engineering music sound reproduction amplifier uses cheap output

engineering music sound reproduction amplifier uses cheap output
AUGUST, 1955
500
ENGINEERING
MUSIC
SOUND REPRODUCTION
Hollywood Bowl's Symphonies I'nder the Stars
are heard in e new dimension with the stereophonic sr.tem recently installed. See page 14.
Good quality can be obtained for low-power applications by the proper
choice of tube types and feedback circuitry without the need for an expensive output transformer. Performance is adequate at both ends of the
frequency scale, and component cost is satisfactorily low. See page 11.
AMPLIFIER USES CHEAP OUTPUT TRANSFORMER
SOLDERING TIPS FOR HOBBYISTS
CARE OF JACKS AND PATCH CORDS
THE LANGUAD EXPERT LOOKS AT HI -FI
www.americanradiohistory.com
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THE STANDARD OF COMPARISON FOR OVER 20 YEARS
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UTC
Shielded Input
Multiple line (50, 200, 250, 500/600, etc.)
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Plate to Two Grids
Primary 15.000 ohms.
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HA-100X Shielded Input
Multiple line to 60,000 ohm grid
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... tri
CASE
LS -1
LS -2
Length 31/2" c -7.16"
Width .. 25ü" : I/2"
Height 31/4" L.3/16"
Unit Wt. 3 lbs. i.5 lbs.
LS -3
5-13/16"
5"
4.11/16"
15 lbs.
-
Plate to Two Grids
15,000 Ohms to 135,000 ohms in two sections .. +12 db. level.
HA -106
Plate to Line
15,000 ohms to multiple line
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Plate (DC) to Line
15,000 ohms to multiple line
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in primary.
Case
N1
23,1'
Width
1.15. 16"
Height
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Multiple line to multiple line for mixing
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30,000 ohms plate to plate, to multiple
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0.9 Plate (DC) to Line
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EXPORT
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DIVISION
13 E.
40th SI., New York 16, N.
Y. CABLES:
"ARIAS'
AUGUST, 1955
VOL. 39. No. 8
Successor to RADIO, Est. 1917.
AU D i 0
ENGINEERING
MUSIC
SOUND REPRODUCTION
C. G. McProud, Editor and Publisher
Henry A. Schober, Business Manager
Harrie K. Richardson, Associate Editor
Lewis C. Stone, Associate Editor
Emery Justus, Canadian Editor
Florence Rowland, Production Manager
Edgar E. Newman, Circulation Director
Sanford L. Cahn, Advertising Director
-
Special Representatives
H, Thorpe Covington and Dick Knott,
7530 Sheridan Road, Chicago 30, III.
-
Mid West Representative
Sanford R. Cowan, 67 West 44th St.,
New York 36, N. Y.
West Coast Representatives
-
lames C. Galloway and J.
W.
Harbison,
816 West 5th St., Los Angeles 17, Calif.
CONTENTS
Audio Patents -Richard H. Dorf
New Literature
Coming Events
Editor's Report
Amplifier Uses Cheap Output Transformer
Nathan Grossman And William Hellman
Soldering Tips for Hobbyists- Leonard Carduner
Stereophonic Sound System Covers Hollywood Bowl- Oliver Berliner
How Valid are Sound Truck Restrictions ?-Albert Woodruff Gray
The Languad Expert Looks at Hi -Fi- George L. Augspurger
Care of Jacks and Patch Cords- Eugene F. Coriell
Tuners
A complete 16 -page section
Employment Register
Audio ETC-Edward Tataal! Canby
-
-
COAST TO COAST
4
(i
8
11
13
14
17
18
20
The famous 655 is now equipped
with removable clamp -on stand
mount. Microphone simply slides
on or off. Extra rugged -praised
for its dependability Response
40- 20,000 cps -widest range of
any commercial microphone Output
level -55 db. High signal -tonoise ratio. Blast -proof grille.
Omnidirectional. Easily concealed
In studio props. Exclusive
Acousta / /oy diaphragm. Impedance
50 ohms easily changed to 150 or
250 ohms. Cannon UA -3 connector
TV gray finish. 20 ft. cable.
Model 655C. List Price $200
21
37
MODEL
38
Record Revue-Edward Tatrral! Canby
New Products
About Music-Harold Lawrence
Industry Notes and People
4?
Advertising Inde
;6
46
4g
;;
AUDIO (title registered U. 8. Pat. OD.) la published monthly by Radio Magazine, Inc., Henry A. Schober. President;
C. 0. blerroud. Secretary, Executive and Editorial Oakes, 204 Front St., Mineola, N. Y. Subscription rates -U. S.
Possessions, Canada and Mexico. $4.00 for one year. $7.00 for two years, all other countries, $5.00 per year. Single
copies 50e. Printed In U. S. A. at Lancaster, Pa. All rights reserved. Entire contents copyright 1955 by Radio Macazine, Inc. Entered as Sernnd Class Matter February 9, 1950 at the Part Office. Lancaster, Pa. under the Act of March 3,
1870.
RADIO MAGAZINES, INC., P. O. Box 629, MINEOLA, N. Y.
AUDIO
JUtLim
CHlit4:e
AUGUST, 1955
654
Response 50 to 15,000 Cps.
Omnidirectional
-55
db
Output
Recessed selector
gives 50 or 250 ohms
impedance Swivel stud
Cannon XL3 connector
18 ft. cable. List.
$95
Available from Authorized E-V Distributors. Normal
bade discount applies. Write for Catalog No. 123,
NO FINER CHOICE
THAN
""ke..te
ELECTRO-VOICE,
INC. BUCHANAN, MICH.
1
www.americanradiohistory.com
AmericanRadioHistory.Com
¡America's most
AUDIO PATENTS
complete line
RICHARD H. DORF*
THE TWO IMPORTANT TYPES Of
distortion
in audio amplifiers and other equipment
are harmonic and intermodulation. The
basic cause of both is amplitude nonlinearity
at some point in the equipment
stage or
device in which the amplitude of the output
is not always exactly proportional to the
amplitude of the input signal.
The two types of distortion are measured
differently. Harmonic distortion is measured by passing a sine wave through the
equipment, filtering out the original frequency, and measuring the amplitudes of
the spurious harmonics. Intermodulation is
determined by passing a low and a high frequency through the equipment and measuring the percentage of modulation of the high
frequency by the low. Both methods are
frequency- sensitive and there has never been
any really successful coordination of distortion tests with the subjective effects distortion has on the listener.
Inventor Barry C. King, Jr., of Collings-
-a
ROTARY POWER
IS
BEST
"clop- clop" of
The
"Old Bess" gave
Grandma's buggy ride
more vibration than the
smooth Rotary Power
of today's modern au-
tomobiles. ROTARY
POWER is best for mobile radio, too
and for all DC to AC
conversion... smoother
.
more dependable.
..
DC TO AC CONVERTERS
For operating tape re-
corders, dictating machines, amplifiers and
other 110.volt radio
audio devices from DC or storage batteries. Used
by broadcast studios, program producers, executives, salesmen and other "field workers ".
DUO -VOLT GENEMOTORS
The preferred power
supply for 2-way mobile radio
installations. Operates
from either 6 or 12 -volt batteries. Carter Gene
motors ore standard equipment in leading makes
of auto, aircraft, railroad, utility and marine
communications.
CHANGE -A -VOLT DYNAMOTORS
Operates 6 -volt mobile radio
from 12 -volt automobile
batteries . - . also from 24, 32
64 -volt battery power.
One of many Carter Dynamotor models. Made by the
world's largest, exclusive manufacturer of rotary power supsets
and
toe
BE SAFE
...
plies.
BE
SURE
.
.
.
BE SATISFIED
AC can be produced by ravers
ing the flow of DC, like throwing a switch 120 times a second. But ROTARY converters
actually generate AC voltage
from an alternator, some as
utility stations. That is why
ROTARY power is such clean
AC, so dependable
.. essential for hash -free operation of
recorders from DC power.
.
1.)MAIL
COUPON for illustrated bulletin
with complete mechanical and
electricaI specifications and performance
r---
charts. Carter
Motor Co. , Chicago 47.
CARTER MOTOR CO.
2642 N. Maplewood Ave.
Chicago 47, Illinois
y__
wood, N. J., has designed a simple method
for measuring the basic cause of nonlinearity distortion-the nonlinearity itself. While
he has not made evaluation of the results
in subjective terms any easier so far as we
know, this method of testing does seem
more basic than usual, and it appears to be
* Audio
.A-t'Ti'
(Continued on page 37)
(A)
(B)
(C)
J
(El
(F)
Consultant, 255 W. 84th St..
lurk 'l.:A -.
STEP WAVE
GENERATOR
Fig. 2
Y.
I
Please send illustrated literature containing com -I
plete information on
Carter "Custom" Con -E
verters and
Dynamotor Powet Supplies
be curved and would show the distortion.
more readily suitable for production checks.
The equipment itself is not especially simple,
but once built it should be quite easy for unskilled operators to use. The covering patent
is No. 2,646,545.
The block diagram of Fig. 1 indicates
how the nonlinearity "meter" works. The
unit first generates a step or staircase wave
such as that shown at (A) in Fig. 2. The
entire step wave is repeated at an audio
frequency which is low enough so that the
amplifier to be tested can reproduce the
straight sides of the steps. The step wave
gives a series of amplitude increments
which ideally are equal. The step -wave output of the tested amplifier may then be
viewed on an oscilloscope. When the amplitude of each step on the oscilloscope is
measured, it is easy to see where in the
amplitude range nonlinearities occur. The
nonlinear scope presentation of (B) in Fig.
2 is an example. Obviously the output amplitude increase for constant input amplitude increases is greater as the absolute
amplitude becomes greater in the wave at
(B) -or, to look at it another way, corn pression is taking place at lower amplitudes.
Measurement of the individual step
heights on the scope screen is rather difficult, however, because each step is relatively small. Continuing with Fig. 1, there-
nQ}lS1,S
\J
fore, the output step wave is differentiated,
a process of passing the step wave through
a high -pass filter, usually simply a series
capacitor and a shunt resistor. If the cutoff
frequency of the differentiator is made sufficiently high with respect to the repetition
rate of the step wave, the voltage will fall
back to the zero axis during each horizontal stair "tread" and the result will be a
series of sharp spikes, each with an amplitude above the zero axis the same as that
of the vertical part of the step which produced it. The result of the differentiation
of a nonlinear staircase is shown at (C) in
Fig. 2. The spike train can be amplified as
much as is desired and since each spike is
much larger than each stair rise it represents, measurements of the amplitude linearity can be made more easily and accurately. The ideal result is, of course, a
straight line increase across the tips. A line
outlining the tips at (C) in Fig. 2 would
AMPLIFIER
TO BE
_
DIFF ERE NT IATOR
AMPLIFIER
MEASURING
MEANS
TESTED
NAME
Address
City
MMMMMMMMMMM
State
E
Fig.
1
AUDIO
2
www.americanradiohistory.com
AmericanRadioHistory.Com
AUGUST, 1955
Since 1935
the Garrard has been
sold and serviced
throughout the United States.
It is recognized every where
for superior
performance, ruggedness
and reliability.
AHSHIP. FEATURES,
CHECK PR
CÉjpND
SERVICE
clearly
del'
Will understand
htg . S
and
is
why this
d chanBet
the wotld'sNo.l
Cour
Re
Ili
distr
et
hoes
.y
"RIGHTS" and "WRONGS"
tar
of record changer design
(important in protecting your records).
RIGHT:
'ravel
e only
Precision Pusher Platform ...
changing device that insures
record
sinus, gentle handling of records with standard
enter holes
RONG:
Overhead Bridges" as
,.
on ordinary changers)
which may damage or dislodge records
Ccidentally.
Y
RIGHT:
Garrard removable and interchangeable
...
Easily inserted; accommodate all
cords, all sizes, as they were made to be
played; pull out Instantly to facilitate removal o;
lovespindles
records from turntable.
BONG:
led Spindles
...
(as on ordinary changers)
require ripping records upwards over
etallic spindle projections after
playing.
er Garrard features include:
4 pole
motor
p
rumble. no Induced hum heavy drive shaft
wows, no waves
weighted turntableflywheel action, constant speed
muting switch
-silence between records
silent automatic
stop -shuts off alter last record no disturbing
"plop ".
easy stylus weight adjustment-proo
-no
-
lects
e
long -playing
records
arm -true tangent tracking
balanced- mounted
universal shell
fits all popular high fidelity cartridges
or
s
Finest
R ec or
anoer
i i
A Quality Endorsed Product of the BRITISH INDUSTRIES GROUP,
which also includes
WHARFEDALE LOUDSPEAKERS... designed and built under the personal supervision of G. A. Briggs...world renowned authority on sound. Wharfedale Loudspeakers
offer the unique construction feature of cloth suspension -a fell buffer between speaker
from* and cone-and cost chassis.
LEAK TL /1O -High fidelity AMPLIFIER complete with "Point One" REMOTE CONTROL PRE- AMPLIFIER. Most economical amplifier combination ever built by Leak.
Harmonic distortion only one tenth of one percent. Insures flawless reproduction.
EXCLUSIVE FEATURE! Convenient tope recorder jacks (input and output) on front panel
use!
for instantaneous
R
-J LOUDSPEAKER ENCLOSURES-"Maximum Boss- Minimum Space" Hearing
believingl R -1 Speaker Enclosures have established on entirely new trend in audio
design with thrilling performance from any loudspeaker. Bookshelf and Floor Models.
THE R -J WHARFEDALE... First and only complete R -1 unit) Two great products
the R -1 single shelf ENCLOSURE and a special WHARFEDALE SPEAKER have been
brilliantly matched in this
the definitive combination among compact high performance speakers.
WRITE FOR A COPY OF
"SOUND CRAFTSMANSHIP"
i
Mail coupon today for a complimentary
copy of "Sound Craftsmanship" 16
pages illustrating and describing all
products of the British Industries Group.
BRITISH INDUSTRIES CORP., Dept. A8 -5
164 Duane Street
New York 13, N. Y.
please send "Sound Craftsmanship" to:
is
-
...
www.americanradiohistory.com
AmericanRadioHistory.Com
Name
I.
Address
City
lonetate
NEW LITERATURE
Apply
Your
Electronics
Experience
ENGINEERS AND
PHYSICISTS WITH
ELECTRONICS TRAINING
ARE NEEDED TO
CONDUCT CLASSROOM
AND LABORATORY
PROGRAMS ON ADVANCED
SYSTEMS WORK IN THE
FIELDS OF RADAR FIRE
CONTROL. ELECTRONIC
COMPUTERS. GUIDED
MISSILES.
The proper functioning
of the complex airborne
radar and computer
equipment produced by
Hughes requires well trained maintenance crews
in the field.
At Hughes Research and
Development Laboratories
in Southern California
engineers assigned to this
program are members
of the Technical Staff.
As training engineers they
instruct in equipment
maintenance and operation
for both military
personnel and field
engineers.
Prior to assignment,
engineers participate in a
technical training program
to become familiar with
latest Hughes equipment.
Alter -hours graduate
courses under Company
sponsorship are available
at nearby universities.
British Industries Corporation, 164
Duane St. New York 13, N. Y., is distributing as service to the electronics industry an entirely new and up -to -date edition
of the world- famous International Radio
Tube Encyclopedia. Published in London,
the encyclopedia consists of 607 pages and
gives all details of more than 18,500 valve
and tube types from all over the world,
including television, industrial, and military c.v. tubes. Tube base connections are
shown in columns immediately following
operating characteristics data. The section
containing technical matter and instructions for using various tables and charts
is written in 14 languages. Available in
limited quantities, the encyclopedia is
priced at $9.00. Orders should be mailed
to Dept. IRT at the address shown abov.
B -1
Micamold
Electronics
Manufacturing
Corp., 1087 Flushing Ave., Brooklyn, N. Y.,
describes its plant facilities, lists typical
capacitor products, and gives a capsule
biography of key personnel in a new twocolor 12 -page booklet which highlights
major aspects in the company's 31 -year
history. Both photographs and text are
used in presenting Micamold's production
facilities, shielded research laboratories.
and test equipment. Plant views show
assembly lines, machine shops, and four
of the Micamold factories. Requests for
free copy should be addressed to Mr. A. S.
B-2
Gartner, vice- president, sales.
Brush Electronics Company, 3405 Perkins Ave., Cleveland 14, Ohio, details the
TapeDRUM, a new type magnetic storage
device which combines the advantages of
a magnetic drum and tape recorder, in a
new folder which will be mailed free on
request. Rapid access time and large
storage capacity at reasonable cost are
the outstanding features of the new instrument. Principal applications are in
the fields of inventory control, data reduction, trend recording and table storage.
The device can also be used as an auxiliary
memory or storage instrument for large
B -3
scale computers.
Permodux Corporation, 2835 N. Kedzie
Ave., Chicago 18, Ill., covers the new Per moflux Model 32KTR super tweeter and
Model NK -60 crossover network in Engineering Data Sheet JC -101 which will be
mailed on request. The sheet contains
schematic diagrams, response curves, and
a detailed description of performance
characteristics on both units. Requests for
copy should be directed to the Distributor
B -4
Division.
Radio Receptor Co., Inc., 251 W. 19th
St., New York 11, N. Y., announces the
availability of Bulletin G -50A, a descriptive sheet which covers the company's new
low- priced transistor Type RR125. The
R11125 has been especially designed to
meet the tremendous demand for a transistor which can be used by the professional or amateur experimenter who desires to familiarize himself with various
circuits utilizing these popular devices.
The bulletin contains specifications and a
diagram for an experimental crystal receiver with one stage of transistor audio
amplification. Requests for copies of Bulletin G -50A should be addressed to the
Sales Department, Semi -Conductor DiviB-5
sion.
RESEARCH
AND DEVELOPMENT
LABORATORIES
Culver City, Los Angeles County, California
Electro- Voice, Inc., Buchanan, Mich,
gives full details for home construction
of the E -V Patrician high -fidelity 4 -way
reproducer in Bulletin 220. Utilizes the
Klipsch principle of folded corner -horn
loading with extended taper rate down to
35 cps for augmented bass reproduction.
Included in the bulletin are a listing of all
components required together with prices
and full constructional details for cabiB -6
netry. Available on request.
AUDIO
4
www.americanradiohistory.com
AmericanRadioHistory.Com
AUGUST, 1955
-
MAGNET WIRE
HOOK-UP WIR
.MICROPHONE CABLE
INTERCOM CABLE
ROADCAST
AUDIO CABLES
SOUND SYSTEM CABLES
AUDIO
o
AUGUST,
1955
www.americanradiohistory.com
AmericanRadioHistory.Com
ç8la kyeNrs
Aug. 24 -26--- Western Electronic Show and
Convention, I.R.E., Civic Auditorium,
San Francisco, Calif.
