
is in
its unmatched performance.
That proof awaits you now at
your Hi-Fi dealer. The Master
Amplifier is of matchless .
quality. The unique self-powered
"Libretto" Remote Control-Preamp,
~.
with its amazing flexibility,
~
is an ingenious innovation. The
laboratory tests are a revelation, but the ultimate proof of
superiority is in the thrilling
listening and operating experience. ';'::;;:::;;:-~I'-':W
The specifications summarized
below can only hint of the quality
of this new dimension in sound.
/
the master amplifier
A truly superb instrument
with frequency response of
± 0.3 db, 20 to 40,000 cps at rated 20
watts output. Harmonic distortion less than
0.5 % at rated output, less than 0.3 % at 10
watts. Intermodulation distortion less than
0.4 % at 1 watt (home level), 0.7 % at rated
output (measured at 60 and 7,000 cycles 4 to 1
ratio). Output imp., 8 and 16 ohms. 4-position input selector-for magnetic pickup, crystal pickup and 2 auxiliary. Dimensions: 14"
x 9 x 8 high.
N
N
the LIBRETTO
remote control
A true remote control, completely self-powered and capable of operation several hundred feet from
amplifier. Uniquely fashioned in the form of
a lu/{uriously bound book (only 8% x 11 x 2"
thick). Backbone lifts to provide easy access
to tuning controls. Operates flexibly in either
horizontal or vertical positions.
CONTROL FUNCTIONS
1. 6-position crossover control (flat, 150, 300,
450, 700, 1000 cycles). 2. 6-position roll-off control (flat, -5, -8, -12, -16, - 24 db at 10,000
cps). 3. Volume Control-instant choice of conventional control or loudness control. 4 . Bass. Tone, +24 db
to -20db at 20 cps (db calibrated). 5. Treble Tone,
+ 18 db to - 30 db at 10,000 cps (db calibrated).
Custom-Engineered, Custom-Styled
For Audio Connoisseurs
See the RAULAND ~
1826 Ultra·Fidelity
ft
ensemble at your Hi·Fi
••
I
dealer, or write for
full details.
RAULAND-BORG CORPORATION
3515 W. Addllon St., Dept. AD, Chicago 18, III.
14 \
if unwise practice to blandly
apply negative feedback and hope that
no troubles will be encountered. T ests
are often limited to simply noting the increased feedback permissible without causing oscillation, and sometimes this test is
sufficient. However, with amplifiers employing secondary or tertiary feedback, the
simple test is sometimes either invalid or
applied only with difficulty. Furthermore,
the situation may be greatly complicated
when light or capacitive loads must be accommodated.
The requirements for stability in feedback
amplifiers have been frequently quoted in
the literature. Simply stated, the amplification around the feedback loop must be
less than unity at the frequency or frequencies at which the phase relations are correct
for oscillation. Exceptions to this rule have
been analyzed in great detail, but would appear to be of little practical usefulness, and
are not considered here.
To assure satisfactory stability in a production design, under the various conditions
imposed by component and tube tolerances,
etc., it is desirable to have a nominal amplitude margin of at least 6 db under the worstcondition of output loading. This is for
Class A or A, operation; for overbiased
operation characteristic of more efficient
power amplifier circuits, a yet higher nominal degree of amplitude margin is required
for unconditional stability, as described below. A good phase margin of stability is
30 deg.; that is, the phase shift around the
feedback loop at any frequency of unity gain
or greater shall be at least 30 deg. different
from that correct for oscillation. For circuits of the so-called minimum-phase-shift
type, this corresponds simply to a rate of
cutoff (around the loop) of no greater than
10 iib per octave, at any frequency for
which the loop gain is at least unity.
The proposition that a feedback amplifier
is stable with any load if it is so with rated
load, no load, and short-circuit load, can be
a painfully erroneous assumption. Most oscillatory arrangements of either R-C or
L-C form require one or more shunt reactances for their operation, and oscillations
cease when one of these circuit elements is
removed or changed to a value incompatible
with the remainder of the loop. Oscillator
forms assumed by unstable feedback amplifiers often conform to the same pattern, despite their relative complexity, oscillations
simply not beginning until suitable reactive
I
T IS COMMON
* RCA
load termination is connected. It follows
that stability is not assured by the simple
test of applying some arbitrary resistive
load, and reducing a series feedback resistor to apply feedback in excess of normal.
The more difficult instability problems
usually occur at frequencies above the audio
band, and output transformer high-frequency characteristics are usually intimately associated therewith. While it could
be that inductive amplifier termination
would produce an oscillatory circuit, capacitive termination is more often the troublesome case. The thought that a loudspeaker
voice coil is inductive at high audio frequencies is little consolation, however, since
the speaker load is usualIy electrically selfresonant below frequencies at which amplifier instability troubles arise, and hence appears capacitive in the circumstances under
consideration.
The basic method for loop tests is that of
I breaking the feedback loop in some convenient part of the circuit, inj ecting a signal
of suitable magnitude, and noting the phase
'shift around the loop by the conventional
oscilloscope method. The gain at each such
frequency is simply the ratio of output and
input voltages.
Primary-feedback amplifiers (any in
which the feedback voltage is obtained from
the primary side of the transformer) are
usually stable regardless of the loading,
while with secondary feedback capacitive
loading usually represents the troublesome
case. When the feedback voltage is derived
from a tertiary winding, various loads must
still be tried, because though the secondary
winding is not ordinarily considered to be
within the feedback loop, the primary-totertiary amplitude and phase characteristics
are usually greatly influenced by the secondary current.
When the loop gain is relatively small
(corresponding to only a small amount of
feedbat:k) , conditions for oscillation (usually in the range of 20 to 500 kilocycles)
may be fulfilled over only a narrow range
of load capacitance; in fact, oscillation may
not occur with any value of capacitive load.
But when the loop gain is high (corresponding to a large amount of feedback),
oscillations may persist over a wide range
of load capacitance, the frequency or amplitude of oscillation simply changing with
different capacitive loading. Obviously an
amplifier which is stable with a small
amount of feedback is sufficiently increased
(high loop gain).
(Continued on page 81)
Victor, Camden, N. I .
AUDIO ENGINEERING
•
SEPTEMBER, 1953
a new concept in radio programming and operation
An Ampex Automatic Station now in
operation a t KEAR in San Mateo, California. It sustains the evening programs
on tapes prepared by the daytime staff.
Now a 16 bour broadcast.day'can be handied by an 8 hour staff.
Commerciafs' and announcements for the:full broadcast day can
be pre-taped: in fast succession and will be automaticilly cued
to prepared program material.
AUTOMA'.fIC CUEING
Your broa~sast time can b~, sustained automatically by alternate
operation gf two Amp'ex450 Contintl0us Tape Reproduoers.
One carti~a program tape-the other has a tape with ,commercials and announcements. One stops-the other starts. It's
"cued automatically" with' sub-audible "trigger signals" recorded
01;1 the tapes themselves. And when desired both machines can
be stoppe nd live programs, separate tapes or discs can still
be broad
in the convensipnal manner.
ELECTRONIC SPLICING
The announcer pre-records his announcements, pressing a button
between each one to place the "trigger signal" on the tape. In
effect he is putting the announcement in its proper place with
a fast "ele+cf'l'onic splice."
.
.
PRE.PLANNED PROGRAMS
Program tapes for use in your Ampex Automatic Station will
coe-tain the cueing signals. Selections and exact performance
times are available to your program director for accurate integration with ~ommercials and local announcements.
-!$~-
•
Sub-audible tones on each tape
stop one machine and automatically start the other.
Write today for further
information to Dept. B· I217A
AMpEX
MAGNETI C RE CO RD ERS
-. iO...-
AMPEX COtl;g ORATION
934 CHARTER STREET,
R EDWOOD CITY, CALIFORNIA
Distributors in prin&ipal &ities
In Canada: Canadian General Electric Company
AUDIO ENGINEERING
•
SEPTEMBER, 1953
13
BOOK REVIEWS
performance
fJ/¥
ECONOMY
GIVES YOU ALL
TURNER
so
You get a dependable, versatile
. performer in the Turner 80. A crystal
mike that takes PA, home recorder,
dictating machine and amateur ~ses in
its stride - brilliantly. And for smart,
modern styling you can see for yourself that
Turner is way ahe.ad of the field. Look
Sensitivity: Approx. 58 db
below 1 volt/dyne/sq. cm.
Response : 80 to 7000 cps
Weight: 5 ounces less cable
Cable: 7 foot attached
single conductor
shielded cable.
Model 80 microphone
List price ____ $15 .95
Model C-4 stand
(illustrated with mike)
List price ____ $5.75
THE
at those graceful lines, and that
satin-chrome plated finish.
For PA use, you're seen as well as heard.
The 80 measures just 41j2 inches from
stem to stern. Cradles in the palm of
your hand. All this at' a popular price!
Yes, you get all three . . . performance,
style, economy . . . in the
Turner 80 microphone.
TURNER
COMPANY
929 17th St., N.E., Cedar Rapids, lawa
In Canada : Canadian Marconi Co.,
Toronto, Ont., and Branches
Export: Ad Auriema, Inc.,
89 Broad St., New York 4, N. Y.
12
RADIOTRON D ESIGNER'S HA NDBOOK, F ourth
Edi ti on. F. Langfo rd Smith, Editor. The
Wireless Press, A ustralia, Publishers.
Photolithographed in the U. S. A. by
the R adi o Corporation of America, 1953.
xl + 1482 pages, $7.00.
Ten authors and twenty-three co-operating engineers have combi ned efforts to
give us here not just another handbook, but
a text treati se annotated with thousands of
refe rences to both book and periodical literature. Seemingly nothing has been omi tted,
and the copiousness of tl1e references make
this book essential for the engineering library of today. Some 38 chapters comprise
the seven sections into which the text is
di vided, and the index is complete and well
cross-referenced.
Naturally the opening section deals with
vacuum tu bes, their theory, physical makeup, pe rformance- rating interpretation data,
determination of non-published parameters,
etc. A complete section on the testing of
valves fo llows. The second secti on deals
with network theory, components as such,
transfurmers ' in theory and practi ce, wave
motion and modulation, and inductor design and calculation. A thorough analysis
of the problems and uses of inverse feedback, conditions for stability over multistage
loops, and similar engineering problems
make this a source manual for anyone desig ning amplifiers or similar e1ectronisms.
But it is the third section that will be of
particula r intere'st to }E readers. In some
409 pages are crammed more audio data of
a practical nature than has heretofore appea red in print in one book. While it is
true that much materia l pertaining to audi o
design is found in other sections, this is
the main center of interest in this volume.
Every angle of voltage amplifier theory and
design practice is covered with rich citations of r eference material. P ower amplifiers
of all types are similarly di scussed and
analyzed, again with valuable reference
data. The data is right up to the minute,
with full treatm ent of such newer amplifier
designs as Williamson, McIntosh, etc.
F idelity and di storti on and their many
forms next come under examination. T o
this r evi'ewel-, however, the highlight of
the audi o section is chapter 15. "Tone Compensati on and Tone Control." This should
be req uired reading for ever y devotee of
hi-fi equipment. Never before in one place
has such a wealth of data appeared. Nor is
th e broadcast engineer slighted. Volume
compressors, mi crophones, preamplifier s. attenuators, and mixers have all been dealt
with in a scholarly manner. Speech clipping
for channel space saving and communication system simplification as a whole is discllssed.
Record reproduction and its attendant
problems are covered with discussions of
styli, recording characteristics, and th e
pl-oper equipment for best r eproduction.
Particularly valuable is a comprehensive
listing of all available commercial test r ecords as to speed, content, and method of
manufacture. Finally the loudspeaker and
dividing network close this section.
P art 4 cover s radio fr eq1:1encies, from
antenna types through all sections of the
r eceive r right up to the transducer. Power
supplies and filt ers comprise the next section, while P art 6 details design factors
affecting th e complete receiver.
Part 7 is a mass of tables, charts, and
sundry data to which the laymen and engi(Continued on page 74)
AUDIO ENGINEERING
•
SEPTEMBER, 1953
with no increase in noise or harmonic distortion!
It's the new
BRAN D
Magnetic Tape
AVAILABLE IN 300,600,1200,2400
and 4800 foot lengths
High-Output and CijQ7 TM 3M Co.
The term "SCOTCH " a nd the plaid design a re registered trad emarks for Sound Reco rdi n g Tape made in U.S.A. by MINNESOTA MINING
& MFG. CO., St. Paul 6, Minn.-also makers of "Scotch" Brand Pressure-Sensitive Tapes, "Unde rseaI" Rubberized Coating, "Scotchlite"
Refl ective Sheeting, "Safety- W a lk " Non-slip Surfacing, "3M" Ab rasives, "3M" Adhesives. General Export: 122 E. 42nd St., New York 1 7,
N.Y. In Canada: London , Ont., Can.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
11
Precision
YOUR PRODUCTION
AT .TS 8EST
,
Constant analyses and sampling of
every processing operation is the
function of this department. Sen·
sitometric operations' test the re·
sponses of raw stock emulsions;
densitometry is employed to check
on developing and printing results.
YOUR ASSURANCE OF
BETTER 16mm PRINTS
16
Years Research and Specialization in every phase of 16mm processing,
visual and aural. So organized and equipped that all ~recision jobs are of the
highest quality.
Individual Attention is given each film, each reel, each scene, each framethrough every phase of the complex business of processing - assuring you of
the very best results.
Our Advanced Methods and our constant checking and adoption of up·to·
the·minute techniques, plus new engineering principles and special machine,r y
enable us to offer service unequalled anywhere!
Newest Facilities in the 16mm field are available to customers of Precision,
including the most modern applications of electronics, chemistry, physics, optics,
sensit.ometry and densitometry - including exclusive Maurer.designed equipment - your guarantee that only the best is yours at Precisipn!
Precision Film Laboratories - a di·
vision of 1. A. Maurer, Inc., has 16
years of specialization in the 16mm
field, consistently meets the latest de·
mands for higher quality and speed.
10
down to 1953. My collection includes such
various types as the very early Zonophones,
G & T's, Odeons, Grammophon Schallplatte,
as welI as more recent e1ectricalIy recorded
domestic and European 78's and all types
of wide-range LP's.
I am using top-flight professional audio
equipment throughouit-1953 vintage-to
play these discs. My one big stumbling
block is the lack of a completely versatile
front-end. Realizing that my problem is
not unique, and that there must be in
America alone several thousand collectors
of old and new discs who are in the same
dilemma, I hope this letter may find at
least one person somewhere who has completely solved this problem.
KEMP BORDLEY,
43 Woodside Lane,
Arlington, Mass.
Ba'iancing Tubes
SIR:
I agree with Mr. Fonseca that a Q & A
department would be a valuable service to
the readers of our magazine.
Situations arise which call for information that may be quite difficult for the
average hobbyist to find. One instance of
this is the "simple" replacement of tubes
which must eventtjally fail. Several times
I have seen reference made to the necessity
for balancing output tubes, yet I have been
unable to find any explanation of what this
involves and I doubt very much if any
local service man would know any more
about it than I do.
Fortunately I have not yet had to replace
tubes in my hi-fi equipment but I should
like to be prepared for the situation when
it arises and should appreciate any information you may care to give or any reference to where this informatiQn may be
found.
ROBERT E. TINDALL,
315 N. Liberty St.,
Independence, Mo.
CA very good question, indeed, for a Q & A
starter. We will answer this reader directly, and save his question for the
Novemb.er issue, which will have the first
Q & A department. Balancing tubes in atl
amplifier which is not equipped with means
for stich balallc·ing and which does not have
provision for metering is quite a problem.
ED.)
September 1-3-INmNATIONAL SIGHT AND
SOUND EXPOSITION, combined with the
CHICAGO AUDIO FAIR. Palmer House,
Chicago, Ill.
September 13-16-THE ELECTROCHEMiCAL
SOCIETY, INC., Sessions on corrosion,
electrodeposition, and batteries. Ocean
Terrace Hotel, Wrightsville Beach, N. C.
September 25-27-NoRTHERN CALIFORNIA
AUDIO SHOW. Palace Hotel, San Francisco.
October 14-17-Fifth Annual Convention
of the AUDIO ENGINEERING SOCIETY, and
THE AUDIO FAIR. Hotel New Yorker,
New York City.
November 3-4--THIRD ANNUAL HIGHFIDELITY CONFERENCE and AUDIO SHOW.
Benjamin Franklin Hotel, Philadelphia.
AUDIO ENGINEEIHNG
•
SEPTEMBER, 1953
,
,
IN
TAPE-WOliND (J01lES
,lUST NAME YOUR REQUIREMENTS!
RANGE OF MATERIALS
Depending upon the specific
properties required by the application, Arnold Tape-Wound Cores
are available made of DELT AMAX
. . . 4-79 MO-PERMALLOY . . .
SUPERMALLOY . . . MUMET AL
... 4750 ELECTRICAL METAL ...
or SILECTRON (grain-oriented
silicon steel).
cores-are manufactured to meet
your individual requirements.
RANGE OF TYPES
In each of the magnetic materials
named, Arnold Tape-Wound Cores
are produced in the following
standard tape thicknesses: .012/1,
. 008/1, .004/1, .002/1, .001/1, .0005",
or .00025", a.s required.
Let us help with your problems
of cores for Magn.etic Amplifiers,
Pulse Tr a nsformers, Current
Transformers, Wide-Band Transfo rmers, Non-Linear Retard Coils,
Peaking Strips, Reactors, etc .
Address: ENG. DEPT, A
RANGE OF SIZES
Practically any size Tape-Wound
Core can be supplied, from a fraction of a gram to several hundred
pounds in weight. Toroidal cores
are made in twenty-two standard
sizes with protective nylon cases.
Special sizes of toroidal ceres-and
all cut cores, square or rectangular
AUDIO ENGINEERING
•
SEPTEMBER, 1953
waD "' 6 13
9
LETTERS
Re: " High Futility"
SIR:
We liked Mr. Dickey's article "High
F utility" (ft., April, 1953) very much, and
were especially interested in his remarks
concerning th e di sappointment and frustrati on of some newcomers to the audio field.
These same feelings have been expressed
by quite a few members of the Audio Club
(of Musicians and Music Lovers, I nc.).
However, the interesting feature is that
frequently the trouble is not due to too
much high-pressure sales manship.
These music lovers-who are not cranks
with t.in ears-have equipment which is the
resul t of excellent engineering design and
practice, and is functioning correctly. They
ch?ose their records carefully, use appropnate playback equalization, and a re still
unhappy with the tonal result.
Where, then, does the trouble lie?
H ere is a partial list of possible sources :
acoustical matching pf speakers and enclosures, the acoustics of the room, the
volume level, and the setting of the bass
and treble controls. .
The other areas pertaining to the ear
which were listed by Mr. Dickey-variations in pitch with changes in intensity
etc.~we believe to be of minor importance:
Of maj or importance are inco rrect tonal
balance, scale distortion, and single-point
sound source.
We are thoroughly in accord with Mr.
Dickey's conclusion: "If we are to reach
the goal of having the recreated seem as
the original, the listener alone can supply
that final measure of understanding which
must take ' over where techniques fail."
H owever, a basic requirement for this
type of understanding is a muscial experience which many music lovers do not have.
This experience is acquired only through
years of listening to th e original and for
a while th ese music lovers will h~ve to depend upon the professional musician. It is
surprising how intelligent use of the volume and tone controls ove rcomes much of
th e disappointment and frustration mentioned above. The solution to the problem
of reproducing a full symphony orchestra
with a reasonable "illusion of reality" lies,
we &~lieve, in the direction of multiple
speakers and channels.
DAVID MANKOVITZ and
FRED F . SALOMON,
Audio Club,
119 West 57th St.,
New. York 19, N. Y.
Never Finished
SIR:
May I take this opportunity to disagree
with Mr. D orf' s letter in the July issue. My
a nswe r, if published, would most emphatically be "You are never finish ed."
After reading Mr. Dorf's letter, I reviewed the a rticles in my file on improvement of home music systems. I was indeed
surprised that this material was refer red to
as an "overabundance of rich es." That to
me is like calling all .up-to-date medical
literature superfluous-like saying let's use
what we have had and used before, and the
heck with any new-fangled ideas.
In my humble opinion, audio engineering
8
- like medical a nd other sciences-will always seek to improve, and the audio eng ineer, like the physician, will never consider
any system fini shed. T he owner of a home
music system is a real enthusiast who a lways seeks and wants the fi nest. To tell
him not to touch his system any more is
paradoxical. For one who wants music in
its true tone, fr ee from th e mental fatiO"ue
o~ in~er.mo~ulation di stortion and freque~cy
dlSCrll111natton, no trouble is too g reat in
the sea rch for any and all improvements.
I am disappointed that Mr . Dorf considers his system finished, since I have enjoyed his many tomes and treatises on what
he calls "gimmicks." Certainly there is no
greater satisfaction than the purchase and
installation of a newly advertised gimmick
whi<;h improves the performance of my
musIC system. My own system will never
be finished, and I shall look forward with
continued eagerness to more stories on
audio tri cks and new product improvement.
It is my sincere hope that Mr. Dorf will
not bury his head in the sand, but that he
will continue to be a comrade to those of
use who investigate every idea, gimmick,
and trick which will make our home systems sound better and afford more enjoyment.
HOW ARD MILLSTEIN, M.D.,
4489 Broadway,
New York 33, N. Y.
Recording Characteristics
SIR:
Whoever started this talk about "recording characteristics" and "curves" back as
far as 1948 or 1949 should have kept quiet
in the first place if such curves and characteristics were to be kept a secret, or if
it does not make allY difference in sound.
If one's equipment were to be made flexible,
why do some people insist that there was
a difference with conforming to each company's curve?
And now there is (possibly) to be a
change of the NARTB to the New Orthophonic. What a vicious circle 1 Why not
forget curves if room conditions or microphone placement affects the kind of sound
obtained? Why not go back to the simple
way, just telling us all that "It didn't make
a bit of sense about trying to standardize
equalizers" ?
If recording companies are afraid of giving away what they call secrets so we have
no basis to go on, then I don't suppose their
records are going to be enjoyed to their
fullest.
F. T. HAYASHI,
235 Kuahiwi Ave.,
Wahiawa, Oahu, Hawaii
(rE's credo has always been, and still is:
Provide mfficient jlex'ibility, then adjust the
controls until the reprodttction is satisfactory to the listener.)
Help Wanted
SIR:
As a regular r eader of ft., I send out a
plea to other readers who might help me
solve a serious problem. I am a collector
of Operatic, Vocal, and Lieder recordings,
ranging in date of manufacture from 1901
AUDIO ENGINEERING
•
SEPTEMBER. 1953
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High-Fidelity
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AUDIO ENGINEERING
•
SEPTEMBER, ],953
Name________________________________________
Address _____________________________________
0' ;;,--E--R-I--C--~--zonc-e___
State
CAMDEN, N.J.
7
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6
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AUDIO ENGINEERING
•
SEPTEMBER, 1953
This brand new baseball glove,
pre-oiled and deep-pocketed,
needs no breaking in.
This new reel of SOUNDCRAFT Tape,
Micro-Polished at the factory,
needs no breaking in.
Now! a "Broken In" Tape
Exclusive. SOUNDCRAFT Micro-Polished* Tape
Gives Stable High Frequency Response right from the start
In the past, all n ew reels of Magnetic Recording Tape
had surface irregularities and protuberances (oxide
nodules) on the ferrous oxide surface. These irregularities and nodules caused imperfect head contact
and a subsequent loss in high frequency response,
until the tape surface was worn smooth by the recor'ding head. This is the reason for the widespread professional practice of "breaking in" a new reel of tape.
This is why engineeJ;s. run new tape through the
recorder a number of times before recording, wasting
time and effort, and causing undue wear of the
recording head.
ONLY SOUNDCRAFT TAPE IS MICRO-POLISHED
There is no break-in period needed with SOUNDCRAFT Tape. Because all SOUNDCRAFT Tape is
Micro-Polished. This exclusive process pre-conditions
SOUND CRAFT Tape befor'e it leaves the plant.
Micro-Polishing subjects the ferrous oxide coating
REEVES
SOUNDCRAFT
CORP.
10 East 52nd St., Dept. B-9, N. Y. 22, N. Y.
*Pat. Applied For.
to high mechanical stresses. It produces a mirrorsmooth tape surface. It achieves immediate stable
high frequency response. And it allows new tape to
be interspliced with tape that has already been used.
OTHER SOUNDCRAFT FEATURES
Not only is Soundcraft Recording Tape MicroPolished, but it is also endowed with the following
features developed by Soundcraft research engineers.
to insure better adhesion, prevent
curling and cupping -
PRE-COATING
DRY LUBRICATION
SPLICE-FREE
to eliminate squeals-
guarantee on all 1200' and 2500' reels.
Why settle for less than the best?
N ext time, insist on Soundcraft Recording Tape.
It's Micro-Poli shed!
falling •••
or rising?
A few false prophets have said that tape
recording will replace discs entirely.
But don't be deceived by such assumptions.
Sales figures prove that the use of PRESTO discs has shown a
steady increase during the past year. They prove something
else, too ... that more broadcasters, recording
companies, and schools prefer PRESTO to any other disc.
The reason is plain ... PRESTO discs are manufactured
from superior aluminum and finer lacquer ...
produced in the world's most modern disc plant
. . . and inspected and selected for quality.
Yes, the use of PRESTO discs is going up
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are flying highest of all.
LISTENING qUALITY IS EVERYTHING
Again and again the question-"What makes the AUDAX CHROMATIC the outstanding instrument that it is?" That is as difficult to answer as the question, "Why that
glorious tone from a Stradivarius?" KNOW-HOW, that comes only with years of specialization, is undoubtedly the most important factor. We list below a few of the salient
features that are responsible for the world-wide acceptalJ-ce of the AUDAX CHROMATIC as the finest, smoothest performing instrum~nt (cartridge) yet devised.
BUT . .. only YOU can decide what sounds best to you. See and hear the AUDAX CHROMATIC and YOU be the judge . . . Yet AUDAX costs no more than ordinary pickups!
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plays any and all home records - and with the same
point pressure fOl' all,
Be it diamond or sapphire
every stylus has only a
limited life; diamond lasts
the longer, Obviously then,
replaceability of the stylus
-AT HOME-is of the greatest importance, Only iIi
AUDAX is each stylus replaceable independently of
the othel"
Near-infinite compliance,
Needle-talk pl'acticaIly nil.
Response 10 c to ovel' 15 kc,
No "Hidden Pull".
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arms and to fit the high quality record changers.
·'Vhen to change stylus
•
•
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Only THREE pal'ts.
No restraint to stylus u'avel.
Frontal oscillation nil.
No springs • • • No fatigue.
• Maintains point-pl'essUl'e gardless of climatic changes,
re-
• Gl'eatest possible distance between styl~s and vertical pivots.
Obtain Free copy of "1953 Electronic Phono Facts" at your dealer
or write us enclosing 15¢ for postage and handling
Also be sure to obtain free descriptive literature on STYLUS-DISK
1. Gives Visual indication (befOl'e your vuluuble recOl'd s
m'e ruined) of whether or
not the stylus is in playable
condition.