Aug. 26-Sept. 4-The Great German Radio,
Television, and Phono Exhibition, Dfisseldorf, Germany.
Sept. 12-16 -Tenth Annual Instrument
Conference and Exhibit (International),
presented by the Instrument Society of
America, Shrine Exposition Hall and
Auditorium, Los Angeles, Calif.
Sept. 23-24 -Fifth Annual Fall Symposium
of the I.R.E. Professional Group on
Broadcast Transmission Systems, Hamilton Hotel, Washington, D. C.
Sept. 23-25 -Hi -Fi Home Music Show,
Claremont Hotel, Berkeley, Calif.
Sept. 28-29-The Industrial Electronics
Conference, sponsored jointly by the
Michigan Section of the AIEE and the
Detroit Section of the IRE, Rackham
Memorial Auditorium, Detroit, Mich.
Sept. 30 -Oct. 2-Third Annual High Fidelity Audio Show, NCAS, Sheraton - Palace
Hotel, San Francisco, Calif.
ELECTRONIC ORGAN
KIT
Think of it! A full -sized concert organ that you build yourself for less than
half the cost of a comparable instrument if you bought it factory built. Two
61 -note manuals and a standard 32 -note pedal keyboard make it possible
for you to play the music you have always wanted in your home, and the
nineteen stops and six couplers give you complete flexibility of tone. The
Schober Electronic Organ is an instrument you will enjoy building -one that
you will be proud to own and play.
EASY TO PAY FOR
EASY TO BUILD
EASY TO PLAY
Construction is not complicated nor particularly difficult, even though there
are many parts to put together. Instructions are clear and complete, the
console comes already assembled and finished, and with all mounting
holes already predrilled. The woodwork is finished, and the bench and pedal
clavier are ready to use. But best of all, you pay as you build -as little as
$22.50 gets you started. As you finish one section, you can order another,
and spread out the cost as long as you wish.
HEAR IT IN YOUR OWN HOME -Send only $2.00 (re-
-
-
fundable when you purchase your first kit section) for a
10 -inch LP demonstration record which shows you just
what your own instrument will sound like when you
complete it. One side, played by a professional organist,
shows the fine tone of the organ. The other side contains
twelve bands of tones, each note of the scale, which
you will use for tuning the organ, or for tuning any other
musical instrument.
THE
Yd2I%.
ORGAN CORPORATION
NEW HYDE PARK, NEW YORK
New York 17. New York
Export Dept. TELESCO, 270 Park Ave.
THE SCHOBER ORGAN CORPORATION, Dept. 18
Dail Street, New Hyde Park, New York
Gentlemen:
Please send me your free booklet describing the new Schober Electronic Organ
completely. I understand that this places me under no obligation whatever, and
that the booklet is to be sent to me at no cost.
Enclosed is $2.00. Please send me the Demonstration Record. Also include the
credit certificate good for this amount on my first purchase of any Schober
Organ Kit sections.
35
NAME (Please print/
ADDRESS
CITY
ZONE
STATE
Sept. 30 -Oct. 2-The 1955 High Fidelity
Show, Palmer House, Chicago.
5- National Electronics Conference,
Hotel Sherman, Chicago.
Oct. 3-
Oct. 13- 16-The Audio Fair and the Seventh Annual Convention of the Audio
Engineering Society. Hotel New Yorker,
\rw York City.
Oct. 21-23-New England High Fidelity
and Music Show, Hotel Touraine, Boston, Mass.
Nov. 3-4-- Eighth Annual Electronics Conference, sponsored by the Kansas City
Section of the IRE, Town House, Kansas City, Kansas. Subjects to be covered:
Components, Microwaves, Automation,
and Audio. (Committee can be reached
at P. O. Box 391, Kansas City 41, Mo.)
Nov. 4-6-Philadelphia High Fidelity
Show, Benjamin Franklin Hotel, Philadelphia. Pa. A fifty -cent admission charge
has been agreed upon to assure attendance
by an interested hi -fi conscious audience.
Nov. 3-6--First Mexican Audio Fair, Hotel
Reforma, Mexico City. For information,
write Mario R. Aguilar, Lopez 43 -301,
Mexico 1, D. F.
Jan. 18- 20- Canadian Audio Show, Windsor Hotel, Montreal, Canada. Managing
Director, Emery Justus, 1022 Sherbrooke
St. W. Montreal, P. Q.
AUDIO
6
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AUGUST, 1955
75 mils
thinner
"SCOTCH " Brand's new
thin groove
reel prevents tape tangles!
NO MORE "ZIG -ZAG" WIND
Write on it!
to tangle tape! "SCOTCH" Brand has
come up with a sure way to make magnetic tape wind smoother
and reduce side play to a minimum. It's "SCOTCH" Brand's new,
103/z " professional reel. Made from glass- reinforced plastic, the
new reel measures just .270' wide
75 mils thinner between
flanges than older type aluminum reels. Offers plenty of other advantages, too! "SCOTCH" Brand's reel spins true because of
W center hole conforming to RETMA specifications. Won't
dent or warp, thanks to tough fiber glass
reinforcement. And you can write on it for
identification. All these features, plus exclusive slot threading
no increase in cost.
...
Won't dent...
won't warp!
-at
/6 center hole
5
for better
balance
REO. U.B. FAT. OFF.
SCOTCH `
BRAND
q
New 101/2:1;
Reel
The term "SCOTCH" and the plaid design are registered trademarks for Magnetic Tape made in U.S.A. by MINNESOTA MINING AND MFG.
CO., St. Paul 6, Minn. Export Sales Office: 99 Park Avenue, New York 16, N.Y.
AUDIO
AUGUST, 1955
7
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EDITOR'S REPORT
1955 WESCON
and not devoted
are the many audio shows
throughout the country -the West's biggest electronic event of the year is the Western Electronic Show
and Convention -WESCON -which opens in San
Francisco's Civic Auditorium on August 24 for a three
day run. Always a good show-comparable to the mammoth IRE show in New York every March
opens
our eyes to the fact that there is more to the electronics
industry than audio, and actually lifts us out of the trees
so that we get a glimpse of the forest.
But even though little audio equipment will be exhibited we must always bear in mind that the components which go into audio equipment come from the
laboratories of manufacturers who also supply the materials that go into microwave, radar, computer, automation, and dozens of other fields. It is the result of
constant improvement demanded by the rigorous requirements of military and certain types of commercial
applications that shows up in more reliable components that go into audio equipment, for continuing
research could not he supported by the audio industry
alone-consider, for example, the improvement in such
a "simple" item as the common 1/2 -watt resistor over
the past twenty years.
But strangely enough, many electronic engineers who
pour over the complications of computers during the
day, or whose work may be with automation or circuit
development or instrumentation or medical electronics
-many of these engineers turn to audio for a hobby.
Electronics is likely to get into the blood to the extent
that a person feels compelled to select it as an avocation
as well as a vocation. As a hobby, audio is rewarding,
for one can see the result -or hear it -and there is
relatively little need in the average home for a computor,
although we did see a $15,000 device used in sonar training during the war that would have made a delightful
game for the play room.
We are grateful for the reception accorded us at the
professional shows and we are constantly pleased that
AUDIO is read and enjoyed by the engineer as well as the
non-technical music lover. So we'll be in San Francisco
with our eyes wide open at the hundreds of interesting
and informative exhibits, and we hope we'll see many of
our old friends there.
WRILE NOT OPEN TO THE PUBLIC
solely to audio
-as
-it
AUDIO IN CANADA
Just as there are Many happenings in Melbourne
which are of little interest or import to the resident of
Memphis, so also are there occurrences in Vancouver and
the world of audio-that might be of great
Toronto
interest to a reader in Winnipeg. And AUDIO has many
readers from north of the border who-so far-have
no direct line on what the audio industry in their own
country may be doing, and judging from the turnout of
non -U. S. equipment at the audio show in Toronto last
-in
April then. is plenty doing up there. To provide a medium for the dissemination of audio information originating in and of interest principally to residents of Canada,
AUDIO will include an additional section in those copies
which go to Canadian subscribers, commencing with
the October issue.
This section will not contain any technical articles,
since these are considered of interest to everyone, and
as such are accepted from everywhere. It will be devoted
primarily to announcements of new products and new
literature and to news of the audio industry in Canada.
Data about equipment that is available in Canada but
not in the U. S. is also welcome, and it is hoped that
this section will serve a useful purpose.
Emery Justus, well known in New York circles and
now the entrepreneur of the Canadian Audio Shows,
becomes our Canadian Editor, with offices at 1022 Sherbrooke St. West, Montreal, P. Q., and will welcome
announcements of new products and literature from
Canadian manufacturers who wish to have them read
by audio engineers and hobbyists in Canada. He will also
accept subscriptions and will act as agent with respect
to advertising in the Canadian section.
We hope our Canadian readers will consider this section as their own and that they will find it useful and
entertaining.
INTRODUCING -THE TIBIA,
a new quarterly magazine devoted to the interests of
those who have nostalgic memories of the theater organ
and who-not wishing to see it pass into oblivion -are
doing something about it. Just before the Audio Fair
in Los Angeles last February, the American Association
of Theater Organ Enthusiasts was formed, and THE
TIBIA was proposed as a magazine to chronicle its
doings. While rather a limited field, it would appear to
the unenlightened, it develops that there is a great number of people who are very much interested in this particular type of organ -as well as almost a whole generation of people who have grown up since the advent of
talkies and who has not been thrilled by the "mighty
Wurlitzer" or Robert Morton, or whatever. THE TIBIA
will be published by Radio Magazines, Inc. for the
ATOE, but one does not have to be a member of ATOE
to read or subscribe to this journal. The first issue
Fall, 1955 -will be out this month.
(For the really unenlightened, Tibia is the name of
an organ pipe that is indigenous to the theater organ,
just as the Diapason is to the classic organ. And
Diapason is a magazine, also.)
-
the 3rd audio anthology
This is not a commercial announcement -just a hint
of the future. It is expected that the 3rd audio anthology
will be on sale at the Audio Fair in October. Saute size,
same number of pages, sane price, but all new material,
covering from July, 1952, to June, 1955. And this time,
we won't advertise it until it's actually on the presses.
AUDIO
8
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AmericanRadioHistory.Com
AUGUST, 1955
... and leaders
today!
Ask those who know -the experienced professionals and the
veteran hi -fi owners -and you'll get answers like these:
"Pickering was first to introduce many high fidelity
features that have become accepted standards today."
"Pickering has always been the pace- setter
in the race for perfection."
"Pickering still sets the goals to which others aspire."
There are good reasons for such praise. Every product bearing the
precision engineered to give optimum performance.
rigidly tested before it reaches the dealer
... subjected to the severest quality control procedures to make sure
that every
component comes up to the high standards expected of
Pickering equipment.
Pickering name
is
Each individual component is
®
If you want the best that high fidelity can offer ... if you are willing to
invest just a little more to get a lot more listening pleasure, now is the time
to ask your dealer for a demonstration with Pickering components. See
if you, too, don't hear the difference!
PICKERING and company incorporated
Oceanside, L.I., New Y
PICKERING PROFESSIONAL AUDIO COMPONENTS
``g; d.ede 164 Ca/74
...Demonstrated and sold by Leading Radio Parts Distributors everywhere. For the
AUDIO
one nearest you and
AUGUST, 1955
for detailed li
;
write Dept.
A -8
9
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AmericanRadioHistory.Com
On the ocean floor... life begins at 5000 hours
Electron tubes (right) for the Transatlantic
Telephone Cable between Newfoundland and
the British Isles are being handmade at Bell
Laboratories. Life test bank is shown left. The
cable system, which can carry 36 simultaneous conversations, is a joint enterprise of the
American Telephone and Telegraph Company.
the British Post Office and the Canadian Overseas Telecommunications Corporation.
When the world's first transoceanic
telephone cable is laid across the
Atlantic it will contain hundreds
of electron tubes needed to amplify
voices. Deep on the ocean floor
these tubes must keep on working,
year after year, far beyond reach
of ordinary repair services.
But survival alone is not enough.
During the test each tube is exhaustively studied for behavior that
may foreshadow trouble years later.
Tubes that show even a hint of
weakness are discarded. For the
good ones, a life of many years can
be safely predicted.
Bell Telephone Laboratories
scientists have developed a tube of
unique endurance. Before a tube is
even considered for use in the cable
it is operated for 5000 hours under
full voltage -more than the entire
life of many tubes.
Bell Telephone Laboratories
scientists began their quest for this
ocean -floor tube many years ago.
Now it is ready -another example
of the foresightedness in research
that helps keep the Bell Telephone
System the world's best.
BELL TELEPHONE LABORATORIES
Improving telephone service for America provides careers
for creative men in scientific and technical fields
www.americanradiohistory.com
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Amplifier Uses Cheap
Output Transformer
AND WILLIAM HELLMAN
NATHAN GROSSMAN
Pleasant sound does not necessarily mean highest fidelity. It can be obtained with inexpensive output
transformers and by using feedback. The authors show designs for single -ended and push -pull jobs.
explore the
possibilities of obtaining high fidelity
from the average service -replacement
output transformer produced by leading
transformer manufacturers. These generally sell for about $3.00, with those
intended for higher outputs running up
to about $6.00. They generally have a
primary inductance of 7 to 10 henries
depending upon whether they are intended for single -ended or push -pull
operation.
It is the low load presented by the
primaries of these transformers which
would ordinarily prevent their use in
connection with quality amplifiers. The
gain of the output stage depends upon
the matching of the plate impedance of
the tube used and the impedance produced by the inductance of the primary
of the output transformer. Thus, a tube
with a high plate impedance requires
greater impedance from the primary
inductance for good results. Moreover,
to obtain the same response in the bass
frequencies as in the middle frequencies
also necessitates a high inductance, because the impedance of the inductance
falls off proportionately to the decline
in frequency.
To get the best results from these
transformers then requires that they be
used in conjunction with output tubes
which require relatively low- impedance
loads such as the 6B4 and the 6L6, which
THE AUTHORS SET OUT to
operate satisfactorily with loads of 2500
ohms, and the 6Y6 and 50L6, which will
do likewise with loads of 1500 to 2000
ohms.
Uniformity of response can be obtained by using inverse feedback in a
proper circuit. For example, 6 db of
feedback in the circuit of Fig. 1 will flatten out the response of such a transformer, when used with a 6L6 in the
output stage, down to 100 cps. Twenty
db feedback will flatten out the response
down to 20 cps (see Fig. 2). These results are much like those obtainable from
increasing the primary inductance by
like factors.
Such a transformer when used in the
circuit of Fig. 1 without R, and fed
into a resistive load produced the following harmonics : at 100 cps :
Watts
1
2
6.5
8.5%
12.0
20.0
3rd
4th
5th
0.49%
0.68
2.00
0.28%
0.50
2.80
0.12%
0.10
1.60
At the same frequency but with the
application of a factor of about 20 db
of inverse feedback through Rs from
the secondary of the output transformer
the following harmonics were produced
:
Watts
1
.St.,
2nd
2017 E. 24th St. and ** 1861 E. 24th
Brooklyn 29, N. Y.
2
4
2nd
3rd
4th
5th
0.80%
0.13%
0.30
0.01%
.03%
1.20
2.20
Fig. 2. Curve
shows original
quency
Fig.
1
.065
0.32
0.90
.04
0.16
Under the same conditions but with
an input frequency of 1000 cps the following harmonics were produced:
Watts
2
4
6.5
2nd
3rd
4th
0.34
0.66
0.14
0.24
0.52
0.90
.02
.05
0.15
1.20
1.6
5th
.04
0.14
0.32
From these tabulations several conclusions can be drawn. First, for the
reproduction of speech and treble instruments this is a very fine amplifier. Second, that the harmonic distortion is reduced roughly by the factor of inverse
feedback. Third, that the difference in
the amount of distortion resulting at the
two frequencies at which the measurements were made corresponds roughly
to the factor of difference in gain response without inverse feedback at the
two frequencies.
In an effort to follow up these conclusions and obtain further improvement a
6S J7 was substituted for the 6SF5 in
the driver stage of Fig. 1. The higher
gain of the 6S J7 would permit more
inverse feedback. As the cathode was not
bypassed a further improvement of 25
per cent in gain, and so also in the
amount of inverse feedback, was obtained by connecting the return lead of
the screen bypass capacitor directly to
the cathode instead of the usual connection to ground. Since the screen is
(A)
fre-
response of
25
(A)
amplifier with -
out feedback. Adding
20 db of feedback
gives
response
of
curve (B).
m 20
ás
w
5
(B1
___
Fig. 1. The basic circuit employs feedback from
the transformer secondary. Value of R determines feedback.
AUDIO
w
FREOUENC .
AUGUST, 1955
IMO
'0p°°
CYCLES PER SECONb
11
www.americanradiohistory.com
AmericanRadioHistory.Com
really acting as the plate of a triode
this change in circuitry avoids degeneration caused by permitting a.c. from
the screen to pass through the cathode
resistor.
It was further observed that to get
the same amount of inverse feedback at
60 cps as at 400 cps it was necessary to
increase the screen bypass capacitor
from 0.5 to 8µf.
By connecting the plate of the output
stage through a resistor and capacitor
to the cathode of the driver stage as
shown in Fig. 3, a further increase in
inverse feedback can be obtained. However, on checking the over -all response
of this arrangement it was found that
with a feedback of only 16 db in the
middle frequencies there was no response
at 20 cps and that above 800 cps there
was a gradual loss which amounted to
10 db at 12,000 cps. This meant that
there was positive feedback present and
more of it at the treble frequencies. The
squeals which emanated from the loudspeaker when rotating the dial of the
FM tuner showed that there was oscillation. This approach was, therefore.
abandoned.
A 6SH7, which has a higher gain than
a 6SJ7, was then substituted, and two
loops of inverse feedback were employed.
The loop through R7 in Fig. 4 served to
flatten out the response from the output
transformer and to reduce any tendency
to oscillate. It also .produced a sweeter
"feel," much like that of a triode, which
the 6L6 resembled after this reduction
in its gain. A 6AU6 may be substituted
for the 6SH7, but a 6BC5, 6CB6. or
6AG5 cannot be used as these radiate
badly.
The following factors of inverse feedback were obtained from the amplifier
FEED-
above tables and compensating for the
increase in feedback, it is estimated that
at the 400 -1000-cps point at just below
3 watts there should be less than 1/3
of 1 per cent harmonic distortion, and
at the 60 -cps point, after allowance for
the lower frequency, 1.5 per cent harmonic distortion.
Where a tone- compensator stage is
desired and where a variable-reluctance
cartridge is to be used, the circuit shown
in Fig. 5 is suggested. It may be necessary to increase the values of either the
capacitor or the resistor, or of both, in
the decoupling circuits at points A or B
in order to overcome motor -boating,
which can occur in this amplifier at
a frequency as low as one half cycle
per second.
A pair of 50L6's connected in push pull were tried in the circuit shown in
Fig. 5. An inverse feedback factor of
about 7 and an undistorted output of
about 3 watts was obtained at 60 cps.
Less inverse feedback was needed for
this result because the push -pull operation cancelled nearly all the 2nd and 4th
harmonics and also the magnetizing
effect of the d.c. in the windings of the
primary of the output transformer. This
latter raised effective input inductance.
The 3- megohm volume control R, permitted the use of a broad -range crystal
cartridge. Capacitor C, and resistor R,
furnished some Fletcher -Munson compensation. Capacitor C, served to overcome losses in the shielded cable from
the pick -up to the amplifier and also
to afford some Fletcher- Munson compensation in the treble frequencies. Various values of C, should he tried until
the most pleasing result is obtained. An
FM tuner with a 1 -volt output could
he used to drive this amplifier to nearly
(Continued on page 54)
TO SPEAKER
BACK
ti
6SJ7
fir
IN
Fig. 3. Obtaining the feedback path from the
plate of the output tube gave higher feedback
but poorer response.
shown in Fig. 4 while using a Stancor
A -3830 output transformer:
Frequency
60
400
1st Loop 2nd Loop
2.8 times
4.2 times
6.5 times
6.5 times
Total
18.2 times
27.3 times
With this amplifier signals were heard
below 20 cps and a slight loss of amplification was measured at 300 kc. The
break -up of the sine wave on the oscilloscope (generally at 3 per cent total harmonic distortion) at 60 cps occurred
at 3 watts, and at 400 cps at about 4
watts. Amplifiers which employ large
amounts of inverse feedback show low
distortion up to a point which is considerably below the ratings published in
the tube manuals and beyond which
there is a sharp and very great increase
in harmonic distortion. Based upon the
1500/I w.
AAN'
R16
12517
0.33 meg.
C4
0 25
rk
e
5016
clo
I00/25
SPKR
CS
CII
e
s
0.33 meg
R13
15/5w..
/VW
I17v. o.c.
I
C7
SEL.
RECT.
RI4
100/5w.
AAM
N
150mlICB
T.01
40/250
t
5016
Fig. 4.
5016
'
C9
TI00,
250
12517
(HO The f'nal single -ended amplifier, with two feedback connections, one from the plate of the output tube to the plate of the 6SH7
and the other from the secondary of the transformer to the 65117 cathode. Fig. 5. (right) The push -pull version of the amplifier.
AUDIO
12
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AUGUST, 1955
Soldering Tips for Hobbyists
LEONARD CARDUNER
Soldering is not at all a difficult operation
if a few simple rulzs of practice are followed.
THAT "n0 soldering is
necessary," which occasionally appears in certain components manufacturers' advertisements, seems to indicate that some audio enthusiasts think
that soldering is a difficult process. However, if a few simple principles are understood and the necessary inexpensive
equipment is available, any audio enthusiast should be able to tackle simple
soldering jobs without trepidation.
While there are both hard and soft
solders, the usual type of solder which
is used in the manufacture of electronic
equipment is of the soft variety and that
is the only type we need consider. The
best solders are made from pure tin and
lead and, oddly enough, the melting
points of these respective metals are both
above the melting point of a mixture of
them, which is called an alloy. Usually,
the solders used for wire -to -lug joints in
electronic work contain percentages of
tin between 40 and 60 and generally the
higher the tin content the lower the melting point of the solder alloy. All the
usual tin -lead alloys start to melt at the
sane temperature which is about 183
deg. C. We say "start to melt" because
all solder alloys (except the eutectic
which is 63 per cent of tin and 37 per
cent of lead) have what is often called
a plastic range. That is, they start to
melt at 183 deg. C. but do not become
liquid until they reach a higher temperature. Incidentally, knowledgeable solderers always quote the tin content first
when describing an alloy.
THE CLAIM
Why 60/40 Is Best
It may well be asked why there are
various alloys of tin and lead at all. The
reason is that aside from the need for
higher melting -point solders in certain
special applications, there is a very considerable difference in price between
the two metals. Tin costs roughly 7 times
the price of lead. When sufficient heat
is available to make the solder joints
there will not be appreciable difference between joints made with 60/40
alloy and those made with 40/60 alloy,
except that the former will look brighter.
However, many of the leading high quality audio component manufacturers
use only 60/40 alloy. and if a few cents
difference is of little consequence, the
knowledgeable audio enthusiast will do
well to standardize on 60/40 alloy, or
at least not use a lower percentage of tin
than 50 per cent.
Solders can be used for joining prac* Ersin Multicore Solders, 164 Duane St.,
New York 13, N. Y.
AUDIO
tically any metals except aluminum. It
is well to realize that when a solder joint
is made it is not just a question of stick ing two metals together. If the correct
soldering technique is employed, the
solder alloy will actually penetrate the
surfaces of the metals by a form of
molecular action.
However, besides having alloys made
from the purest tin and lead, it is also
necessary to use a flux. Most metals,
unless protected by a coating such as
nickel, tin, or paint, tend to oxidize and
euthu.iast to use a nonacid type in order
to ensure that solder joints do not become corroded. When solder is used in
the fabrication of nonelectrical equipment, ranging from automobiles to jewelry, acid fluxes are usually employed
because the manufacturer does not have
to worry about corrosion ; the soldered
surfaces are always subsequently washed
and it is best to use the fastest possible
flux because the parts to be soldered
are often contaminated with grease or
oil. Luckily, the surfaces that have to
be soldered in an electronic equipment
are usually fairly free from contamination and thus a noncorrosive flux can be
used. Most noncorrosive fluxes are made
largely from rosin which has been specially activated by complex and secret
processes to allow very much faster
soldering than the natural rosin. Kester
5 flux and Ersin Multicore 366 are
examples of these activated, noncorrosive fluxes incorporated in solder wire.
Although cored solders vary in diameter from 0.12 to .028 in., any of the
liner gauges may be used, and recently
.064 and .048 in., otherwise known as
Fig. 1. A new iron or one which has lost its
brightness should always be tinned. Clean the
tip to brightness with sandpaper or a fine file
and apply cored solder, making sure it adheres
to the entire tip surface. If a tip is untinned
it will not conduct heat to the work.
it becomes difficult to get the solder alloy
to penetrate the surface. In addition,
when metals are heated further oxidation
tends to form. A flux is, therefore, used
in order to remove the surface oxides
prior to the application of the solder
alloy as well as to prevent them from
forming during the soldering operation.
About a quarter of a century or so ago,
most soldering jobs were undertaken
with a separate flux and a stick of solder.
and were it not for the introduction of
cored solder in wire form it is doubtful
that the complex assembly of hundreds
of different components in amplifiers,
television sets, and the like could have
been economically possible.
Cored solder containing one or more
cores is usually supplied in wire form
with the flux in a central core or, in the
more modern type of solder, in 3 or even
5 cores. The idea of the multicore solder,
which originated in England, is that
by having several cores of flux, it is certain there will be no interruptions in the
flux supply and that the flux melts out
of the solder more quickly than when it
is contained in one core.
In considering the use of cored solder
it is absolutely essential for the audio
AUGUST, 1955
16 and 18 S. W. G. have become the
usual standards for electronic work.
The 60/40 alloy in 18 gauge is usually
found to be especially suitable for fine
electronic soldering.
Soldering Tools -Guns Or Irons
While a good- quality cored solder
can, under some circumstances, be used
without any soldering implement, it will
usually be found far more convenient to
use either a soldering gun or a soldering
iron. Solder guns are transformers
which reduce the a.c. voltage to about
4 and then apply it across a copper wire.
which heats up very rapidly. The advantage of using a solder gun is that it heats
up in a second or two. The disadvantage
is that it is usually rather heavy and
more expensive than the simple form of
electric soldering iron. Some soldering
irons work from a low voltage and require a transformer. The majority, however, operate directly from the a.c. line
and consist of a heating element wound
around or buried in a copper rod, the
end of which is called the soldering bit.
Whether a soldering gun or a soldering iron is chosen, it is essential that
the end of the gun or the solder bit be
properly "tinned." This job is done by
heating up the tool, rubbing it with sandpaper or a file to remove oxide, and
applying cored solder to the tip as in
Fig 1, until it is evenly coated with the
solder.
(Continued on page 51)
13
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This photo, taken during an evening concert, gives
a
small idea of the Bowl's size. In the right foreground
is
the brick control tower.
Stereophonic Sound System
Covers Hollywood Bowl
OLIVER BERLINER
One of the country's biggest and newest sound reinforcement systems has been set up for stereophony.
The stereophony and the over -all sound quality make the reinforcement as unobtrusive as it should be.
CnMMERCIAL
SOUND
SYSTEMS
have
come a long way, from the early
trial- and -error days of carbon mi-
crophones and electrodynamic loudspeakers to the present broadcast -quality
apparatus and sound -level measuring.
The industry in all its phases-paging,
warning, background, music, intercommunication, and sound reinforcement
is slowly progressing from an art to a
science.
A prime example of this coming of
age is the new sound reinforcement system at the world famous Hollywood
Bowl in California. Sound reinforcement is probably the most critical of
the various types of audio systems; and
at the Bowl the designers' conclusions
are put to the most grueling tests. The
object is to provide wide- range, undistorted sound to 20,000 patrons in the
open air in such a manner that whenever
possible they are not conscious that there
is sound reinforcement.
*1007 No. Roxbury Dr., Beverly Hills,
-
Calif.
First it is necessary to review the
objectives of the Hollywood Bowl, which
was started in 1925. About three seasons
ago the authorities decided that the Bowl
could be used to greater advantage if the
scope of its operations were increased
beyond the customary summer concert
sessions and the usual Easter Sunrise
Services. With proper planning, the
operating season could be lengthened
and the number and types of functions
materially increased. This could include
plays, musicals, meetings, television and
radio shows, political and other special
events.
To properly accomplish this meant
complete redesign of the lighting and
sound systems. Besides this, rebuilding
of at least part of the seating area, plus
construction of new audience entrances
and ramps would be required. For our
purposes we are concerned principally
with the effect this plan had on the sound
reinforcement system, the most critical
and important part of the Hollywood
Bowl's production facilities.
At this time, Mr. A. W. Leach, a
prominent sound engineer, was engaged
to act as impartial supervisor, designer,
and coordinator for the Bowl. And in
the winter of 1952, RCA's John Volk mann was brought out to make the basic
sound measurements and surveys. Upon
these results would depend the success
of the system acoustically.
Taking a cue from the popularity of
stereophonic sound systems in theatres,
Leach decided that perhaps this could
be incorporated into the Bowl's facilities
and that not only would it provide a
touch of realism, but it might be generally better and more workable than a
standard (previously used) monaural
channel. Volkmann's measurements
proved this theory valid, and the stereophonic sound system plan was adopted.
Ultimately the acoustic measurements
were completed and the specifications
set. Three important local suppliers of
sound systems were invited to submit
bids and to submit their designs for the
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AUGUST, 1955
the Bowl has a fourth stereo channel
available for special effects or emergencies.
Control Console
Fig. 1. View from rear of the shell shows one
of the twin loudspeaker towers as well as the
three speaker systems atop the shell.
electronic phases of the system. After
careful examination. Leach decided that
all proposals were unacceptable in original form, but that the best parts of each
could be combined to make a final workable plan. Subsequently, the Otto K.
Olesen Company, distributors of RCA
equipment and one of the nation's largest
sound systems suppliers, was selected
to provide and install the equipment.
At this point, it is necessary to take
note of certain aesthetic and nontechnical aspects of the Hollywood Bowl
sound system. Famous musicians, speakers, dancers, and actors from all over
the world come to perform at the Hollywood Bowl. For this reason, the equipment must be so operated and placed that
the audience would be relatively unaware of its use and even existence. Second, a minimum of equipment should be
onstage. Finally, for best realism, the
orchestra should control its own volume
level rather than letting the audio operator do it.
Figure 1 shows a rear view of the
shell covering the stage and of the stage
left (audience's right) loudspeaker
tower. On top of the shell you will see
three RCA theatre-type low-frequency
speakers, each with its own wide -angle
high -frequency horn. These assemblies
were designed by Volkmann and are now
standard RCA theatre equipment. Note
an important fact: these three speaker
combinations represent only the center
stereophonic channel ; for to have them
function as all three channels, would
be to lose the stereophonic effect a mere
few feet from the loudspeakers.
The tower to the left of the shell, containing four loudspeakers (two high frequency units in the center plus a low frequency radiator at the top and at the
bottom) provides the right -hand stereo
channel ; and a similar tower on the
opposite side makes up the necessary
third channel, for a total of seven low and high- frequency assemblies. It is interesting to note that the average
motion -picture-theatre
single -channel
sound system utilizes but one or at most
two of these combinations.
For special productions requiring a
large stage, the shell is rolled off to
stage right on tracks provided for that
purpose. Obviously, the center stereo
channel is lost; so under these circumstances a two -channel sound reinforcement system consisting of the stage
right and left towers is used. Actually,
AUDIO
The main control console is a custom
built unit designed by Walter A. Midcalf, Jr., who is responsible for the design of the entire electronic system, and
consists of a three- section turret and
desk, Fig. 2. It is presently situated in
the front of the second box seat section,
closer to the right side of the audience.
The left element in the photo contains
the patch bay. All of the 36 microphone
receptacles terminate here, as do preamplifier inputs and outputs. Below the
patch bay are decibel meters which are
used for checking output level of the
four main power amplifiers. Many circuits are "normaled" to minimize the
amount of patching.
The center element of the console is
the main operating section. At the top
are the VU meters with their multipliers,
which read output level of the three
stereophonic-channel line amplifiers and
the spare /utility channel. Below these
are gain controls for 10 BA -11A broadcast -type 2 -stage preamplifiers ; and
above each attenuator is its 3- position
transfer key. In the center position the
preamplifier is not in line; press the key
to the right and it is connected to the
program line, while in the left position
it goes to a special audition amplifier.
This is the only amplifier actually in
the console and it allows the audio operator to test the condition and level of
each microphone (and the preamplifier)
before putting it "on the air."
Although there are 36 separate microphone receptacles and circuits, only a
maximum of any 10 may be operated at
a time on this console. On the occasional
situation where more are needed, the
patching bay makes it convenient for
portable mixers to be connected to handle the additional microphones.
Except for the theatre loudspeakers,
all equipment, including the main power
amplifiers, is of broadcast type. This is
essential, not merely to obtain the highest- fidelity sound reproduction, but to
make the system capable of feeding
broadcast and recording studios with
high -quality audio. Among other things,
this helps to minimize the number of
microphones used on the stage. However, since broadcasting necessitates
microphone gain settings different from
those of the public address system, broadcast preamplifiers are bridged across
the outputs of the public address microphone preamplifiers before the gain control. In this manner, the public- addresssystem and broadcast engineers may set
the gain on each microphone to suit
their own separate tastes and requirements, yet only one set of microphones
is used.
Part of the Hycor (Model 4201)
equalizers may be seen at the far right
of Fig. 2, and between them and the
center section of the board are the line
selectors and gain controls for the
binaural headphones. Here either ear
may listen to any one of the four sound
channels for testing or monitoring the
stereophonic effect. Separate volume
control for each earpiece is provided.
Line equalization is a new experiment
at the Hollywood Bowl. So far it has
been used principally for sound effects,
and on concerts of popular music it has
been advantageous in providing for the
audience a sound duplicating that produced in the recording studio, especially
in making certain vocalists sound in the
Bowl as they do on phonogroph records.
Other uses, such as overcoming atmospheric conditions and the immensity of
the Bowl, besides feedback reduction
and to enhance the stereophonic effect,
may serve to show further advantages
of equalization.
Situated below the equalizers on the
console are the power- supply and loudspeaker transfer keys. In the event that
a preamplifier power supply should fail,
depressing the appropriate switch key
will cut it out of the circuit and simultaneously connect the spare. A tally
light indicates this condition both at
the console and in the equipment room.
If one of the loudspeaker driver or power
amplifiers fails, a switch operated at the
console or at the racks transfers the
loudspeaker associated with that amplifier to the spare amplifier. The audio
r
Fig. 2. The main con-
trol console contains
the microphone controls, one of the duplicate patch bays,
and other facilities
described in the text.
AUGUST, 1955
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operator need only patch in the proper
input circuit and the channel is fully
restored. Preamplifiers are substituted in
emergencies merely by patching.
Another switch cancels any patched -in
monitor loudspeaker near enough to a
microphone to cause feedback. The remaining two switches operate a signal
light and buzzer at the lighting control
room and audio equipment room, respectively. This indicates that the audio operator wishes to communicate with that
particular party.
In the desk area of the console, and
directly in front of the center section
are the four master gain controls, one
for each loudspeaker channel. Once the
individual microphone levels have been
set, the equipment may, in most cases,
be controlled by the master gain attenuators, thus greatly simplifying operation.
Where possible the orchestra may control its own level, which is highly desirable and can be done only in public
address work, not in broadcasting or
recording due to the need of a restricted
dynamic range.
former, and an output of 10 ohms. As
the theatre speakers have 250 -ohm dividing networks, high -level impedancechanging transformers mounted in a
subpanel on the wall make this conversion, which also reduces the necessary
wire size of the cable running between
the racks and the loudspeakers. The
Altec A -127A and A -287F amplifiers
contain a meter for checking tube condition.
Rack No. 4 is the principal operations
center of the control room. The main
patching bay is the same as that at the
control console, except that the rack's
bay has precedence over the console.
This means that if a patching operation
is made here it will cancel any setup
that has been or could be made at the
console for that particular circuit. Above
the twin -jack bay is a meter panel for
checking various stages of audio, and
hanging over this is a sound powered
intercom phone.
Directly below the patch bay is a monitor amplifier for checking any of the
The Equipment Room
The sound- equipment room is located
at the base of tower number two (not
the loudspeaker tower), on the right
side of the stage when facing it (see
shell-view photo). A large window
allows the performance to be watched
from here, and the audio console may
be operated from one of the rooms in
this building if desired, along with the
portable remote amplifiers provided by
broadcasters for their own use.