2. Will test ANY type of stylus,
in any type of pickup-in a
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3. Neithel' the stylus nOl' the
cartddge need be removed
fOl' the 'test, Nothing need be
disturbed,
4, The grooves may be used ovel'
Send fOl' free copy of 1953 ELECTRONIC PHONO FACTS
AIJDAK COMPANY
SOO Fifth Avenue
42nd Floor
New York 36, N. Y.
Creators of Fine A,u dio-Electronic apparatus for over 25 "ears
and ovC(' again, until finally
worn 01' defective stylus
sCl'apes the delicate gl'oovewalls,
5, Should lust for years with
ordinary cure in using and
stOl'ing,
6. Costs only
$3.90 net.
EDWARD T ATNALL CAN BY':'
Paris, France
now comfortably
lodged overni ght in the most hair-raising city of Europe from the traffic standpoint (I have my own car, H eaven help me),
has but r ecently emerged from the densest
fog in memory-a fog of the moist sort that
covered astonishing area s of the g reater
North A tlantic, the Irish Sea and the E nglish Channel, during the halting voyage of
a vessel of doubtful ancestry named the
T.S .S.Neplnllia, buIl t in Holland (so we
heard ), registered in Panama, operated by
the Greeks and sta ffed with a crew of Germans, a mix ture that is not her eby recommended for any sort of fog penetration. A
thousand or so crammed souls and myself
took 80 days to fi gure out what that
mysterious T.S.S. meant, during the r are
moments when 'We were able to speculate at
all on anythi ng less immediate than the
angle from th e hori zontal then existing underfoot. (The entire cocktail ba r and human
contents sfid to one side of th e ship in a
welter of glass and spilled cha irs during one
of our more terrifying lurches.) The explanation which we got finally from a
stewa rd, was simple and he was utterly
as tonished at our ra ucous laughter when we
heard it. T .S.S. means merely T win Screw
Steamship. Most of us, you see, have r eturn
tickets on the same fl oating palace. T wo
propellors, he insisted. . . .
I didn't sail fo r th ese parts without a
good mental cargo of audio stuff that ha s
been accumulating for just such a happy
occasion and so, if the editor can believe
my good typing ( a new feather weight
H ermes in my lap) I'll get on to some more
observati ons concerning the still hot binaural situation, roun ding out the comments in JE for last A pril.
T
HIS
DEPARTMENT,
True-Binaural and Panoramic
Most of th e trouble and confusion over
"binaural" and associated systems and phenomena is due to the dismal hodge-podge
of terminology, official and unoffi cial, now
being muddied a bit more by the a dvent
of asso rted kinds of "3-D," both sight and
sound. It's bad enough to have solid and
respectable terms like binaural a nd stereohonic used in contradictory ways, but
that' s only the half of it. For th e presently
• official terminology · in the sound fi eld is
linguistically badly out of line with that
of th e seeing area. H ow can we. help li ning
up "stereophonic" in one area with "stereoscopic" in the other, g iven the two ears
and eyes that a re in plain sight on every
one of our faces ! A nybody with common
sense will assume that the two r epresent
* 780 Greenwich St., New York 14, N.
AUDIO ENGINEERING
•
Y.
pa rallel effects, one with two ears and the
oth er with two eyes. U nfo rtunately. the
specialists in these two fi elds were not in
communication when they got to inventing
words. T he two are not pa rall el at a ll.
Wh er eas a "stereoscopic" p.icture is
com posed of two pictures, one exclusively
for each eye with complete separation, the
is
cor responding
sound
reproduction
properly called " binaural," not stereophonic.
T he latter term is officially applied to the
type of multichannel reproduction via loudspeaker s wher e the sound channels are Hot
separated, all of them reaching both ears.
Tough on the uninitiate.
Personally, I am afraid th at until we
somehow manage to by-pass this linguistic
road block we'll never get ourselves into
the clear. You just can' t have that sort of
out-of-line wordage in general use without
troubl e, quite aside from the furth er confusion represented by the current usage of
"binaural" for two-loudspeaker sound t hat
is not actually binaUl:al at all since it does
not provide the separation, one channel fo r
each ea r, that is necessa ry for true-binaura l
reproduction. Gerald Schoenwald, in the
Bo le.,,; Repo1'te1' (Bolex sell s 16-mm home
stereo movie cameras) makes a valiant
stab at the confusion by switching "stereophonic" arbi trarily to a di fferent meaning,
to bring it into line with ~'s ter eoscopic";
fo r him, stereophonic now means t wochatmel separated sound- in my language,
true-binaural. But whoa ! It's too late to do
that ; let's leave stereophonic where it is
and avoid piling confusion upon confusion.
Schoenwald makes a fur ther sugges tion,
however, that's a lot more practi cal. He
'calls the multichannel loudspeaker type
of reproduction "panoramic," a word that
nicely desc ribes the effect of the spaced-out
sound samplings projected to the listener
in that kind of system. W hether it's two
channels, as in home "binaural" sound, or
up to six, as in Cinerama and other theatre
fi lm systems, "panoramic sound" is a ppropriate, sim ple, and has the advantage of a
good correspondence with the panoramic
type of wide-screen film proj ection. I n
both hearing and seeing by the panoramic
methods there is no separation-no earphones, no glasses, both eyes seeing the
whole projection, both ears hearing the
whole sound. A nd so I vote fo r P ANORAMIC,
as a popul ar term to supplement th e quas iofficial STEREOPHONIC.
I am very much against the current use
of "bi naural" indescriminately to cover
two-channel reproduction both via phones
and via speakers, not because it really
matters what word you choose fo' a given
phenomenon, dictionary or no, but r ather
because whatever ,terminology we choose,
SEPTEMBER, 1953
we must not fly against the facts and lump
into one ar ea two phenomena that a re
basically di ffe rent, in the most fundamental
respects extending into every phase of
recording, r eproduction and listening.
To . the best of my under standing', as
noted here earlier, two-speaker "binaural"
does not involve any significa nt true binaural effects in the listening (separati on of
the two tracks, one for each ea r ) and therefo re is l~Ot binaural. The very definite improvement that, under the right conditions,
can certainly be had with the loudspeaker
two-channel system occurs for quite diffe rent r easons-as plainly di ffe rent as the
obvious differ ence between ,w ide-screen
movies without glasses and true stereo fi lms
that require the polaroid separating spectacles. T erminology in the film s is as vague
as in audio, but the general public has got
the idea of the basie difference there pretty
clearly now, thanks to actual experi ence.
E ither you wear glasses or you don't. Our
audio fri ends are still in a state of utter
confusion, by comparison, over the pa rallel
difference we have. E ither we wear earphones or we don't ; we have the same three
systems ( counting the old "standard" or
"or dinary" reproduction ) as the fi lms and
sooner or later we've got to understand
how each works and what the diffe rences
a re.
Earphones-There Isn't Any Other Way
E nough. I'm su re you share my own
sense of fru stration at this point, though
I've been doing my best, these many
months, to fi nd a way to make these practical di stincti ons both clear and interesting
in the explanation. Let us at least, at this
point, take the difference between earphone
and loudspeaker two-channel as a fact,
which it is; here are two di fferent systems,
whatever we call them. Everybody's been
trying loudspeakers fo r two-chann el sound.
R adio sends it out via F M and A).II. LP
r eco rds. have it, tape machine and sp eak~ r
compani es promote it, a vast amount of
demonstration has been done with it. Loudspeaker two-channel sound is in good hands
and I could not possibly find anything
wrong with it except its limitations-it is
not always as glorious an improvemen t over
sing le-channel sound as it has been cracked
up to' be, nor is it sure-fire in results, and
it requires ver y tricky operation. (It's
expensive and impractical for average home
use at the moment, but that can easily
change. )
L ook, then, at what I can only call T rueBinaural, two-channel reproduction via earphones. W hat has it to offer? ·
F rom current implicati ons, you mi ght
think nothing more than a couple of sore
47
ears and a headache I The feeling seems to
be that loudspeakers are more practical.
Practical, yes- but for what? Not for
true binaural! I hold no brief for earphones
as such and I'm quite ready to groan at a
moment's notice about their sheer nuisance
value as a promoter of extreme annoyance.
I wear the things too much of the time.
But nuisances are tolerated according to
. necessity. Will people ever want to bother
with earphones for binaural listening?
They'll rush for 'em, if the result is worth
it. I'm here to say that it is, decidedly. The
genuine binaural reproduction is a sound
that can be extraordinarily interesting
and important and unique-and there's only
one way (at present) to hear it in sound
reproduction. Earphones.
I spent most of the e~rly part of this year
experimenting on my own exclusively with
binaural via earphones. Last December,
I decided that as far as I was concerned,
T he complete, up-to-date
bible of Hi-Pi
Edward Tatnall
Canby's
HO ME MUSIC
SYS TEMS
How to Build
and Enjoy Them
•
Writing with the ease and
clarity that distinguish his
column in Audio-Engineering,
Edward Tatnall Canby presents a comprehensive account
of every aspect of the hi-fi system, . from the initial ordering
of parts, through the building
of the set, to locating the
sources of breakdown once the
system is in use. Beginning
with a discussion of the various definitions of high fidelity,
he then examines each part of
the system: speaker, amplifier,
speaker housing, etc., in terms
of function, the various types
manufactured, and specific assets of each brand. Complete
with lists of hi-fi dealers, supply houses, custom builders and
a special appendix on load resistances for magnetic cartridges, Home Music Systems
gives you all the information
you need for immediate reference, in convenient, up-to-date
form, as well as new ideas and
recent developments in the
fi eld.
At all bookstores $3 .95
HARPER & BROTHERS
49 East 33rd Street,
. New York 16
48
I had done about all I could usefully with'
loudspeakers and so, as a kind of challenge,
I dispensed entirely with my speaker system
and set out to find what could be done with
the true binaural effect, via phones. Since
then I've been 100 per cent busy following
up true binaural leads-and here I am en
route to Switzerland for a consulting job
with a Swiss firm on an exclusively earphone binaural proj ect, as merely one result .
Believe me, once you have opened your
eyes (ears) to the reality of earphone binaural as a phenomenon in itself utterly unlike anything else in the entire world of
sound reproduction, you begin to discover
an astonishing array of potentialities. The
first thing I discovered was that truebinaural is not merely to be consider.ed as
an uncomfortable and inconvenient alternative to loudspeaker listening; instead, here
is a sound reproduction system that is virtually unrelated to any that we now have and
its possibilities-granted the inconvenience
of phones-are in the most unexpected new
areas.
Music on True - Binau ra l
Music is the first thought for most 'of us.
Via earphones (and from mikes closely
spaced, not more than 15 or 20 inches apart
at maximum) musical sound is heard in
the reproduction as it sounds on the spot.
There, I'd guess, is the understatement of
the year! No other system of sound reproduction can remotely approach this special
effect, and there are no words left to
describe it further. No matter that our
senses, confused a bit by the contradictions of our eyes being in one place and
our ears just as definitely in another, tend
to distort the directionality of binaural
music, sometimes placing the musical source
wrongly-behind the head or slightly above
when it should be in front. This is of very
slight importance in binaural musical hstening; the exact direction is inconsequent, the
feeling of being on the spot, in the music
is the exciting part. What makes the earphones bearable is a kind of realism that
makes people of a musical turn of mind
gasp, on first . hearing. Don't think you've
heard binaural sound until you hear a good
earphone two-track recording.
Moreover. for reasons previously discussed in this column, the live ness of a
true-binaural transmission, via phones, is
that of two ears on the spot. Therefore a
true-binaural transmission, not to be reproduced on speakers but by phones only
can be miked anywhere at all that normai
ears find pleasing. That means music from
concert-seat distance, if you wish-or
close-up, to taste. The entire technique of
monaural pickup goes out the window.
Binaural mike technique-phones only
:emember (I can'~ repeat that too often)--':
!s that of the ordmary human hearing and
It has all of the flexibility, the adaptability,
tbe tolerance of normal binaural hearinO'.
This is decidedly not true of 10udspeaK;r
"b~naural", v.:hich, not being binaural, reqUIres a modIfied monaural technique. For
loudspeakers, two-channel music must be
miked close-to, more or less as is the usual
recording set-up.
I have, for example, a true-binaural
recording of a harpsichord recital in a
large stone chapel. My recorder was set up
so that the two mikes were in the center
aisle about si.t:ty feet-deliberately-from
the stage. The recording (via phones)
sounds exactly as it did in the church to
those who had choice seats in that area. The
performer's remarks, reinforced by a lowlevel p.a. system, are inaudible in the far
distance when heard via a speaker, but via
phones every word can be understood. (The
same performer, Fernando Valenti, has been
recorded monaurally by Westminster at a
distance of about three feet.)
I also have a splendid organ tape, from
the same chapel at Washington University,
which makes a good monaural recording
and is plenty effective even via monaural
phones. But switch to binaural, after a few
moment's listening and watch for what I'm
beginning to call the "binaural face" -that
expression of astonishment and pleasure
that comes over people's fizzes when bl11aural hits them for the first time. I also
have an orchestral tape that was made,
ncessarily, at close range, about 20 feet
from the conductor. It is an ideal monaural
sound-but, thanks to the flexibi lity of binaural, it is 'iuite spectacular on binaural
phones, too.
You can record music anywhere, then,
close or far, if you are willing to use only
phones for listening, and the results are
almost sure-fire. It's very nearly impossible
to go wrong with binaural for phonesexcept in one paradoxical way: monaural
technique will not work-record a string
quartet or a clarinet and piano at a mike
distance of a few feet, as in monaural, and
you'll get a most unpleasant closeness, not
at all proper for the music. That, of course,
is exactly what would happen if you were
to listen at the usual monaural location. I've
heard a number of binaural recordings that
were poor for this very reason-too much
monaural thinking. Back away, then, and
set mikes where the music sounds good to
you. That's true binaural.
Bi rds, Organs, Folk Tales
Space runs out-but look for a brief
moment4:lt a few of the other true-binaural
possibilities that I ran into. Remember tllat
true-binaural mike pickup, unlike all other
kinds including speaker "binaural", is not
limited by the usual monaural acoustical
necessities. This is of far-reaching significance .
Birds, for example. I took my binaural
recorder out on the front porch of a
Missouri farm house and let it TUn, early
in March. The three-dimensional space in
which flocks of spring birds were singing
was "even more realistic than the sound
itself", as the farm's owner, Leonard Hall
put it. He swore he heard birds in the
recording, off in the distance, that he could
not have heard on the spot. This is commendable exaggeration, but it does express
the feeling that true-binaural gives to most
li~teners. Binaural bird-song recording,
WIth earphones only, of course, will soon
open up a whole new field of useful research
and pleasure for bird lovers and especially
for bird experts. My tapes have been heard
by a number of the latter, including Prof.
Paul Kellogg, of the Cornell bird song records, who hopes to be in the field with a
portable binaural Magnemite before the
summer is over as a result. Again, the
usefulness of this method depends directly
up,on the true binaural effect, which in
thIS ca~e places the birds in space, gives
them SIze and perspective and. above all ,
allows the ears to sort out individual sounds
out of a confusion of noises, as no monaural
recording can ever do even with the ratheI:
artifical aid of the parabolic reflector used
by most bird song recordists under p~esenf
monaural techniques.
By sheer accident I discovered that binaural sound pickup, with phones, can be of
immense usefulness in the building and installation of pipe organs. It is extremely
difficult to judge organ sound and balance
from the playing console; binaural mikes
set up -a hundred feet away and fed to binaural phones on the organist's ears allow
AUDIO ENG IN EERING
•
SEPTEMBER, 1953
him to hear his organ as others hear it,
from any part of a church or auditorium.
The general manager of one of the Big
Three organ makers tried out my Magnecorder with me and went away muttering
that his firm could have saved thousands of
dollars with such a gadget. T hey had tried
monaural recording and earphones, with
dangerously false results. Organists themselves should benefit, too, from the selflistening potentialities of binaural pickup.
Phones, only, of course. Incidentally, this
gentleman was at first apparently not too
well impressed with the sound he h ea rd in
the phones as he played-until, rea lizing
what was the matter, I wa lked O).1t to the
mikes and talked into one of them at close
range. A hundred feet away, he turned to
one side to answer me; he thought I was a t
his side. That did it.
I haven't had a chance to explore fo lk
music collecting via binaural phones yet,
except to the extent of one set of humorous
local Missouri Ozark stories, told to a
group of us around the binaural mikes by
Leonard Hall, who owned the farm mentioned above. But the extraordinary sense
of presence (at ten feet mike distance, not
one or two) that is heard in those recordings-especially the comments and
laughter of the other people, around and
about you (as you listen) on all sides,
makes me sure that here, too, is a field
that should be of immense importance for
folk lore experts. The likelihood that there
will soon be a binaural portable Magnemite
makes this possibility even more a ttractive.
(The Magnemite is definitely steady
enough for virtually any musical purpose;
I have one along with me, for experiments
yet to begin.)
Binaural Home Movies
What am I doing in Switzerland wit h
binaural recordings? Thanks to Magnecord,
I have shipped my loan Magnecorder ahead
and will find it waiting for me a t Yverdon,
in French Switzerland, where the Paillard
Company makes the Bolex 16-mm movie
camera-with the new stereo attachments.
Weare about to t ry true-stereo, truebinaural sound photography, with earphones and glasses. I have very positive
indications that it will work, too; we've
tried it. 1'1.1 have more to say on this aftel'
our experiments, but meanwhile, after
perusing this installment, you may be able
to figure out for yourself why true-binaural
recording, with phones, is the only possible
means of making genuine sound home
movies- anywhere, indoors or out, with the
microphones always mounted at the camera.
No patent on the idea-yon can try it
yourself if you want .
Just before I left for Europe, Editor
McProud and I took a good look into the
nooks and crannies (and files) of the new
(to me) JE office in Mineola, Long Island;
we turned up, to our surprise, a golden
cache of unpublished Canby record reviews
that had been quietly pruned away over a
period of months, to fit space requirements
in the various issues. Never one to miss
such a fine opportunity, I stuffed them
into my suitcase and present some of them
herewith. They aren't brand new, but they
aren't very old, either, and aside from the
fact that newer reco rds of th e same works
or types of music may have appeared since,
they are as good as new. All, of course, are
still available.
of the American Broadcasting Company
PLAYS FLAWLESSLV. • •
G eorge Sopki n
, Joseph Stepansky
Leona rd Sorkin
Irvi ng IIme r
They record
, their music faithfully
with the .gONOoyNE M,~~~~~CNE
-
I
,
r------------------,
~
The Fine-Arts Quartette is famed
throu ghout the country among
professionals as a group of "musicians'
musicians." Staff artists of the American
Broadcasting Company in Chicago,
the Fine-Arts Quartette is known for its
unsurpassed tone quality and technical
perfection. Consistent recording of all
rehearsals h as helped this renowned quartette
achieve t he high standards of perfection
for which it is known.
High-fidelity enthusiasts, as well as
professional recording artists, are using the
"Sonodyne" in ever-increasing numbers.
Home users of tape-recorders are finding that
the "Sonodyne" reproduces voice and music
with a remarkable degree of "naturalness."
It makes the "Sonodyne" the ideal highquality, moderately-priced replacement for
the conventional microphones supplied
with tape recorders.
Model "51" Sonodyne. list price, $47.50.
Available at Shure Distributors everywhere.
~~,:=. ,- -
Model "51"
__________
.J
. .;:::.
c:::.==:::::::::::=-~::::,.::::,.:::.=..=-=-=-=-=-:::;..~
RECORDS
• Wagner: Excerpts from the Ring des
Nibelungen, vols. 1, 2. Munich State Opera Orch., Kowitschny.
Urania 7063, 65
(Also album 603)
AUDIO ENGINEERING
THE FINE-ARTS QUARTETTE
•
SHURE BROTHERS, Inc.
* Microphones and Acoustic "Devices
225 West Huron Street, Chicago "lO, Illinois
SEPTEMBER, 1953
•
Cable Address: SHUREMICRO
49
'-, Wagner: Overtures (Flying Dutchman,
Rienzi, Die Feen, Das Liebesverbot). Mu nich State Oper-a Orch ., Kow itschny.
Urania 7069
Three of the hest orchestral ''If agner discs I've
ever heard, musical1y in the playing and technically in fabulously big, clean, well·miked record·
ing. Real hi·fi stuff of the first water, especially
the four overtures-with a tremendous drum,
r at tles, cymbals etc., etc. The two earliest overtures, Liebesverbot and Die Feen, are most
interesting t o hear, one full of Weber a nd
Schumann, the other as Italian as spaghetti,
reeking of Rossini!
Urania is fina lly getting out of its German
radio reissues, with t heir so-so quality. These
must be brand new. Or a miracle.
Bernstein: Fancy Free. Copland: Rodeo.
Ballet Theatre Orch ., Levine.
Capitol P-8196
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Power Amplifler A 1-300
Deluxe Tone Arms :
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AI-SOl (16")
Dual Coaxial
Ideally matched high-fidelity units that
offer every home new sound quality ...
new pleasure in favorite recordings!
Individual General Electric <;omponents
will improve your present system or,
get a complete ensemble for the finest
home-decorator installation. Call a local G-E distributor today! Sec, 449 3 ,
General Electric Company, Electronics
Park, SyraCltse, New York.
Speaker
A1-400
Speaker
Enclosure (Blond
or Mahogany
Veneer) A 1-406
*
*
*
See and hear the General Electric Custom Music Ensemble at the International Sight and Sound Exposition,
Palmer House, Chicago, Sept. 1-2-3.
An int:iguing musico-technical probJem here.
Presumably the two sides were pretty much iden·
tical in recording-why, then, does the Copland
ballet seem so much more "high fidelity," so much
richer in so und, fuller, better balanced? I'm inclined to think it's in t he music.
These are near-relatives in style. Both are in
that racy, high-strung, jazzy-brassy manner of
recent American ballet, full of blats, squawks,
violent syncopation, mixing jazz and cowboy into
the symphonic; but Bernst ein, the yo unger m an
and pupil, sounds strangely ineffective, small, even
a bit childish here, whereas the older Cop land
(who. after all, m ore or less originated the style)
is immediately m a ture, vigorous, potent in sound.
Y et in its proper surroundings "Fancy Free" is
delightful-why this reaction now? F irst, I t hink,
is the direct comparison with Copland, much to
Copland's advantage. Second, Bernstein as a
younger and more " m odern" composer is m ost
a t home in a relatively dry, close- up acoustical
situation j his music scintillates in a n ight-clubby
recording. Copland can easily fi ll the big, concert·
like Iiveness o f Capitol's present recording, but
Bernstein is somehow out of place in it.
If you want to hear som e of Fancy Free in a
different and better acous tic, try Decca's recent
lO·inch excerptin g.
De Falla, The Three Cornered Hat (Complete). Opera-Comique Orch. of Paris,
Martinon; Amparito Peris de Pruliere, sopr.
Urania URLP 7034
This is a find! Several dances rrom this hallet
are conven tionally played and recorded again and
again in th e standard suite-but the rest of the
m usic, including the t antalizing short solos for
soprano here, the shouted interjections of a
chorus, are unknown to most of us. A beautifully
played performance and nicely recorded.
Some Recommended Bach-Period Music
Bach, Clavier Concertos # 1 in 0 mi" #5
in F mi. Lukas Foss (piano); Zimbler
String Sinfonietta.
Decca DL 9601
* Bach Organ Works: 5 Chorale Preludes,
6 Chorales. Helmut Walcha , organ.
Decca DL 9569
* Bach Organ Works: Six Trio Sonatas.
Decca OX 114 (2)
A blind German organist does a fine job on two
different old German organs with the intrigning
h ighly colored "Baroque" tone color of Bach's
own reriod. The most colorful and easiest to follow ar" the Trio Sonatas; the chorales (hymns)
are m orc 5erious.
,:,1 Handel, Water Music Suite, arr. Chrysander. (Complete). Berlin Philharmonic
Fritz Lehmann.
Decca DL 9594
The complete Water Music is about lour times
as long as the la!Jliliar s uite, and mostly worth
it, too. This is not unlike the familiar H arty
a rrangem ent; horns, trumpets, strings, here plus
harps ichord, a big. symphony sound, not really
authentic and with rather stunty tempi, mostly
fast, but very easy listening for m ost folks not
specialists in the Bar:>que.
50
AUDIO ENGINEERING
•
SEPTEMBER, 1953
THE CASE FOR MUSIC
CANNON
PLUGS
(from page 32)
Probably the most important single
thing to do to broaden one's musical
. knowledge is to make a point of hearing
all the fine live music available nearby.
A season ticket to the local symphony is
a good beginning. Local music schools
have recitals at least weekly, and usually
stage choral and orchestral concerts once
or twice a year. It is important to keep
in mind that the music is the vital element in all of these performances, and
that the performer is of secondary importance. Thus a flawless performance
is not necessary to enjoy the evening.
(Listening to live music helps to solve
"tone control" and "recording character~
istic" problems. If one has just heard
the local orchestra playa concert, a good
reference for proper dial settings is still
ringing in one's ears.)
Another step, which is probably the
most painful but also the most rewarding
to one's generq.l musical education, is to
learn to play an instrument. By far the
most rewarding . of all musical activities
is ensemble playing. Since some instruments fit into many ensembles, and others are useful mainly as solo or orchestral instruments, careful consideration
should be given to selecting the particular instrument to be studied. During the
first period of study, the pain usually
outweighs the pleasure, but after the initial stages ·are past, the musical rewards
are very great.
Books about composers and their music, about theory and the technical aspects of music, and about music history
and literature are all valuable contributions to general musical knowledge.
Careful reading will increase the pleasure of music listening all out of proportion to the effort involved.
One is likely to derive satisfaction approximately in proportion to the effort
and understanding one expends.
In music-as in other artistic fieldseffort is amply repaid, but a genuine, sincere, and sustained effort must be made.
All auxiliary devices-recording machines, records, phonographs, speakers,
vacuum tubes, and output transformersare at best but aids to the enjoyments
music can provide, and at worst, are
makers of noise without artistic conscience.
get good reception
WRITE FOR
PRICE FOLDER
C-l09
The high quality audio connectors shown
above are available from all Cannon Franchised Distributors. In their great variety of
sizes, shapes and contact arrangements there
is no problem or technical requirement in the
radio, sound, TV or related fields that cannot
be met. Cannon plugs are standard on leading
makes of audio equipment and microphones.
M1SERIES
' ~
.
.
.... , : . . .
'
.
.
<
~;,
-~,
CANNON ELECTRIC
Since 1 9 1 5 .
HOTEL NEW YORKER
J4th ST {, 8th AVE
HEW YORK CITY
OCTOBER 14. 15.16.17.1951
AUDIO ENGINEERING
•
Factories in Los Angeles, Toronto, New Haven, Benton Harbor. Repr~­
sentatives in principal cities. Address inquiries to Cannon ElectrIC
Company, Dept. 1-109, P.O. Box 75, Lincoln Heights Station, Los Angeles 31, California.