The other room contains the five
equipment racks, four of which are
shown in Fig. 3. Rack No. 1 (on the
far left, not shown) houses amplifiers.
terminations, repeat coils, and accessories for feeding telephone-company
broadcast lines. Rack No. 2 contains the
10 microphone preamplifiers, the four
program amplifiers, and the four preamplifier power supplies. Drop-front
panels permit easy access to above -chassis components. The meter panel allows
the audio operator to make a quick check
on the preamplifier and line amplifier
tubes by cathode- current readings. Below the four BA -13A program amplifiers
are three power- supply-failure switches
with their tally lights. These are duplicates of those at the console and cut in
the spare BX -IE power supply to the
appropriate circuit in the event of a
failure.
The third rack houses the four driver
amplifiers which feed the four main stereophonic loudspeaker power amplifiers
with up to the required 15 watts of audio
power which drives each main amplifier
(rack 5, far right) to a full 75 watts
output. However, each driver /power
amplifier chain is operated at far less
than full power which will greatly prolong their life and minimize components
replacement.
The drivers have 600 ohm input, 15
ohm output, and a maximum gain of
66 db, while the main power amplifiers
have but one stage, with a gain of 7 db.
There is a special 15 -ohm input trans-
Fig. 3. The equipment room contains five racks,
the first being out of sight in this photo,
at
left.
stereophonic channels (this also serves
as a grounds paging amplifier when not
used for concerts) ; and beneath this are
the
loudspeaker - amplifier - failure
switches, which, as do those at the console, cut in the spare driver /power amplifier combination to any circuit where
trouble is encountered. Another switch
on this panel is used for signaling the
console operator that the booth wishes
to converse with him.
For utmost flexibility, it was decided
to place all loudspeakers on a patching
system, but since high currents are encountered in these circuits, Cannon Type
XL connectors were used instead of
standard twin -jacks. This arrangement
appears at the bottom of rack 4. In view
of the fact that it is often essential to
place temporary portable loudspeakers at
certain points, especially for backstage
monitoring or cueing, the loudspeaker
patching bay is a necessity.
Certain additional interesting features
have been incorporated into the Bowl's
over-all sound setup, one of which is a
warning light attached to certain key
microphones. This red light, actuated by
the lever above the gain control for the
microphone, indicates to the performer
that his microphone is on, especially
helpful in cueing and for offstage microphones where the performer cannot
readily follow the action. A tally light
at the audio console announces this condition to the audio operator. All tally
lights and relays are 24- volt-d.c: operated, as is broadcast standard.
Another extremely helpful feature
provided by the Bowl in its endeavor to
deliver complete facilities to outside
organizations, is a special patch bay
which will provide program material
at virtually any desired impedance and
level to newsreel services for feeding
their single- or double- system cameras.
Not only does this greatly simplify their
setup problems, but it eliminates the
cluttering of the stage by a battery of
newsreel microphones. This patch panel
is wired to connectors located just outside of the sound control room, where
the motion picture equipment may be
installed as requirements dictate.
The intercommunication system at
the Hollywood Bowl consists of sound powered telephones, but in a unique
system. The earpieces are bridged
across the terminated output of a 6 -watt
amplifier, while the transmitting pieces
are connected to the low- impedance
microphone input. With this arrangement the possible number of phones in
the system is virtually limitless and the
volume may be adjusted to any required
level. Although sound -powered phones
were not designed to be used in this
manner, the system has been found to
function perfectly.
In an installation of this magnitude,
there naturally are certain acoustic difficulties which must be overcome. One of
these is the problem of echo wherein
the sound from the orchestra bounces
off the front pair of brick lighting towers
and cuts across the first box -seat section
in such a way that these patrons receive
an echo of certain instruments in the
orchestra, depending upon where they
are sifting. The installation of weatherproof (this is a problem in itself) sound
absorbent or deflecting material is being
considered and tested to meet this condition.
Secondly, it was found necessary to
tilt forward the fronts of this first box
section, so that the sound coming directly
to it would be deflected downward rather
than back to the stage. In addition, all
speaker assemblies are directly on a
plane with the front of the shell covering
the stage. This brings them as far forward as possible without being too
close to the audience area and being too
obtrusive; and also it gives the essential
illusion that the sound is coming from
the orchestra, an effect that is so very
necessary for realism.
The volume level of the sound- reinforcement system is set at that point
where the lowest -level musical passage
can just barely be heard at the farthest
point of seating from the stage. This is
determined during the daily rehearsal.
Once this has been set, the orchestra
will control its own dynamic range for
the most part. Of course, where soloists
are concerned, the gain must be carefully watched by the audio operator.
The average power output on each chan(Continued on page 52)
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AUGUST, 1955
How Valid are Sound Truck
Restrictions ?
ALBERT WOODRUFF GRAY
When we see them on the streets we may be inclined to say "There oughta be a
a law agin ..." but we should be informed first. There are laws, but not all "agin."
of the California State
Federation of Labor recently sued
to prevent the enforcement of a
Fresno County ordinance against the
use of loudspeakers.' Labor union members, arrested for violating this ordinance, had contended in their defense
that the ordinance was an invasion of
their right to freedom of speech, guaranteed by the First Amendment of the
United States Constitution.
The ordinance was, "It shall be unAMEMBER
lawful for any person to wilfully make,
emit or transmit or cause to be made,
emit or transmit any loud or raucous
noise upon or from any public highway
or public thoroughfare or from any aircraft of any kind whatever."
The ordinance refined "loud and raucous noise" as "The human voice or any
record or recording thereof, when amplified by any device, whether electrical
or mechanical or otherwise, to such an
extent as to cause it to carry onto private property or to be heard by others
using the public highways or public
thoroughfares. Any sound not included
in the foregoing which is of such volume, intensity or carrying power as to
interfere with the peace and quiet of
persons upon private property or other
users of public thoroughfares."
The California appellate court said a
few months ago in forbidding the enforcement of this ordinance, "It should
be here noted that the emission or transmission of such sounds are made unlawful irrespective of whether such sounds
are of such volume, intensity or carrying
power as to interfere with the peace and
quiet of users of the county highways or
owners of private property.
"Such a limitation upon the use of
the human voice or any recording or
amplification thereof is, in our opinion,
an unconstitutional abridgement and denial of the right of free speech. Under
the provision of this ordinance the use of
radios in private automobiles on county
highways will be prohibited if the sounds
therefrom carry to private property or
could be heard by others using the highways and even the use of the human
voice when amplified otherwise than by
any mechanical device would constitute
a violation of the ordinance when carried
onto private property or heard by others
using the highways."
The distinction of sounds tending to
interfere with the peace and quiet of
highway users in relation to the con*
3712 75th St., Jackson Heights, N. Y.
Haggerty v. Kings County, 256 P.2d
393, California.
AUDIO
stitutional guarantee of free speech,
which has been made by the courts, is
more easily understood when read in
connection with a decision rendered by
a court of that state the previous year.
The ordinance in that instance was in
part, "It shall be unlawful for any person other than a law enforcement or
government agency, to employ a speaker
mounted upon a vehicle for the purpose
of giving instructions, directions, making talks, addresses or lectures, to any
person or assemblage upon or over any
highway without first obtaining a permit
therefore as herein provided. * * The
Board of Supervisors shall grant such
permit at said time unless there is presented to the Board at the time of said
consideration substantial and convincing
evidence of a clear and present danger
that the granting of such permit will
result in the obstruction of the orderly
movement of traffic or the peaceable
passage or presence of persons to, over
or upon the public highways and other
popular places, or disorder or unlawful
conduct, or unlawful injury of persons,
or destruction of life or property, or
tending to incite crime, or an invasion
of the rights of privacy, or threatening
the overthrow of the lawfully established
government by force, in which case said
permit may be denied."
Here the court held that this ordinance, which restricted but did not prohibit the use of loudspeakers, did not
violate the constitutional guarantee of
free speech.
"This ordinance regulates the use of
loudspeakers and is not in our opinion
unconstitutional and void as an unlawful restraint upon the right of free
speech. It is the privilege of all persons
to use the public highways and the right
of free speech thereon cannot be
abridged or denied. However the use of
such highways may be regulated and
controlled in order to assure the safety
and convenience of the traveling public.
The Board of Supervisors of the county
has authority to specify without unfair
discrimination the time, place and manner of such use in relation to other
proper use of the highways.
"The use of vehicles equipped with
loudspeakers emitting loud and raucous
noises and objectionable amplified sound
on public highways is subject to legislative control. This ordinance does not
deny the right of free speech or assembly. By its terms a permit to use a
loudspeaker can only be denied upon
presentation to the Board of Supervisors
of substantial and convincing evidence
AUGUST, 1955
* * The
standards controlling the action of the
Board of Supervisors are specifically
set forth and enumerated."
This rule of law that permits a state
or municipal government to regulate or
control providing that it does not deny
the use of loudspeakers on the streets or
highways, is now firmly established by
two recent decisions of the United States
Supreme Court.
The first involved an ordinance of
Lockport, New York, that, "It shall be
unlawful for any person to maintain or
operate in any building or on any
premises or on any automobile, motor
truck or other motor vehicle, any radio
device or loudspeaker or any device of
any kind whereby the sound therefrom
is cast directly upon the streets or public
places and where such device is maintained for advertising purposes or for
the purpose of attracting attention of
the passing public, or which is so placed
and operated that the sounds coming
therefrom can be heard to the annoyance
and inconvenience of drivers upon any
streets or public places or of persons
in neighboring places.
"Exception.- Public dissemination,
through radio loudspeakers, of items of
news and matters of public concern and
athletic activities, shall not be deemed a
violation of this section provided that
the same be done under permission obtained from the chief of police."
A member of Jehovah's Witnesses
was granted a permit by the chief of
police to deliver religious lectures from
the top of his automobile. Complaints
were made and a second permit was
refused. Nevertheless he continued the
loudspeaker talks, was arrested, convicted and sentenced to fine and imprisonment.
He appealed the conviction to the
highest court of the state,2 contending
that the ordinance was a violation of
the First Amendment of the Federal
Constitution that, "Congress shall make
no law * * abridging the freedom of
of a clear and present danger.
speech."
That court affirmed the conviction and
the controversy was carried to the Supreme Court of the United States. That
court in setting aside the conviction
and holding the ordinance unconstitutional and void, said,
"The right to be heard is placed in
the uncontrolled discretion of the chief
(Continued on page 45)
a Sala v. People of the State of New
York, 334 U.S. 558, rev'g. 72 N.E.2d 323,
New York.
17
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The Languad Expert Looks At Hi -Fi
GEORGE L. AUGSPURGER
This could happen -provided we don't run out of adjectives.
OF PEOPLE don't believe me
when I tell them that my friend,
George Anthrubus, is a "languad"
scholar. They always think I'm saying
"languid" and then yes, yes, they know
the type: stoop -shouldered, horn -rimmed
glasses, and all the rest. Why do I associate with somebody like that? And then
I have to tell them that what I really
said was "languad" which is Mr. Anthrubus' own word for the kind of
language that ad writers use. "Only in
advertising nomenclature-in languad, to
coin a word
says Mr. Anthrubus.
"are the traditional iambic pentameter
of Shakespeare, the grandiose adjectives
of Milton, and the polished phraseology
of Pope synthesized into one artistic
triumph of our age." He really means
it too. He spends his time copying and
classifying top-notch examples of languad and having them printed up in
bound volumes at his own expense. All
of which may go to make a slightly
ALOT
-"
* Audio Research Laboratories, 7041 N.
14th Place, Phoenix, Aria.
eccentric character, but still a real char- the pile of stuff with my hand and said,
acter, if you know what I mean. When "I knew you were sort of a hi -fi fan,
you start feeling complacent, there's but isn't all this a little overpowering
nothing like a little chat with George for an amateur ?"
Anthrubus to make you comfortably dis"Of course not," answered George,
oriented once again.
"although, as you say, I am merely, as
Last week, for example, I suspected Pickering puts it, 'a connoisseur of
that perhaps things were running a little music.' But we are assured that hi -fi
too smoothly so I took off the afternoon must be experienced to be appreciated,
to pay a social call on Mr. A. personally. and according to my languad references,
George seemed happy to have somebody this amount of equipment is the very
to talk to, as usual, but I noticed that he minimum for such an experience."
had sort of a sly smile on his face as if
"How does it work ?" I asked, a little
he had a big secret and just couldn't jealous at the comparison with my own
wait to get across the punch line. Sure small installation.
enough, I walked into his big studio,
My dear boy," responded Anthrubus,
and there besides the usual magazines "This system brings you music as you
and clippings littering up the place, were have longed to hear it. It is so life-like
enough top -quality tape recorders, and natural it cannot be described. It
speakers, amplifiers, and turntables to has an on -stage realism of tone and a
make NBC jealous. Anthrubus stood in naturalness of reproduction unparalleled
the middle of the floor just sort of idly in the art. I ani satisfied that only the
adjusting his necktie and beaming like a best engineering resources can produce
TV announcer.
such gratifying performance."
I sensed that I was expected to pro"I suppose the response curves look
vide something in the way of a fanfare, pretty good," I said surveying the array
so in my best awed manner I indicated of chassis and cabinets.
"I assure you," said Anthrubus archly,
"that the psychological factors affecting
music are given as much weight as the
measurable quantities."
By this time I had wandered over to
a series of chrome -plated, rack -mounted
devices which proved to be two enormous power amplifiers and a series of
preamps and equalizers that filled up the
rest of the rack. "This, uh, really does
the job, eh ?" I asked lamely.
"This," said George patting the electronic skyscraper fondly, "is designed
for the audio enthusiast with the professional ear. It is a perfect companion
for those who hear the difference; for
those who treasure the art of listening."
"It does look professional." I ventured.
"It is the very picture of scintillating
synmietry," said 11Ir. A., by now rising
to the eloquence of his languad quotes.
"It uses an ultra- linear circuit that
captivates music lovers with its thrilling
accurate reproduction. It is paramount
primarily by the excellence of its balanced frequencies, but it has a galaxy
of other features that total to the finest
instrument that electronic engineers
have been able to devise. It has perfect
stability, a hunt level below the threshold of audibility. absolute tonal balance,
and a sweep and brilliance of reproduction unsurpassed. Furthermore, reserve
power has not been !"
"Reserve power has not been what ?"
I murmured, scarcely daring to interrupt.
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AUGUST, 1955
tioned, trying to catch up with my and demanded, "Do you know what this
results in ?"
friend.
"Full-bodied response, I should say."
"Of course," snapped George, "It
brings out the latent music that other I hazarded.
"Not only full -bodied response," said
pickups leave untouched. It brings you
record fidelity that you never believed the expert scornfully, "but minimized
possible. And it gives reproduction ..." speaker hangover, unequalled realism of
tone, room- presence sound, perfect aural
George hesitated.
"Reproduction unparalleled ?" I tried. balance, and sufficient definition to suit
"No," responded the languad expert. the fastidious listener. Not only that,
"Reproduction so long sought after and but it trumpets. Do you know what it
trumpets ?"
now a ..."
I was taken off guard and said I
With a flash of inspiration I finished
up, ". . . now a fact !" snappy as you didn't know it trumpeted. Glad tidings
came to mind, but I didn't think that
please.
"Bravo !" cried George. "You'll be a answer would improve Anthrubus' dislanguad ham yourself before you know position.
"It trumpets a vibrant quality of timit." I tried a deprecating smile, but I
was really touched. Exhilarated by my bre altogether unique in the reproducsuccess, I turned to a giant theater horn tion of music !" shouted George, his
good spirits restored. "Think of hearing
in one corner and said lightly, "I suppose that gives you plenty of full, clean natural sound across . .." he said, grinning.
bass ?"
"Across ?" I repeated blankly.
George beamed. "It is really music
"Across the entire musical spectrum."
you can feel," he said. "It is more than a
speaker it has a simulated point- source, finished Anthrubus. "Its dynamic energy
radial diffraction and projection prin- adds a flood of color to the musical
ciples, high acoustic damping, a care- canvas. It has clarity and crispness
fully designed throat configuration, a rivalling the original."
"What about resonances ?" I asked.
reflector-diffuser element which distrib"There are no perceptible resonances."
utes the high frequencies throughout the
listening area, and a driver cone im- he answered. "As a matter of fact it
pregnated with cellulose and molded with has nonresonant response realizing rologarithmically graded corrugations bust, live, bass necessitating only one
or two watts of audio for sensational
from cone to rim."
After sipping a drink of water from results."
"Full tonal realism, no doubt," I murthe decanter at his elbow he cleared his
throat and went on. "You will notice mured in an offhand way.
"Full tonal realism and unparalled
the asymmetrical speaker mounting and
the consequent avoidance of spurious listening ease," said George looking at
peaks. The horn is complemented by me with admiration. "It is a fitting
two independent Helmholtz resonators complement to existing systems and it
and intermodulation in the middle reg- is limited only by the quality of the
associated equipment. How uniform
isters is kept to a minimum."
"What about intermodulation in the would you say it was ?"
"Essentially uniform, obviously."
outer registers . . . is it allowed ?" I
George clapped his hands. "And with
asked innocently.
(Continued on page 53)
Anthurbus withered me with a glance
;
Anthrubus looked at me through the
bottom half of his bifocals. "Not been
sacrificed, of course," he said in an injured tone.
"Oh, yes, of course," said I, trying to
look as if I'd followed his arguments.
"It has the highest -fidelity circuit ever
built into a superfidelity amplifier. It
has optimum fidelity that subjects the
loudspeaker to rigid discipline," declaimed Anthrubus in his best Barry more manner.
"Talking about speakers ..." I said
"It is an engineer's dream, a musician's delight," Anthrubus went on,
ignoring nie. "It supplies perfect audio
designed by experts for expert ears and
as such can be assured of an endlessly
useful life. The companion preamplifier
and control unit here in the hand-rubbed
cabinet has both signal modification controls and a continuously variable electronic filter. It too was designed for the
discriminating music lover." George
stared at me as if daring me to utter a
word.
After an unpleasant few moments of
silence I cleared my throat and said, "I
suppose the distortion is
"Distortion is virtually unmeasureable," finished Anthrubus triumphantly.
I winced slightly and in an effort to
cover my defeat I took a sudden interest
in one of the transcription arms mounted
on a giant broadcast turntable console.
"An excellent pickup," I remarked, trying to sound authoritative.