SEPTEMBER, 1953
51
NEW PRODUCTS
• Non-Corner Horn-Type Speaker Enclosure. Known as the Purest, a n ew baffle
r ecently introdu ced employs a h orn loa d
o n the back side of the speaker it encloses
fo r optimum low -frequency response, at
t he same time permits direc t radiation of
• Schoo1-Sound-System Console. M6 dulartype constru ction is feat ured in a n ew line
of centra lized control con so les for sc hool
sound systems, r ecently introduced by the
David Bogen Compa ny, 29 N in t h Ave. ,
New York 14, N. Y. In a ddition to flexibility of installation a nd operation, t h e units
afford convenience of expansion as the
f u ture demands. In t h e ir basic form the
n ew consoles provide three primary services--(l) a means for transmitting emergency announcements to t h e entire sch ool
or to any d esired g r o up of c lassrooms, (2)
a m eans for tran smitting live, recorded,
or broadcast program material to any
classroom or group of classrooms, or from
a ny classroom to any other c lassroo m or
room s, a nd ,<3) an intercom system be-
high freq u encies. It is d esigned for u se
a long any fl a t surface an d d oes not re ly
on the walls of the room in which it is
used to act as a n extension of the horn.
Ad eq u ate horn mouth area is gained by
exhausting on three sides of the encl osure.
Total fold of the horn is 180 d eg. Dim ens io n s of the Purest a re 38 in. high x 28 in.
wide x 18 in. d eep. T echnical literature a nd
prices will be mailed on request by Gately
Deve lopme nt L aboratory, Barrington, N. J.
• Hi-Fi Table-Model Phonograph. Com pactly styled to meet the r eq uireme nts of
small homes a nd apartments, the new
tabl e mode l phonograph recen tly announced by Sound Works hop, 75 N. 11th
St., Brook lyn 11, N . Y., is d esigne d t o
u t ilize the complete housi ng as a speaker
baffle , and thus provides a s t an da rd of
performance compa rable to conventional
consoles considerably larger in size.
Known as the Superb, the new phonogr aph
is equipped with an amplifier based on the
Williamson design, and contains separa t e
\lass a nd treble contro ls as well as a control for new- an d old-record equalization.
Webcor record changer is eq uipped with
GE magn eti c cartridge. For o p er ating con venien ce the changer is mounted on
drawer slides and is withdrawn for record
replacement. Obtainable in hand-rubbed
mahogany, walnut, and korina, with
wro ught-iron matching b ase for ch a i rside
use available as an accessory.
• Improved Soundcraft Recording' Tape.
Micro-Polishing is t he d escriptive term
applied t o a new p a ten ted process now
being u sed in the manufacture of a ll magnetic recording t ape produced by Reeves
Soundcraft Corporation, 10 E. 52nd St.,
New York 22 , N. Y. Use of the process results in a mirror smooth recording surface
a nd th e virtual elimination of microscopic
protuberances which often cau se inconsistencies or interruptions in the recorded
signal, particularly in telemetering and
calculating applications. Use of the MicroPolishing process assures surfa ce uniformity and stability of tape output right
from the first playing, thus eliminating
the "weal' in" period Which heretofore was
necessary before new tapes could be interspliced with older ones. There will be no
change in existing price schedules.
52
• Miniature Audio Transformer. Although
tiny in size, the new Triad J AF ~eries
a udi o transformers are
magnetically
s hie lded a nd hermetically sealed. Designed
for use with transisto.,rs a nd SUb-miniatu re
tub e a mplifyi ng equipme nt, t h ey achieve
t h e extrem e in minia turiza tion with out
compromise on insula tion or mo isture protecti on. Ci r c ui t 'a nd winding data for each
t r ansformer are carr ied on a permanently
attached d ecal. All units in the new series
a r e described in Catal og TR-53, copies of
w hich may be obtained by writing T riad
Transformer Corporation, 4055 Redwood
Ave. , Venice, Calif .
tween the console and all classrooms. The
new co n so les a r e being offered in two
basic lin es, the SCH single-channel series,
a nd the DU dual-chann el series. The b as ic
single-chann e l syste m includes a radio
tuner, a t h ree-speed transcrip t ion player,
a nd three high-impe dance microphone inputs. It affords one ch annel for program
distribution, an d another for intercommunication. The latter m a y be u se d witho ut program interruption . Th e system is
s upplied to serve any multiple of 15 classrooms. Where less than 75 c lassrooms nre
involved, on e 30-watt amplifier is provided
for the program c ha nn el. Larger single chann el systems h ave two 30-watt amplifiers. The basic dual- ch annel system includ es an ad dit iona l channel f or program
distribution a nd an additional microphone
inp u t. It is designed for any multiple of
12 classr ooms. Further details are avail ab le from the manufacturer .
• Distortion Filter. Designed fo r the
elimination of distortion from signal
sources, the new T ype DE filt e r s will reduce h a rmonics from the second to the
eighth by a minim um of 60 db. They are
so constructed that a drift of ± t h ree per
• RCA Home-Model Tape Recorder. P us hbu tton cont r ol of a ll mechan ical operatin g f unctions is feat ured in the n ew RCA
portab le tape recorder. Packaged in a lugg a ge-type carryi ng case, the recorder
weighs but 25 lbs, and measures onl y
cent in signal source frequency w ill n ot
affect fi ltering action. The filters are availa ble in a varie ty of impedances and can
be made for any frequency from 20 to
20,000 cps. Through their use in production tests, low values of distortion measurem ents can be made u sing any avai lab le
signal generator. Full technical specifications will be supplied upon req u est to
Orth o F il ter Corporation, 196 Albion Ave .,
Paterson, N. J .
14 x 12 x 9 ins. Capable of using all sizes
of t ape spools up to 7-ins. , the dual-spee d
machine can record or play back up to two
ho urs, and can be rewound in a pproximately two-and-three-quarters minutes.
Operating s p eeds are 3 %. and 7 ¥., ips. The
recorder is equipped with both input and
o utpu t j ack s to permit easy attachment to
phonographs, radio tuners, and public address systems. Engineering Products De]Ja rtment, Radio Corporation of America,
Camden, N. J.
• Presto Tape-Transport Mechanism: Replete with improvements over earlier models is the new Presto Model RC-ll tape
transport mechanism, a unit of almost ab solute a ccuracy, w ith separ ate h eads for
record, playback, and erase. Compac!ly
built on a " unitized" construction prmciple, the RC-ll employs a capstan drive
unit which conta ins a precision motor,
endless Nylon belt, brass flywheel, cll:Pstan shaft, ' pressure pulley, and so~enol~.
This enti r e segment of the m echamsm IS
self-contai n e d and instantly r emovabl e for
servicing or replacement. Other feat ures
include a heavy cast-aluminum panel for
rigid support of all components, enclosure
for recording heads, and complete push
button operation. R eels up to 10¥.,-ln. di-
AUDIO ENGINEERING
•
SEPTEMBER, 1953
HARVEV the House of Audio.
PILOTUNER
Model AF-824
FM-AM TUNER
Portable, Professional Disc Recorder ·
and Playback Phonograph
For making pe rmanent, high quali ty disc rec ordings from edited tapes ,
off-the-oir, and live program material. It is the only portable 12" recorder
thot hondles 13'1,," masters; driven by a hyste resis synchronous motor;
and is equipped with a professional overhead recording lath e with interchangeable leads crews for standard and microgroove recordings.
The CholJ~nger operates at 78 and 33 V3 rpm (on accessory idler is avail able for 45 rpm) . The amplifier has a response from 30 to 20,000 cps, .
± ldb with equalizer controls for bo ss and treble . It is provided with
duol stylus magnetic pickup, and a wide range 10" PM loudspea ker.
$459.95
Complete with standard leadscrew .................................................
A sens itive, se lective, and stable tuner designed for high fidelity appli cations . FM section is provided with temperature compensation against
drift, as well as AFC which can be cut out by means of front panel dis abling switch . Effects 20db quieting with anly 10 microvolt signal. AM
section employs separate tuning condenser. Output is .2 volts with 10
'microvolt signal.
Model AF·824 has built -in preamp-equalizer for lP, NAB, AES, and
Foreign recordings . Frequency res ponse is ± 1f1.db from' 20 to 20 ,000
cycles. Separate bo ss and treble control circuits permit up to 19db boost
or attenuation at 20 and 20,000 cps . Cathode follower provides low
impedance, permitting long line to main amplifier without high frequency
loss, and without hum pickup. Power supply is self·contoined.
Complete wi t h Tubes and Front Escutchean ..................
REK-O-KUT
FISHER HIGH FIDELITY UNITS
12-inch, 3-Speed TURNTABLES
Model L-743
Moster Audio.<ontrol
Preamplifier-Equalizer
Mode150-CB
A broodcast quality turntable designed for
discriminating users . . . professionals and
audiophiles. Driven by "-pole motor. Turntable
itself is mode of cost aluminum , and exerts no pull
on magnetic cartridges. It is precision machined with
dynomically balanced flywheel action.
A single 'knob per,mits instantaneous selection of any record speed: 33113,
45, or 78 rpm. Record slippoge is eliminated through use of new mot
material. There is virtually no rumble, wow or flutter. Complete with 45
$59.50
rpm r.cord adapt.r ..............................................................................................
Model T-12H
A Deluxe version of the above for the ultimote in turntable design for 33V3 and 78 rpm only . Driven by constont speed
hysteresis synchronous motor.....
...... ····· ........ ·········.. ···· .... ······..
·$11 9.50
·$11 9.50
HARVEY carries
a complete line of
AMPEX
A high quality, h'igh gain, all-triode circuil
with virtually no distortion. Ha s shielded,
se lf·contoined power supply with DC for tub e
heater.s thus eliminating audible hum . Cathode follower input and two
cathode follower output stages assure isolation of all control circuits, also
providing low oulput impedance, permitting long leods without frequency
discrimination.
Five inputs provide occommodation for microphone , magnetic cartridge,
tuner, tope reco rder, and other signal sources. There ore eight controls:
1. Volume which operates either conventionally or as a loudness con·
trol. 2. Lou d ness Control Switch which selects the function of the
volume conlrol. 3. Selector Switch for the five input positions. 4 & S.
Low and High Frequency Switches provid e 16 combinations of low
frequency turnover and high frequency roll-off. 6 & 7. Boss and Treble
Tone Contro ls produc e up to 16db of boost or attenuation ot 50 and
10,000 cycles resp e ctively. 8. Power Switch tUrns units on and off and
furnishes AC power to three spare· receptacles. There ore also five
independent leve l controls , one for e ach input.
Complete wi t h Tu b es....... ............................. .
. . . .. · .. · ....
·$97.50
LABORATORY STANDARD AUDIO AMPUFIER
PRECISION MAGNETIC
RECORDING EQUIPMENT
Model 50-A
All models are on Demonstration at the Harvey AUDIO·
torlum, and are Available 'or Immediate Deliveries
directly 'rom Stock. Write for Complete Details.
JIM LANSING
0-130 LOUDSPEAKER
A high quality, 15 -i nch, general purpose
speaker capable of continuous 25 walt operation. The 0·130 employs a large Alnico V
per manent magnet field. It has an edge-wound
ribbon voice coil, 4" i n diam eter. A coaxial aluminum diaphragm covers
the high frequency rang e. This is rea( ,ve nt ed to eliminate nonlinear
compression effects. The nominal impedance is 16 ohms.
$70.40
Through the emp lo yme nt of a spe·
cial type of cathode follower driver ,
a we ll reg urat ed bias and high voltage power s·upply, · the · 50-A has·
ochieved on undistorted power output for in excess of 40 wotts. Tri ode-connected type 1614 tubes are
used in the oulput. Th e overall reo
suit is extremely lo w hum ond nois e
(-92db), good
good linearity,
response: 20
± .ldb, and 5
transient handling.
and wide fr eq uency
to 20,000 cycles
to 100.000 ± ldb .
Power supply is built-in. A jack is provided for measuring plote current
of the output tubes. Damping foctor is 31, and efficiency in excess of
55%' Harmonic Distortion : .05% at 5 watts , .08% at 10 wotts, and
.3% at 40 watts. Intermodulation Distortion : .4 0/ 0 ot 10 watts, .8% ot
40 watts, on.,d 2% ot 45 watts.
Complete with Tubes ...
.Visit the HARVEY AUDIOtorium
If you want to See and Hear the
finest . . . the widest selection of
high' fidelity equipment . . • be sure
to visit the HARVEY AUD IOtorium.
It wi II thri II ,you.
NOTE: Prices -Net, F.O.B., N.Y.C.
Subj'ecl to change wltho!)t notice.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
53
You asked for all the features in this NEW
~
HIGH FIDELITY
PROFESSIONAL TAPE RECORDER
ameter can be acco mmoda t e d a nd r ecording s p ee d s a r e 7'h and 15 i ps. Brakes a nd
Gap sta n p r ess u r e pulley are actu a ted by
sole no id s , making the RS - ll idea l for r emote co ntro l. Presto Recording Corpor ation, Pe:l.1"a nlUS, N . J .
• New Coaxial Speaker. A 7 'h -lb. A l nico
V mag n et is e mploye d in the new Mode l
20SA.,'C s p eak e r wh ic h is t h e most r ecent.
a d d i t ion to the Tru -Son ic line of hig h
Ade lity e qu i pme nt p r od u ce d by Ste ph e n s
l\i(an u fact uri ng Corporation, 8538 "'i'Va rn er
~~
Top Professional Quality
Single Speed Model HF-500
~
- now at moclerate cost, for the
first time! - for Easy Portable or
Fixed Operation with Self-Contained
Speaker or with your Separate Speaker.
, ,
COMPARES WITH THE fINEST
Advanced de velopm en ts by TapeMast er m a k e it easier and
more economical now for r ecor dists to enj oy the ad vantages
of professional high fidelity l(ecord a nd playback.
The n ew Tap eMaste1' HF-500 is single speed (7.5 " p er
second). It provides full r an ge r espon se 30 cps to 15,000 cps.
Illuminated professional VU m eter gives level indication in
both recor d and pla yback positions. H as internal a mplifier
and 6" extended r ange speaker. Ca n b e switched t o external
amplifier and speaker. Inputs for microphone and r adio
phono. Uses Brush p r ofessional h ead .
Ideal for broadcast r emotes, r ecording studios, schools
and hi-fi enthusiasts. Easily por table in fine grain m orocco
leatherette case, 19% " x 8%" x 13" high. Operates on 105125 volt, 60 cycle, AC .
50
Model HF-500 T a p e R ecorder, NET ..... . ..... . .
Drive, C ul ver C ity, Calif. Other d esig n
features in c l ude a n improy e d di a phragm
apd hig h -frequency t h r oat str u c t u r e. A
die -cast a lU1l1in u nl fra nl e pr ovid es exceptio n a l r i g idity a nd e liminates possibility of warpage.
• Hig h-Quality R a.dio Phonogra.ph. One
of th e t r ul y fine "packaged" sound syst ems to be i ntroduced with i n r ecent weeks
is t h e n ew Stromberg-Carl son co mbin a tion r a dio -ph o nograph . H ou sed i n m a h ogan y or blond, the unit is bui l t a r o und
$279
Model HF-200 Tape Recorder. Similar to above, but is
dual speed a nd h as m agic eye in place of VU m eter.
Uses Shure wide r an ge head .
Net, $227.50
(Pri ces sli ghtly higher W est and South)
Expo,t: Scheel International, Inc .
4237 N. Lincoln Ave., Chicago 18, U.S.A.
Cable: Ha,scheel
54
t h e Stromberg-Carlson C u stom 40 0 highfidelity co mp on e nts. Include d is a hi gh l y
selecti ve, drift-c ompe nsate d FM-AM tu ner
w ith m a t ching 10-w att ampliA e r. Fre q u e n cy r es p onse is 20 to 20,000 c ps with
n egli gib le
di stortion at f ull o u tput.
Speaker system is t h e well-kn own Stromb e rg-Ca r lson acousti cal la byrin th with coaxia l 12-in. speaker. Record c h a nge r is the
Garra rd Model RC-80, equ i pp e d with m agneti c pick u p and j ewel sty l us. Bass :l.nd
treble con t ro l s a re separate; vo lum e co ntrol i s to n e compensated. Stromb erg-Carl"'on Company, Roc h e ste r 3, N . Y.
AUDIO ENC.INEERINC
•
SEPTEMBER, 1953
• Twin-Speaker Hi-Fi Sound system. An
a dvanced ve r s ion of t h e origina l Rek-OK u t single-speak e r Ryt h master, the new
Model RT- 43VC is a twin-speaker porta bl e sound system designl'ld primari ly for
use i n ed u cationa l and recreation a l activi t ies. Like its namesake, the new Ryt h mastel' is eq u ipped wit h the Rek - O-K u t continuous ly-va riab le-speed turntab le which
ON ANY STRINGED INSTRUMENT
r·
Apuil¥ ~e q~~
I
IAMPERITE "KONTAK MIKE" I
THE ONLY NO-DISTORTION "KONTAK' MIKE"
pe r m i ts any d esi red reproduction speed
from 25 to 100 r.p.m. Indoo rs, the uni t will
acco mmodate gro u ps up to 1000 in ballrOoms a nd a u ditori u ms. Outdoors, trumpet
s peak e r s may be p l u gged d i rect ly into
o u tp ut provided for ath letic fi e lds, camps,
a nd the llk e. Th e porta b le speakers a lo n e,
M ode l SPK- 43, a re availab le at moderate
cos t to owners of earlier Rythmaster mod~ l s . For a dditional informati on, write RekO·Te u t Co mpa ny, 38- 01 Q u ee n s B l vd., Long
Island City I, N. Y.
I
• Slim Ci:rysta1 Microphone. Exception a lly
s m a ll in s ize, economically priced , a nd
capab le of good·q u a lity reproduction, the
new Shure Model 777 "Slim·X" crystal
nl iCl'ophone is an ideal "walk-around"
ha nd·h eld u nit for a u dience p ar ticipation
·1
Used with most amplifiers, inclu8ing most
electric guitar amps.
A nthony A ntone, wid e ly known
a s " the most versatile ortist
of the fre ts ", is a n e nthusiastic
user of Ampe rite Kontak Mik es.
s h ows, sports, lecturing, home recording,
a nd other applications where mobility i s
a facto r . Frequency response i s smooth
f r om 60 to 10,000 cps. Dim e nsi o n s are
4 'h-ins. long by I - in. dia m eter. Finish is
sat in c hrome. Supplied with 7·ft. cabl e.
Necl<lace · type cord for n eck s u s pe n s io n of
t h e mic r ophone is availab le as a n acces:lO I' y. Complete specifica tion s will be s up·
plied by Sh u r e Brothers, Inc., 225 W.
Huron St., Ch icago 10, Ill.
• T a pe Recor ders . Excellent audio quality
is afford ed by both the l ow- and medi um-
No changes in amplifier,
instrument, or strings.
Attached without tools.
The Amperite "Kontak Mike" improves the tone
and volume of any Stringed or Fretted Instru·
ment - also Pianos. Accordions. Harmonicas.
etc. It is the only "Kontak Mike" that does not
introduce peaks or distortion.
....... List $12.00
Model SKH, hi·imp...
Model KKH
(with hand volume control)
......List $18.00
AMPER IT E
STUDIO MICRO PHONES
01 P. A. PRI CES!
1deat pe CLOSE TALKING
or DISTANT PIC KUP
You can shout right into it, or
stand away; in either case, the
quality will be perfectly natural.
Model RBLG (200 ohmsl. ... List $42.00
Model RBHG (hi·imp) ........... List $42.00
AMPERITE CARDIOID
DYNAMIC MICROPHONE
AUDIO ENGINEERING
•
SEPTEMBER, 1953
55
priced models of the new Crestwood tape
recorder, recently announced by the Day strom Electxic .Cot:pora,t Wn, Poughkeepsie,
N. Y . The Crestwood Model 303 is a singlepackaged unit for home and general r ecording, with a frequency range stated by
the manufacturer to be 50 to 10,000 cps.
It is equipped with power amplifier and'
speaker. Model 401 consists of tape-transport mechanism and preamplifier in a sing le housing, and is designed for use with
its (wmpanion Model 402 power amplifier
and speaker, or with allY other hi-ft ampli'fier-and-speaker combination. Frequency
respon se of the 401 is stated to b e 30 t<1>
13,000 cps. Both models are of the dualtrack type and record at 71h a nd 3,* ips .
Rewind and fast forward are 20 tim es
faster tha n recording speed . P rovision is
m a de for head alignment. In the M od el
401, d. c. is applied to low-level tube heaters to minimize noise level. Teohni cal
sheet is available from the manufacturer .
• Mult i -Speaker Hi-Pi Tab l e Phonog r aph.
Three speakers, a loudness control, and a
variable-reluctance pickup are among the
features which contribute to the quality
performa nce of the new Webcor "Musicale." Despite its small size the unit has
Ultra High Fidelity
a n audio response of 50 to 12,5 00 cps_
Changer is the Webcor Type 121 which
plays records of aU sizes and speeds automatically, and which is equ ipped wit!}
a utomatic shut-off. A five - tube am plifier
affords five watts output with low distor..tion. Webster·Chicago Corporation, Chicago, Ill.
• Miniature Audio Mixer. A n ew advance
in input mixing equipment is the "MiniMix," a tiny two-position mixer which:
plugs d irectly into the regular high-impedance input of any recorder, a mplifier
or musical instrument. Measuring only
2 1/ 16 x 1 13/16 x 1 1/16 ins. and weighin g '
but th ree ounces, the Mini-Mix offer s the
advan t ages of a full-size mixer. Short lead
leng·ths inside a shielded h o using minimize·
stray pickup. Separate gain controls for
each ch a nne l are afforded by recessed
knobs. The Mini-Mix is availab le with
eith er stand ard jack or microphone-connector fit tings. Full information may be·
obtained by writing the manufacturer,
Switchcraft, Inc., 1328 N. Ha ls ted St.,
Chicago 22, Ill.
56
AUDIO ENGI NEER ING
•
SEPTEMBER, 1953:
NEW llfERATURE
• General BadiO-Company, 274 Massachusetts Ave., Cambri.dge 39, Mass., has pertormed a notable service to the a udio industry with the publication of " The Hand:book of Noise Measurement," a 100-page
treatise which covers thoroughly the
measurement of airborne sound s, and in-eludes definitions, standa rds, measuring
-eq uipment, procedures, a nd interpretation
of results. The book is a u thored by Dr.
.A. P . G. Peterson of the GR engineering
s taff, an d Dr. Leo L. Beranek of M. I. T.,
voth of whom are well known in t h e field
of aco u stic measurement. Copies of the
Handbook lore a v a ilable at a price of $1.00
"postpaid.
look to
for the Hmissing links" in
EXACT REPLACEMENT TRANSFORMERS FOR
• United Transfonner Company, 150 Varick St., New York 13, N. Y. illustrates a nd
<describes the comp lete line of UTC transfo r mers, reactors and filters in new lypublished Catalog 630. In addition to conventional buying information, the book is
·.. eplete with technical data to ai d in the
selection of units for highly unique a ppl!-cations. A truly wort hwhile assemblage
-of helpful information for which UTC is
to be highly commended.
• Amperex lliectronlc Corpora"tion, 230
D u ffy Ave., Hicksville, N. Y., has' issued "
new condensed catalog in which are listed
a ll of the tube types manufactured by th e
com pany, togelher with mechanical and
elec t rical specifications. Tub es listed in<'Iude types for the g r eat ma j ority Of in dustria l and amateur applications.
• General Electric Company, Schenectady
:5, N . Y. has produced a new bulletin on
uses of miniature se leni u m rectifier stacks
in electronic circuitry. Designated publi-cation GEA-59 36, the 4-page pamphlet
-contains information on the appli cations,
c onstructional feat u res, and electrical
c haracteristics of small selenium rectifiers. Included a lso are tab les of ratings
and dimensions, plus graphs on the effect
of temperatu re and the life expectancy of
various types of stacks.
.• Precision FUm Labora tories, 21 W. 46th
St., New York 36, N. Y. covers a ll aspects
<of 16- a nd 35-mm film processing in a new
and informa tive booklet which will be
mailed free in response to requests on
-company letterheads. Printed in color and
effectively illustrate d, the booklet simulates a persona lly conducted tour through
t he Precision plant. The reader is escorted
figuratively through each department, and
is s h own exactly what happens to film
f rom the moment it is re-ceived until it is
-shipped.
• Bucha nan Electrica l Products Corporation, Hillside. N. J ., de~ribe s a compl ete
line of solderless wire connectors and spe-cialized e l ectrical fittings in its n ew 16page catalog No. 53. Included are complete specifications, dime nsiona l d ata, application instructions, and ordering inf ormation. An exceptiona lly well-conceived
booklet, Catalog 53 should be in the h ands
of everyone with professional interest in
equipment of this type.
• Kess, Goldsmith &: Co., Inc., 1400 Broadway, New York 18, N. Y., introduces th e
use of glass fabric in modern industry
with a handsomely- produced 32-page booktet titled "G lass T extiles for Industry."
Discussed are three basic fibre textile
forms, together with end u ses for each
product li sted. Copy of the booklet m a y
be obtained by writing Industrial Pr'oducts Division at the a ddress shnwn above.
• Federal Telephone a nd Badio Company,
100 Kingsland Road, Clifton, N. J. is distributing a new catalog which lists the
wide range of cab l es which a re now available from the company's Selen iu m-Intelin
Division. Devoted essentially to sol id-dielectric cables , the 24 -page book covers
many types of cab Ung for transmission of
radio frequencies, including vhf and uhf
comm unications.
For m any years, CHICAGO
has made most of the
transformers and fil ter
r.eactors for Link R adio.
equipment which is widely
used in police communication
and other mobile applications.
CHICAGO Exact Replacement
Transformers for this equipment
are now available through your
electronic parts distributor. The
CHICAGO catalog numbers are identical
to the Link pa rts numbers . See your
distributor for these components.
IN SrOCK FOR IMMEDIArE DEliVERY
CHICAGO
CAT. NO.
TR·l034
TR·l 035
TR-l040
TR·l050
TR·l054
TR·l056
TR-l 063
TR-l065
TR·l072
lR-l073
TR-l077
TR-l081
Vibrator Transformer (6 v.)
Vibrator Transformer (12 v.)
Plate Transformer
Vibrator Transformer (6 v.)
Plate Transformer
Filter Choke
Filament Transformer
Power Transformer
Power Transformer
Vibrator Transformer (6 v.)
Filter Choke
Output Transformer
(Plate to Grid or Line)
TR·l082 Filament Transformer
TR-l083 Filament Transformer
TR·7074 Vibrator Transformer (12 v.)
•
REPLACES LINK RADIO
PART NUMBERS:
MTG. LIST
TYPE PRICE
TR·l034 and 12534
TR·l035, 14269
TR·l040 and 11862
TR-l050
TR-1054, 11944, 4891
TR·l056,0122U
TR·l063, 11992, 7211
7650N, TR-l065
TR-l072,6248
TR-l073, 6250, TR·l080
TR ·l077,7282N
TR·l081
V $ 9.50
9.50
V
FS 97.50
9.90
V
V 18.50
V 10.85
V 10.50
S 13.50
V
9.50
9.25
V
BX 24.25
S' 15.00
TR ·1082
TR ·l083,8218N
TR·7074
TX·l 31.25
TX 20.50
V 11.50
*!in-t ype terminels in place of solder lug s.