"Yes indeed," rejoined Anthrubus, "It
captures the sound exactly as it was
originally produced. No compromise has
been made with quality and as a result
it releases elusive pleasures that often
remain hidden in the grooves of fine
recordings. It is a reproducer sensitized
to the nth degree and with its near perfect tracking it brings out every
subtle shading. It captures the missing
music. It is the ultimate in record reproduction."
"Hidden in the grooves ?" I ques-
..."
AUDIO
19
AUGUST, 1955
www.americanradiohistory.com
AmericanRadioHistory.Com
Care of Jacks and Patch Cords
EUGENE
F.
CORIELL
The author points to the importance of a supposedly
humble device and tells how to keep it functioning.
necessary. To get at the screws holding
the spring pile -up to the jack frame it
may be necessary to remove the jack.
While it is on the bench, it is a good
idea to check the condition of the normal
contacts on the auxiliary springs. These
may be dressed if required with a Western Electric burnishing tool? Occasionally, a tip spring may be found bent up
or down enough to prevent insertion of
the plug.
Look for loose, broken or otherwise
defective soldered connections to the jack
lugs, including the cable shield connection. (In some installations, the shields
are connected to the terminal blocks in
the bottom of the rack, rather than to
the ground lugs on the jack frames.)
Also make sure that a frayed strand of
the opposite conductor or of the shield
is not contacting the circuit lugs. Once
or twice a year, it is well to check the
continuity of cable shields to ground
with an ohmmeter, and to check the
bonding of each jack frame to its neighbors. Bonding is necessary even in systems in which the cable shields are not
grounded to the jacks, in order to prevent crosstalk that might otherwise result from capacitance between jacks.
Clean the patch cords frequently. An
easy way to do this is to put jeweler's
rouge or other cleaning material on the
plug and polish it on a long cloth fastened at one end to the wall or other
support as shown in Fig. 2. The cloth
* Major, USAF, Armed Forces Radio
is pulled taut with one hand and the
Service, New York, N. Y.
rubbed against it with the other.
' Howard A. Chinn and Robert B. Mon- plug
Test all patch cords regularly for conroe, "Single jacks for broadcast applicatinuity of each conductor and of the
tions," AUDIO ENGINEERING, July 1947.
shield. Test also for shorts between conductors and between conductors and
shield. The fact that a cord appears to
work satisfactorily when patched into a
circuit does not necessarily indicate the
cord is OK. In some circuits, a short of
a conductor to shield might not show
up; also, breaks in conductors may heal
themselves temporarily, due to the firmness of the cord structure. The cord
should be flexed under test, and a convenient way of doing this is to plug the
cord into a pair of jacks mounted at opposite ends of a board as a test fixture.
A diagram of the fixture appears in Fig.
3. The jacks are wired through a selector switch so that each conductor in
turn becomes the connection between the
leads of an ohmmeter (switch positions
1, 2, and 3). Continuity of the shield
can also be checked in this way if the
shield is grounded to both plugs. The
ONE OF THE MOST IMPORTANT Studio
control room elements-and one
sometimes overlooked in maintenance operations -is the patch system
the lowly jacks and patch cords. The
main audio circuits are generally interconnected or "normalled" through contacts on the auxiliary springs of the
jacks, and in meeting emergencies or
requirements for special hookups there
must be immediate and dependable access
by patch cords to the tip springs on
double jacks or to the tip and ring
springs on the CBS -pioneered single jack system.' Failure or noise in any of
these springs and contacts may jeopardize the entire audio channel. The patch
system is therefore the nerve center of
the entire studio installation, and as
such deserves the same careful, regularly
scheduled maintenance as other plant
elements.
We might start with the jacks. Insert
a plug rapidly several times into each
jack to loosen any dirt collected on the
springs and contacts. Suction out the
dirt with a vacuum cleaner fitted with a
tapered rubber nozzle that fits snugly
into the jack barrel. Clean the barrel
with a rotary brush chucked in an electric drill, to assure good grounding contact for the plug sleeve.
Make sure each jack is tight in the
panel assembly. Check for loose, bent, or
misaligned springs, and realign them if
-
Fig. 1.
Clean jack barrels with a brush chucked
in
a pistol -grip
drill.
2 Harold
E. Ennes, "Broadcast Operator's
Handbook," 2nd Ed., John F. Rider Pub fisher, New York, p. 150.
20
fixture can also show shorts (positions
4 and 5). The advantage of the fixture
is that it provides firm connections and
leaves the hands free to flex the cord.
Tie a knot in any cord found defective
and get it out of the control room pronto.
Neglect of this little precaution can be
very embarrassing, as the writer can
testify.
Check the cord connections to the
plug. If the conductors and shield have
been soldered directly to the plug elements, the residue from the soldering
flux may have left a high -resistance
shorting path from one conductor to the
other or to ground. Wash the soldered joint and the intervening insulation with carbon tetrachloride. This is
one reason why cord conductors should
be soldered to small lugs provided, and
the lugs installed in the plug by the
screws furnished.
The conductors in some patch cords
are tinseled-that is, they consist of
strands of copper thread wound over a
cotton core. It is almost impossible to
solder this material without burning it
up. However, if a break must be repaired
in such a cord due to lack of spares, the
ends to be soldered can be wrapped with
fine copper wire. This provides a satisfactory soldering surface.
Troubles due to polarity errors while
patching may be blamed on patch cords
or associated gear. The plug should be
inserted in the jacks with the edge containing the notches or serrations always
on the sane side. Broadcast practice is
to have the notches on the left, but left
or right, the convention must be consistent. This is necessary to preserve the
relative polarity of the circuits patched.
(Continued on page 53)
Fig. 2. Plugs can be polished on a long strip
of cloth saturated with jeweler's rouge.
AUDIO
www.americanradiohistory.com
AmericanRadioHistory.Com
AUGUST,
1955
TUNERS
A
AU D Io
..
urning to ,ou
dirr
Irons Philharnsoni,
For most complete utilization of our home music systems, we can resort to
an almost unlimited supply of music which is offered at no charge to us
from broadcasting stations. This is also an efficient means of auditioning
phonograph records before buying them for a permanent collection. But
even soap operas and news broadcasts sound better over a hi -fi tuner.
www.americanradiohistory.com
AmericanRadioHistory.Com
llall."
The A -310 Theme has been termed the "definitive AM -FM tuner ". Reflecting the most sensitive styling
in the high fidelity field, it also delivers the measurable optimum in both AM and FM performance.
View of Model A -310 with
cage removed
Mcdel A-310
FUNCTIONAL FEATURES
Functional Features: tal Illuminated Tuning Meter; (bl Counterweighted Tuning
Control; (c) AFC defeat available on function switch or momentarily by depressing
tuning knob for center channel tuning; (d) Cathode follower output to drive tape
recorder.
RF SECTION
Circuits: FM: Armstrong Circuit with Dual Limiters (Double Tuned) and Foster
Seeley Discriminator. Automatic Frequency Control. Low noise, all triode front end
with tuned cascode RF amplifier and triode mixer. AM: Superheterodyne with
tuned RF stage, and ferrite loop antenna. Two IF stages. 10 KC whistle filter.
AVC operative over three stages.
Sensitivity: FM: 1.8 microvolts for 30 db quieting; 1.2 microvolts for 20 db quieting. AM: Terminal Sensitivity: 3 microvolts. Loop Sensitivity: 15 microvolts/meter.
Selectivity: FM: 200 KC bandwidth: 6 db down. AM: 10 KC bandwidth: 6 db
down. FM Discriminator peak to peak separation: 375 KC.
Frequency Range: FM: 88.108 MC
AM:530.1650 KC.
FM Drift: ± 2% KC with AFC on; ± 20 KC with AFC off.
Image Rejection:
FM: 50 db.
AM: 50 db.
IF Rejection:
FM: 70 db.
AM: 50 db.
Antenna Input:
FM: 300 ohms AM: Built -in low noise ferrite loopstick plus
high impedance terminal for external antenna.
Distortion: Less than 1% harmonic on FM. Less than 1% harmonic for up to 80%
-
s
11000.1, IMOCITAIS
AM and FM selectivity characteristics
mod. on AM.
s
Frequency Response: FM: ±'/2 db 20 to 20,000 c.p.s.
AM: 3 db 20 to 5,000 c.p.s.
Hum Level: 65 db below 100% modulation.
AUDIO SECTION
Circuits: Cathode Follower Output
Output Level: FM: 2% volts for 100ó modulation;
AM: 1 volt (average).
Output Impedance: Low Impedance Cathode Follower
$
r
ii
1
volt for 30% modulation.
300
OVERALL SPECIFICATIONS
Controls: (Total 2) Function (OFF -AM -FM with AFC -FM without AFC) and
Tuning /momentary AFC defeat.
Tube Complement: (Total: 12) 1.6BK7A, 1-12AT7, I.6AB4, 1.6BE6, 3-6BA6,
1.6AL5, 2-6AU6, I- 12AU7, 1-6X4.
Dimensions: 12t
wide x 4" high x 8%" deep (including ferrite loopstick-not
300
FM discriminator characteristics
/"
including knobs).
Power Consumption: 50 watts
Shipping Weight: 14 lbs.
Finish: Chassis, escutcheon and cage: brushed copper- Display panel for escutcheon and knobs: matte black -Edge lighted dial glass: yellow and white.
Hardware and Accessory Material Furnished: Mounting screws, template, FM
antenna wire, instruction booklet, shielded output cable.
Special Notes: (a) Can be stacked with C -300 amplifier in total height of 8 ", with
C -100 amplifier in total height of 7Mt "; b) Face up mounting of Theme permissible
without special precaution.
2,
200
«. y,r..,
Ou
NOVI
SU?
wet ma
voturet
MM.
LOW-
SOO OasS
SRASI.
30,1,
10071,61130 13.53 400 C
s
1
OPTIONAL ACCESSORIES
(a) Brass finished escutcheon available on special order.
(b) Brass finished cage available on special order.
(c) Vertically calibrated dial glass available on special order.
Write Dopt A8 for
Free New Catalog
SO
SO
PRICE: $125.00 NET
Slightly higher i^ the N
harman kardon
r
www.americanradiohistory.com
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200
500
irt
SP
OR
FM detector output voltage characteristics
520 Main Street, Westbury,
INCORPORATED
100
L. L, N. Y.
2
AM -FM
Tuners AM, FM,
C. G. McPROUD
Introduction by Richard H. Dorf
The radio tuner often becomes the mainstay of home entertainment, introducing us to new music and giving us a wider choice than our meager
record collections generally do. Here's how they work and what they're like.
A VERY STRANGE FACT that the
audio hobbyist who spends so much
time building amplifiers, checking
ickup response curves, and stringing
sires all over the house when he should
e outside mowing the lawn, joins the
:ife and kiddies in becoming a simple
.utton- pusher and dial twiddler when it
comes to picking up radio programs. The
trouble seems to be that those radio frequencies inside that complicated box are
way out of the audio band and therefore
the product of an exclusive engineering
cult which deals in such weird items as
tuned transformers- without iron cores
-and variable capacitors. The same man
who unblushingly exhibits to admiring
( ?) friends his new audio creation with
9 inputs, 20 different fixed equalization
curves, a three-way speaker system with
crossover, and an amplifier with four
separate feedback loops develops a classic
case of cold feet when anyone suggests
he ought to know at least something
about how his radio tuner works.
This preoccupation with one band of
frequencies and horror of others is endemic throughout the electronics industry, including hobbyists. There are
microwave men, r.f. men, and audio men,
each of whom sticks to his own part of
the spectrum and resists being contaminated with very much knowledge about
the others. The fact is, however, that
it pays to be broadbanded on the subject
for the simple reason that each group
must use some of the products of the
others.
This insular attitude among audio
hobbyists stems on the whole from the
fact that for some reason it doesn't seem
very difficult to understand how audio
circuitry works, while r.f. receiver circuitry is too complicated to bother about.
Since receiving circuits bring a great
deal of audio enjoyment to sound enthusiasts, however, it is worthwhile to
know something about them. R.f. is not
any more complicated than audio and
requires no different basic knowledge.
In fact, áudio engineers regularly point
out that the audio band covers some ten
octaves, while the entire broadcast band
covers only one and a half, and that
techniques differ appreciably in radar
bands not more than two octaves apart.
Furthermore, important as r.f. is, audio
people will remind you that the r.f. exists
only to transmit audio intelligence, and
also soap operas and some TV programs.
In this article we shall cover the subject
as it applies to modern tuners so that
the reader will know what goes on inside
IT IS
!
AUDIO
the box, how to take best operating advantage of available tuners, and how to
use intelligence in selecting one for purchase. In beginning at the very start
of the subject, we shall take the risk of
temporarily boring readers who are
more advanced technically. But we shall
at least be able to say that we have covered the subject and that there will
henceforth be no excuse for putting the
tuner -one of the more useful pieces of
audio -system equipment -into the "black
box" category.
The basic idea of transmitting audio
by radio is predicated on a simple premise. The nature of the universe just happens to be such that electrical audio frequency waves will not ordinarily
travel very far without being carried
by wires, while waves of higher frequencies can be made to travel tremendous
distances without wires. Just why this
is so
and the physical mechanism of
space wave propogation we will not go
into ; the fact is that it works. All broadcast systems take these two factors into
account by using radio-frequency waves
(which cannot operate a loudspeaker)
as vehicles or carriers on which the
audio waves (which can) ride. At the
destination-your home-the tuner intercepts the desired carrier from amongst
many, strips away and discards the r.f.,
and extracts the audio "passenger" which
it passes on to the amplifier.
In all r.f. -audio transmission, the audio
is put into the r.f. wave by modulation.
This means that the two waves are cornbined in such a way that the audio alters
the character of the r.f. without making
the r.f. unsuitable for wireless transmission. Modulation is really a mixing
process in which waves of two different
frequencies are mixed in a nonlinear
stage. The lower- frequency wave produces changes in the character of the
other and the mixing produces frequencies equal to the sum of the two and the
difference between the two. This sort
of mixing within an audio amplifier is
intermodulation and it produces audio
distortion ; but in a radio transmitter it
is desirable, as we have seen.
Amplitude Modulation
The earliest and still most common (in
radio broadcasting) method of modulation is AM or amplitude modulation,
shown graphically in Fig. 1. In (A) is
an unmodulated carrier which is the
sine -wave radio frequency-something
between 550 and 1600 kc in the standard
broadcast band. At (B) is shown a single cycle of audio which happens to be
a complex wave such as might be pm-,
duced by a musical instrument. (C)
shows how the two are combined when
the audio modulates the r.f. The r.f. carrier departs from its normal constant
amplitude and changes amplitude from
instant to instant in accordance with the
audio. Depending on the polarity of connections at the modulator, a positive
audio excursion causes an increase in
r.f. amplitude and a negative one causes
a diminution in r.f. The audio amplitude
required for full or 100 per cent modulation is that which causes the r.f. amplitude to double on positive peaks and
diminish to exactly zero on negative
peaks.
File in your memory for use later that
this process causes the r.f. to have an
audio "envelope," the dotted outline
shown across the tops and bottoms of
the modulated r.f. in Fig. 1. These lines
^,
III
IIIIIItIIIl
(A)
UNMODULATED
CARRIER
(B)
SINGLE CYCLE
OF
AUDIO
MODULATED
CARRIER
1. Waveforms encountered in AM broadcasting. (A) is unmodulated carrier, (B) is audio
signal as fed to modulator, and (C) is carrier modulated by the audio signal. Note that the top
half is the mirror image of the bottom half, and that the envelope of the carrier corresponds
to the audio signal.
Fig.
23
AUGUST, 1955
www.americanradiohistory.com
AmericanRadioHistory.Com
are not actually present in an oscilloscope picture, but notice that they are
two mirror images of the audio waveform.
The modulated r.f. is still r.f. and as
such it can be transmitted without
wires. However, after modulation the
wave contains not only the single generated radio frequency, but also the results
of the mixing-that is, frequencies which
are the sum and the difference between
the mixed audio and r.f. For instance, if
the carrier is at 1,000 kc and the audio
tone (assuming it to be a pure sine
wave) is 1,000 cps or 1 kc, then the
modulated r.f. wave contains three main
frequencies. These are (1) the original
carrier frequency of 1,000 kc, (2) the
sum of the carrier and the r.f. which is
1,001 kc, and (3) the difference between
the two which is 999 kc. The sum and
difference frequencies are known as
sidebands and in standard broadcasting
every carrier is accompanied by sidebands on each side of center frequency
equal at every instant to the audio modulation frequency.
It is obvious, therefore, that a broadcast station occupies not just a single
frequency in the assigned spectrum bu
a band of frequencies equal to twice the
r4-16KC-1
-10 -8 -6 -4 -2
+2
CARRIER
+4 +6
8 +10
FREQUENCY~
Fig. 2. Representation of selectivity curves in
AM. (A) is ideal curve, with 16-kc bandwidth
which would pass an 8000 -cps audio signal
without sideband cutting. (8) is curve typical
of conventional radio receiver. (C) is sharp
curve used in communications receivers when
unmodulated signal is transmitted and received,
with audio signal being introduced in receiver
by beat frequency oscillator.
maximum permitted modulation frequency. If, therefore, a station is on
1,000 kc and is permitted to use audio
frequencies up to 10 kc, then it occupies
a band of frequencies from 990 to 1010
kc. In allocating the spectrum among
the various stations, the Federal Communications Commission decided many
years ago that to accommodate all qualified applicants for licenses, the broadcast
band had to be split up into segments
no larger than 10 kc each. This indicates
that AM stations must restrict audio
modulation to 5,000 cps if the sidebands
are not to spill over into an adjacent
channel. In practice, however, most stations broadcast overtones in music up
to about 8,000 cps, and many well above
that. This is possible because sideband
energy above around 4,000 cps on each
side of carrier is usually relatively small
since it represents overtones rather than
fundamentals in music, and stations on
directly adjacent channels are located
far enough apart so that there is little
I
7ND
ST
TRF
TRF
;TAGE
STAGE
Fig.
3.
y
3RD
TRF
TRF
OR
DETECTOR
ti.
DIC
MVLIIER
*-
Block schematic of tuned -radio- frequency receiver.
interference. However, in some locations,
adjacent-channel stations can be received
and the receiver itself must then have a
narrow reception band to eliminate the
interfering sidebands. If sidebands of
two stations are received, they cross modulate each other in the receiver and
produce what is called "monkey chatter,"
a phenomenon anyone with a shortwave
receiver or a wide -band "hi -fi" AM
tuner knows well.