• stevenS-Arnold, Inc., 22 E lkins St.,
South Boston, Mass., describ es the entire
line of Millisec p lug-in r elays in recently
p u blished Catalog 337. Explained is the
use of gold contacts in place of p latin um-rhodi u m for l ow-cu rrent applications
where ultra-high-speed operation is a
necessity. Included in this pamp hlet is n
great deal of technical infol-mat ion of
value to u sers of high-speed r e lays.
AUDIO ENGINEERING
TYPE O F UN IT
SEPTEMBER, 1953
Free "New Equipment" Catalog
You'll want to have th e full d etails on CHICAGO'S
New Equipment Line, co ver ing th e complete range of "Seal ed - in Steel" transformers for eve ry mod e rn circuit application . Write
for your Free copy of Catalog No . CT-153 today, or g et it
from your e lectronic parts di stributor.
Export Sales Div.:
Schee l Inte rnational , Inc.
4237 N . Lincoln Ave.
Chicago, III., U.S.A.
CABLE ADDRESS :
HARSH EEL
57
Use and Abuse of the Tone Controls
FLEXIBLE TONE CONTROL CIRCUIT
(fram page 29)
of 10 db is required at both extremes of
the audio spectrum, then 7 db of negative feedback will still remain at both
extremes, and 17 db at the mid-frequencies. At " flat" position, the circuit
has a loss of 1 db 5 which is negligible.
The circuit can therefore be inserted
anywhere with no complications.
The only disadvantage is that the input to the tone control must come from
a low-impedance source, but not neces-
sarily from a cathode follower as shown
in Fig. 3. A source impedance of 10,000
to 15,000 ohms will have no adverse
effect, and this impedance can be readily
attained from a low-mu tube such as a
6SN7 or 12AU7.
Because to the large amount of negative feedback employed, the output source
impedance is low, giving the circuit all
the advantages of a cathode-follower
output stage.
BEST VALUE IN TAPE
RECORDING HISTORY!
HEAR US AT TH E SHOWS
Hear and see the new Cres t woods at t he Sight and Sound Exposit ion,
Ch icago , Se pt e mber 1-3 . Room 77 8 in t he Parmer House ; and t he
Au dio Fair, N.Y.C., Octobe r 14- 17 , Room 703 in t he Hotel New Yorker.
HiFi~400's
Crestwood engineering
makes tape recorder history!
Matches the finest professional equipment in hi-fi
performance- frequency response of 3 0 to 13 ,OOocycles
at 7Y2" per second tape-speed .
Yet COStS only $199.50 to
$299.50 (taxes not included) .
All Crestwoods exceed
NARTB standards.
TAPE RECORDERS
Open a Brand New
World oj Recorded Sound
.-------------- - --- SEND I N COUPO N TODAY.·------------ - --- --/
:
I
:
I
:
' Crestwood Division of Daystrom Electric Corp_, Dept. AE·9, Poughkeepsie, N. Y.
Compensation for the Fletcher-Munson curves with the tone controls would
seem to make them perform a function
actually belonging to a loudness control.
In addition, once the tone controls are
set on the reciprocal of the FletcherMunson curves, their usefulness for any
other function will be restricted, if not
nullified.
Speak er
The most serious misunderstanding
seems to be on the question of speaker
compensation. It is well known by now
that phase as well as amplitude response
of a speaker plays an important role on
the quality of music reproduction. A
speaker, being essentially a non-linea r
electromechanical transducer, has a
phase response which includes several
reversals, rendering any effects for eff~ctive c?mpe~sation rather futile, espeCially WIth SImple networks. Circuits
have been designed which effectively
compensate for some speaker deficiencies, using variable slope as well as vari~b l e turnover frequency, but their cost
IS usually several times the price of the
average speaker, making any impendinO"
" Fire Sale" on high-quality loudspeaker~
highly improbable.
Why use tone controls at all then?
They fill a definite need and most of
their functions are covered in Mr. Villchur's article and can be summarized as
providing:
Since the total gain in a negative-feedcircuit is equal to the forward gain
dIVIded by one plus the loop gain. In our
case, this ratio is less than one. In addition
there is a slight reduction in gain due t~
the cathode-follower input, but the circuit
parameters have been selected to keep the
total loss less than 1 db.
b~c.k
/
My nom e ________________________________________________
AcJdress _ __________________- - - -- - - - - -- -- - - -- - - -- -- - - - - - -
ll _____________________ _ __ _ ____________
Zone _ _
Stote· ____________
_ _______
. _ ,. _ ___________ _ J
58
There are scores of well designed circuits which offer adequate flexibility and
adaptability to meet any record characteristics and their deviations without resorting to tone-control compensation.
Since the low-frequency turnovers and
the high-frequency Ilre-emphasis fall
well below and above the "center" frequency of the tone controls, no adequate
compensation can be attained.
As for reducing any record noise, hiss,
or rumble, the tone controls are not
especially effective since, at best, most
of them have an attenuation rate of 6
db / octave, hardly adequate for any
effective suppression without sacrificing
the musical content of the program.
5
Please send me complete information about the new Crestwood models.
City
Preamplifier
Lau,dness Cantral
N EW~ 3 03
Nothing like it at the price
- little like it at many times
the price! Unusual high-fidelity performance- 50 to
10,000 cycles frequency response at 7Y2" per second
tape"speed - for on l y
$199.50 (taxes not included).
Smart styling, too.
:
While the writer is not naive to the
point of believing in "ideal curves," flat
speakers, and acoustical heavens in general, it is believed that in a reasonably
high-quality preamplifier-equalizer the
tone controls should not be called upon
to perform functions which they were
not originally designed to perform.
Following are the areas where abuse
is most likely to occur:
AUDIO ENGIN EERING
•
SEPTEMBER, 1953
1. Over -all tonal balance of the complete system.
2. Compensation for any acoustical
such as resonance, fo r exampl e.
3. Compen sation fo r any deficiencies
of stu dio eq uipment, means of transmiss ion, or for fau lty records.
4. Bass r eduction to el imina te boominess of male vo ices, especially on low
settings of the loudness control.
A new concept
01 recorded music
THE HEATHKIT
Z)e«tt
RECORD
PLAYER KIT
ApPENDIX
Negative feedback can be employed to
transform? net work into its reciprocal, as
shown below. Although the fo llowing derivations are ror ideal lead and lag netwo rks, they apply equally on actual networks having two break fr equencies, both
being impor tant in determining the over-all
frequency response of the circuit.
1. Tmnsformation of a, Lag into a Lead
Network (Bass) .
Referring to the upper section
we have,
1000
r--'\i'V\r--- TO GRID
0.47MEG,
100"101'
0 .1 MEG.
TREBLE
BASS
Fig. 5. Suggested wiring arrangement for the
tone control. The two potentiometers R, and
R, could easily be combined as a concentric
control.
from which
•
•
•
•
•
Here is a new introduction to
quality record reproduction. A
simple to operate compact table
top model with none of the 'specialized custom installation problems usually associated with high
. fidelity systems. Two matched
speakers mounted in an acoustically correct' enclosure reproduce
all of the music on the record, reproduction with the unique sensation of being in a halo of glorious sound. This
spectacular characteristic is possible only because
of the diffused non-directional properties of the
matched speakers. The, performance.level of the Heath'. '
kit Dual is easily superior to that of the ordinary
console selling for many, many times the price of the ' Duai.
record changer plays all three sizes at all three speeds with automatic
for both changer and amplifier after the last record is played. A wide
. cartridge features an ingenious "turn-under" twin sapphire stylus
or 78 records without turning the cartridge. Simplified easy to assemble
tube amplifier featuting compensated volume control and separate tone conProxylin impregnated fabric covered cabinet supplied completely assembled.
build only the amplifier from 's imple detailed step-by-step instructions. No
tools or knowledge required.
project has ever tempted you here is the perfect introduction to an
and exciting pastime. The Heathkit Dual Kit includes cabinet, record
6" speakers, tubes and all circuit components required for amplifier
cOI$:ruction. Build the Heathkit Dual and enjoy unusually realistic room filling
uction of fine recorded music.
K , (T.+1)
l +K,K ,
ei
=(
1
) TS+ 1
1 + K .K ,
The original lag (B), has been therefore
transformed into a lead network (B') having two break frequencies, 1 + K,K, apart.
2. Transformation of a Lead into a Lag
Network ( T reble)
Referring to the lower section of Fig.
we have,
[e/- [K,(TS+ 1)leol K,=eo
from which
eo
Plays all record sizes, all speeds
Newly developed ceramic cartridge Dual Matched speakers
Acoustically correct cabinet enclosure
Autoniatic shut off for changer
and amplifier
K,(TS+1)
= TS+l +K,K,
Model A-9A
Ship. Wt. 17 Ibs.
\f
.A 20 watt high fidelity amplifier especially
; designed ior custom in.
stallations. Low hum and noise level
9 pin miniature dual triodes in pre·
amplifier and tone control circuits.
FOUl;,switch selected. in'puts. Frequen.
cy te$llonse '± 1 db 2:() to 20,000
cycles. Output impedances of 4; 8,
and l6 ohms.
K,
=--===-=="'
-K,K, ) T ,S+ l
l +K,K,
( l+K,K,
The original lead network (C) has been
transformed into a lag network (C').
The method of combining the two original
networks (A) and (D) and the two modified networks (B') and (C') to obtain an
overall response ( boost in this case) is
show n in Fig. 2,
I
When Tb> T a a~d T a> T o, th en an
att~nuation of both extremes is attained' i
while at Ta=Tb and T o= Ta, we have a
completely flat frequency response.
AUDIO ENGiNEERING
•
Write For Free
CATALOG
New 32 page 1953
Catalog lists all kits,
specifications, schematics and latest
price information.
YOU
SEPTEMBER, 1953
SAVE
BY
ORDERING
DIRECT
FROM
FACTORY
59
NO W A VA/LABLE
The GRAMOBON Feedback
DECADER
(from page 34)
yided . Six " decades" a re used, each of
which has nine resistors of the same
value connected therein, the several
values being 10, 100, 1000, and 10,000
ohms, and U.1 and 1.0 megohills. But it
is immediately apparent that the permanent interconnection of aU these six decades into one resistance unit is not desirable. For example, when work with
triodes is underway, it would be possible
to vary simultaneously both the plate
load resistor and the cathode bIaS resIstor if the resistor decades were split
into two sections. This Dermits the user
to determine quickly the proper combination for any particular tube type
under study. This feature has been incorponlted as detailed below.
Another censideratioR was the u e of
decimal values vs. the "preferred values"
of resistor. The former were chosen .
because it is imposs ible to secure simple
ratios of resistance with any combination of the preferred values,.. thus imposslble to secure known divi sion of
voltages with their use.
Disk Recording Cutterhead Unit
Engineers and musicians now real ize a perfect transient res p 01}se
of any recording sys tem is of pa ramount importance-the Grampian
c utterhead w ith its precision-made true ba lanced armature and flux
correcting feedback roop obtains this ideal.
The Grampian Is used by International rad io n.tworks to guarantee Hi-Fidelity
so und re production. You can aehleye the same high quality results In your disc
re cord ing with the Grampian.
After testing and experimenting with all types of equipment many fa mous
reco;d manufacturers. such as CAPITOL, are convertina to the Grampian Feedback Cutter for the best resu lts.
for more information, write to
Wide frequency range •
30C/ s to 20 kc
Low Distortion
Superior transient reo
sponse
1
I
N
R E EVE
10
5
E QUI P MEN T e O R P.
EAST 52nd STREET • NEW YOR K 22 . N . Y. • U. S. A.
CAB LE. RHVESaU IP . N . Y.
The Bridge
These V-M 555 features are PROOF of QUALITY:
• THREE 5" matched ultra-wide range speakers with heavy duty Alnico 5 magnets.
• 20 to 15,000 c.p.s. response from special, ceramic all-weather "Rip-under" cartridge
with 2 new type SAPPHIRE NEEDLES.
• Exclusive, resonance-free aluminum DIE CAST TONE ARM.
• 5 TUBE PERFORMANCE from 4 rube (plus rectifier) amplifier with push-pull
output and dual purpose rube.
• NEGATIVE CATHODE feed back circuit eliminates intermodulation distortion.
• FULL RANGE CONTROL with convenien tl y located tone and volume controls.
• Free 12" LP Demonstration Record.
• WORLD FAMOUS V-M CHANGER eli minates record holders that grip the grooves,
records LOWERED (not dropped ) to spindle shelf. Siesta Switch automatically
shuts off everything (amplifier too) after last record plays.
• TWO FURNITURE FINISHES, mahogany or limed oak. Handsome modern design, finest qua lity construction.
• Made by V-M Corporation, World's largest manufacturer of phonographs and
record changers exclusively.
MAIL .THIS
COUPON
FOR
COMPLETE DETAILS
60
------------------,
V-M Corporation, Benton Harbor 6, Michigan
I
Please se nd me illu strated data on the V-M 555 high fide lity phonograph.
Name ___________________________________
~~
'-:i~
I
:
________ ,Sta~ _ _ _ _ _ _ J
Hav ing analyzed these possibilities,
this p roject was further studied to see
just how serviceable such an instrument
could be made from a laboratory point
of vi ew. The availability of 1 per cent
depos ited carbon I-esistors for use in the
decades makes possible a Wheatstone
bridge of the same percentage accuracy
by combining the decades with a galvanometer and a set of ratio arms. This
has been done, using a fixed 1: 1 ratio,
because of the wide range of val ues on
the "known" resistor arm. Figure 1
shows the completed instrument in its
case, while the interior construction and
mount ing of the battery is illustrated in
Fig. 3. Incidentally, attention is drawn
to the mothballs clearly shown in this
latter picture, which have purposely
been left in the case. This is a simple
but va luable trick which will preserve
low inherent contact resistance over
long periods of time by retal-ding tarnish
formation on the silver switch contacts.
The schematic of the instrument IS
shown in Fig. 2.
To achieve the desired flexibility of
circuitry, General Radio No. 938 binding posts and No. 938-L inter-connecting li nks are used. The grouping of six
binding posts on the hexagonal pattern
permits the following combinations to
be achieved: the three low-value decades as a unit and the three high-value
decades as a unit, independently but
both at the same time; all six decades
as a wide-range substitution resistor,
the six decades as the known R of the
bridge; as a bridge with the use of an
external resistance box for the known R
of the bridge; and fina lly as a bridge
with a given resistor as the known R for
purposes of matching pairs, without
determination of the exact values of resistance. It is believed that no bridge
commercially on the market today wiII
AUDIO ENGINEERING
•
SEPTEMBER, 1953
make all these various facilities available through its tern~inals. FigU!re 4
shows the 'proper interconnections of
the three links and the external connections. A s a bridg.e , tlije unknown resi stance is connected to the left pa ir of
terminals, those marked "X" on F ig. 2.
Conshuction Details
Ease of servicing as w ell as protection 'of the components require a workmanlike type of construction , and to
keep the costs down a s imple 10 x 12
in. bakelite panel is combin ed with a
10 x 12 x 3 chassis as the ca,se into which
to build the unit. The selection of
switches is not so simple, for there are
many types available, and some thought
here led to the choice of a continuously
rotating type. Anyone who has u ed a
bridge or decade resistance box will
immediately appreciate the conven ience
of continuous rotation. When thi s is
coupled w ith a 20-position unit, so that
sta rting with zero as a center it is possible to add either one or nine units of
the decade with only one step of the
switch, the ultimate in convenience has
been achieved. The switches shown, by
cross-wiring of the d0uble set of contacts wi ll afford this faci lity. Just why it
is so desirable is easy to explain-when
determining the value of an unknown
(@
8
3~
~
~
SERIES uSO"
0
Fig. 4. Detail of terminal arrangement. Interconnections provide the following combinations:
CoD
E-F
C-E
Strap D- F
-HIGH FIDELITY MAGAZINE
@)
Z-8£6~~ ®{
Terms
A-B
"Of the very best!"
Function
Known R arm of b ridge to use
external known resistor. Used to
match a given resisto r by connecting desired resistor to A-B and
t he unknown to X-X.
Termi nal s of the three high de- .
cades; provides values from 10,000
ohms to 10 megohms in 10,000ohm steps.
Term inal s of three low decades ;
provides va lues from 10 ohms to
10,000 ohms in 10-ohm steps.
All s ix decades in series , values
from 10 ohms to 10 metohms in
10-ohm steps.
To use the decades in the bridge.
Strap A-C,
S-E, D-F
Note : In ·asse mbly. the /"inks are permanently
affixed to terminals C, D, and E.
R, and the introduction into the known
circuit of another step of lUx ohms is
too much , then the addition of 9 x 10X - ]
ohms will ba lance the bridge. If the inclusion of the larger resistor is just over
the balance point, then commencing
with nine times the smaller value will
expedite the balancing operation.
The four push buttons beneath the
meter serve to operate the bridge and at
the same time shunt the meter at the
outset to protect if from wild swings
before the bridge is brought into balance. These are all DPST switches, the
second, third, and fourth of which have
been rebuilt so as to provide two pairs
of contacts, one normally closed and one
normally open, while the first push button has both pairs of contacts normally
open. This rebuilding operation merely
AUDIO ENGINEERING
•
• It is only natural that more than one manufacturer will c la im his
product is the best. For that reason it remains for you to be the judge.
We say - demand the specs. Then check workmanship, performance
and beauty of appearance. If you do all these things, the answer will .
inevitably be ... THE FISHER 'SERIES "50." There is no finer made.
FI~~~R
Master Audio Control N~~~~L
' . "One of the finest units yet offered to the enthusiast or audio engineer."
-Radio and TV News. Can be used with any amplifier. 1M distortion virtuall y unmeas~rable. Complete, profess ional equalization settings and tone
controls; genuine F-M loudness control; five inputs. five independent input
level controls, two cathode follower outputs. Self-powered .
Chassis, $89.50 . With blonde or dark cabinet, $97.50
MODEL
50-R
• Featu res ex:rellle sensitiv i!y (1.5 mv for 20 db of qui·eting) ; low distortion (less than 0.04 % for 1 volt ou.tput); loIV hUll"! (more than 100 db below
2 volts outpuL) Armstrong system, adjustab le AFC with switch, adjustable
AM selectivity, separate FM and AM front ends (shock-mo unted), cathode
fo llower output, full y shielded, aluminum ·chass is, seJ£-powered. $164.50
FI~:~R
SEPTEMBER, 1953
50-Watt Amplifier
MODEL
50-A
• Truly the wo rld's finest all-triode ampl ifier, yet moderately priced. A
man's size unit! Less than 1 % distortion at 50 watts (.08 % at 10 watts.)
1M distortion below 2% at 50 watts. Uniform resPOnse within .1 db from
20 to 20,000 cycles ; 1 db,S to 100,000 cycles. Hum and noise more than
96 db below full outpuL Quality components throughout.
$159.50
Prz.ces slig/Llly highe r wes t
0/
th e Roclci:s
WRITE TODAY FOR COMPLETE SPECIFICATIONS
FISHER RADIO CORPORATION' 37 EAST 47th STREET' N. Y.
61
The Model R-701 is a truly superb FM-AM radio receiver designed expressly for the discriminating listener. It provides a
quality of perform,mce so brilliantly real and so vastly superior
to standard mass produced receivers that it must be heard to
be believed. Handsomely styled for custom installation, it is
easily adaptable to any wall or cabinet closure. ·Six position
function selector switch, volume control, and separate bass and
treble correctors centralize all operation on one panel . . .
permit remote location of the audio amplifier.
MODEL H010 - A slJperb all triode amplifier providing
minimum di st ortion (less than 0.3% at 10 watts), max i mum
respons e (flat 10-5 0 ,000 cycl es ), tremendous d y namic range
and overall balance. Ideal for use with the R701 Tun er.
MODEL 0010 - New populor priced Hi -Fi custom Amp lifier, designed for use with the new R701 Tuner. Can be
mounted direct ly behind the tuner in most installations .
Ten watts output at less than 1 % distortion. Response flat
20· 20,000 cps.
WRITE FOR 9'TER ATURE
DAVID .BOGEN CO.,
,,.e.
N I NTH ~V E., NEW Y (1) R' K 14, 1,1, Y.
Z;'t.eeJ:I,~t:e
~ E~t S/i«I4lq4tUie'
the most widely
used Electronic
Supply Guide
requires loosening of the spring pile-up
screws and reversing of two of the contact springs, slightly bending them to
secure a good firm closing of the contact when the button is in the non-operated position .
The galvanometer is quite a sensitive
instrument, and was used because it was
on hand . The over-all cost of the unit
can be reduced by us ing a less sensitive
unit, say 50-0-50 microamperes, with a
slightly less sensitive indi cation on
higher values of unknown r esistance.
Consequently it is necessary to determine experimentally the values of the
meter protective shunts for any specific
meter. The values shown he re a re recommended for the met'T used.
The accuracy of the instrument as a
bridge is determined by the accuracy
of match of the ratio arms. Here some
outside ass istan<;e w ill be needed, either
by ordering a pair of resistors matched
to better than one per cent accu racy or
by actual ly selecting a matched pair with
the aid of an accurate bridge. While
exact value of resistance is uni mpor tant,
so long as they match perfectly, something in the vicinity of 10,000 ohms for
these ratio arms seems desirable, being
a good median for the range over which
the bridge will operate successfully.
W ith the internal battery of 7.5 volts
the sensitivity is excellent to a megohm,
and to 10 7 ohms w ith a lower degree of
precision. For best accuracy, a higher
voltage is needed, say 45 volts, with a
res istor of the order of 1000 ohms in
seri es with the battery to protect the
meter.
It is true that the acc uracy of this
instrument is onl y 1 per cent a t best.
which is less than a good commerically
built bridge, but it is more accu rate
than any ohmmeter device, whether that
be the oile included w ith the usual
multi meter or a vacul1l11 tube voltmeter.
Conseq uently the author felt that the
inclusion of the bridge fea tu re was well
worth the added cost and' the sl ig ht increase in phy ical size of the unit. It
has already well repaid the expenditure
of time and money in simplify ing ' the
design of several front-ends. as well as
other devices for the des ign of which it
has been util ized.
P ARTS LIST
the World's Largest stocks of
We specialize in
Electronic
Equipment
for Research,
Development,
Maintenance
and Production
Operations
COMPLETE EXPERT
Industrial Service
,
(,
One .complete
dependable source
for· everything
in electr'!.nic,
ELECTRONIC SUPPLIES FOR INDUSTRY
Simplify the purchasing of all your electronic supplies and
equipment . Send your orders to us at ALLIED-the reliable
one -supply-source for all your electronic needs . Depend on
us for quick shipment from tire world's largest stocks of
specia l-purpose e lectro n tubes, test instruments, audio
equipment, electronic parts (transformers , capacitors, controls, etc.) and accessories-everything for industrial and
communications application. We make immediate shipment
from complete quality lines that are always in stock. S end
today for your FREE copy of the 1954 ALLIED Catalog-the
complete up-to-date guide to the world's largest stocks of
Electronic Supplies for Industrial and Broadcast use .
ALLI E D RADIO CORP.
100 N. We.stefn Ave., Dept. 17-1-3
ChIcago 80, Illinois
~ee~~
62
4
6
8
8
3
9
2
~
_
~
3
Bakelite gane!, 10 x 12 x 3/ 16 111.
Steel chassis, 10 x 12 x 3 in.
Weston Model 801 microammeter, 10-015 !La (see text )
Switchcraft # 1004 switches (see text for
rebuilding data)
JBT MS-20-1-S switches, with EP-20
dial plates
General Radio 938-A binding posts
General Ramo 938-Z 'insula tors
General Radio 938-L links
each Welwyn type A-2 deposited carbon
resistors, or equivalent, 1% accuracy.
Values: 10, 100, 1000, and 10,000 ohms,
and 1.0 megohms-total, 54 resistors
matc hed resistors, Welwyn A-4 or equivalent, approximately 10,000 ohms. (For
ratio arms, see text.)
resistors, for meter shunts, Values used
here are 600, 2700, and 5100 ohms. See
text if used with other type of meter.
Battery, 7.5 volts
AUDIO ENGINEERING
•
SEPTEMBER, 1953
HORN ENCLOSURE
+
(from page 23)
place after all testi ng was completed.
Plain ~ -in. fir plywood was used for all
internal members, a nd 2 x 2 in. square
bracing material wa's used throughout
for reinforcement.
.
Assembly of the horn is quite simple,
as it had to be since no power tools were
available. The total construction, including photographs and measurements, took
slightly over two days. The fir plywood
fo r the horn sections was r ipped by t he
lumber-yard personnel into 13-in. st r ips,
and one width of the birch plywood was
ripped the long way into similar strips.
The 2 x 2 braces were, for the 1110st part,
nai led and glued to the birch sheets, and
to the horn sections. T his work was done
from the inside so that when completed
there would be no na il [email protected] to fill, and
an unsullied surface would appear. Gaps
were left deliberately between the segments of the horn curve, with the reasoning that there would . be less tendency
fo r strong vibrations to develop if each
section of the curve were isolated from
its neighbor. After ~h e fas t drying wood
glue had set, felt strips were ta mped into
place between the loose joints on the
curve; these can be seen in the photog raph of the rear of the horn Fl:g. 6. The
reflecting baffle at the base of the horn
was made of a 13-in. st rip of plywood
oriented at approximately 45 deg., and
braced between the upr ight 2 x 2 bl·aces.
Screws were then r un in from the ends,
through the side plates of t he enclosure,
and then covered . T he two-inch space
left between the top edge of t he baffleplate and the rear of t he horn was fi lled
with a pi ece of 2 x 2, a nd insulated f rom
the baffle by a strip of under -rug matti ng, to prevent squeaks and ra ttles from
developing due to intermi ttent contacts . .
T he back was screwed' on. with approxi mately half a gross of 2-in. wood screws
run throug h the back a nd into the 2 x 2
braces along the horn, down the sides,
a nd across the back-load ing cavity ..
A previous article 2 prompted the use
of an inexpensive speaker for the horn
,
°
-,
•
Fig. 9. Measured frequency response of
the complete horn,
including the mid range unit.
-10
- 1
•
,
J\,.
./
'\
\
\
\
\
\
.. CROSS-ovER
,
,,
J
/
,
~INIMUM TRE~LE CONTROl -
i ill' THEiTICt i/OiFlliiENCY.......
- 20
20
'"
-
\
i'"
'
11m
. ..
. III
F REOUENC Y
"BALANCED"
TV TRIPOD
mounted on
3-wheel
portable
collapsible
dolly
iIIustrated_
' 000
IN C YC LES PER
. ..
SEC OND
We THREW THE book a way a nd engineered a
brand new "BALANCED" Tripod for every photographic and video need. The result- a revelation in effortless operation, super-smooth tilt
and 360· pan action.
PERFECT BALANCE prevents mishap if the lock
lever is not applied. Quick release pan handle
locks into desired position. Mechanism is enclosed, rustproof, needs no lubricati on. Tension adjustment for Camera Man's preference.
Built-in spirit level. Telescoping extension pan
handle. We defy you to get anything but the
smoothest, .most efficient operation out of this
tripod beauty_
2 Cameron Barrit t, "Speaker trea't ment
for improved bass." A U DIO ENGINEERI N G,
Dec. 1952.
WE DESIGN
and manufacture lens
Mounts and camera equip ment for
WE CALIBRATE lENSES . . .