The sidebands are not mere incidentals
with which we can do as we will. When
an AM wave is modulated, a substantial
portion of the radiated power is contained in the sidebands. If the receiver
is so sharply selective as to fail to receive the sidebands, a proportionate
amount of the audio will be lost. Stated
another way, the band which the receiver will pass determines the audio frequencies which can be received. If the
receiver can pass a band only 6 kc wide,
then the maximum audio frequency received is only 3 kc, remembering that
audio sidebands appear equally on each
side of carrier. This brings up the important question of selectivity in AM
tuners. To receive the maximum audio
range transmitted, the receiver must be
rather unselective and should pass frequencies at least, say, 8 kc each side of
carrier equally well. However, to eliminate adjacent- channel interference bandwidth should be considerably smaller
than that. Reduced bandwidth also helps
reduce noise, since in any communication system noise is proportional to bandwidth.
Figure 2 shows three possible receiver
bandpasses. Curve A shows an ideal
situation in which the tuner can receive
frequencies from 8 kc below to 8 kc
above the carrier equally well-the characteristic is flat-and receives nothing
outside than 16 -kc band. Such a flatopped curve is hard to attain, especially
STAGE
6.
STAGE
MI%ER
since a tuner must be tunable over the
entire broadcast band and such things
as coil Q in each tuned circuit vary. A
curve more usual in cheap receivers is
shown at (B) in Fig. 2. Such a curve
is normally obtained with tuned circuits
of moderate Q without any special provisions. Since the curve bends downward
as the sideband frequency increases,
audio highs are rolled off rather steeply.
Curve (C) shows response of a receiver
that might be used for c.w. or code reception, where there is no modulation
and thus no sidebands, and the object is
to eliminate surrounding interfering signals as much as possible. Such a response
is almost useless for audio reception.
AM Tunen
There are two general types of AM
receivers and tuners. The earliest is the
tuned- radio -frequency circuit or t.r.f.
This is the simple, straightforward approach illustrated in block form by Fig.
3. The antenna feeds signal to one to
more cascaded amplifier stages, each of
which is tuned to the station frequency.
This means that the stages are transformer- coupled with (usually) air -core
coils, either the primaries or secondaries
of which, and sometimes both, are used
as the inductors of tuned circuits and
have a variable capacitors across them.
All the variable capacitors are ganged
on a single shaft so that the tuning knob
tunes all circuits simultaneously to select
the station. The last t.r.f. stage is followed by a detector and audio amplifier
stages if any.
The second and more common tuner
type is the superheterodyne, block -diagrammed in Fig. 4. The signal from the
antenna is fed either to a tuned-radiof requency amplifier stage if there is one
or directly to the mixer through at least
one circuit tuned to the r.f. carrier fre-
DETECTOR
AUDIO
AMPLIFIER
-
AUDIO
OUTPUT
LOCAL
OSCILLATOR
Fig. 4.
Typical block schematic for superheterodyne receiver.
AUDIO
24
www.americanradiohistory.com
AmericanRadioHistory.Com
AUGUST, 1955
-
CURRENT
FLOWS
-
((r fifi``
ríIIIIII1TRÁii
ighd
-Of
CURRENT
CANNOT
(A)
MODULATED CARRIER
FLOW
(B)
RECTIFIED CARRIER
Fig. 5. Representation of action of diode detector. Modulated carrier (A) is fed to diode, and
only the positive excursions of the voltage can pass through. Remaining portion of signal,
is passed through a filter to remove carrier frequency, leaving only the audio as shown by
the dotted line.
(I),
quency. To the mixer also goes signal
from a local oscillator. In the mixer
stage, which is usually a multigrid tube,
the r.f. and oscillator signals are mixed
nonlinearly and sum and difference
beat frequencies are produced. The difference frequency is passed on via tuned
circuits to the i.f. stages.
At least two circuits are gang -tuned
to select the station. One of these is
tuned to the signal frequency and is between antenna and detector. The second
tunes the oscillator so that no matter
what the station frequency, the same
difference or beat frequency is produced
at the mixer output. For example, suppose the difference frequency selected
is 455 kc. Then the ganging of tuning
capacitors is so arranged that when the
r.f. tuning is at 600 kc, the oscillator is
at 1055 kc ; when the r.f. is tuned to 1200
kc, the oscillator is at 1655 kc ; and so
on. It is also possible to have the local
oscillator operating below the r.f. frequencies, but the range of the oscillator
in octaves is then too great to cover
easily with one capacitor.
At all times, then, the mixer output
is at a single frequency, 455 kc in our
example. This is the intermediate frequency and it is amplified in a series of
cascaded i.f. stages, detected, and the
audio amplified.
There are advantages and disadvantages to each of the two types. The
reason for the existence of the superheterodyne and its almost universal use
despite its apparently (but not actually)
greater complication is that it is easier
to design an amplifier for one frequency
than for a whole range of frequencies
such as are used in broadcasting. The
i.f. amplifier, which does almost the
entire amplification job, has fixed-tuned
transformers, the response curves of
which can be shaped as desired, an almost
impossible job with variable- tuning
transformers. At the lower intermediate
frequency, more amplification may be
realized per stage without oscillation,
and the selectivity curve -always related
to the signal frequency as a percentage
-can be made sharper. For example,
if a tuned circuit can be made to be 10
db down at 1 per cent off the signal frequency it will be down 10 db at 10 kc
off a 1000 -kc carrier, and down the same
10 db at 4.55 kc off the 455 -kc i.f. signal.
Equivalent selectivity and performance
can he had at much less cost with a
AUDIO
superheterodyne than with a t.r.f. tuner.
As many stages as may be necessary can
be used without the necessity for endless
rows of variable capacitors on a single
tuning shaft ; only two capacitors need
be varied in tuning, though the better
tuners usually add an extra one together
with an r.f. stage. In addition, the frequency handled in the i.f. amplifier is
lower than the r.f., and it is axiomatic
that handling lower frequencies is always
easier than handling higher ones.
The t.r.f. tuner is traditionally the one
with the wider band, though the uniformity of response depends on design. For
one thing, variable- tuning transformers
are not as selective as fixed ones in practice. For another, there are fewer tuned
circuits in a t.r.f. receiver, but since
all operate at the same frequency, the
tracking problem is reduced. All of the
tuned circuits can be identical in a t.r.f.
receiver, whereas in the superhet, the
r.f. and oscillator circuits are different
and must remain tuned to frequencies
exactly 455 kc apart as the dial is turned.
This requires circuit design which provides for padding -to make the circuits
match at the low- frequency end of the
band-and for trimming, which makes
them match at the high- frequency end.
Even so, they do not tune to the theoretically correct agreement points at more
than three places in the band, though in
a good design the error is negligible in
effect. The t.r.f. tuner is not ideal, however, when there is interference because
it can rarely be narrow- banded sufficiently to reduce interference effectively.
It is also a poor performer where signals
are weak, since it is not practically capable of the amplification of a superhet.
might be supposed that this wave could
he applied directly to an audio amplifier
stage, on the theory that the envelope
amplitudes would produce stronger and
weaker instantaneous signals at the
audio rate. The fallacy here is the mirror -image repetitions of the audio outline. The period of the r.f. waves is so
short that as far as the ear is concerned
they do not exist, and what does exist
is the envelope only. If that is so, then
a positive excursion of the envelope is
accompanied by an identical negative
excursion, so that the average value of
the two mirror -image audio outlines is
always zero.
The cancellation effect of one of the
mirror images is removed simply by rectifying the modulated r.f. as in Fig. 5
(B). The rectifier used is a half -wave
type and the portion of the r.f. signal
below the a.c. baseline is simply thrown
away after rectification (unless it is used
for a.g.c.) . We are left in (B) with r.f.
having only an upper outline of audio.
This can be applied directly to an audio
amplifier. As a matter of practice, a low pass filter is always inserted to suppress
the r.f. pulsations, leaving only the recovered audio as in (C).
Several types of detectors exist. The
simplest of all is the diode detector diagrammed basically in Fig. 6. R.f. from
the last i.f. transformer or an r.f. stage
is rectified by the diode, and appears
across the diode load resister (R),
which usually has a high value to develop as large a signal as possible.
Capacitor C bypasses the load resistor
for the r.f. pulsations so that the audio
emerges clean. An additional series resistor and shunt capacitor may be used
for further filtering.
The diode detector is simple and cheap
but it has some disadvantages for high fidelity use. The first is that is gives
linear results only on large signals, and
the distortion increases with the percentage of modulation. This is because
the curve of applied voltage versus conduction in a diode is nonlinear for weak
voltages. If the voltage is high enough
and the modulation percentage low, the
envelope variations will all take place in
a fairly linear region ; but if the signal
is weak or the modulation percentage
high enough so that negative peaks extend into the diode's nonlinear region
distortion can be quite high. Under nor-
AM Detectors
After r.f. or i.f. amplification of the
modulated r.f. signal, the audio must be
recovered and the r.f. stripped away.
The stage which does this is the detector.
Sonic old- timers refer to the mixer stage
as the first detector, and the demodulator
as the second detector. Modern practice,
however, is to call the superheterodyne
mixer just that (or the converter) and
refer only to the demodulator as a de
tector.
The action of the detector is shown
by Fig. 5. At (A) appears the modulated
r.f. coming from the r.f. or i.f. amplifier.
Note the envelope which outlines two
mirror -images of the audio wave. It
Fig. 6. Typical diode detector circuit. Rectified
carrier passes through diode and develops audio
signal across resistor R. Filter Re and Ca filter
out audio and leave only a d.c. voltage which
is negative with respect to ground and which
may be used for a.v.c. Audio signal is passed
through C, to volume control.
25
AUGUST, 1955
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mal conditions, a diode detector can
cause over 10 per cent harmonic distortion at full modulation, even in a good
design. Modern circuitry has ways of
improving this situation, however. One
of the causes of distortion at high percentages of modulation is the presence
of the capacitor Ct and the volume control which are in parallel across the diode
load resistor R, as well as the decoupling resistor Rt and the decoupling
capacitor Cd in the a.g.c. circuit. For
minimum distortion at high percentages
of modulation, the a.c. impedance of the
diode load-which consists of the resistor R, the capacitor Cr and any other
impedances shunted across
should
be as close as possible to the d.c. resistance of the diode load. In most practical
applications, R is likely to be of the
order of 0.25 to 0.5 megohm, whereas
the volume control may he as low as,
say, 0.5 megohnt. Neglecting the impedance of the coupling capacitor Ce-at
the signal frequency, not audio-this results in an a.c. impedance across the
diode load which can range from 0.66
to 0.5 times the d.c. impedance. The
value of the diode load resistance R may
be reduced to 50.000 obtus, which will
offset the effect of the shunting resistors
to a large extent, but this is not a complete cure.
A detector which gives very good quality sound is the infinite -impedance
circuit diagrammed in simple form in
Fig. 7. This has been most often used
in past years (particularly before the
high -fidelity era) in t.r.f. receivers, simply because these were the receivers most
people built when they wanted quality.
The detector resembles a cathode follower. The cathode resistor has such a
high value that the tube operates close
to cutoff. The negative r.f. input excursions simply drive the tube to cutoff and
cause little output; the positive excursions drive the tube toward conduction
and therefore appear across the cathode
resistor with large amplitude. Cr has a
value which bypasses r.f. while not affecting audio. Therefore, the cathode-toground voltage assumes a value which is
proportional to the r.f. envelope but cannot change fast enough to follow individual r.f. cycles. That being so, the
cathode voltage is the recovered audio
from the positive modulated -wave envelope outline, and it is passed on to the
audio section via blocking capacitor C,.
While this detector does not amplify
the signal as some other types do, it
gives linear results over wide ranges of
signal inputs and modulation percentages, and does not load down the previous r.f. or i.f. stage. The reason for
both these quality factors is its cathodefollower identity. Input of a cathode follower is always high in impedance because of the degeneration or feedback.
For the same reason, linearity is aided.
And to accommodate wide signal amplitude ranges, the cathode resistor sets the
tube's bias always in accordance with
requirements of the signal.
All AM tuners have some forni of
what used to be called automatic volume
control (a.v.c.) but is now more properly called automatic gain control
it-
he found which could be modulated
with
the program at will but which was not
affected by static -man -made or natural
-the
result would be a transmission
completely free from disturbWhile this is not 100 per cent
true in practical systems, there is a definite improvement in the system that was
means
ances.
developed.
1Vith the frequency modulation system of transmission, the modulating inFig. 7. Typical infinite impedance detector for
high audio quality. Signal is developed across
resistor in cathode circuit of tube, but polarity
of d.c. is not correct for a.v.c. uses, and voltage
for o.v.c. must be obtained by some other
meons.
(a.g.c.). The necessity for this provision
great because the signal strength of
is
AM broadcast station determines how
loud the program will sound compared
to that of another station and signal
strengths vary widely. Without a.g.c.
the user would tune away from a comparatively weak station and run across
a powerful station which would blast his
ears off. A.g.c. is so easy to obtain that
there is little point in not having it.
The basic concept of a.g.c. is very
simple. The signal from the r.f. or i.f.
amplifiers is rectified and filtered, developing a d.c. voltage which is always proportional to signal strength. This voltage, negative with respect to ground,
is applied to the grids of the i.f. amplifier tubes. When the signal strength
rises, therefore, more negative bias is
applied to the amplifiers and the gain
is reduced. A.g.c. voltage is obtained in
many different ways from circuits similar to that tied fiir the diode detector.
an
Frequency Modulation
In his continuing search for
method
a
-
iii transmission that would eliminate, or
at least minimize the effect of noise
either from atmospheric causes or from
man -made sources -the late Edwin H.
Armstrong developed frequency modulation. Since the effect of the noise -producing devices is to add to or subtract
from the amplitude of the radio signal,
any means that employs a variation of
amplitude in accordance with the desired intelligence is susceptible of modulation by the unwanted noises, since it
is not practical for the detector to discriminate between noise and program
when both are of the sane general pattern. Therefore, if some means could
AUDIO
I I
MODULATED
CARRIER
II
II
IIIIIIIIII
IIIIIIIII
I
I
I
II IIII
Fig. 8. Representation of FM modulation. Frequency of carrier is varied at an audio rate by
the modulating signal.
telligence is applied to the signal in
such a fashion as to vary the frequency
of the carrier without changing its amplitude. The frequency of the modulating
signal governs the rate at which the
carrier frequency is varied, and the amplitude of the modulating signal governs
the amount of deviation from the center
frequency. Thus a very low level of
modulation may cause the carrier to
deviate only a kilocycle or so from its
center frequency, and a very high level
of modulation may cause the carrier frequency to deviate as much as ±75 kc
from the nominal or center frequency.
This being the case, it becomes necessary only to utilize some "detector"
which is frequency sensitive, and thus
translates the rate at which the frequency is varied into an audio signal
whose amplitude is proportional to the
amount the frequency is varied. In other
words, the "detector" must translate
frequency modulation into amplitude,
and it must be insensitive to amplitude
modulation that may happen to appear
on the carrier.
Figure 8 shows a representation of the
modulated carrier signal when the modulating voltage is a sine wave. For 100
per cent modulation, the deviation of the
carrier above and below the nominal
or center frequency is 75 kc, according
to FCC regulations, in the FM band.
Frequency modulation is also used for
the aural signal on TV transmissions,
and here the deviation is ±25 kc.
While the FM carrier is subject to
the same disturbances from static as an
AM carrier, the difference between the
two occurs in the receiver. In the AM
receiver. it is not practicable to differentiate between the desired modulation
and. the undesired modulation or noise,
since they are both of the same type.
In the FM receiver, it is possible to remove practically all of the amplitude
modulation from the signal before it
is fed to the "detector" and the detector
itself then converts frequency modulation to amplitude modulation which it
can convert readily into the desired
audio signal. Furthermore, there are
certain kinds of detector circuits which
are practically insensitive to amplitude
modulation, but react only to frequency
changes.
The discussion of frequency modulation could be expanded to occupy several
volumes, if one is to consider the many
aspects of the modulating process, the
formation of sidebands, the comparative
freedom from noise, and so on. But for
our purposes, let us content ourselves
with the knowledge that there are some
very important advantages to FM. The
most important is that of noise reduction, of course, and it can be shown
AUDIO
26
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AUGUST, 1955
THE
311
FM TUNER
New tuner makes FM reception
better than ever before possible
Here are the reasons why the new 311 FM Tuner
far outperforms tuners of conventional design
The 311 uses the new wide-band circuits that audio experts have called the most significant development in tuner
design in many years." Now. for the first time. you can
easily separate stations so close together on the dial that
ordinary tuners would pass right over them. Distant stations. that you wouldn't even know were there. come in
as clearly as locals. Stations never drift out of tune. and
both strong and weak signals tune with equal ease. This
outstanding performance is made possible both by the
wide -band circuits and the very high sensitivity of the 311
(3 microvolts sensitivity for 20 db of quieting).
air." A beautiful accessory
case, finished in durable, leathergrained plastic. is available to enclose the tuner for use
on a table or shelf.
A completely new chassis design makes custom installation or panel mounting easier than ever before. All
you need to do is make a simple cutout in the panel, and
slide the entire tuner in from the front. No disassembly of
any kind is required.
Type 311
FM tuner
In
custom
High -speed tuning, that locates stations quickly, plus slow
speed tuning for precise station settings, is provided by a
smooth planetary drive mechanism. The edge -lighted
lucite tuning dial has both frequency and logging scales.
For visual tuning on weak signals, and for indicating best
antenna orientation. the tuner is equipped with a signal
strength meter.
-
-
Stations never fade in and out, because automatic gain
control
another special feature
always keeps the
tuner adjusted for perfect reception no matter how the
signal may vary.
Dual output jacks permit simultaneous operation of your
amplifier and a tape recorder for program recording "off the
Tuners
-
Amplifiers
-
Turntables
installation
The 311 is the only FM tuner in its price bracket with
all these outstanding features. Once again H. H. Scott
engineering leadership has made a significant contribution
to the audio art. Ask your dealer to let you fry the 311. and
see for yourself how much better FM reception can be.
TECHNICAL SPECIFICATIONS
3 microvolts on 300 -ohm input for 20 db of quieting
Wide -hand Circuitry: 150 kc IF passband, 2 megacycle detector band -width
Spurious-response rejection: 80 db rejection of spurious response from cross -
Sensitivity:
modulation by strong local signals
Audio output: 4 volt output for 75 kc deviation. Two output jacks including
one for tape recording. Low impedance output so long connecting cables
may be used
Meter: Calibrated meter functions as tuning and signal strength indicator
Controls: Precision and quick tuning; level; power
Price:
311 -A $99.95 East Coast
$104.95 West Coast
Accessory case $9.95 East Coast
$10.45 West Coast
WRITE FOR FREE
BULLETIN
For perfectionists and connoisseurs H. H. Scott also manufactures the 310 FM
tuner. High Fidelity Magazine says: The 310 "
is a tuner that seems as
close to perfection as is practical at this time." The Audio League Report
says: "The 310 is the most sensitive tuner we have yet tested
"
Price, including case $149.95 East Coast; $157.45 West Coast.