Precisi on "T" STOP CALlBRA·
TlON of all type lenses, any focal length. Our method is
approved by Motion Picture Industry and Standard Committee of SMPTE. Lenses coated for photography.
Special TV coating.
16mm -
3Smm and TV cameras.
WE RENT AND SERVICE
CAMERAS
-!<
DOLLIES • •.
7'
-It
Complete line
It will pay you to get to know us.
of 3Smm and 16mm equipment available for rental.
MITCHELL:
HOWELL:
Fig. 8. Throat for low-frequency driver.
AUDIO ENGINEERING
MOV/OlAS
•
Standard, Hi-Speed,
Standard,
Shiftover,
BNC, NC, 16mm.
Eyemos.
MAURER:
Bell
&
16mm
Cameras. ARRIFLEX. MOVIOLA: Editing mllchines, Synchronizers.
SEPTEMBER, 1953
The country's foremost
professionals depend upon our
portable, versatile, adaptable
equipment.
63
.
driver. The speaker used was a 12-in.
model, which was treated with glycerol,
GC cement, and by slitting the rim.
Figlt1'e 7 shows the details of the modifications, and Fig. 8 shows the loading
applied to the speaker at the throat of
the horn. The, resonant frequency of this
speaker was reduced from 70 cps to 53
cps. H.owever, if a good ·woofer had
been available, the special treatment
might nO,t have been necessary.
Performance
"
THE NEW BNj mn DUAL PURPOSE
"PREAMPLIFIER" DESIGNED BY COOK
AT AN AMAZINGLY LOW PRICE
Built to the highest specificatians, and engineered by the
originators of the Binaural recard .
,AT YOUR DEALER,
"
COOK
LABORATORIES
114 MANHATTAN ST,
STAMFORD, CONN,
• Th e best ,performance at any price for single-ch'a nnel
listeni qg
• . Flexibility of operation - new features
• Built in equalization for both BN and mn compensation 6db / octave 20-20,000
• Single unit ganged controls for volume, treble, bass
(boo$t & droop)
• BN focus cont rols fOT 'balancing speaker volume levels
• BN channel .reversing switch "puts strings on left"
• Selector switch provides for 2-spea ke r Monaural Playbock
• Cathode follower outputs for distortion less response
The enclosure ' is large, and there is
no gainsaying it. However, in the months
s ince it first sounded (and magnificently) , it seems to the writer's family
t hat it actually absorbs less living space
than a corner horn. Probably this is due
to the narrow upright structure, rather
than one which juts out into the room,
as a folded horn does.
A note should be added about the frequency response curve shown in Fig. 9.
T his curve, like all such curves, is an
approximation,.. rtIade. wLllh all ·the itwnitUITe in the house in FlOrma! pesition.
D uring the measurement of the system,
definite changes were noticed as the
writer moved about the room. After
graphing several curves, experimental
curves were made, each time moving, er
. removing; a staPl6a:ro item of furniture,
such as a chair. Each change caused the
response curve to change mankedly _
EQUIPMENT REPORT
WRITE FOR LITERATURE & SPECIFICATIONS
(from page 43)
NEW LO RE NZ SPEAKERS
Immediately after avowing (in last
month's LETTERS column) not to report on
speakers, this department was shown a
two-way system employing a pair of
speakers imported from Western Germany
by Kingdom Products, Ltd. On first heat·ing, these units appeared to have considerable promise, so they were checked by
comparison with a large comer speaker
considered by this r~porter to be a standard,
us ing the technique of making measurements over the frequency spectrum at ten
different points throughout the room and
then averaging. The results are shown in
-
This unit has been developed to
meet present day req uirements
for compactness. The filter requires
only 31/2 inche s of rack space.
H -MFHHI -- _ I .. TO " SPKR
s
H'Tt-ttttt-- __ REB E.L I V
Features" , ,
lOW HUM PICKUP t hrough the use 'of ·toroid coil s. Th e' un it may be used In ci rcuits having signa l
levels as low as -40 dbm without the necessity for t aking speCia l precaution s agai nst hum pickup.
• lOW DISTORTION: The filte r may be used at level s up to plu s 20 dbm with neg ligible Inte r-modu,
.
lation distort ion.
• RELIABILITY: All capacitors and inductors are hermetically sea led for lifetime service . Ag ing effects
are :negli gible .
•
DIMENSIONS: Standard ra ck panel , slotted, 3112" high. Maximum depth 7W' ,
CONTROLS :
low frequen cy cutoff selector knob, high frequ ency cutoff se lector knob, on·off key,
RANGES :
Both low and high frequency cutoff controls cove r 100, 250, 500, 1000, 2000 , 300:-,
4000 and 5000 cycles.
ATTENUATION: Appro xi mat ely 16 db , per octave on both high and low frequency cu toff points.
IMPEDANCE: 500/ 600 ohm s, in-ou t.
.
Engraved panel fin ished in med ium gray baked enam el.
FINISH:
(Special colors ava il abl e upon request.)
The fi lter ha s standard input and output jacks located on
the front panel in addition to the terminal block at the rear,
I
i5!ail
Manufacturers of Precision Resisto rs, Toroid Inductors and Electric W ave Filters
REPRESENTATIVES:
Jack Beebe, 5707 W. lake Street, Ch icago, il linois
Georl1e E, Harris & Co ., Box 3005, Mun icipal Airport, Wichi ta, Kansas
Marvin E. Nulsen, 5376 E. Washington St., Indianapolis 19. Ind iana
9urlingame Associates, 103 lafayette Street. New York City
64
•
For turther intormatlon
contact yo ur nearest
Hyco r repr-esentative or
write for Bulletin S
-:!\l-l~~I---J
~-
H-:oHf-H1+l- DIFFERENC E BETWE EN -I-I-+++!j~'--l
,.
BARON E T AND STD .
nUO U CHeY oN CYCL..LS " " 5lCOND
/-I-+-++I+H+l- -+-I-I+I./-Ji ~_
' - '-'--IIll.IIU_ _ V.C. IMPEDANC E
SUnset 3·38'0
.-
BARONET
. ,+-.1 11 1
.
General Specifications, , ,
11423 VANOW'N ST., NORTH HOLLYWOOD, CALIFORNIA
. ....
REBEL IV
1--bH-tttlolil<::::-..,
~ 1.1lJl
1-i-+ t+ t+H----'1 I I 1-111 1
-I--l-l..j..j.j-IJ---J
I.
Fig. 4. Performance curves for the' Loren z un its
in two enclosures, as compared to a standard
t hre.e-way corner speaker.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
•
Fig. 5. The three components of the Lorenz
system-8 Yz" Woofer, 2Yz" tweeter, and
dividing network.
Fig. 4 as a comparison, and also with the
difference plotted for one of the cabinets.
The "Woofer"-although only 8Y; in.
diameter-has a free-air eeme· resonance of
83 cps. It mounts over a 70 -in. hole, and
has a measured nominal impedance of 6.5
ohms. The tweoter-a design using a
transpa rent plastic cone and a solid-backed
cage so it can be mounted inside an enclosure with the woofer-has a higher
impedance, and works with a dividing network which is also available. These components are shown in Fig . 5.
Measured in the Cabina rt "Rebel IV"
enclosure, Fig. 6, there was nearly as much
output at 30 cps as in the comparison
speaker, but there is a slight peak in the
100--150 cps range, a"S would be expected
from the size of the Rebel IV . Measured
in the E lectro-Voice "Baronet," Fig.. 7,
the low-frequency radiation was ' only
slightly less, and the character of the peak
in the middle lows was different. In either
cabinet, however, subj ective reaction was
excell ent. The units were not tested wi th
a balancing pot in the tweeter circuit,
which accounts for the relatively high output in the range from 3000 to 9000 cps.
A pot would correct this. It is believed that
the Lorenz units with either of these
cabinets would provide good quality
reasonable cost.
W-2
Amplifier- Kit (Incl . Ma in Amplifier
with Pcerless Output Transfonnc r,
Power
S upp ly
Preamp l ifier
K i't)
and
\VA·PI
S hi pping
Wei g ht 39 Ibs. Shipped exp ress
on ly.
S69 50
•
S49 75
W-2M Amplifie r Kit (lncI. Main Amplifier
with Peerl ess Ou tput Transfonner
and Powe r Supply) Shipping
Weight 29 Ib s. Shipped express
only.
W -3
Ampl ifier Kit (lncl.
•
Main Ampltfter
S69 50
with A crosound Output Transfonner, Power Supply and WAP I Preampll fler Kit) S h ipping
We igh t 39 l bs. Shipped e x press
•
on ly.
W -3M Amplifie r Kit (lncI. Mai n Amplifler
with Acrosound Output Transfonn e r and Power S Upp ly) Ship- .,
ping Weight 29 lbs. S hipped ex•
press on ly.
WA-Pl P~a mplifier Kit only. Shipping
Weight 7 lbs. Shipped express ('
or parce l post.
.,
1:49 75
19 75
Fig. 6 (left), The Cabinart "Rebel IV," and
Fig. 7 (right), Electro-Voice "Baronet."
AUDIO ENCINEERINC
•
SEPTEMBER, 1953
.
65
DICTATINCi MACHINE
(from page 28)
"NON-METALLIC TABLE
-Solid. %~. thick. dimensionally stable die
stock---cork latex covering
-non-bell-Iike-never needs
lifting from well_
slot on the top of the machi ne. Th is is
accomplished by two knives which ride
under the slip and move up to perforate
it when the keys are pressed.
A neoprene-covered friction wheel
drives the turntable. This wheel is clutch
operated, due to the fast start and stop
requirements. The clutch electroma.gnet
is energized through the hand m Icrophone switch bar. This bar is depressed
whi le dictating and may be locked for
prolonged recording or pl~ybaek. The
magnet armature moves a ' linkage that
forces the drive wheel against the turntable rim. The angle of contact between
the turntable and' drive wheel is such
that the dr,ive wheel is self-binding, ensuring 'agai-nst slippage. To compensate
for drive wheel wear, the linkage incorporates a -bow-spaped spring which
has a pull curve matched to the pull
curve of the armature. Two views of the
mechanism are shown in Fig. 14.
Primary drive comes from a 3400r.p.m. vertically mounted induction motor. Drive is transmitted by a neoprene
belt to an intermediate pulley and from
the shaft of the intermeCliate pulley by
friction to the drive wheel. In general,
sleeve bearings are employed in dictating equipment because of their quieter, smoother operation. However, the
intermediate drive in this instrument
uses small ball bearings because of the
pull of the belt and thrust of the drive
wheel.
'
A worm gear on the t urntable shaft
turns the feed screw, g iv ing' lateral motion to the reco rder-reproducer carriage
by means of a feed wheel driven by the
feed screw threads. The feed wheel is
frict ioned against rotation during driving, but is slipped readily by the control knob during scanning. Movement of
the recorder-reproducer carriage is
transmitted to the indexing mechanism
through the gear-rack arrangement previously described.
DR-12. a completely
new
d e sign. allowing
improvements in
basic enqineering
never before possible!
' CONSTANT SPEEDS
33_33. 45. 78 .26 "Floating Idle r" d e couple.
motor vibration from chassis s turdy, m icrobalanced 4-pole induction motor on isolation
mountings, carefully pos itione d fo"r minimum hum.
Complex mechanisms are eliminated in
the NEW D" R DR·12. the most significant advance in turntable design in 17
years!
A new magnitude in low noise level
and 1M distor tion due to minimum flutter
and vibration . , , a ll parts e a sily
Tu rntable
only.
with
standard panel mounting • • •
$68.50
mahogany box mounting, extra
accessible, machined · to professional talerance . . . especially designed for th e
more exact reguirements of LP record
reproduction.
Acclaimed by HI-FI experts a n d broadcasters as the ideal combination of laboratory q u a li ty and moderate cost.
See the NEW DR-12 at leading HI-FI dealers. or write for
des criptive literature to • . • Audio Equipment Diyisi0!l'
D & R. Ltd .• 402 E. Gutierrez St .• Santa Barbara. Cahforma
"SO METHI NG FABULOUS LY BEAUTI FUL
.. . A mazed by new purity of sound . ..
clarity _. . clean deft nition! "
/jill{£,!ILD ,
HIGH COMPLIANCE
The Amplifier
Diamond Cartridge
First to a chieve n e a.·-pe.-fect lat e r a l complia n ce - fr eedom of s ty lus to y ie ld to r a pid d e fl ections of sen siti ve
mic rog roove recordin gs - th e a maz in g n e w Fa irchild
Seri es 215 provides a ll th ese exciting improvem ents : ,
*hi ghN ewvoshlumadese piaofnotonech orcolds!or *fr om
fin e reco rdin gs! * New clea r timhre in
R ieh l ow-freq ue ncy tones never p rev iousl y
h ea rd ! * Need le talk, reco rd hi ss, hase co ncent ra li on ea used b y arm resona n ('e-red ul"ed to a new low l ow! * Stylus wear vastly red uced, record
quality p rese rved! * A nd above all - TRACK ING DtSTOIIT ION ELI MINATED!
ORDER FROM YOUR
AUDIO DEALER
or
Mail Coupon for
FREE "HI-FI Facts"
folder
~-------------------------~
I
Fa irchil d R er-o l'd ing Equ ipm ent Co rp.
9th Ave. & 1541 h St. , Wllites lone, L.I., N .Y.
P lease m a il folder "Hi-F i F acts" to:
Name
A
ddress
L __ __
___ _ _____ _ _ _ __ ____ ___ ~:
City
State
I
VISI T US AT ;rHE AUDIO FAIR, HOTEL NEW YORKER, OCT. 14- 17
66
I
I
I
I
The compact two-tube, three-stage
amplifier was made possible through
the development of an entirely new magnetic recorder head. This head, equ ipped
with a permanent dia mond embossing
stylus, employs a reed-type armature
damped only by the record groove. By
elimination of the usua l heavy external
damping, efficiency was raised about
12 db, with only a 5-db rise at resonance. T he ampli fier has three R-C
coupled stages using a 12AX7 tube for
two stages of voltage amplification and
a 6AK6 tube for beam-power singleended outout. The secondary winding of
the output transformer provides a 4-ohm
impedance to match the recor der in the
h ig h-frequency region. Figu,re 15 shows
the complete schematic of the instrument.
Change-over from the recor.ding to
the reproduce circuit is obtained through
AUDIO ENGINEERING
•
SEPTEMBER, 1953
- - - - Vi
12AX7 - - - - -
)Famous Williamson type
M ODf,L AA-903
AMPLIFIER
_ with built-in pre-amplifier
S1' RECORO - REPflOOUCE
SWIT CH
POWE R
Fig. 15. Schematic of t he VP Edison Voicewriter.
a specially designed 3-pole doublethrow switch which incorporates flushset silver contacts in a fu lly shielded
design. This switch permits noiseless,
undistorted change-over of high-gain,
high-impedance circuits .
The playback circuit uses only the
last two stages of the ampli fier. In the
reproduce position, playback is normally
heard through the controlled-reluctance
microphone. Connection is made to the
microphone from the plate of the output
tube through a coupling capacitor. At
the same time, the secondary of the output trainsformer is connected to a receptacle in the back of the instrument.
When the VP is used as a transcription
instrument, the secretary plugs a listening device into this receptacle and starts
and stoos the turntable w ith a foot control phigged into the hand microphone
socket.
The design of the power transformer
called for the smallest practicable size
due to saace limitations. A full-wave
selenium -rectifier-doubler circuit is. employed to cut down magnetization current and to enable the use of a high
voltage.
The power transformer delivers 25
rna at 210 volts and isolates the instrument from the power line. Two stage.
capac;;itor-input L-C filtering for the B
supply is obtained by using the coil of
the clutch electro-magnet as a choke in
conjunction with two 40-I·t,f and one
lO-lJ.f capacitors.
The amolifier tubes and most of the
associated 'comoonents are assembled on
a compact mouiIting as a separate, easily
replaceable unit. 'Most of the resistors
and caoacitors are soldered with short
leads directly to the tube socket. Shielding problems are materially reduced in
this way.
Co nclusion
Many interesting problems must be
solved in the design of the electronic
circuitry in dictating machines which
are not shown up by the schematic diagrams of the finished product. As these
instruments are connected at random
into existing. power outlets-often f ro111
improperly filtered inverter power supplies-they must operate satisfactorily
with the plugs connected in either direction, grounded or ungrounded, and
over a wide voltage range of 105 to 125
volts. As the experienced dictator rarely
listens back to his recording, it can be
seen that these requirements must be
met without interest or knowledge on
his part. This is quite different from
devices in which the user 's interest is
primarily in listening, such as rad ios,
phonographs and so on. To accomplish
these results, it is important that currents in the chassis structure are either
well controlled or well isolated from the
wiring; that unknown, uncontrolled inverse feedback between wires and components does not take place; that shield·
ing is complete and automatic so that
service personnel cannot readily defeat
it ; that switching and other manually
operated circuit devices manipulated
during normal use of the equipment
must have lives many times that found
in apparently allied equipment. Further more, the whole electronic design must
be such that proper results can be obtained by ordinary factory pel'sonne!.
The dictating machine is in fact a
highly speciali zed recqrding system constructed to meet its requirements which
differ so materially from those of other
recording and/ or playback dev ices.
PATENTS
Holland-l ,229,749, June 12, 1917
Holland-l,420.317. June 20, 1922
Hueniich-2,042,228, May 26, 1936
De Berard-2,066,672, January 5, 1937
Hueniich-2,092,917, September 14, 1937
La Forest-2,218,s42, October 22, 1940
Williamson type 10 watt Amplifier. 7 tubes
including Rectifier with push.pull output
tubes . Controls are mounted behind dec·
orative front panel which may be easily
removed for cabinet installation, and include On·Off Volume, separate Bass and
Treble Controls and Equalizer se lector
switch for lP, NAB, AES and Foreign Recordings. Frequency Response ± 1 DB 15
to 40,000 cycles . Distortion less than 1 %.
Hum level 700B below 1 volt. Three in·
puts are provided for Radio and Auxilia ry equ ipment and one input is pro·
vid ed with adjustable impedance for
matching the various magnetic ca rtridg es.
FM-607 FM PILOTUNER
8 tubes incl. Rectifier with two stage
audio Amplifier and Cathode Follower
Output for use with up to 100 feet of
connecting cable. Audio Distortion .2 %
at 1 volt output, Frequency Response
± .50B, 20 to 20.000 cycles. Sensitivity
5 microvolts fo r 2008 quieting with hum
leve l 7008 be low 1 volt. Slide Rule dial
with illuminated scale and self-contained
front panel assembly with be.autiful gold
finish enables unit to be left open on
sh e lf or easily mounted in cabinet. Three
simpl e controls: On·Off Volume; Selector
Switch for fM, FM with AFC, or Phono;
and Tuning . Built·in line cord antenna .
Write lor free brochure AE 5
T H E AU DI O FAIR IS YOUR AFFAIR
AUDIO ENC INEE Rti NC
•
SEPTEM BER, 1953
67
ORGAN FOR
ONE-FINGER ARTISTS
(f1'01'/! fag e 21)
Type BA-4-E
OUTPUT
H I G H GA I N
CO-MPACT
I U watts, ± l db from 50 to 15,000 cps, w ith
1'/, % or less distortion
105 db ... use ~or .talkback, transcription cu e, and
playback appltcatlons
Requires only 4 rack units of space- 7"
ACCESSIBLE
Hinged panel permi tS easy access to all com·
ponents . . . speeds maintenance
Choose from a complete Gen eral Electric Ampli fier
line to fit every broadcast audio requirement.
. For in!ormo/ion wri/e: General Elec/ric Compony.
Sec/ioll 4493, Elec/ronics Pork , SyracIISe, New York
GENERAL. ELECTRIC
o
UNIFORM
DEPENDABLE RESPONSE
D
EXCEPTIONAL
CALIBRATION STABILITY
LAB·ORATORY AND INDUSTRY-
for precision sound measurements
and high quality recording
For more than sixteen years Kellogg Midget
Condenser Microphones have been serving Industry and Research in sound measurements.
Ruggedly constructed and humidity-proof, this
mkrophone ·"fully satisfies the exacting requirements of Laboratories for reliability and accuracy.
KEllDS&iF0.
A Div is ion of
Users include government laboratories, universities, audio development laboratories, sound studios, and industrial plants manufacturing sound
equipment.
International Telephone and Te legraph Co ·: ra tion
KELLOGG SWITCHBOARD AND SUPPLY COMPANY •
68
Write to Dept. 27-1 today for full inform ati on
·sales Office" 79 W . Monroe 51., Chicago 3, III.
C.) A second projection connects the
D#-E oSClilator output to the chord
signal busbar. A third tunes the G-Gil
oscillator to G by closing the tuning contact for that oscillator. A. tou rth closes
the contacts carrying G-G# osc illator
output to the chord s ignal bar. This
completes the formation of the chord.
In addi tion a fifth lever projection
connects a B-C oscillator output contact
to the left pedal-signal busbar and a
sixth connects the G-Gii oscillator output
to the right pedal-signal bar.
The chord output signals from the
chord signal bus bar go to the chord
control tube, shunted on the way by the
MUTE switch which places a capacitor
across the line to produce more "mellow" quality · when desired. The tube,
VlJ normally has 35 volts of negative
bias on the grid from a fixed source,
cutting off plate current. \iVhen the
chord bar is pressed the bias disappears,
allowing the chords to come through.
Chord signals also go through the
SUSTAIN CANCEL switcl1 to the input. of
the preamplifi-er, the· grid of V~o, to the
same point reached by the outputs of
the solo and organ divisions. The preamplifier output goes to the second half
of V: o, bypassing the chord control tube.
Thus when the SUSTAIN CANCEL switch
is closed a · reduced-level chord signal
comes through even though the chord
bar may not be pressed.
The outputs of the two pedal-signal
bus bars go to the two pedals, which are
mechanically . interlocked. Considering
only the signal contacts of the pedals,
fo r the moment, output from whichever
pedal is pressed goes to the input of a
t~o~stage frequency divider
exactly
Similar to those used in the solo division.
In this way pedal tones two octaves below the chord tones are produced. The
output of the freq uency dividers goes
through an R -C tone modifying network
to the grid of the pedal control tube, V 8 .
The grid is normally at 35 volts neo-ative. When a .pedal is pushed, a control
contact on it removes the tube bias,
allowing the tone to come through. The
mechanical interlocking of the pedalsignal contacts is such that when the
pedal is released the last signal contact
made is maintained. This keeps the tone
going while the bias on the pedal control tube slowly returns through tlle
time-constant network and the tone dies
away. The pedal FAST ATTACK switch
modifies the time constant to make for
fas ter attack and decay.
The output of the pedal control tube
joins all the other signals at the grid of
amplifier V 20, after passing through a
pedal balancer potentiometer. The VOLUME SOFT switch in the grid circuit
simply shunts the line to ground through
R 272 , reducing the volume of the entire
instrument.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
SCREWS HOLD
TOP
•
For maximum performance
at the lowest possible price
Fig. 8. Rear view of
the instrument to
show mounting of
the various chassis .
The AF-723 HI-FI
FM-AM PILOTUNER
•
OSCILLATOR
A SSEMBLY
The 0utput of the ampli fier triode which can be adjusted somewhat by a
. goes to the expression control. This con- variable capacitor. The vibrato of the
trol is a special variable a il' capacitor
Chord Organ is similar to that in the
with two stator plates. One stator is
Solovox, a phase-shift oscillator and
connected directly to the amplifier plate switch tu be connected to the g rids of the
through a blocking capacitor C229 • The oscillators through a switch which
other stator plate is connected to the
amplifier plate through a tone-com- grounds the g rid circuits when vibrato
pensated attenuation netwo rk. The rotor is not desired.
is connected to the No.2 grid of a phase
Organ Division
splitter of the common-cathode type.
The ci~'cuit of the organ division is
The position of the rotor, controlled
through a knee level' extending from shown in Fig. 7. The generator system
the underside of the organ keyboard,
fo r the 37 tones consists of sixteen L-C
controls the level of the signal reaching
oscillators, each of which can be tunecl
the phase splitter.
to either of two frequencies, except for
The phase splitter is the driver for a
the lower fo ul' and upper one, which can
conventional push-pull 6V6 output stag-e.
be tuned to three frequencies.
Radio-phonograph inputs are provided
The tuning is done automatically
at the phase-splitter g rid. The ampl ifier
when a key is pressed. Normally the
has a negative-feedback connection from - lowest oscillator, for instance, the fi rst
output transformer to the phase splitter triode of V 12, is tunecl to the frequency
g rid, the frequency characteri stic of
of low G by C8 7 across the tuning in-
8 tubes, two stoge Audio Amplifier with
cathode follower . 10 MV sensitivity on
FM ond AM. Hum level 70 DB below 1 V.
Audio output 5 V, audio distortion .2%
at 1 V, audio frequency response ± .5
DB, 20 ta 20,000 cps . Built·in FM and AM
antennas, AFC Switch disables AFC on
weak stations .
THE AA-902 AMPLIFIER
$46.95
Williamson Type Amplifier with inter·
leaved wound Output Transformer and
push.pull output. Cantains 5 tubes. Fre·
quency Respanse ± lDB, 15 to 40,000
cps at TO walls. Distortion less than 1 %
at 10 watts.
THE PA912 PRE-AMPLIFIER
~---
16 ORGAN OSCILLATORS
~m#s ~
:l!
Q.
o
....
4 tube self.powered. Voltage output 5 V.
Frequency Response 1 DB, 20 ta 100,000
cps. Distartion .2% at 1 V. Bass and
treble controls. Selector switch to choose
signal from anyone of 4 playback equal.
izers. Attractive bronze cabinet.
Underwriters Approved
Write for free brochure AE 5
r:::~:=!:~=::;:::;=!~~~
+--ORGAN TUNING BUSBAR
+280 +-ORGAN CONTROL BUSBAR
~
KEYS F
F-
C.
G
DOE
Fig. 7. Simplified schematic of the "organ" section. Sixteen separate oscillators provide 37
notes, each oscillator being tuned to one of either two or three adjacent tones.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
69
. if
y~-=-
---7l
-concerned with
CONTROL
TABLETS
j_
k
POWER
•
Fig. 9. Top view of
the organ with the
upper chassis swung
down for test or
repair.
.j
<
:SU~PLlES
il
you should have
. the ·new,and
'comprehensive
•
,'LAMBDA
SOLO MAIN TUNING
CAPAC ITOR
catal.og
at electronically
regulated
laboratory
Rower supplies.
Manufactured' by
;-..~'ne of America~s
pioneer specialists;
this fiero-proven
precision equipment
~is priced
surprisingly low.,
>-
~
.
~
t
)"
TUNER ASSEMBLY
ductor. When the F# key is pressed a
contact connected ' to the lower end of
C~ O strikes the upper busbar, connecting
C89-R1l7-C90 across half the coil and
lowering the frequency. When the F
key is pressed a contact connects only
C8 9 across the lower half of the coil,
further lowering the frequency to F.
The organ oscillators are normally
not operating because they have no plate
voltage. Whenever a key is pressed, a
contact in the lower row strikes the
lower busbar. This carries the B-supply
of 280 volts to the plate of the corresponding oscillator through a simple
R-C network which softens the attack
somewhat.
Each organ oscillator has two outputs, one from the upper end of the
tuned circuit giving a sine-wave or flute
tone, and the other from the lower end,
giving a waveform like that shown,
known as the string tone. All similar
outputs of all oscillators are paralleled
and brought through tab switches and
tone modifying networks to the organ
division balancer, the arm of which goes
to the common preamplifier grid.
It should be noted that four busbars
run under all the keys. T wo are shown
in Fig. 7 and two in Fig. 5. The idea
of using one oscillator for two or three
notes is that not too much music calls
for simultaneous playing of two adjacent
notes, especially the fairly simple music
which a typical [email protected] Organ player
would probably use. The frequencies
covered by the organ oscillators are
174.6 to 1397, the F below middle C to
that three octaves higher.
Construction
Despite the apparent complexity of
the Chord Organ it is extraordinarily
compact. Fig1tre 1 shows the main con·
troIs. Figure 8 is a rear view showing
how the electron isms are mounted in
the case. Figure 9 is taken from above
the rear of the organ with the top removed and the upper chassis swung
down for test or repair. The 0 gan
works with the chassis in this position,
except that the expression control lever
will not actuate the control. The linkage
for it can be seen in the chassis. Figure
10 is the front of the organ with top
removed, and the board [email protected] the tab
switches taken off and lying upside
down.
/&-
•.............•
•
SEND FOR NEW CATALOG
Lambda Electronics Corp.
103·02 Northern Blvd., Corona 68, N. Y.
Please send me the new Lambda Power
Supplies Catalog as soon as it comes oli
the press.
Fig. 10. Front view
with the key section
exposed.
Name' ______~~--~~------(Please print)
Titie'_______________________
•
Company_____________________
StreeLt__________________
City
Zone_State_ AE.953
- •••••••••••••••• _ ••••• _•••••••••••••••• J
70
AUDIOENCINEERINC
•
SEPTEMBER, 1953
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.,. .,. .,. .,. ...,
.'
HALF FULL?
OR
HALF EMPTY?
UNIVERSAL AMPLIFIER
(from page 44)
ously employed. This permitted the use
of a 4-section electrolytic capacitor for
plate-supply decoupling and for bypass
across the cathode resistor of the output
stage, since space enough for this capacitor (a Cornell-Dubilier UP-2224SC),
was available along the rear of the chassis. The feedback capacitor C" is
mounted between the output transformer
and the filter capacitor.
With all of the transformers and these
two capacitors mounted along the rear
of the chassis, space was available for
the mounting of the tubes in a row, thus
making it possible to locate all six of
them on a single rubber-mounted aluminum channel, basically similar to that
used for the first four tubes in the original construction. The resistors and capacitors related to the tubes are mounted
on a resistor board which is spaced about
~ in. below the socket terminals. This
For the ultimate in
HIGH FIDELITY
TUNERS
the
AF-824 FM-AM
PILOTUNER
$119.50
10 tubes, with two stage pre-amplifier
equalized according to LP NAB, AES and
foreign recording standardS' selected by
Switch. Three magnetic phono and crystal
and AUX. inputs. Two stage audio amplifier with cathode follower output. Sensitivity on FM·AM 10 MV. Audio frequency
response ± %OB, 20 to 20,000 cps. Hum
level 800B below one volt with hum balancing adjustment provided. Controls:
Volume, Equalizer, Treble, AM·FMPHONO·AUX, Bass, Tuning and AFC onoff. Built·in antennas for FM and AM.
Don't rely on ad;ectives!
Performance is no longer
a matter of opinion!
THE REVOLUTIONARY
NEW COOK SERIES 50
N-A BEAM
12" TEST RECORD
• rigorously tests tracking of
cartridges distortio'n of
amplifiers, speakers
THE AA-901 AMPLIFIER
• just play it and listen for
the /I A" or the "NI/*
• without meters or instru- ,
ments
• impartially selects the best
equipment
• repays the user 100 fold
If not in stock at your dealers
write direct.
$4.80 plus 50¢ packing and
postage.
*code II A" (dot-dash) means all right (Jess than 2% cross modulation distortion at high frequencies)
**code UN" (dash-dot) means nof all right
- sweeps entire upper audio range
from 20 kc down.
COOK LABORATORIES
114 MANHATTAN STREET
STAMFORD, CONN.
AUDIO ENGINEERING •
Fig. 3. Bottom view of second model of t he
amplifier to show placement of volume con·
trois and short flexible shafts from knobs on
panel to the controls. This permits considerably
shorter leads from the tube-mounting channel
and the associated circuits to the controls,
with appreciably less need for equalization to
maintain high-frequency response.
resistor board was made up from a
punched phenolic strip and a number of
terminals supplied by NAALD. With these
terminals and the punched strips, and
using the small staking tool designed for
applying them, it is possible to make up
any kind of terminal strip desired. For
this particular application, a total of 31
resistors and capacitors are mounted on
a single strip just below the tube sockets,
thus making for short leads from the
socket terminals to the associated components.
The volume controls are mounted on
two brackets-one holding RII, and the
other holding R. and the inclusive control, R... Short flexible shafts are used
between the knobs and the controlswith panel bearings and shaft extensions
SEPTEMBER, 1953
New improved Williamson type Amplifier
using famous KT·66 tubes. Power Output: 10' wdtts": less than 0.1 % distortion, 25 watts - less than 0.3.%
distortion, maximum output - 30
watts. Frequency Response ± 1DB 15 to
50,000 cycles. Hum Level 90 DB below
10 watts. Speaker output impedance 8
ana 16 ohms. Tube complement 6SN7GT.
6SN7GT (2), KT·66 (2) Push-Pull Power
Amplifier, 5U.oIG Rectifier.
Underwriters Approved
Write lor Iree brochure AE 5
71
You
hear it
allas though
you were
there •••
when
you use
a
Stephens
TRU-SONIC
SPEAKER
. Regarded as the international standard in high
fidelity sound equipment,
STEPHENS speaker systems
are used throughout
the world by the most
discriminating . listeners.
:,u,u"u
72
PRINCIPLE
used at the panel to provide a good bearing for the knob shafts. The flexible
shafts can be seen in Fig. 3.
The principal change in circuitry is in
the cathode-follower section, V. in the
original circuit, and V GIL and V,b in the
revised arrangement. This provides some
additional gain so that when the unit is
used with a home radio system, the outJlut at terminal 3 of J, is at the same level
as the signal fed into terminal 2-the
' loop circuit between the FM tuner and
the remainder of the system. One section
of the 12A U7 is employed as an amplifier, with about 10 db of gain; the other
section is a cathode follower, and feeds
the signal out at a low impedance. J10
has been added, with the voltage divider
R 4, and R,o, so that an ordinary patch
cord may be inserted between J'0 and J.
to permit the use of the amplifier as an
artificial . reverberation generator. Performance is somewhat improved, and the
level available at J,0 is just sufficient for
convenient operation of the gain control,
R" . Note that the voltage divider consists of a O.l-meg resistor and a 27-ohm
resistor, which provides only a very
small portion of the total output signal
at the cathode of V6b foJ;' feeding back
into the circuit on the grid of V •.
One other refinement in the circuit is
the addition of a dialogue equalizer between the plate of V. and the gain control of the microphone channel. This
equalizer consists of R" and C.o, and
serves to reduce the gain approximately
10 db at 100 cps, with a gradual slope up
to normal gain at 500 cps. A SPST
switch, Centralab 1460, is mounted on a
bracket attached to the side apron of the
chass is, with the shaft extending through
a hole in the front apron, as shown in
Fig. 3.
The use of a 12A U7 instead of the
5879 in the monitor circuit changes the
requirements of the heater circuit somewhat, and the new wiring is shown in
Fig. 1. The VU meter lights were
changed to No. 47's, and the resistor between them in the meter case was increased to 32 ohms to reduce the illumination to a suitable intensity.
Construction
The basic construction plan is the
same as in the original model-minor
changes being made to accommodate
the components used in the improved
version. The 4-section filter capacitor
is mounted directly on the chassis in
holes punched, drilled, and filed by hand
-rather than on a standard phenolic
mounting wafer-in order to save space.
The 2-section capacitor C.a and C,b is
mounted on the right side apron of the
chassis just behind the front panel as
shown in Fig. 3. The two cathode bypass
capacitors C,a and Cn are mounted on the
resistor board, and are CoD BBR 50-6
capacitors, 50 flof at 6 volts, and quite
small.
The components of the dialogue
equalizer, R" and C.o, are mounted directly on SW6, and the components of
the tape playback equalizer are mounted
on a small resistor board just above the
dialogue equalizer switch. By using two
to the
E. E.
or
PHYSICS GRADUATE
with an interest
or experience in
RADAR or
ELECTRONICS
Hugh es R esearch and
Development Laboratories, one
of the nation's large electronic
organizations, are nolV creating a
number of new openings in an
important phase of operations.
Here is
what one of
these
positions offers
you
OUR COMPANY
located in Southern California, is presently
engaged in the development of advanced
radar devices, electronic computerS and
guided missiles.
THESE NEW POSITIONS
are for men who will serve as technical advisors to the companies and government
agencies purchasing Hughes equipment.
YOU WILL BE TRAINED
(at full pay) in our Laboratories for several
months until you are thoroughly familiar
with the equipment that you will later help
the Services to understand and properly
employ.
AFTER TRAINING
you may (1) remain with. the Laboratories
in Southern California in an instruction or
administrative capacity, (2) become the
Hughes representative at a company where
our equipment is being installed, or (3) be
the Hughes representative at a military base
in this country-or overseas (single men
only) . Adequate traveling allowances are
given, and married men keep their families
with them at all times.
YOUR FUTURE
in the expanding electronics field will be
enhanced by the all-around experience
gained. As the employment of commercial
electronic systems increases, you will find
this training in the most advanced techniques extremely valuable.
How
to
apply
If you are under 35 years of age
and have an E.E. or Physics
degree and an interest or
experience in radar or electronics,
write
to
HUGHES
RESEARCH AND DEVELOPMENT
LABORATORIES
Scientific and Engineering Staff
Culver City,
Los Angeles County, California
r------------------- - --~
1
I
I
Assurance is req uired that the relocation of the
applicant will not ca use the di sruption of an
urgent military project.
:
I
I
~----------------------~
AUDIO ENGINEERING
•
SEPTEMBER, 1953
Mallory extension bushings, SWI has
been lowered to a position where the
terminals are about flush with the chassis deck. A small resistor board, located
between R-, and R22 and mounted on the
bracket which holds the two pots, provides for RI7, Rrs, and RI9, the mixer network, as well as for R". R50 connects directly from one of the terminals of the
capacitor C, to the ungrounded end of
R" . R ,. is connected directly hom terminal 4 of the output transformer to a
term inal of C 12.
A small shield made of tin was required to eliminate all traces of oscillation due to the proximity of J, and J,.
·the
worlds
finest
Microphones
Extremely smooth frequency response, wide
dynamic range, complete absence of distor-\
tion and noise. Readily changeable field
pattern. Small outside switch provides either
highly directional or non-directional characteristic.•
MODEL U-47M
Condenser Microphone,
power Sltpply, cables
al1d plugs.
Complete
$39 000
Specifications - U47 M
Frequency response ........ ± 3db 30-16,000 cps.
Output impedance ...... 30 / 50, 200/250 ohms, bal.
Field pattern
....... non-directional or cardioid
Output level at 1000 cps.
Matched with 200 ohmscardioid 2.8 mV per dyne / cm" (--49 db)
non-dir. 1.7 mV per dyne / cm" (-53 db)
Residual noise level equivalenL24 db loudness
Non-linear distortion ......................Iess than 1%
TV-520
REMOTE CONTROLlED
VHF-UHF
24~ 2711 TELEVISION
RECEIVER SYSTEM
.;
Fig. 4. View of right end of the chassis to
show placement of tube channel on which all
six tubes are mounted.
Before this shield was installed, the
amplifier would go into oscillation when
R,. was turned up past 50 per cent rotation. The shield eliminated the troub le
completely.
The new model has all of the operating
conveniences of the ori ginal, together
with improved freq uency response and
the added advantage of the dialogue
equalizer on the microphone channel.
If necessar y, a similar equalizer could be
wired into the second channel, but th'~
writer's requirements have not made it
necessary yet. Perhaps that will come in
the third version-although to date there
have been no indications that this second
model will be rebuilt.
m
w
POSITIONS OPEN and AVAILABLE PERSONNIOL
may be listed here at no charge to industry
01' to members of t he Society. For insertion
in this colnmn, brief annonncements should
be in the ha nds of the Secretary. Andio Engineering Society. P . O. Box 12, Old Chelsea
Station, New York 11, N. Y. before the ·first
of the month preceding the date of issue.
+: Positions Open
• Positions Want ed
* ENGINEER.
A progressive organization
engaged in designing, developing, and
manufacturing of electro-mechanical equipment fo r the geophysical industry and for
the Armed Forces is in need of a graduate
P hysicist or E lectrical Engineer with at
PARTIAL LIST OF USERS
least three years development experience to
develop low-frequency audio circuits.
RCA Victor
Cinerama, Inc.
Reeves Sound Studios
20th Century fox
Established in 1930, our company and subAmpex Corp .
Decca Recording
sidiaries total about 2000 people. We op.erate in Asia, South America, Canada, and
Write us for information
the United States. Manufactur ing involves
on the Mighty Midget Mike #20 1M
more than 900 people, including 220 in the
Research and Engineering Division. Reply
by letter, giving resume of training, experience, salary requirements, and a recent
1775 Broadway' New York City' PLaza 7-7276 photograph to P. O. Box 7045, Love Field,
Dallas, Texas.
Sole Importer, and U. S. Agent
Note
c/eancut
design
;n rear
view
Remote Control Unit - Separate unit
in mahogany, or limed oak, veneered
cabinet includes VHF and UHF Tuners.
Self-powered, can operate more than one
picture unit. Incorporates on improved
high fidelity intercarrier sound system,
and is designed to receive color. Contains
12 tubes plus rectifier.
Picture Unit - Maior picture controls
available from front panel, improved synchronizing circuits assure positive picture
lock, automdtic vertical retroce blanking
and positive, steady interloce. Contains
17 tubes, with 10 walt push-pull high
fidelity Amplifier and 40' interconnecting
cable.
TV-S20 - $346.00
less picture tube and speaker
Mounting Kits - Designed for single
point suspension of 24"_ or 27" tubes.
Ready for quick assembly complete with
plywood base, front panel, mask, hordware and safety glass. Oversized panel
can be cut down to fit custom installations_ Supplied in mahogony or \ limed
oak finish.
TM-S27, TM-S24-$53.50
Write for free brochure AE 5
AMERICAN ELITE, INC.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
73
~"''''~''''''''''''' ",/
,>••~.,w~ ...,~.", <_.,{"''''-'"''''''''''''';~');,,~~'"_~j '''''-:::-''''~~~.("'''''_""'''.'''}
PATENTS
For the perfection you dream of .~
Hi-Fi Amplifier. '
Power: 12 watts at less than 1 %. Peak
16 watts.
Frequency
Response: 20 to 20,000 cycles
plus or minus 1/2 db, with controls set
for
flat
response.
Inputs: Radio, crystal, mag. (2.), TV and
tape.
Controls: Selector with record equalization; Bass; Treble with AC s"X'; compensated volume; Motor rumtile sw.;
Loudness camp. in or out sw.
output Imp.: 4, 8, 16 ohms. __r-----'-.a..:.,
jack for tape recorder."
Pwr. Cons.: 80 watts;
117 volts; 50-60 cycles.
.
.
Complete I y new! BeI I engineering
rna k es
this an audiophile's dream ! 12 watts or more of
d'Istortlon. f ree power. P nnte
' d CIrCUit,
' .
99 01
-t o
co mpe~sated volume control. Bass and treble
boost and cut, a switch to cut loudness
compensation in or out, and a motor rumble
suppressor switch give assured control
for best performance!
BEL L Sound Systems, Inc.
559 MARION RD. , COLUMBUS 7 , OHIO
EXPORT OFFICE : 401 BROADWAY, N . Y. 13
WRITE FOR CATALOG NO . 101
Authoritative and:
Enligh tening ...
Acknowledged the Leading Publication
in the Field of Sound Reproduction
If you are novice, hobbyist,. experimenter, or engineer ... if you
are a lover of music ... and in pursuit of sound, undistorted
.. . Audio Engineering will be your faithful, reliable companion all the way. You will find no more pleasureable and
stimulating reading than there is in AE; absorbingly interesting material, valuable and authentic data, workable detailed instructions ... all comprehensively and yet practically presented.
"What to Do" and "How to Do" will guide your every move
through this thrilling experience we call Audio.
Each new issue brings New Ideas, New Slants, and Latest Developments ... month in and month out ... twelve times a year.
D.C.
BE SURE to get your copies REGULARLY.
BOOK REVIEW
i--------------------------
(from page 12 )
AUDIO ENGINEERING
P. O. Box 629, Mineola. N. Y.
MAIL this
Enclosed is 0 Check 0 Money Order for $
'
.
':~n~~hto~·W i .. u. of Audio Engln.erlnt for the next
~e~~e ':::tt.~
ct;:
Plea18 Print
N.l'mo _ _ _ _ _ _ _ __ ____
Addr8.5..'_
_
_
_ _ __
_ _._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __
City
Zone _ _ Sta.e' _ _ __
Subscription Price: U.S.A., Canada and Pan Am8flcan Union: 1
$3.00 2· yea,. . . $5.00. Other countrl ... 1 y_ . . $4.00 2 yoart •. $7.00.
year.:
...
I
I
I
I
,.
I
I
,
----.~~~~-.---.~~.-.- -~---- ~~-----.I
74
(fro11v page 4)
of the tape holding the three tracks affected by the 1200-cps wheels. The magnetism shown on the tracks was produced
by the beating of an 1800-cps signal frequency with the 1200-cps modulator wheels.
During the first third of the 1800-cps signal
it was most nearly in phase with the upper
wheel teeth. As the signal cycle came into
its second third, its phase advancing with
respect to the modulator fr equency, it was
most nearly in phase with the second wheel
teeth. And so on for the remaining third.
At the beginning of the next cycle the whole
process is repeated. We thus have for any
signal frequency, a beat on the tape, a. third
of each cycle in one of the three tracks,
with the track of g reatest magnetism shifting from top to bottom whenever the signal
fr equency is higher th an that of the modulator. Whenever it is lower, the shift will
be from bottom to top, as in Fig. 4.
When the tape is played back on the same
mechanism, exactly the same action takes
place in reverse. In each case the reproduced frequency is either the sum or difference between the tone actually on the tape
and the frequency of the associated modulator wheels, the choice depending automatically on the direction of phase rotation.
When a given signal frequency can pI-oduce
beats with any other of the wheel frequencies the same action takes place simultaneously and in playback the signal is again
reproduced and combines with the same
signal r eproduced from any other beats.
The 9-wheel modulator system described
is just a sample. Its maximum signal-frequency handling capabilities would be only
aoout 4800 cps, assuming the speed to be
slow enough so that the tape could handle
beat frequencies up to 2400. T o produce a
system capable of 9000-cps performance at
1 ips, 21 modulator wheels would be needed,
3 each with 8, 16, 24, 32, 40, 48, and 56
teeth, g iving modulator frequencies of 1200,
2400, 3600, 4800, 6000, 7200, and 8400 cps.
Then the tape speed can be cut down to
where 1200 cps r epresents the top r ecordable frequency (actually only 600 is needed,
and a 100 per cent margin is added) while
the system as a whole can record and r eproduce everything up to 9000.
The tape savings of such a machine would
be enormous. How noisy it would be, how
faithfully it would r ecreate complex waveforms from the recorded beat frequ encies,
and how precision of construction and rotation of the high-speed modulator would af~
fect practicality, I have no idea. If you'd
like to have more detail and a fuller explanation, you can obtain a copy of the
patent for the standard 25 cents from The
Commissioner of P atents, Washington 25,
neer alike will make frequent reference.
This reviewer feels that the chapter on
mathematics in Section 2 might better have
been here, for easier reference in the book.
This is a long r eview-it covers a
"whale" of a book. At its price, no one who
is seriously interested in problems of audio
can afford to forego it for his reading
shelf. It is a goldmine of information not
only for what it contains within its own
pages but also for the entir'e technical
literat ure to date.
-L. B. Keim
AUDIO ENGINEERING
•
SEPTEMBER, 1953
D. C. PACK
(from page 33)
For all field recording without AC power!
Smaller and lighter than a portable typewriter, the Magnemite * actually makes
field recordings that can be pl ayed on any
studio console equipment. Completely
self-powered, the Magnemite':' does away
with bulky and cumbersome generators.
storage batteries and rechargers.
Just check these unusual leatures:
• Noiseless and vibrationless governorcontrolled spring-motor assures constant
tape speed.
• 100 operating hours per set of inexpensive
flashlight-type dry cell batteries.
• Earphone monitoring while recording, and
earphone playback for immediate quality
check.
• Operates in any position, and is unaffected
by movement or vibration during operation.
• Warning indicator tells when to rewind,
and shows when amplifier is on.
• Broadcast models weigh 15 pounds. Slowspeed models weigh only· 10 pounds.
• Requires no more desk space than a letterhead, measuring only 11 x 8 V2 X 5 V2 inches.
There's a choice of 5 different models for
any recording need. High fidelity units,
meeting primary and secondary NARTB
standards, which record and play back
frequencies up to 15,000 cycles, are available for broadcast stations, critical music
lovers, and scientific research. For investigation, missionaries, reporters, and general
dictation while traveling, there arc< units
whi~h play up to 2 hours per reel of tape.
Write Dept. AE today for complete descriptive
literature and direct factory prices.
AMPLIFIER CORP.
of AMERICA
398 Broadway, N. Y. 13, N. Y
·Trade Mark Reg.
AUDIO EI'IGINEERING
•
using a shunt ar bleeder resistar, as required, So' that the praper current will
flaw thraugh the heaters. If a suitable
pawer supply is available, this is the
simplest and cheapest methad. The valtage drap acrass the heaters is sametimes
used as bias far the pawer autput stage,
eliminating the need af a relatively highwattage cathade res is ta r.
The secand methad, aften used in
cammercial equipment, is to' cannect the
heaters in 'parallel and aperate them fram
a law-valtage, high-current pawer supply. Parallel aperatian af the heaters is
canvenient, but suitable r ectifiers and
transfarmers are nat readily available
fram the usual parts distributar, and the
cast af such parts tends to' be high.
The third methad, used in the supply
described in detail here, emplays an isalatian transfarmer with a Il7-valt secandary, a selenium-cell bridge rectifier,
adjustable series resistar fa r valtage adjustment and filtering, and t wa lsO-valt
electralytic capacitars. All parts are
standard items, readily available. The
part values are chasen sa as to' furnish
I SO ma at any valtage fram 12 to' 72, as
may be required, with a ripple af 1 per
cent ar less. Althaugh there is nO' abjectian to' aperating any af the tubes in an
amplifier an d.c., it is usually not necessary far hum reductian in stages where
the sigNal valtage averages ane valt ar
sa. In practice, the phana, tape and micraphane pre-amplifier and the tubes in
the equalizing pre-amplifier are d.c.-aperated t o' advantage. It may alsO' be desirable t o' supply d.c. t o' the heater af the
high-frequency ascillatar af the FM
tuner, if madulatian hum is encauntered.
As almast all 6.3-valt tubes currently
used in ascillatars and law-level audiO'
stages have l2.6-valt equivalents, nO' difficulty will be experienced with tube selectian. The tube heaters shauld be cannected in series with the first, 0'1' lawestlevel tube, cannected to' the negative terminal af the pawer supply.
Anather feature af this supply is its
ability t o' furnish up to' 90 valts ar so af
fixed bias far the mare efficient aperatian
af Cla~s' A ar Al autput tubes. The bias
is adequately fil tered and adjustable fram
zer-a to' the maximum value. Far experimental ar test wark, the isalatian transfarmer can be used separately, being
switched to' a twa-pale utility receptacle
far that purpase.
SPECIFY
"EMITRON
' KT66~1
• WORLD'S FINEST
•
•
Construction
The maunting af the parts is nat critical, pravided a narmal amaunt af ventilatian is furnished. The unit built by the
authar was maunted an a 5 x 7 x 2-in.
chassis, the parts being arranged as
shawn in Fig. 1. The cardbaard cavered filter capacitars R s and the fuse are
mounted underneath the chassis. On the
frant can be seen the bias-adjusting pat
and the a.c. an-aff sw'itch. On the back
SEPTEMBER, 1953
•
POWER TETRODE
PERFECT COMPLEMENT
TO WILLIAMSON
CIRCUIT
INTERCHANGEABLE
WITH 6L6
SOLD EVERYWHERE
r-Ki N'Gr)()'M ~!" PRODUCTS
f·
W'
.
'"
• .~
'
')"'
~
'"
LTD.
.
..,
'
<
45 W. 45th" ST.; NEW YORK 36
"
v","
"y
75
T1
F1
,~II
R1
R2
- HEATER
S1
C1
C2
+
+
.
N
+ HEATER
- BIAS
C3
~+aIAS
Fig . 2. Schematic of the d.c. power supply.
of the chassis are the line cord, the 4terminal output socket, the two-pole receptacle, and the secondary switch for
the transformer. The fo ur rectifiers a re
mounted by passing a th readed rod 4 in.
long through the center holes and supporting it at the ends with two 10 x
0 -in . angle -brackets. Small rubber
SOUND INSTALLATIONS SOUND GOOD
~~ L
~~ ,
'j ... ,
~
'"
(
-THROUGHOUT THE ROOM
~.
i...--' -' - 1
~
.- ~
grommets protect the leads passing
throug h he chassis. The values of R
"
R 2 and C 2 are selected from Table 1.
Fig·nre 2 is the complete schematic for
the unit.
For increased tube life-and in some
cases for lower tube hiss-it is recommended that 12 volts be applied to 12.6volt tubes and 6 volts to 6.3-volt tubes.
A fine adjustment of the heater voltage
is made by varying the position of the
tap of R , . It should be noted that there
is no direct connection 'between the
heater supply a nd the chassis, which is
g rounded. This is done so as to permit
a wider choice in the selection of a
heater grounding point in the amplifier.
The proper point to ground the heater
string is determined by turning on the
amplifi er and then running a lead from
the point w here the audio input jacks
connect to the amplifier chassis to the
tube heater pin w hich produces the least
hum . U sually this is either the more
negative terminal of the first tube or between the first and second tubes.
~
TABLE 1
'"'-
SPEAKER BAFFLES
"WITH FLOATING CONICAL ACTION"
BL Series • Speaker
Baffles
for
normal
height ceilings. Sizes
for 6" to 12" speakers .
Handsome Lowell ceiling speaker baffles are accurately engineered to provide 360 · of distinct, low level sound coverage
without distorting echos. Perfect speaker cone loading reduces
feedback to absolute minimum to .help you solve the most difficult acoustic problems. Conical diffuser mounting through soft
rubber grommets eliminates metallic resonance, Lowell baffles
are heavy _gauge aluminum spinnings finished in brushed satin.
coated with colorless lacquer. Lacquer is excellent primer if
on-the-job painting is desired.
PLEASE WRITE FOR COMPLETE SPECIFICATIONS AND LOW PRICES.