...
...
H. H. SCOTT Inc. 385 Putnam Ave.
Cambridge 39, Massachusetts
AUDIO
AUGUST, 1955
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turers' engineers that FM sets operating
in the vicinity of 100 megacycles have
been developed to the point where they
can be turned on and satisfactory reception follows automatically. Many of
Fig. 9. When FM carrier is tuned to slope of
resonance curve, output potential varies as frequency does. Slope is not linear over wide
enough range for good FM quality.
mathematically that there is an improvement of 18.75 db before pre- emphasis,
and when the added advantage of pre emphasis is taken into account the total
improvement is some 32 db. Another
advantage is the possibility of transmitting a wider band of modulating frequencies within the allowable frequency
band. Whereas an AM receiver capable
of receiving an audio signal of 10,000
cps is readily possible, it is likely to be
noisy unless the receiver is located in
an area of high signal strength. On the
other hand, an FM receiver can receive
an audio signal of 15,000 cps with little
or no noise, and frequencies as high
as 40,000 cps are commonly transmitted
for control purposes along with the
audible signal. In fact, the proposed
multiplexing of FM signals involves the
transmission of one audio signal extending up to 15,000 cps and another of the
same width on a sub-carrier operating
in the range from 20 to 40 kc. Thus two
signals can be transmitted on one FM
carrier with no interferences. Some
receivers are already equipped with
output connections which may be connected to multiplex equipment when
and if it becomes available.
can remember when AM reception
in the vicinity of 18 megacycles was
unreliable and difficult to handle, even
with the better grade of equipment.
The principal differences in the circuit arrangement of an FM tuner hinge
on the detector circuit, and the functioning of this circuit varies considerably
with different types of FM tuners.
All, however, must be able to convert
a variation of frequency at an audio
rate into a variation of amplitude at an
audio rate, the latter being the description of an audio signal, in effect. There
are several different types of circuits
which will do this, the simplest being
shown in Fig. 9. In this case, the frequency- modulated carrier is tuned to the
side of a resonant circuit to the point O;
as the frequency varies, the signal slides
up and down the curve, as from O to
A, then back to B, and then back to O
again. With no modulation, the frequency is at O, and the output is represented by En; at a higher frequency, the
output is Ea, and at a lower frequency
the output is Ea. While this is simplified
somewhat, it is adequate for an under-
FM Receivers
The block schematic of an FM receiver is basically similar to that of an
AM superheterodyne, in that equivalent
sections will be found. However, most
FM receivers employ one or more limiters, which are used to remove the amplitude modulation from the signal before it is fed to the "detector" and the
detector itself is different in operation.
However, there is an r.f. stage, a mixer,
a local oscillator, an i.f. amplifier, and
the detector -which in the FM receiver
is called discriminator or radio detector.
depending on the circuit configuration.
With the discriminator,
a
limiter will
always be found, consisting of one or
more stages.
Although the basic arrangement is
the same in both AM and FM receivers,
the physical components differ materially because of the difference in the
frequency ranges in which the two types
of receivers work.. The AM broadcast
tuner operates in the band between 550.
and 1600 kilocycles, while the FM tuner
operates between 88 and 108 megacycles.
Thus the coils and capacitors in the FM
receiver are considerably smaller (electrically) and greater care must be taken
to avoid stray capacitances, unwanted
oscillation, and frequency instability.
Actually it is a fine tribute to manufac-
Fig. 10. By combining curves of two circuits in
reversed polarity, straight portion of curve can
be made much longer.
standing of the action of an FM detector. We now have a carrier which varies in frequency passing through a
circuit which acts upon it to make it
vary in amplitude in proportion to the
frequency variation. If we now detect
the signal in the usual way by eliminating one half of the signal just as we do
in an AM tuner, and then filter out the
r.f. component, we have an audio signal,
which is what we wanted. This type of
circuit works -and is actually employed
in the cheapest of FM receivers-but it
has the disadvantage of having two
points at which the signal could be
tuned in, O which we have discussed.
and X on the other side of the slope.
Furthermore, it is difficult to design
such a circuit to have sufficiently low
distortion to take advantage of the high
quality of FM transmissions.
The most commonly used circuit for
converting the frequency modulated signal to an amplitude modulated signal is
known as a discriminator. Reduced to
its simplest form, it consists of two circuits similar to the one of Fig. 9 placed
back to back and tuned to slightly different frequencies, as in Fig. 10. In this
arrangement, the curvature at the toe
of the upper curve can be counteracted
by the curvature of the toe of the lower
curve, resulting in a longer straight line
over which the signal varies and greater
linearity throughout. The operation of
this circuit is considerably more complicated than this simplified description,
but the basic idea is similar. In either of
these arrangements, the output is also
dependent on the amplitude of the signal
fed in, and some means must be employed to eliminate unwanted amplitude
modulation of the signal by noise. This
is usually done by limiters, which are
in most instances-tubes which operate
over a portion of their characteristic
where any increase in input signal does
not result in an increase in output.
These stages are then operated in the
saturated condition with all normal signals so that regardless of the amount of
input signal, the output remains constant in amplitude, although the frequency still varies in the output as in
the input. When such a signal is fed to
the discriminator, the audio output
having two "dimensions," frequency and
amplitude
of a frequency equal to
the rate of frequency variation of the
input signal and of an amplitude dependent upon the amount of frequency
-
-
-is
variation.
When used with two well designed
limiters, the discriminator delivers a
noise -free signal with very low distortion, provided the signal is tuned in accurately so that the center of the frequency band is accurately centered on
the slope of the discriminator curve.
Normal drift in the receiver will act to
cause the signal to move away from
the center, with the result that distortion
may occur as the frequency swing
reaches the peaks of the curve. However. this can be compensated readily
by the use of automatic frequency control, which will hold the signal correctly tuned over an adequate range.
The discriminator exhibits one characteristic which is considered a disadvantage. and that is the "three point tuning" which is sometimes confusing to a
person not familiar with the use of an
FM tuner. Referring to Fig.
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fo
Fig. 11. Linear portion of curve is used for optimum quality; short linear portion at f, and f,
will give distorted audio signal.
AUDIO
28
11,
represents the correct tuning point, and
the allowable frequency swing before
distortion is observed is shown to extend over a fairly wide range. As the
receiver is tuned, it will be noted that
points f, and f, are also on the center
AUGUST, 1955
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www.americanradiohistory.com
AmericanRadioHistory.Com
of a straight -line portion of the curve.
This will result in an audible output
signal, but the straight -line portions of
these two sides of the curve are much
shorter, and distortion will be observed
on signals with medium to high levels
of modulation. Since the d.c. output of
the discriminator can be measured-and
after proper filtering it follows the curve
of Fig. 11
will be noted that there is
only one point at which it is zero, and
that is at fo. Thus an indicator that will
show when the d.c. voltage at the output
of the discriminator is zero will also
serve to show when the set is properly
tuned in. However, assuming that another station should happen to be on a
frequency which caused it to be tuned
in at f, or fr when the desired signal was
tuned in at fo, then both would be heard,
which would be undesirable.
In an effort to avoid this possibility,
considerable design work has been done
in the past few years, and the wide -band
discriminator is the result. In this circuit, the slope of the discriminator circuit is made to extend over a very wide
band
the order of two megacycles
and the tuning of the receiver is dependent only on the pass band of the
i.f. amplifier, which is usually designed
to have a flat -top curve and to extend
over a 200 -kc band width. Since the
deviation of the carrier is ± 75 kc, the
pass band must be at least 150 kc wide.
-it
-
-of
and to allow for slight inaccuracies in
tuning there should be some margin.
Thus with the wide -band discriminator
tuning of the signal depends only on the
i.f. amplifier. and so long as the signal
is centered in that pass band, there will
be no distortion in the discriminator
circuit.
Thus the selectivity of the i.f. amplifier is the controlling factor in tuning,
and only one point will be found at
which the signal is tuned in properly.
This circuit demands a reasonably flat topped i.f. amplifier. but it is much
easier to tune in a station correctly and
without distortion.
Ratio Detectors
Another circuit arrangement which is
often used in tuners is the ratio detector.
wherein the output is dependent on the
ratio of the voltages developed in the
detector circuit, rather than upon an absolute value. This circuit has two advantages -the first being that it does not
require limiters and is thus less costly
to manufacture, and the second is that
between stations there is very little or
no noise. Since the discriminator
amplitude sensitive, and becomes insensitive to noise only by virtue of operating the limiters at saturation with the
presence of a signal, it follows that in
the absence of a signal the limiters are
acting as amplifiers, and all atmospheric
noises are passed on to the discriminator. Therefore, FM tuners which employ discriminators often resort to the
use of a squelch circuit to silence the
audio portion of the set when no signal
is present.
With the ratio detector, however.
there is no output at all unless there ia signal because the detector is only
i
AUDIO
America's TOP Tuner!
THE
FISHER.
FM TUNER
MODEL
FM -80
Worlds Best by LAB Standards
almost two decades we have been producing audio equipment
outstanding quality for the connoisseur and professional user.
In the cavalcade of FISHER products, some have proven to be
years ahead of the industry. THE FISHER FM -80 is just such a
product. Equipped with TWO meters, it will outperform any existing FM Tuner regardless of price! The FM -80 combines extreme
sensitivity, flexibility and micro-accurate tuning. Despite its full
complement of tubes and components, the FM -80 features an unusually compact chassis of fine design. Chassis Only, $139.50
Mahogany or Blonde Cabinet, $14.95
FOE
Outstanding Features of
THE FISHER FM -80
TWO meters; one to indicate sensitivity,one to indicate center -of- channel
Armstrong system, with two IF stages, dual
for micro -accurate tuning.
Full limiting even on signals as weak
limiters and a cascode RF stage.
Dual antenna inputs: '2 ohms and 300 ohms balas one microvolt.
Sensitivity: I 1/2 microvolts for 20 db of quieting en
anced (exclusive!)
72 -ohm input; 3 microvolts for 20 db of quieting on 300 -ohm input.
Chassis completely shielded and shock-mounted, including tuning condenser, to eliminate microphonics, and noise from otherwise accumulated
Variable AFC /Line -Switch, Sensitivity, and
Three controls
dust.
Two bridged
Station Selector PLUS an exclusive Output Level Control.
outputs. Low- impedance, cathode -follower type, permitting output leads
supplied.
Beautiful,
1l
tubes.
Dipole
antenna
up to 200 feet.
WEIGHT: 15 pounds.
Self-powered.
brushed-brass front panel.
CHASSIS SIZE: 123/4" wide, 4" high, 8138" deep including control knobs.
-
Price Slightly Higher West of the Rockte.
WRITE TODAY FOR COMPLETE SPECIFICATIONS
FISHER RADIO CORP.
21 -27
AUGUST, 1955
44th
DRIVE
L. I. CITY 1, N. Y.
29
www.americanradiohistory.com
AmericanRadioHistory.Com
sensitive to the ratio of two voltages,
both of which are a function of the carrier. Many of the better FM tuners employ a ratio detector and one or two
limiters in addition to eliminate completely the possibility of any noise
reaching the output. It is unfortunate
that ratio detectors have been employed
in the cheapest forms of FM sets, for in
many instances they have not been well
engineered and have not given satisfactory performance, and have thus gotten
a poor reputation. This is not clue to the
circuit itself, but only the effort of the
manufacturer to produce an FM set
which could sell at a price. In well designed circuits, the ratio detector is
easily the equal of the discriminator, and
does offer some additional advantages.
Wide -band circuitry is also employed
in some ratio detector arrangements for
the same reasons, and with generally
improved performance.
Audio Systems
Most tuners are provided with some
form of audio output stage following the
detectors of the AM section or the discriminator or ratio detector of the FM
section. In most tuners there is a volume
control, which may or may not be a
panel control -being in some models a
control on the rear apron to adjust the
outputs of the two sections so that they
are approximately equal. Hi -fi tuners
generally employ a cathode follower for
the output stage so that the impedance
is comparatively low and is thus subject
to a minimum of frequency discrimination due to capacitance of the output lead.
COMMERCIAL TUNERS
Up to this point, the discussion has
been general, and has not been confined
to those products of any particular manufacturer. The remainder of the section
will be devoted to descriptions of the
tuners that are currently on the market
or to be introduced this Fall, with an
attempt being made to point out the
characteristics that are of special interest in the individual units. The writer is
indebted to the various manufacturers
for their co- operation in furnishing photographs, schematics, and operating instructions on all of this equipment, without which this section could not have
been possible.
Knight "Bantam" tuner.
Pre -emphasis and De- emphasis
According to the ,tattdards set forth
by the FCC for F \l transmission, the
audio signal being fed into the transmitter is to be altered from a flat characteristic to a curve which is described as
having a pre -emphasis of 75 microseconds. Thus the high frequencies are
boosted by a fixed amount -13.75 db at
10.000 cps. which corresponds to a turnover at 2120 cps (the point at which the
curve is up 3 db above the flat level).
This can be clone without increasing
distortion because there is relatively little
sound energy in the usual audio signal
above 1500 cps. But the principal advantage is that in order to secure a flat response from the receiver, it is necessary
to introduce a de-emphasis of the same
amount. Since noise is usually considered
to consist of the higher frequencies-in
fact, random noise is proportional to frequency-the rolloff in the receiver gives
the same advantage to radio reception as
it does in the reproduction of phonograph records. This accounts for the additional 14 db (approximately) of improvement in signal -to-noise ratio which
which was mentioned as being due to
pre -emphasis in the transmitter. This
does require, however, that measurements of frequency response be made at
some 10 to 15 db below 100 per cent
modulation in order to avoid overloading
the audio stages in the transmitter and
overmodulation in the r.f. stages. All
FM receivers have the de-emphasis built
in, usually between the discriminator or
ratio detector and the audio output stages
of the tuner.
with conventional TV receiver for video
presentation. Also available are amplifiers which match the two types of tuners in appearance and size.
A.
R. F. Products, Inc.. 7627 Lake St.,
River Forest, II..
BT -2
-
Three models basically in chassis
form. Model 400 provides continuous
tuning from 54 to 216 tic, and thus
covers both low and high VHF TV
hands in addition to the FM band. Sensitivity of 5 microvolts for 20 db quieting, cathode follower output. Employs
"Inductuner" to cover the wide tuning
range without switching. Model 500
similar in performance, but covers only
the 88 to 108 me F \l band. Model 600
covers the FM band and the clontestic
broadcast band -550 to 1600 kc.
Bell Sound Systems, Inc., 555
Road, Columbus 7, Ohio.
Marion
BT -3
Neat and compact, the Bell 2255
AM -FM tuner is styled to match the
12 -watt Model 2256 amplifier. Both are
four inches high, nine and a half inches
wide, and nine inches deep, and finished
in satin gold and soft brown, with fully
enclosed and amply ventilated housings.
The tuner employs 8 tubes plus rectifier,
and has a sensitivity of 4 microvolts for
20 db quieting on FM and a sensitivity
of 26 microvolts on AM, using the built in loopstick. Frequency response on FM
is 20 to 20,000 cps ±0.5 db; on AM 20
to 5000 cps ± 3 db. No volume control is
provided, but two output jacks are available so as to be adaptable for feeding an
an audio system and a recorder at the
same time. Employs r.f. stage on FM,
two i.f. stages, limiter, and discriminator, plus audio stage and cathode fol-
A.R.F. Model 400 tuner covering TV and FM
channels in continuous ronge.
Allied Radio Corporation. 100 N. Western
Ave., Chicago 80, III.
BT -1
Two AAI -FM tuner models are offered : the Bantam. with a 7 -tube cire
(plus rectifier). 5- microvolt sensitives
for 20 db quieting on FM and 20 -volt
sensitivity on AA1 for 1 -volt output, automatic frequency control, and ferrite loop
antenna for Ail:: and the Deluxe tuner,
11 tubes plus rectifier, 5 microvolt sensitivity for 30 db quieting on FM and
3.5 microvolt sensitivity for I -volt output on AM, a.f.c., ferrite loop antenna,
dual limiters and discriminator. Response on both. models ± 0.5 db 20 to
20.000 cps on FM on AM, 20 to 5000
cps, ±3 db on the Deluxe model, ±4 db
on the Bantam.
Also available is the new TV audio
tuner, which plugs into the Deluxe
AM -FM tuner and obtains operating
voltages from it. Employs turret -type
selector and fine tuning control and
feeds i.f. section of A \l -F\1 tuner to
provide the sound signal from TV channels. Switch on A\I -F \i tuner controls
operating voltages. Useful for feeding
tape recorder when desired. or to permit use of high- quality audio system
Bell Model 2255.
lower for output circuit. One i.f. stage
used on AM. A.f.c. on Fil may be cut
out when desired.
While both tuner and amplifier are
designed to be usable in their cabinets,
both may be removed for panel mounting. Volume and tone controls, phono
preamp controls, and loudness control
on amplifier unit.
David Bogen Co., Inc., 29 Ninth Ave., New
BT -4
York 14, N. Y.
The Bogen line-one of the largest
of three basic tuners
(without preamplifiers), two with built in preamplifiers and control facilities,
and two which have integral power amplifiers built in.
available-consists
AUDIO
30
www.americanradiohistory.com
AmericanRadioHistory.Com
AUGUST, 1955
Model AM901 -1 is intended for hi -fi
installations where AM only is available
but where above -average quality is required. This tuner uses five tubes including rectifier, vet has a tuned r.f.
stage, linear diode detector, and a cathode follower output stage. Two positions
of selectivity permit wide band reception when conditions permit, with a.f.
response extending up to 7500 cps at
only 3 db down, or the band may be narrowed so as to be down 3 db at 4000 cps.
A filter is in circuit in the wide -band
position to eliminate the 10,000 -cps interchannel whistle. Sensitivity is 5 microvolts for 30 db signal -to -noise ratio
for an output of 1 volt.
Model FM -400A is a basic FM tuner
with 6 microvolt sensitivity ( IRE measurefnent), r.f. stage, two i.f. stages and
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1955 MODELS!
Bogen Model R765.
limiter, and discriminator. Temperature
compensated oscillator provides freedom
from drift. and frequency response is 20
to 15.0(X) cps ±
db.