LOWELL MANUFACTURING COMPANY
3030 Laclede Station Rd., St. Louis 17, Mo.
In Canada: Atlas Radio Corp., 560 King St., West, Toronto, Ontario
CP and XCP Series
Back Cover Speaker
Enclosure for new or
existing construction.
Protects speaker from
mortar, rodents, flre.
All . t,,1 construction .
( Model CP shown.)
AT LAST!
THE CD-53 "SYMPHONY"
Highest Quality
and Performance
Yet Acbievecl in a
Record Cbanger
• Plays nine 10" and 12" records mixed
in any order, or twelve 7" records at
33-1/3, 45 or 78 rpm.
• Two motors E 53 with precision
governor.
76
After the g round connection to the
heaters has been made, then the fixed
bias is adjusted to the desired value by
means of the 50,000-ohm pot.
The a dvantages of using d.c. on the
heaters of low-level stages can be fully
appreciated when it becomes possible to
turn the gain up to maximum- with no
signal input-without any output f rom
the speaker, except a possible increase
in tube hiss. When such a condition is
reached, the system may be said to compare w ith professional installations, assuming that its other characteristics are
equally ideal.
PARTS LIST
CI, C.
C.
F,
PI
P.
DISPLAYED IN ROOM 718
• PLAYS BOTH SI DES of all micro-groove
and standard records at
33-1/3, 45 and 78 rpm.
Values for R Ro, and Co
"
R,
Output
C.
Rl
ISO-v.
So-w
So-w
(volts)
Electroadj .
fixed
lytic
12
500
200
80 Ilf
80
500
200
18
100
40
500
24
100
80
30
500
100
80
36
500
250
40
42
250
40
250
250
48
40
150
54
250
150
40
250
60
100
80
200
66
40
100
72
200
RI, R.
Palmer House, Chicago
R,
SEPTEMBER 1-2-3
R,
or write to
THORENS COMPANY
NEW HYDE PARK, N. Y.
made in Switzerland
by
THORl!S
S,
S.
SR , .•.•. 1
T,
40 Ilf, ISO-volt, elect.
See text and Table I
I-amp. fuse
2-pole female receptacle
4-hole socket
SO-watt wirewound; see text and
Table I
SO,OOO-ohm potentiometer
47,000 ohms, I-watt
SPST toggle switch
DPDT toggle switch
ISO-rna, 130-v,olt selenium rectifiers
I solaton transformer, 117/ 117
volts (Merit P-3096 or equivalent)
Fuse clip
5 x 7 x 2 chassis
Knob for R.
Line cord and plug
AUDIO ENGINEERING
•
SEPTEMBER, 1953
VOLUME VISUALIZER
(f'ro l/l page 31)
Fig. 6. Rear view of the chassis. The unit is
arranged for rack mounting, and occupies
3 V4 in. of panel space.
and rear, respectively, the 'former with
a conventional oscilloscope connected to
the Visuali zer by the two output cables.
Applications
.
T hose experienced in recording will
immediately recognize the value of a n
instrument of this type. With instantaneous peak indication of signal level,
there should be no poss ibility of overmodulation, regardless of the system of
record ing being employed. With controllable delay time, it is easily possible
to record a piano wi th full knowledge
of the maximum peak value of the s ignal at any time with an indication that
is easy to read and which is not tiring
to the eyes. Various types of signals will
be fo und to require the use of diffe rent
types of presentation and different delay times, but the eng ineer will quickly
learn which is 1110st suitable fo r his
own method of operation.
Vl hile some types of recording are
not degraded greatly by minute amounts
of overmodulation, it is well agreed
that when recording .on fi lm overmodulation is objectionable. This in strument
provides a reliable indication of the
r ecorded signal at all times, and permits
some fle x ibility of indication to suit
the needs of the engineer.
.... . ......
.. . .. . .. .....
~
"
~
· . .... .......
. '.- . . . .......
. .......,. ..
......
•
••
•••••••
~
~
•
'0
•••
••••••
~
:::-::::::;::: j :::: :: :::
::.......
~.~ ~ ~ ~ ~ ~ ~ ~ ~ ~ i' : .;: ::::
.... ... ... ....
·" ... '.'
... . ,. ; ...... ..."'...
" . ' •••• ,;.......~,/, '..,:,··l ••••• • ••
: : :: : : ::: :: :: '
..... .
~
.. . . . .
~
04 • ... . • •
":
~
~~.
. .. . . . . . . . .
;
;,-,
,,~
Every essent ia l for superb tone-Y2"
wood sides, Y2" acoustic lining, 4.3 cu. ft.
capacity, heavy construction (wt. 31 lbs).
But moderate cost with leatherette
covered sides. Hand rubbed solid mahogany
or blonde hardwoJd around front adds
genuine richness . Compare it with a ny
other a nd see for yourself. Only $45.00
net (slightly higher west of Rockies).
...
Send for FREE Folder
Fig. 5. Panel view of the instrument with a conventional oscilloscope.
SOUND HANDBOOK
(froln page 38)
about five watts, after which the bias
shifts progressively through the range
of Class AB, into Class ABo. This is
done in order to maintain the optimum
bias for a given signal a mplitude, a nd
the amplifier power output capabilities
at low di stortion are increased.
The Output Transformer
A generator faci ng a load through an
ideal transformer w ill be blind to the
transfo rmer and will only see the load
connected ac ross the seconda ry, stepped
up or down in value by the impedance
ratio of the windings (the sq uare of the
Fig.
Equivalent
cir- r-------;::::::::==:;:=======~====:;_-_,
cui t 12-25.
to output
transformer.
Rw
LL
Cwo
(The transformer itself is
assumed ideaL) R", = d.c.
RW
winding
resistance; LI =
Leakage inductance; R, =
Shunt resistance equivalent
L.
R.
Cw
to core loss; C", = Capacitance across windings; Ls =
Shunt inductance of winding; Cws = Capacitance between wind ings (eliminated
by el-actrostatic shield.)
1..-------------------------'
AUDIO ENGINEERING
•
SEPTEMBER, 1953
/
*By makers of famous TV Tube Caddy®
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•
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AUDIO AMPLIFIERS
Fig. 12-24. Automatic bias control providing
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Only data of its kind available on hundreds
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illustrated volumes-absolutely indispensable to audiophiles, engineers and students.
, 1\
VOL. 4. Covers 75 audio amplifiers and important tuners produced during 1951 and 1952.
Never before available ina single compilation.
352 pages, 8~ x 11".
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"The Recording and
Reproduction of Sound"
Only complete reference on
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Chapters on sound wave
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2201 East 46th St., Indianapolis 5, Ind.
$. : ... .. ... enclosed. Send following books:
DAA.l ($3.95) DAA.3{$3.95) DRR.2{$7.95)
DAA-2{$3.95) DAA.4{$3.95)
Name •••.••••••••.•••••••••••••••••••
Address .••••••••••••••••••••••••••••••
t :i1:.::..:.::..:.:~:.::..:.: :.:'::": .:~::..: .:.s.:~::.:
78
:.:::. J
turns ratio).
This ideal case is never realized. Distortion is introduced by non-linear magnetization characteristics of the core, frequency transmission falls off at extremes
of the reproduced spectrum, and phase
shift is introduced to sabotage feedback
circuits. In Fig. 12-25 the transformer
itself is assumed ideal, but circuit elements equivalent to the physical characteristics of actual transformers are inserted, in series or in parallel as they
appear to the generator, as "lumped"
impedances. The labels on these impedances are self-explanatory except in the
case of leakage inductance. This is the
effect of the less than perfect magnetic
coupling between primary and secondary
-all of the magnetic flux produced by
the cnrrent does not lie within the core
cmd does not perfectly link all the turns
of both windings. The appearance of a
primary winding shunt inductance of
finite value is an indication of the fact
that, even with the secondary unloaded,
some signal current flows through the
primary.
Energy dissipation will take place due
to the added resistive elements, there
will be treble losses due to the shunt
capacitance and series inductance, and
bass losses due to the shunt inductance.
The effect of core non-linearity does not
- appear in the equivalent circuit.
The output transformer is normally
the most critical unit of the audio amplifier, and, if it is included in the feedback
loop, the number of db of compensatory
feedback tha.t can be applied over the
output stage is limited by this same component.
Other Characteristics of the Output Stage ·
Transformers for Television
... Radar . .. Aircraft . ••
Geophysics . .. Radi()
You will find Thermador ready, willing
and fully qualified to handle your trans·
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experience and manufacturing knowhow, developed over a period of 35
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Thermador today's largest West Coast
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transformers. We would like to work
with you on your next project involving
the design and production of transform·
ers for specific requirements .. .including
joint Army-Navy specifications.
transformers:
Audio Auto
Geophysical
1. Power Sensitiv-ity. This defines the
relationship between output signal power
and input signal voltage. Expressed in
mhos (a unit reciprocal to ohms) :
Driver Filament High-Fidelity Audio
Input-Output Midget Plug-In
Plate Power Television
Tube to Line
·· .
P
P ower S enslbvlty=
(Bg) 2
... also Chokes and Reactors
where P = output power in watts
Bg = input signal voltage
Power sensitivity is a more useful
index of power amplifier operation than
voltage gain, since we are not directly
interested in the output voltage as such.
THERMADOR ELECTRICAL
;. ( MANUFACTURING CO.
3·320
5110 District Boulevard. Los Angeles 22, Calif.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
Pentodes and beam:.power tetrodes have
a higher power sensitivity than triodes,
and negative feedback reduces the power
sensitivity (not the power capability)
of both. The use of additional pairs of
. tubes in parallel-push-pull does not increase the driving signal voltage requirements where no power is consumed
by the input circuit, but does increase
the power output, thereby increasing
power sensitivity.
2. Frequency Response. The power output vs. frequency curve of the output
stage is controlled by the effect of the
speaker load reactance, as discussed,
and by the reactive characteristics of
the output transformer. Frequency discrimination may also be introduced by
the input network coupling the voltage
drivers to the output stage grids, a topic
which will be discussed in the section on
voltage amplifiers.
Audio Devices
3. Harmonic Distortion. The harmonic
distortion rating of a power amplifier,
in its most useful form, lists the percentages of distortion separately for
each of the harmonic orders instead of
presenting them as a single vector sum.
A rating of this type will show, for
example, that pentodes and beam-power
tetrodes produce more odd and higher
order spurious harmonics than triodes,
increasing the need for feedback in their
cases. It is also useful to know the distortion percentages as a function of
frequency.
4. OPeration of Pentodes as Triodes.
Pentodes may be used as triodes by tying .
screen and plate together, either directly
or through a stopping resistor of 100
ohms or so. The tube then takes on
triode characteristics. A type of inbetween operation is also possible, in
which the connection between the screen
grid and the output transformer primary
is made neither at the center tap (pentode operation) nor at the plate end
(triode operatiqn), but at a point intermediate between the twO.12 The load
is thus distributed between the plate and
screen, and the voltage on the screen
grid varies inversely with the signal,
constituting negative feedback to the
screen. The circuit, which is called
"Ultra-Linear," (See Fig. 12-26) may
make possible a reduction in the cost of
high-quality amplifiers, since more
power at low distortion levels can be
drawn from the same tubes. It has been
criticized,13 however, a~ requiring especially rigid production control over the
output transformer . .
S. Plate Dissipation. Kinetic energy of
the electron~ ip the cathode-plate stream
is converted into heat when the electl'Ons
strike and enter the plate. The allowable
amount of energy that can be so dissipated is limited by the fact that high
Aero. Ampex
Astatic· Altee
Atlas Sound
Amplifier Corp
of Amerca
Audak • . Amphenol
BrOciner
Browning
Brook' Bell
Bogen· Brush
Cabinart • Centra lab
Clarkstan ~ ·Crescent
Concertone
Cook· Conrae
Duotone • Espey
Electro·Voice
Fisher. Fairchilc[
General Electric
General Industries
Garrod· Gray
Grommes
Hallicrafter
I.R.C . • Jensen
Karlson· Leak
Lowel. Llvlngst'!.!!.
Market
Mcintosh
Minnesota Mining
Masco • Meissner .
Magnecord
Newcomb
.·Permoflux
~~~~1~o. p!~~r~ijlnl
• Pilot
Reeves Soundcralt
R·J • Rek·O·Kut
Rauland • Revere
River Edge' R.C.A.
Radio Craftsmen
Reeotro" • Racon
Stephens
Stromberg Carlson
H. H. Scott
Sonotone • Shure
Standard Wood
Products
Tech Master. Thorens
Tapemaster.
University
GARRARD 3 Speed
AutomatiC Recor.d Changer
Model RC·90
Ultrasonic
U.T.C. · V.M.
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The TERMINAL W
to Your A
Over 130 pages packed with
everything you want to know
about all the latest High
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Equipment ... The most Com·
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for Music Lovers, Aud io Engi.
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12 David Haller and Herbert I. Keroes,
"An ultra-linear amplifier," AUDIO ENGINEERING, Nov. 1951, p. 15.
lS D. T. N. Williamson and P. ]. Walker,
"Amplifiers and superlatives," Wireless
World, Sept., 1952, l?' 357.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
79
SAVE
Measurements Corporation
MODEL 31
33~~o
Fig . 12-26. Ultra-linear output circuit, in
which the screen grid is connected to tap of
output transformer, taking up part of the load
and receiving a lIegative feedback voltage.
This is our
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AUDIO ENGINEERING is still
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entirely to
•
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Audio
Broadcasting equipment
Acoustics
Home reproduction systems
Recording
PA systems
Psychoacoustics
( Please print)
Name
Address .... , . .. .. . .. .... . . ... .. ... . .
Position ... . .. • . . . Company . . .. . . . . . .
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Address .... . ... ... .. . . . ... .. . . . . , .. .
Position ... . . .•. .. Company .. ... .... .
Name . . . " " ••. " .. " ., . . .. .. . . . .. . .
Address
-
~
...... ... .. .. .. . . .. ..... . .. .
Position ..... . . .. . Company ... , .. .. . .
Name . . .. . , .. " . ... . . . . . .. . ...•... ..
Address , . , . ... .. .. . . ... . , . . " . . .. . . .
......
,
.. - ..
. . .. .. -,.
-,
.... .... ... . .
Position . . ,' ... .. . Company .. ... . ... .
Name .. :" , ... • " . .. ... " . .... . .. . . .
Address ., . , . . ... .. , .. " ., . .. , . . . .. . .
Position ... . .•... . Company . ..... .. . .
Name . . . , . • . . . . . , . ... . . , ......... . . .
Address " " ., ., . .... .. ... . .. . . . .. . . .
.. . .. ... .. .... ... . - .. . .. .. . . . ... . .
-,
Position .... . . . ... Company .• . .... . ..
U . S. , Possessions, and Canada only.
RADIO MACAZINES, INC.
P. O. Box 629, Mineola, N. Y.
80
INTERMODULATION
METER
• Completely Self-Contained
• Direct Reading For Rapid,
Accurate Measurements
plate t emper atures will cause seconda ry
emi ssion of electrons or will r elease g as
from the plate. Oper ating conditions
fo r output tubes-the magnitude of the
plate and screen voltages and the amount
of current allowed to flow--;-r a rely a pproach the point of maximum plate or
screen diss ipation, but the ex tent to
which they do will be an index of the
life expectancy of the tubes. Class A
operation h as the highest no-sig nal plate
diss ipation.
6. Pla,te E ffic iency. Plate effici ency refers to the r elationship between signal
po\'Ver output and B supply power consumed; the miles per gallon r ating, so
to speak, of the output stage. This r ating
describes the distribution of power between plate-screen diss ipation and the
output sig nal. It may be of importance
i.. large commerci al installati ons or in
communities where the price of el ectrical
power is hig h. Triodes have a much
lower plate efficiency than pentodes or
beam-power tetrodes. Class A operation
provides the lowest plate effici ency; the
plate efficiency of a power amplifier increases a,s th e no-sig nal plate current
is r educed and the class of operation is
changed towards Class C.
The plate efficiency of a stage may be
expressed as follows:
Plate Efficiency ( at.) 10
-
P
E av I av
To insure peak performance from all
audio systems; for correct adjustment
and maintenance of AM and FM receivers and transmitters; checking linearity of film and disc recordings and
reproductions; checking phonograph
pickups and recording styli; adjusting
bias in tope recordings, etc.
The generator section produces the
mixed low and high frequency signal
required for intermodulation testing.
A direct-reading meter measures
the input to the analyzer section
and indicates the per·centage of
intermodulation.
MEASUREMENTS
CORPORATION
BOONTON
AItee
Y·M -
I
0
Brook -
NEW JERSEY
Bell -
hnsen
1EXAS-TV
"Southwest Sound Hq."
.
c
...
.c
.
~
co.
en
"
x 100
wher e
en
Eav = Average d.c. plate voltage
I nv =Average d.c. plate current
P = P ower output in watts
REFERENCES
Lawrence B. Arguimbau, "Vacu~lm-T-llbe
Circl{its," John Wiley and Sons, Inc.,
New York, 1948 ; Chapters 6 and 8,
Albert Preisman, "Loudspeaker damping,"
AUDIO ENGINEERING, March, 1951, p. 22,
and April, 1951, p. 24.
H erbert J . Reich, "Theory a.nd A pplica.lions
of Electron T ubes," McGraw Hill Book
Co., Inc., New York, 1944; Chapters
5, 6, and 7.
F. Langford Smith (Editor) " T he R adiotron Designel" s H a.ndbook," 3rd ed.
W ireless Press, Sydney, Australia (Reproduced by Radio Corp. of America)
Chapter s 2, 3, 4, 6, and 26.
R. C. A. R eceiving T ube M a.n1{a. I, R. C. A.
Tube Department, H arrison, N. J ., 1950,
pp. 3-30.
]. G. Frayne and Halley Wolfe, " E lements
of S ound R ecal'ding," J ohn Wiley and
Sons, Inc., New York, 1949; Chapter 5.
"CI
..
~
A corner of one of the Texas-TV air-conditioned
Hi-Fi demonstration rooms in which ali major
lines of sound and recording equipment can be
C;
demonstrated "at the Dick of a switch".
:r
WEATHERS FM PICKUP. .
~
-
gram
sty lus
pressure
f
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One-;':
eliminates
record
;:I:
wear. 20-20,000 response with negligible ;.
~ distortion, Supplied with oscillator deliver-
$37.50
"HOME MUSIC SYSTEMS" . .. New
Zing .5 volt into high impedance.
.c
L;:
book by Edward Tatnall Canby explains
Hi-Fi recommends bra nds & models, tells
how 'to test and repair equipment, build
baffles, install units. Gives list of nearest
dealers.
$3.95
HORN LOADED SPEAKER KIT . .
C
by Cabinart. Gain a full octave of smooth
::!!
~
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For 15-inch speakers $23.95 . .. 12-lnch
,
$19.95 ~
$AVE-We Prepay Between
Alleghenies & Rockies
TEXAS-TV
~
506 W. Hildebrand Avenue
San Antonio 12, Texas
Clark,tan -
AUDIO ENGINEERING
Unher,lty -
•
Ampex -
_
~
f
I
Cabinar
SEPTEMBER, 1953
makes the
AUDIOLOGY
(from page 14)
'FORMULAE
FAMOUS
Class AB, Operation
When the output stage employs a more
efficient class of operation, such as pushpull Class AB high conduction by one tube
" by essential non-conduction
is accompanied
by the other tube. The result is that the
output transformer half-primary on the inactive side is temporarily unterminated, and
with likely detrimental effect upon the gainphase characteristics of the feedback loop.
Another difficulty is that tube transconductance during signal peaks may be twice
(or more) its no-signal value. Such an amplifier may be stable at no-signal, but oscillatory during part of a large-amplitude
signal cycle. Under such cir-€umstances,
quenched oscillations occur, and a monitoring oscilloscope (of adequate band-width,
of course) lVill show a "bubble" of highfrequency oscillation riding on a portion of
the audio signal cycle.
Thus in evaluating amplitude margin of
stability noted in conventional loop gain
and phase measurements, due -allowance
must be made for the probable increase in
transconductance during signal peaks. A
suitable factor may be roughly estimated
from graphical examination of the path of
operation along the load-line corresponding
to rated resistive load. If tube transconductance during low negative grid potential
is (say) twice the no-signal value, then
6 db must be added to the amplitude stability margin qtherwise required, if quenched
oscillations are to be avoided. When beampower tubes are used in the output stage,
the added factor may be 10 db or more;
this is a strong argument favoring the use
of more linear tubes, or for tube-characteristic linearization by auxiliary feedback
(over extra-wide bandwidth) within the
main feedback loop, such as cathode-follower output with main-loop feedback to an
earlier stage. 1
There appears to be no simple, readily
applied test by which one can directly and
quantitatively examine susceptibility of a
feedback amplifier to such quenched oscillations, since the circumstances 'permitting
them are not continuous. But there are rela- /
tively simple qualitative tests, readily applicable to most audio feedback amplifiers,
representing in effect the various worstconditions imposed by later equipment usage; these include capacitive loading, as
well as any effects of half-primary untermination by a temporarily inactive tube of
a push-pul1 pair.
The method is to begin by monitoring for
oscillation with an oscilloscope (useful to
at least several hundred kilocycles) while
capacitive load only is varied through the
range 0.001 to 1.0 ""f in roughly 20-per-cent
steps. Experience shows this range to be
adequate for voice-coil output taps; for
higher impedance taps, use inversely proportionate capacitances. If no osc~l1ations
are observed, proceed by applying a lowfrequency signal (preferably the lowest .frequency for rated power output) of amplitude to produce no-load output voltage
within a db or so of overload ("flat top"),
and monitor for quenched oscillation as
capacitive load only is varied throughout
the appropriate range. Next repeat the capacitance variation with rated resistive load
parallel thereto, to produce high-transconW. R. Ayres, "Choice of electron tubes
for audio circuits," I .A .E.S., p. 49, Jan.,
1
Once again this famous 'e' core Audio
Transformer is available OFF THE SHELF.
Manufactured by highly skilled workers
from the finest materials available, the
CFB maintains a consistent performance
hitherto only associated with specialist
laboratory" equipment, and is the result of
untiring research into grain-oriented stripwound 'c' core transformers.
These figures spf!ak for ' themselves:
Series leakage induct 10 mH; Coupling
between primaries-leakage induct. for
one half (other shorted) 30 mH: D.C.
resist. per half primary 88 ohms; Pow er
up to 60 w. from 22 ci s to 30 Kcls; dis-
tortion less than 1 % with no negative feed
bock!
PRICE $40 _DUTY PAID
Should you experience any difficulty in obtaining CFB transformers, please write to us,
mentioning the name and address of your
local lobber. Remember, there is no substitute for the Partridge CFB.
PARflPDGIl
TRANSFORMERS LTD
TOLWORTH. SURREY. ENCLAND.
Now! Dear Sensational New
3-D SOUND ... At Leonard!
I
Livingston Binaural Arm
Livingston StereophoIOic Amplifier
Here at last is a complete stereophonic
twin-channel amplifier for any 3-D sound
source. Unit consists of two 10 watt hi-fi
channels from cartridge to loud speaker; 3
twin inputs for disc, tape and binaura l
broadcasts; separate tone-controls for
highs and lows; edge
lighted lucite rear-engraved panel. Supplied
on two chasses with individual cabinets and
three foot interconnectnet
ing cable.
149.50
Mail
Cj
Complete with the finest cartridges available .•• the new Fairchild Diamond Stylus Model 215 •.. the Livingston Binaural
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wear and maximum fidelity to the amplifier input. Cartridges, $37.50 each.
Binaural Arm. $35.00.
Complete unit , •....
net
Phone Orders. 25% Deposit, Balance COD
LEONARD RADIO, INC.
69 Cortlandt Street, New York
COrtlandt 7-0315
, AE8
1953.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
/
81
RECORDINC TAPE
(PLASTIC BASE)
at NET PRICES
in Cartons of 12
WAS HINGTON , D. C.:
WHERE ELSE WOULD THERE
Magnetic
BE MORE RED
1\ TAPEr
• 1200 ft. plastic t ape with plastic reel included.
• Each reel individually boxed.
• Choice of nationally famous top quali ty
brands such as:
Webcor (2906) 3.20; R eeves (SPN-12) 3.20;
Audio (1251) 3.23 ; Scotch (Ill-A) 3.25;
Panacoustic (711-A) 3.25; lrish, Professional grade (211 RPA) 3.30.
• Recording studios, schools, radio stations
and other large quantity users-write for
bulk price.
************************
USED RECORDlNC TAPE (PLASTIC BASE)
1.99 for 7"-1200
•99 for 5"- 600
•59 for 4"- 300
. 29 for 3"- 150
Plastic re.1s Included
all above sIzes.
foot
foot
fool
foot
with
ductance tube operation during signal peaks.
Such dynamic tests are not only more
representative of amplifier usage, but expose feedback system weaknesses which
would not be exposed by simple static tests
with resistive load. If, in addition, the
amount of feedback has been increased sufficiently to represent higher loop gain due
to likely component and tube tolerances, <1:n
amplifier design which passes these dynamiC
tests is probably unconditionally stable. It
is possible to make a feedback system which
would oscillate only with inductive load,
but such is hardly representative of commercial practice, and need not be included
in tests of common audio power amplifiers.
The method is only qualitative, with no
indication of the nature or extent of any
corrective measures required. But besides
being a powerful exploratory method, it
tells the specific range of load impedances
to be considered when conducting further
work with static gain-phase measurements
around the feedback loop, as may be required in completely solving a stability
problem .
IIoney cbeerfully refunded If you do
not find tbls tape cleanly erased and ..
,DOd as new. (If Y<lU are skeptical and
Irom MIssouri send ns 12¢ In stamps
and we'll roll you a .ample.)
Ne. empty plastic reels In boxes for easy
lab.llna. 3" 10;; 4" 22;; 5" 24¢; 7"
30;; 7~ Profes.lonal reel (20/4" hab) 75;
oa. EMPTY BOXES: 3" 3¢; 4" 5;; 5" 5;;
7" 10; el.
W. carry new recorders, recording blanks, tape, tape
r.....den, etc. It larKe savlnKS. PLEASE INCLUDE
SUFFICIENT POSTAGE.
COMMISSIONED ELECTRONICS CO.
2503 Champlain St. N. W., Washlnaton 9. D. C.
for every application •••
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Books and Manuals
GERNSBACK PUBLICATIONS-Added No. 48 "HI-Fidelity
Design, Construction, Measurements" at $1.50 net.
RIDER, JOHN F.-Dlsrontinued No. 121 "Installation an d
Servicing of Low Power PA Systems".
Recording £quipment, Speakers,
Amplifiers, Needles, Tape
AMERICAN MICROPHONE-Discontinued Model CL-3 Crystal
Lapel Microphone.
DUOTONE-Discontinned Rerordlng Blank No. 109-10".
GATELY DEVELOPMENT LABORATORY-Addded new series
or 12" and l !)n Purest Speaker Baffles.
GENERAL ELECTRIC-Added Model Al-900 Becord Compensator at $8.95 net.
GRAY RESEARCH-Added FalrcblJd Cartridge sUdes: 6
gram slide at $2 .20 net; 26 gram slide at $2.20 net.
KARLSON ASSOCIATES-Added Model 15PK Loudspeaker
Enclosure Kit at $45.00 net.
PILOT RADIO-Added Model AA-903 AmpUOer (Williamson
tl'1le) at $69.50 net; Model FM-601 FM Tuner at
$59.50 net.
RACON ELECTRIC-Added P.A. speakers Model RE-l8 at
$11.10 net ; Model RE-20 at $29.25 net.
RECORDISC CORP.-Discontinued '1.- and 'h-bour recordIng wire spool.
RECOTON-Added Model 200 Magnetic Turnover Cartridge
with two sapphire needles at $5.94 net.
RIVER EDGE INDUSTRIES-Added new series 01 HI-FI
Rnd TV Cablnels.
THORENS CO.-Added lIodel CD-53 three-speed doubleside record ebanger with pause mecbanlsm at $292.50
net.
Test Equipment
ALTEC LANSING-Added Model TI-401 Signal Generator
at $340.00 net; Model TI-402 Intermodulatlon An'!Jzer
at $450.00 net.
CBS-HYTRON-Added Test Adaptors Model SH-28 tor 8-pln
octals at $2.25 net; Model SH-29 tor 9-pln octals at
$1.15 net.
Tubes-Receiving, Special Purpose
~
•
MONTHLY SUMMARY of product developments and price changes of radio electronic-television parts and equipment.
supplied hy United Catalog Publishers. IDc.,
110 Lafayette Street. New York City. publishers of Radio's Master.
These REPGRTS will keep you up-to-date in
this ever-chang!nl!: industry. They wi11 al80
help you to buy anrl specify to best advanta.:e.
A complete description of most products wlll
be found In the Official Buylnl!: Guide. Radio's
Master-available throul!:h local radio parts
wholesalers.
A
. , 1448-39th Street, Brooklyn 18, New York
In Cenode. Atla. Rodi. Corp., tid .. Toron'o, Onto
CBS-HYTRON-Deereased price on radio receiving tube
6V6GT to $2.00 list. Increased price on transmUting
tube 3D21A to $11.90 list.
LEWIS & KAUFMAN~Added 3B24W rectifier at $11.15
net; 8C24/24G triode at $7.50 net; 4D21/4-125A
tetrode at $30.25 net.
RA YTH EON-Added radio receiving tube 12AZ1 at $2.50
JIst.
SYLVANIA-Added radio receiving tube 19V8 at $3.55 JIst;
special purpose tube 5906 at $25.15 net; transistors
2N32 at $15.40 net; 2N34 at $18.40 net.
rlLASSIFIE
Rat,,! lOt lIer word per Insertion for noncomm,,.lal
advertllaments; 2S¢ per word for eomnlflrelal
un,-
tl ..... ntl. Rates art net, an. no .nUtaata will ...
allowed. Copy must be accompanied ~y renaltblct II
fUll, and mUlt reach thl New York offiCI lIy till
ftrat .f thl month preceding the dati of ' .. Ufo
THE AUDIO EXCHANGE, INC. buys and
sells quality high-fidelity sound systems a!ld
components Guaranteed used and new eqUIpment. Catalogue, Dept. iE, Hi9-19 Hillside
Ave., Jamaica 32, N. Y. Telephone OL 8-0445.
FAIRCHILD 541Al Cutterhead, equalizer,
microgroove, thermostylus attachments. Box
101, St. Albans, N. Y.
KITS assembled; units constructed from
schematics. Audio amplifiers our specialty.
Neil Laboratories, 4A, 164 Prospect Place,
Brooklyn, N. Y.
FOR SALE: Presto 6-N recorder in pOI·table
case. 1-D cutter. Like-new condition. Reasonable. Box CS-1, AUDIO ENQINEERING.
AUDIOPHILES MUSIC HOBBHSTS .
Carryon exchanges between · other l-ll-FI
ent hus iasts via wirespondence or tape talk•
Registration $3 year. Global Talkawire Club.
Box 630, Marvista 7S, California.
Twin-Trax portable tape recorder-radiophono~raph, $200; Conn t!!nor saxopho_ne,
case, $200; Sunkraft ultraYlolet l~mp, ~oO !
Smith-Corona silent deluxe typewrlter. $45,
Shure 55 dynamic microphone, $35; Garrand
RC-60 record changer, GE cartridge. $25 ;
Brush PL-20 transcription pickup, equalizer,
$20 ' Alliance ATR antenna rotator. never
outside, $20; back issues AUDIO ENGINEERING,
best offer. Everything guaranteed excellent,
priced FOB. V. R. Hein, 418 Gregory, Rockford, llllinois.
SELL: Brook 12A3 remote control aml, lifier, new condition, neve r used. FOB, $150. R.
E. Ridenour, 839 Wildwood Parkway. Baltimore 29, Md.
ALTUEC 603-B, perfect, $52; Bogen
DB10-1, perfect, $35; Craftsmen 400, new,
$36. Lyons, 38 Roosevelt, Palo Alto, California.
WILL SELL Hallmark Williamson amplifier, new condition, $135; Brooks FM-AM
tuner, model ST-15A, n ew condition. $95;
used Browning RV10-A FM tuner, excellent
condition, $60 ; Livingston Universal arm,
$12. S. Roberts, 33 Sky Top Drive, Bridgeport
29, Conn.
WILLIAMSON AMPLIFIERS. dual chassis,
30 watts, oil condensers, cabled power s upply.
components power-rated 100% to 500% over
speCifications. Nicely ASSOciates, Kenton, Ohio.
CRAFTSMEN outfit for sale: C500 amplifier, C300 preamp. Electro-Voice SP12B
speaker, Jensen cabinet, turntable, GE pickup
and arm, 55 classical LP records. $250 takes
a ll. Paul Bixler, 2330 Euclid Heights Blvd.,
Apt. 210, Cleveland, Ohio.
WANTED: Vertical transcriptions, vintage
1935--45. Cash, or will trade WE 9A pickup
with arm, IS-in. Cinaudagraph speal,er, RCA
15-in. duo-cone, other equipment. D. Pace,
560 Audubon Ave., New York 33, N. Y.
FOR SALE; Presto 1-D disc recording cutter, 500 ohms impedance. $100. K. A. Maxwell, 1550 Vermont, McKeesport, Pa.
FOR SALE: Altec L a nsing 604B with network, $85. L. Jacobson, 1772 47th &t .•
Brooklyn, N. Y.
FOR SALE: Allied overhead and turntable.
new G.E. motor and mercury switches, Fairchild 542K arm in custom plywood cabinet,
$450. Ampex 401 in perfect condition, certified
by distributor, $660. N. Y. Area.... BE 3-6587.
MUST SELL. Box CS-2, AUDIO .lliNOINEERING.
ALTEC 800 bass horn, $45; 6 RCA Accord ion speakers, bamed, $35; 2 Pickering
diamonds, new, $40. Will trade for FM tuner.
Box CS-3, AUDIO ENGINEERING.
300/0. DISCOUNT on factorY-freSh, guaranteed LP records. Send card for catalog and
literature. SOUTHWEST RECORD SALES,
Dept. AE. 4710 Caroline, Houston 4, Texas. ,
WEBSTER 356-27 3-speed ~.hanger, 2 CAC-J
cartvldges, $25. Pilot AF-605 10-tube AM-Fl\1
tuner, $25. Charles Leigh, 162 Passaic St.,
Trenton, N. J.
AUDIO ENGINEERING
•
SEPTEMBER, 1953
j~
On the iob!
Our volunteer speakers are
saving thousands of lives today . .. in factories and offices,
at neighborhood centers and
at organization meetings all
over this land ... showing people what they can do to protect themselves and their families against death from cancer.
For information just telephone
the American Cancer Society
or address a letter to "Cancer,"
care of your local Post Office.
American Cancer Society
Custom-Built Equipment
(0.
1121 Vennoat Ave., Washingtoa 5. D. C.
LIncoln 5-2705
(
AUDIO ENGINEERING
•
Reflecting growth of the sound equipment industry, Hudson Radio and Television Corporation's new Newark, N. J.
salesrooms will include "Studio 35"-one
of the east's larger and more complete
facilities for demonstration and comparison of audio equipment-formal opening
is slated for approximately September I
· .. International Resistanoe Company has
started construction of its second plant in
North Carolina-located in Boone, it will
employ 500 persons, of Which 80 per cent
will be women, when production capacity
is reached.
Minnesota Mining' &; Manufacturing Co.
has purchased Irvington Varnish and insulator Co., Irvington, N. J.-management
team and operating policies will remain
unchanged, according to Herbert P. Buetow, 3M president, with Arthur E. Jones
continuing as president of what will now
be known as the Irvington Division of 3M
· . . CBS-Hytron is latest tube manufacturer to announce mass production of
transistors for military and civilian use
· .. The Hallicrafters Company has broken
ground for a new $400,000 plant in Toronto
-daily production capacity will be 200 TV
receivers and 400 radio and communications sets.
Gates :Radio Company has opened a new
West Coast office and distributing branch
at 7501 Sunset Blvd., Los Angeles, which
is completely stocked with all types of
equipment for broadcasting, television,
and industrial electronics . . . Audio Devices, Inc., has expanded its plant at Glenbrook, Conn., to increase production of
recording tape by at least 50 per cent . . .
Berlant Associates, Los Angeles, has more
than doubled floor space for manufacture
of Concertone tape recorders-production
can be increased 300 'Per cent due to reorganization of equipment and introduction of advanced manufacturing techniques. New sound proof test lab will
speed up final test assembly.
j~peopk ...
PROFESSIONAL
DmBcroBY
U. S. Recording
Noiu ...
David Oppenheim, director of Columbia
Records Masterworks Division. assuring
friends that the coming season's releases
will be the super-best LP's ever produced
-is completely re-tubing his Brool{ amplifier just to make certain he gets full
enjoyment from his day's efforts when he
gets home in the evening . . . Operator
38X reports that Leroy Anderson is latest
in the list of noted musicians to install
lavish a,udio systems in new homes-he
lives out Woodbury, Conn. way . . . Larry
Epstein, sales manager, University Loudspeakers, Inc., pepping UP everyone he
meets wlth optimistic predictions for fall
business in the audio industry-says that
sales will be considerably greater than
most of us realize.
Frederick G. Su1fleld is new assistant to
President L. W. Howard of Triad Transformer Corporation . . • Earl W. Jense.n ,
vice-president, Jensen Industries, Inc.,
Chicago, is new chairman of the Association of Electronic Parts & Equipment
Manufacturers, trade association comprising 120 midwest firms; Theodore Rossman, general manager, Pentron Corporation, is new vice-chairman, and Helen
Staniland Quam, executive of QuamNichols Co. was reelected treasurer for
her sixteenth annual term.
George B. Fraser, treasurer since 1936
of the Astatic Corporation, Conneaut,
Ohio, was elected company president at
recent board meeting-he will continue to
act as treasurer . . . Recent RCA personnel changes include naming of Roy :H.
Nelson as manager of transistor sales.
and appointment of A. C. Duncan as manager of merchandise operations of the
Home Instrument Division.
Floyd W. Bell, president. Bell Sound
Systems, Inc., Columbus, Ohio. was recently elected to the board of directors
of the RETMA for a two-year term-he
will also serve as chairman of the association's Amplifier and Sound Equipment
Division • . . Thomas :H. Lynch, director
of ordnance products development, and
William P. Short, director of piezoelectric
and sonic products development, have
both been promoted to vice-presidencies
of Clevite-Brush Development Company
· . . C. G. Barker has resigned as sales
manager of Magnecord, Inc. . •• Everyone
glad to see F. Sumner Hall, president of
the AES, back on the job at Audio Equipment Sales, Inc. after a threatening illness.
SEPTEMBER, 1953
SlLvl'1l
ThIs I. the Sliver
year
of
Jubilee
Savage Transformers
and we have pleasure
In
IntroducIng
a
whIch
transformer
we thInk Is worthy
of It.
The
Outstanding
3c67A
Output Transformer
Primary 10,0000 cen tre tapped,
100 hys minimum measured at 5v 50 cis
- 900 + 900 D.C. resistance
Leakage reactance
Whole primary to secondary 16 m/Hys
Half primary to secondary 8 m/llY'
Half primary to other half 17 m/Hys
Secondary impedances 0.450, 1.80, 40, 70,
110. 160, 220 and 300. Frequency response
within 0.25 d.b. from 12Y.
cis to 25 kc/s. Power hanPrice $1 8.00
dling capacity 15 watts at
12Y. cis, 60 watts at 25
cIs. Size: 5Y:z" x 4" x 6" delivered free by par·
eel post, Insured,
high F.C. 314" x 4%".
but Import duty unWeight: approxlIDately 12
Ibs.
paId.
SAVAGE TRANSFORMERS LIMITED
Nursteed Road ' Devizes • Wiltshire ' Engrand
Telephone: Devins 536
Selects and cortectly
compensates for the characteristics of TV
tuner radio tuner, crystal phonograph pick·
'up: pius magnetic phonograph pickup equal·
ized for FfvE different recording character·
istlcs Including the NEW ORTHOPHONIC
RECORDING CURVE.
Wide range frequency response - 20 to
20,000 cycles ± If.! db. Ten watts of power
output at less than 1 % harmoniC distortion.
Recorder output JaCk permits record ing
While IIslenlng:
Unsurpassed In high lonal definition, In
faithfulness of reproduction, In
hearIng satislaclion. Hear
11 loday al your dealer·s.
, 83
SOUND FOR LISTEN ING ENJOYMENT
HARTLEY 215
.. . with the
U
·L 0
D S PEA K E R
~ad sound is an imposition. Aside fl'om contdbuting nothing to
listening enjoyment, it is actually a disturbing e leme nt. The only
thing it Ct'eates is the wish fOt, I'elief . . • the desire to shut it off.
If sound is intended for liste ning enjoyme nt, then obviously it must
be fl'ee fl'om distortion. The choice of loudspeaker then becomes one
of vital importance. When Hartley owne l's confirm that the Hartley
215 sounds ele an and can be listened to fOl' hoUl's, they mean that it
is free from bo~my bass, stride nt highs, resonant peaks, and other
forms of distortion. They mean that the Hal'tley 215 was designed
and built for listening enjoyme nt. The most I'emal,kable fact, they say,
is that the Hartley 215 sells for only $ 57.50.
Hartley Products are now available ill America
through franchis ed Hartley dealers.
For complete information regarding the Hartley 215, and the
new Bome Speaker Enclosure, Preamplifier, and Main Am·
plifier, write to Depar tment AE·8
Prices slightly higher West of the Rocki es
H.
A.
HARTLEY
521 East 162nd
LUdlow 5-4239
Street,
CO. ,
Bronx
INC
51 ,
N .
Y,
~ ~'ZfI~'1 'Zead4 t~
audio anthology
and
the 2nd .audio anthology
The original audio anthology is still
being ordered by people who have
worn out their first copy or who have
just learned about the book, Contains
reprints of 37 articles which appeared
in AUDIO ENGINEERING from May
1947 through December 1949. An invaluable reference work on aud io in
the home .
- - - - - - - - - - - - CUT OUT -
the 2nd audio anthology continues
from where the first left off and contains reprints of articles from January
1950 through July 1952. In both
books the articles were brought up to
date , corrected where necessary, and
assembled by subject. the 2nd a a may
still be had with board cover,
MAIL TODAY - - - _ _ _ _ _ _ _ _ _
Book Division, Dept. 3S,
Radio Magazines, Inc.,
,P, 0, Box 629, Mineola, N. Y,
Sirs·: Enclosed is D
copies
copies
copies
Name (please prir.lt )
check D money order for $.
of
audio anthology
of the 2nd audio anthology
of the 2nd audio anthology
, , , , . , Please send me
(paper cover)
(paper cover)
(board cover)
@ $2.00 each
@ $2.00 each
@ $3 .00 each
... ... .......... ........ ... ... .. ... ... ......... .. , .. . . .. ... .
Address . . . . . ...... ... .. " . . .. . . . .. . . . . ... , . .. " ... ... . .. .. . . . . .. . .... . . . . .... ,
City . ... . , ... . , ... . . . . . . . . , ... . . .. ,."
84
Zone " " ., State , .... . .. .. . . , . . .. . " ..
ADVERTISING
IN DEX
Alli ed Radio Corp . .. . . . . . .. .. . 6 2
Ame rican Elite , Inc . . . .... . . . . . 73
Ampe rite Co. . . . . . . . .... .. ,.. 55
Ampex Corp . .. . . . .... .. .... . 13
Amplifier Corp . of America . . ... 75
Argos Products Co. ' . . . . . . . . . . . 77
A rnold Engineering Co. . . .. ,. . . 9
At las Sound Corp . . . . . . ... . . .. 82
Audak C~ , " " . ,. " . " .. . ' 47
Audio Devices, Inc . . .. .. . Cove r 2
Audio Fair . , .. . , . . .. " .. . .. . 41
Be ll Telephone Laboratories .. . . . 18
Be ll Sound Systems, Inc . . . . .. . . 74
Bogen, David , Co., Inc . . . . .. . . . 62
British Industries Corp. . . . . ... . 3
Brook El ectronics, Inc . . . . . .. ... 79
Brush Electronics Co . . . . . , .. . . . 4
Camera Equipment Co. . . . .. , .. 63
Cannon Electric Co . " . . .. .. .. . 51
Chicago Transformer Co . .. .. . . . 57
Cinema Engineering Co . . . .. . . , . 8
Classified Ads . , . . " . . . . . ... , 82
Commissioned Elect ronic s Co. . . . 82 .
Concertone Recorders . .... ... . . 65
Cook Laboratories . . .. .... , 64, 71
Crestwood Div., Daystrom Elec. Corp. 58
D & R, Ltd . "" ,. " .. " ." .. 66
Electro-Voice, Inc. "." .. " , . 35
Fairchild Recording Equipment Co, 66
Fisher Rad io Corp . . ... , .. " . " 61
General Electric Co . ... . . . . 50, 68
Harper & Bros. . . . .. .. . . .. . . , 48
Hartley, H. A. , Co., Inc . . .. . .. . 84
Harvey Radio Co., Inc . . , .. .. . . , 53
Heath Co. " ,.. .. . .. . ... 59, 65
Hollywood Electronics ... .. ... . 83
Hughes Ai rcraft Co. .. ...... 2, 72
Hycor Co., Inc. .." " . . . .... . 64
Jensen Mfg. Co. . ... . .. . .. . .. . 39
Kellogg Switchboard and Supply Co. 68
Kierulff Sound Corp. . . . .. ... .. 83
Kingdom Products, Ltd . . . .. ... . 75
Lambda El ectronics Corp . . . ... . , 70
Leonard Radio , Inc. . , . ... .. , .. 81
Lowell Mfg . Co. .., . . .. . . . ... . 76
Measurements Corp. " . . . " . . . 80
Minnesota Mining & Mfg. Co. ,. . 1 1
Orradio Industries, Inc, , ... Cove r 3
Partridge Transformers, Ltd . . , .. . 81
Pickering and Co., Inc . . ,. " , ., 17
Pilot Radio Corp . . " 67 , 69 , 71 , 73
Presto Recording C'O rp. . .... .. .. 45
Precision Film Laboratories, Inc . . . 10
Professional Directory " ,. .... . 83
Radio Corporation of Ame.rica . . 6 , 7
Rauland-Borg Corp. " . . . ..... . 14
Reeves Equipment Corp. .. , .. . , 60
Re eves Soundcraft Corp . .. .. . .. 5
Rek -O-Kut Co. . . . . " . ....... 43
Rockbar Corp. . . ... " , . . .. ... 15
Sams, Howard W ., & .Co., Inc . . . . 78
Savage Transformers limited , .. , 8 3
Simpson, Mark, Mfg. Co., Inc . . . , 83
Shure Brothers, Inc . . . . , . . .. . , . 4 9
Ste phens Mfg. Corp . . , . , . . . .. .. 72
Stromberg-Carlson . , .. , . . . . . .. 37
TapeMaster, Inc. · . ... . .. . , . . . , 54
Te rminal Radio Corp . . ... . . . . " 79
Texas-TV , ." ." " " . , . . . . , . 80
Thermador Electrical Mfg. Co. .. . 78
Thorens Co. .. , . , . . . , .,.. . . .. 76 .
Triad Transformer Corp. . .. . . . ..
1
Turner Co, " , .. .. . " ,. " . .. . 12
United Transforming Co .. , . Cove r 4
U. S. Recording Co. . . . ..... . .. 83
V- M Corp. , .. . . . . .. . , .... .. 60
White Sound, Inc . . . .. . . .. ... . 56
AUDIO ENGINEERING
•
SEPTEMBER, 1953.
/
•
•
III
ORRADIO makes a grade of
SOUND RECORDING TAPE
for your SPECIFIC Requirements
If your tape recorder is inten.led for I"o""e or
office "se . .• we reconlmend:
IRISH Brown Band, No. 195 RPA
High quality, plastic-base tape, specially deve loped to re produce with extreme
fidelity, the frequency range between 100 and 8000 cps.
1200 Feet on plastic reel. .. ........ .............................. ............. $3.50
If your tape recorder is designed for professional
application, you should use . •.
IRISH Green Band, No. 211 RPA
Supe r-se nsitive, long-l ife, professional tape, offering greate r output vol ume,
greater amplitude constancy and greate r signal to noise ratio. Manufactu red to
exact standards set by NARTB and RTMA.
1200 Feet on plastic reel. ............... ... ............. ............. ......... $ 5.50
2400 Feet on metal reeL ....... ..... ........... .... ........................ 13.85
If your tape recorder is intended for broadcast
progra,nming, professional d~bbing, or any application wllere pllysical strength is an important
consideration, OBBadio offers you . ..
IRISHIISound Plate~No.220 RPA
New, revolutionary BREAK-PROOF tape . Will not tear o r brea k at speeds up to
500 feet per second . Has the same high qual ity magnetic and audio features
that have made IRISH 211 RPA the byword among profe ssional tape users.
/'
1200 Feet on plastic reel. .......... ...... ...... .. .. ......................... $15.50
2400 Feet on meta l reeL ................ ................................... 33.85
UTC Ultra compact audio units are small and light in weight, ideally suited to remote amplifier and
similar compact equipment. High fidelity is obta inable in all individual units, the frequency response
being ± 2 DB from 30 to 20,000 cycles.
.
True hum balancing coil structure combined v ith a high conductivity die cast outer case, effects good
inductive shielding.
Type
No.
A·l0
A·ll
A· 12
A·14
A·20
A·21
A·16
A·17
A·18
A·19
A·24
A·25
A·26
A·27
A·30
A·32
list
Secondary
Price
Impedance
Primary Impedance
Application
$16.00
Low impedance mike, pickup, 50, 125/1 50 , 200/2 50 , 50 oh ms
or multi~ l e line to griG
333, 500 / 600 ohms
18.00
50,000 ohm s
Low impedance mike pid tup, 50, 200, 500
or lin e to 1 or 2 grids ,multipl e alloy shi elds for low hum pickup)
Low impedance mi ke pi , kup, 50, 125/ 150,200 /2 50 , 80,000 ohms overall ,
16.00
in two section s
or multi~le line to grid :,
333, 500/ 600 ohms
50,000 ohms overa ll,
Dynam ic mi crophone t o one 30 ohms
17 .00
in t wo sections
or two grids
Mixing, mike, pickup, vr mul· 50, 125/ 150, 200/ 250 , 50, 125/ 150, 200 / 250,
16.00 333, 500 / 600 ohms
tiple line to line
333, 500 ~ 600 ohm s
18.00
Mixing , low impedance mike , 50, 200/ 250, 500 / 600
200 / 250, 500 / 600
pickup, or line to lin& (mult ipl e alloy shie lds for low hum pickup)
15.00
60,000 ohms, 2: 1 ratio
Single plate to si ngle [ti d
15,000 ohms
17.00
As above
Singl e plate to si ngle. grid
As above
8 MA unbalance d D.C.
80,000 ohms overall ,
Single plate to two gri us.
15,000 ohms
16.00
2.3: 1 turn ratio
Split primary.
Single plate to t wo gr id s.
80,000 ohms overall ,
15,000 ohm s
19.00
' 2,3: 1 turn ratio
8 MA unbal anced D.C .
50, 125/ 150,200/ 250 ,
Singl e plate to mult iple li ne 15,000 ohm s
16.00
333, 500 / 600 ohms
50 , 125 / 150, 200 / 250 ,
Single plate to mult ipfl! line 15,000 ohms
17.00
8 MA unbala nced D.C.
333, 500L600 ohm s
50, 125/ 150, 200 / 250 ,
Push pull low level pl ~ te s to 30,000 ohms
16.00
multi~le lin e
•
33;3, 500/ 600 ohms
plate to plate
Crystal microphone to mul·
100,000 ohm s
50, 125/ 150:200/250,
16.00
333,
500
/
600
ohms
ti~le line
Audio choke , 250 henry. ~i' 5 MA 6000 ohms D,C., 65 henrys ~" 10 MA 1500 ohms D, C, 12.00
Hr.nO _
Filter choke 60 h e nr~s ;', 15 MA 2000 ohm s D,C. , 15 henrys (,,) 30 MA500 ohm s D,C.
UTC OUNCER components represent the acme in compact quality transformers. These units, which weigh
one ounce, are fully impregnated and sealed in a drawn aluminum housing Ys" diameter . • . mounting
oppOSite terminal board. High fidel,ity characteristics are provided, uniform from 40 to 15,000 cycles,
except for 0·14, 0·15, and units carrying DC which ,are intended for voice frequencies from 150 to
4,000 cycles. Maximum level 0 DB.
OUNCER
CASE
Type
Application
No .
0· 1
Mike, pickup or line to
1 grid
0·2
Mike , pickup or line to
2 grids
0·3
Dynamic mike to 1 grid
0·4
Sin~le ~I a t e to 1 grid
0·5
Plate to Grid , D.C. in Pri.
0·6
Single ~I ate to 2 grid s
0·7
Plate to 2 gri ds,
D.C. in Pri.
0·8
Singl e plate to li ne
0·9
Plate to line, D,C. in Pri .
0·10 Pu sh pull plates to lin e
0· 11
0·1 2
0·13
0· 14
0·15
Pri. Ime.
50 , 200 /2 50
500 / 600
50, 200 /2 50
500 / 600
7,5/ 30
15,000
15,000
15,000
15,000
15,000
15,000
30,000 ohms
elat e t o pla te
Cr~ s t a l mike to line
50,000
Mixing and matchin g
50, 200 1250
Reactor, 300 H~s. - n o D,C,; 50 H~ s .- 3 MA, D,C"
50:1 mike or l ine to grid
200
10: 1 sin&le plate to grid
15 ,000
Sec. Imp.
50,000
li st
Price
$14 ,00
50 ,000
14.00
50,000
60,000
60,000
95,000
95 ,000
13,00
11.00
1-1.00
13,00
13.00
50 ; 200(250, 500 / 600
50, 200 / 250, 500 / 600
50, 200/ 250 , 500 / 600
14,00
14,00
14.00
50, 2001250, 500 / 600
50, 200 / 250, 500 ' 600
6000 ohms
'/2 megohm
1 megoh m
14 .00
13,00
10.00
14.00
14,00
. TYPE A CASE
,lY2" X lY2" X 2" high
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