Model R640 is a combination AM
1
and F \i tuner nvith 5- microvolt sensitivity for 20 db quieting on FAI and a
\ for 1 -volt
5- microvolt sensitivity on Al
output. R.I. stages are employed on both
sections. with two i.f. stages. limiter,
aid discriminator on F\[ and two i.f.
stages and linear diode detector on ANI.
Spring return switch can be used to defeat a.f.c. when desired, permitting use
to tune set accurately. As with most
Bogen tuners. this model can be had in
several different housings-gold cage.
mahogany or blonde wood cabinet, or
as chassis alone.
Model R765 is an AM -F \[ tuner with
built-in preamplifier and control section.
It has 3-microvolt sensitivity for 30 db
quieting on FAI and a 5- microvolt sensitivity on AM for a 30 db signal -tonoise ratio. In addition to excellent performance as a tuner, it contains all
necessary control facilities for a home
music system. One unique feature is the
"Auto- Lock," a circuit which operate
to cut out the a.f.c. action while you are
tuning in the desired station. A second
or so later, an indicator lamp on the
panel lights up and the a.f.c. circuit is
again functioning. Controls include volume and loudness contour, seven positions of record equalization. and Baxendall -type bass and treble controls.
Available in chassis form, or in mahogany or blonde finish wood cabinets.
Wide -band AM circuit provides response down only 3 db at 750(1 cps when
desired.
AUDIO
Ale
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HUNDREDS SOLD TO ENTHUSIASTIC USERS!
FM TUNER $39.95
ARMSTRONG FM WITH FOSTER-SEELEY DISCRIMINATOR!
5 MICROVOLT SENSITIVITY FOR 30 DB QUIETING!
TUNED RF STAGE! DOUBLE -TUNED LIMITER! AC SUPPLY!
AUTOMATIC FREQUENCY CONTROL (AFC)! 180kc BANDWIDTH!
AUDIO OUTPUT 1V FOR 100% MODULATION! HUM 60 DB DOWN!
FREQUENCY RESPONSE 20- 20,000 CYCLES PLUS -MINUS 1/2 DB!
DIRECT -FEED TAPE RECORDER JACK! AUX. PHONO INPUT!
POWER AND TUNING CONTROLS
ULTRA -COMPACT
ORDER NO.
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36.888A
H
x
9'/2"
-
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EXACT MATCH OF REALIST FM TUNER! SAME COMPACT SIZE!
TUNED RF STAGE! AC SUPERHET CIRCUIT! AC SUPPLY!
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5 MICROVOLT SENSITIVITY!
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POWER AND TUNING CONTROLS
ORDER NO. 36.887A BY MAIL! ADD
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BUILT -IN TAPE JACK!
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USE WITH ANY AMPLIFIER!
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BUILT-IN RIAA -EQUALIZED PREAMP!
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ORDER NO. 33 -3034 BY MAIL! 10 LBS.
$2995
411
RADIO SHACK CORPORATION
167 Washington Street, Boston 8, Massachusetts
and 230 -234 Crown SI., New Haven 10, Conn.
AUGUST, 1955
31
www.americanradiohistory.com
AmericanRadioHistory.Com
short-wave use and broader response
for better audio quality for domestic
broadcast reception.
Model RV -32 is a more elaborate FM
tuner employing a cascode r.f. stage,
two i.f. stages. and two limiters with
a sensitivity of 2 microvolts for 20 db
quieting. Temperature compensated oscillator and a.f.c. serve to maintain a
high degree of stability.
Model RJ -43 uses the same FM circuitry, but has in addition an AM secBrainard Model ITA.
Brainard Electronics, 8586 Santa Monica
Blvd., Los Angeles 46, California. BT -5
Combined with either a 14- or a 25watt amplifier on the same chassis, the
Brainard AM -FM tuner has an FM
sensitivity of 4 microvolts, and an AM
sensitivity of 15. Frequency response is
20 to 20,000 cps on FM, 30 to 9000 cps
on AM in broadband position. A.f.c.
with provision for disabling, but drift
reduced to minimum by temperature
compensation. Amplifier has six -position compensator, preamp with 10 my
sensitivity, bass and treble controls, loudness control. Construction is on printed
circuit panel, and three feedback loops
are employed.
Unique feature is Acoustic Balance
Control which offers six positions of
compensation which is claimed to correct for any acoustic condition likely to
be encountered in the home. User consults chart which indicates acoustic values of listening room and adds up various acoustic weights from which ABC
Guide number may be determined, then
sets ABC control to correct position for
optimum quality in that particular room.
Patents are applied for on this feature.
Browning Laboratories, Inc., 750 Main St.,
Winchester, Mass.
BT -6
Most recently introduced Browning
tuners include the L-300 and L -500,
known as the "Brownie Twins." Both
are of the sanie size, 9 in. wide, 4% in.
high, and 8 in. deep, and may be had as
a chassis, or in small cabinets finished in
either mahogany or blonde wood, or
with a Telechron tinier in either type of
wood cabinet. The L-300 is an FM
tuner, with sensitivity of 3.5 microvolts
for 20 db quieting, by IRE measurements, temperature compensated oscillator. a.f.c., and a cathode-follower output. The L -500 is an AM tuner covering
the domestic broadcast band and the international short wave band from 19 to
49 meters. Sensitivity is under 2 microvolts for a 1 -volt output, and two band
widths provide sharp response for
tion which is completely independent
except for the coupling of the two tuning capacitors. Model RJ -49 is electrically identical, but the two tuning capacitors are separately controlled by two
tuning knobs and the two sections can
be used at the same time, making it
possible to receive stereophonic broadcasts transmitted over AM and FM
channels simultaneously. All the last
mentioned models are available in chassis form, or in wood cabinets with either
mahogany or blonde finish.
Collins Audio
field, N.
Products Co., Inc., WcztBT -7
J.
-if
not the only
One of the very few
-AM t.r.f. receiver on the market is
the Collins, which is patterned after the
old Western Electric l0A receiver that
was famous twenty years ago for quality
reception. This model employs three r.f.
stages with two tuned circuits between
Collins DeLuxe tuner, with t.r.f. AM section.
the antenna and the first stage and two
more between the first two stages. The
tuned circuits are coupled with a "negative mutual" coil which gives a broadband tuning curve with steep sides for
optimum AM quality. These stages are
followed by an untuned r.f. amplifier
stage and a diode detector, followed in
turn by a volume control, an audio amplifier stage and a cathode follower.
Such a circuit is capable of AM reception of the highest quality. The FM section employs a cascode r.f. stage, three
i.f. amplifiers and two limiters, followed
by a discriminator. The output of the
FM section may be fed to the volume
control and the audio section as desired
by the user. This model is equipped with
a large tuning meter, and is particularly
suited for feeding a recording channel
for superior quality. A push- button remote control unit is available for use
with this tuner, if desired, and tuning,
control of volume, and selection of AM
or FM may be accomplished from your
easy chair.
Electro -Voice Sonamusc, Model 4403.
with a sensitivity of 1.5 microvolts for
20 db quieting and a 200 -kc bandwidth,
continuously variable a.f.c., squelch circuit to eliminate noise between stations,
cascode front end, and tuning indicator.
The AM section has a sensitivity of 5
microvolts for 2 volts output, whistle
filter and squelch circuit. Both sections
are separately tuned, and dials are entirely separate, so that stereophonic programs may be received on AM and FM
channels at the same time. Model 3303
has in addition, a complete preamplifiercontrol unit with provision for magnetic
and ceramic -type pickups and several
high-level inputs. Bass and treble tone
controls are provided, as are volume and
loudness controls, and a new presence
control which has three positions to give
near, medium, or flat characteristic.
Presence control is designed to provide
boost at approximately 5000 cps of up to
12 db in NEAR position. Response on
AM is only 5 db down at 9000 cps with
the whistle filter out of circuit, and flat
to approximately 7000 cps and then an
abrupt cutoff when the whistle filter is
in circuit. Styling on these two models
is modern and attractive, only difference
being in the panel of controls along the
bottom. Model 3303, having complete
music center control facilities, has more
knobs. Main tuning knob moves to left
on toggle action to actuate FM tuning
and to right to actuate AM tuning.
Radio Corporation, 21 -27
Drive, Long Island City 1, N. Y.
Fisher
44th
BT -9
Fisher tuners have long enjoyed a
good reputation-the Model 50 -R for use
with external preamp- equalizer, and the
Model 70 -RT with preamp -equalizer
built in. Both of these models have a
sensitivity of 1.5 microvolts for 20 db
quieting, and both use cascode front end
on FM, with two i.f. stages, two limiters, and discriminator, while the AM
section employs an r.f. stage, two i.f.
stages with adjustable band width, and
detector. Response down 3 db at 7000
cps on wide -band AM. Cathode -follower
Electro- Voice, Inc., Cecil & Carroll Sts.,
BT -8
Buchanan, Michigan.
Two new tuners are being introduced
this Fall by Electro- Voice -the 3304
Sonantuse dual tuner set, and the 3303
Browning Model RJ49 -B.
Dynamuse AM -FM tuner and music
control center. The tuner sections are
identical, and comprise an FM section
Fisher
AUDIO
32
www.americanradiohistory.com
AmericanRadioHistory.Com
Model FM -80.
AUGUST, 1955
output permits long connecting cable to
amplifier when necessary without deterioration of frequency response.
The 70 -RT provides, in addition, bass
and treble tone controls, loudness balance, four phono equalization positions.
and channel selector. Hum and noise exceptionally low on both models.
The new model FM -80 employs similar circuitry in an FM -only tuner, and
is provided with two meters for tuning indicators -one to indicate signal
strength of received station, other to
indicate exact center of discriminator
curve. This model is compact, being
only 4 in. high, 124 in. wide, and 73,fi
in. deep. Sensitivity control is provided
on front panel, and level -set control on
rear apron permits adjustment of audio
output level.
ALWAYS IN
STOCK AT
ALLIED
*Ref
bination of high fidelity components
based on recommendations made
by the noted "Saturday Review"
hi -fi book. While it is very moderately priced, this system provides exceptional
audio fidelity and smooth, dependable performance. System includes: 1. Bogen DB110 10-Wan
Amplifier (
1 db, 15 to 50,000 cps; calibrated
bass and treble controls; record compensation;
shock- mounted preamplifier; attractive gold and
turquoise chassis). 2. Garrard RC-SO 3 -Speed Record
Changer with jewel- mounted arm; 4 -pole, shaded pole motor (less 45 rpm spindle). 3. G.E. Cartridges, RPX-040 with sapphire stylus for 78 rpm
records, and RPX-061 with diamond stylus for
microgroove records. 4. Electra -Voice SP12-11 12"
Speaker for remarkably clean bass and treble response. System comes complete, ready for easy
installation. For 110 -120 volt, 60 cycle AC operation. Shpg. wt., 60 lbs.
94 PA 132. Complete Phono System. Only $156.50
SYSTEM WITH FM-AM TUNER. System as above, with
addition of the Bogen R640 FM-AM Tuner, noted
for high sensitivity (includes drift compensation
and automatic frequency control).
94 PA 133. FM -AM -Phono System. Only.. ;261.25
t
New Bogen Deluxe FM -AM Tuner With
" Autolock"
Latest model R765 Tuner -Preamp. Tunes "on
station" in any area by means of delayed AFC
with "Autolock" feature. AFC is off when tuning
between stations; comes on automatically when
signal is present; locks -in for perfect tuning. No
interstation noise on FM. Exclusive "red dot"
controls for simplified operation. Tuner response:
± .5 db, 20- 20,000 cps. Sensitivity: FM, 2 mv
for 30 db quieting; AM, 5 mv for 30 db signal -tonoise ratio. Preamp response: ± 1 db, 10- 200,000
cps. Controls: Tuning; Record Equalization; Bass;
Treble; Volume-On-Off; Loudness Contour Selector; Input Selector. 3 inputs; 2 outputs; 16 tubes.
x 14U x 9' deep. For 110 -120 v., 60 cycle AC.
Sispg. wt., 17 lbs.
93 SX 887. Bogen R765 FM -AM Tuner. Net $199.50
EASY TERMSz
Hi -Fi is available from
ALLIED on easy pay-
ments: only 10^ ;. down, 12
full months to pay. Write
for the attractive details.
Bogen B50-4LC Variable -Speed Turntable
A quality manual record player with speed variable
from '29 to 86 rpm. Speed control notched for quick
selection of 331i, 45 or 78 rpm. 12' weighted (354
lbs.) turntable has rubber padded surface for record protection. Less than 1% fluctuation in speed
on line voltage variations from 95 to 125 volts.
4 -pole, heavy -duty motor. Ball- bearing mounted
pickup arm has adjustment for stylus pressure.
Takes any standard cartridge. Supplied with one
plug -in head, 45 rpm record adapter, 3 -foot phono
cable, and 6-foot AC line cord. Mounting space:
15 x 12' and 3! ' above mounting board; 2 .Ç
below. For operation from 110 -120 volts, 50 -60
cycle AC. Less cartridge. Shpg. wt., 15 lbs.
96 RX 696. Bogen B50-4LC Turntable. Net $40.40
Harman- Kardon,
AUDIO
a
15619
deep.
grid amplifier feeding conventional triode mixer, followed by two i.f. stages,
limiter, and discriminator. A.f.c. is provided, and may be defeated by pressing
in on tuning knob while selecting station. AM section consists of converter
stage feeding one i.f. stage, followed by
detector.
The Theme, Model A -310, is larger
and employs cascode front end, two i.f.
stages, two limiters, and discriminator,
with a.f.c. AM section has tuned r.f.
stage, and uses two i.f. stages. Sensitivity on FM, 1.2 microvolts for 20 db
N
only
Designed to provide the advantages
of FM reception where the cost of many
of the more elaborate models might be
a deterrent, the Granco line offers e\
cellent value for the price. While both
Inc., 520 Main
Westbury, L. I., N. Y.
BT -I1
Three models of tuners are available,
and two models combined with power
amplifiers are available, each being particularly suited for certain types of installations. Model A -200 is the smallest
model, and has a sensitivity of 3 microvolts for 20 db quieting on FM, and a
sensitivity of 20 microvolts for 1 -v. AM
output. R.f. stage on FM is grounded -
E
Famous "Saturday Review" Custom Phono System
I lere is the extremely popular com-
Granco Products, Inc., 36 -07 20th Ave.,
Long Island City 5, N. Y.
BT -10
AM and FM receivers- including power
amplifier and speaker -are available,
the model of greatest interest to the
audiofan is likely to be T -160, which
employs coaxial tuning, offers a 180-kc
linear response at the ratio detector, and
180 -kc bandwidth at the flat top of the
i.f. curve, 220 -kc bandwidth at 3 db
down, and 300 -kc bandwidth at 6 db
down. Circuit employs five tubes and
selenium rectifier, and is designed to be
plugged into the phono jack of an already- existing receiver while the phono
pickup could be plugged into the FM
tuner so that the phono switch on the
receiver would serve switch between
AM and FM, and when the FM tuner is
in the off position the phono pickup is
connected through. Sensitivity is 5 microvolts for 20 db quieting, and audio
output is 2 volts maximum. Unit is cased
in walnut plastic case with gold trim,
and is 7 in. wide by 5 in. high by 4g in.
BOG
ALLIED RADIO
CD)
ALLIED'S
68 -PAGE
HI -FI CATALOG
.
America's
r
Your guide to a complete understanding of Hi -Fi, including tips on how to
select systems at lowest cost, as well
as installation ideas -plus the world's
largest selection of complete systems
and individual components from which
to make your money-saving choice. To
own the best in Hi -Fi for less, you'll
want this FREE book. Write for it today.
ALLIED RADIO CORP., Dept. 17 -H -5
100 N. Western Ave., Chicago S0, III.
Send FREE 68 -Page Hi -Fi Catalog No. 144.
Ship me the following-
enclosed
s
Name
Address
City
AUGUST, 1955
Hi -Fi Center
Zone.
.State
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33
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3 microvolts for
-volt output. Cathode follower used for
output, and illuminated tuning meter is
employed to indicate proper tuning
point.
The Counterpoint, Model A -400, uses
a pentode r.f. stage and triode mixer,
two i.f. stages and two limiters in an
FM -only circuit. A.f.c. and tuning meter also used on this model, which has
sensitivity of 2 microvolts for 20 db
quieting. and cathode follower output.
The Recital, Model D -200, is similar
to the A -200 plus the addition of a
12 -watt Ultra- Linear power amplifier
using 6L6GB's and offering loudness
contour control, bass and treble tone
controls, and six positions of phono
equalization with the preamplifier. Tape
recorder output on rear apron is feci
from circuit ahead of tone controls.
20 db quieting, and employing a tuned
r.f. stage, two i.f. stages and ratio detector. an amplifier stage and a cathode
follower. A.f.c. is available, and is defeated by a switch on the front panel
quieting; on AM,
1
National Criterion tuner
control unit which may be plugged into
open in front panel. Separate level -set
controls on tuner chassis permit adjustment of level to balance two channels for
stereophonic reception, and then use of
volume control on preamp will vary volume of both channels simultaneously.
Flexibility of the Criterion tuner makes
it particularly desirable for the user who
is likely to demand variety of different
services from his tuner.
Pedersen Electronics, P.
0. Box 572, Lafay-
ette, California.
Harman -Kardon Model A -310
Model D -1000, The Festival, employs
an AM -FM tuner essentially similar to
the A-400 combined with a 30 -watt
Ultra- Linear amplifier using 5881's.
Other features are essentially the same
as in the D -200, except for addition of
tuning meter.
BT -13
Two tuner models are offered by this
company, whose products are well known
on the West Coast, though not so often
seen in the East. Model AFM -2, the
Paragon. offers sensitivity of 3 microvolts on FM for 30 db quieting, and of
3 microvolts on AM for 1 -volt output.
A.f.c. may be defeated when desired, and
cathode follower output is employed.
Multiplex output is available for use
when necessary. Aluminum panel and
chassis, together with special filament
system and power transformer give
better signal -to -noise ratio. AM response
is flat to 7000 cps.
National Company, 61 Sherman St., Mal-
BT -12
den, Mass.
The new model of the Criterion tuner
which has just been introduced continues
most of the features of the original model,
and offers some minor improvements.
The wide -band discriminator is still
used. and the squelch circuit functions to
eliminate interstation noise on FM. The
i.f. amplifier serves for both AM and
FM, and is so arranged that both can be
used at the same time for stereophonic
reception or for any application requiring both AM and FM signals simultaneously. Such an arrangement is particularly convenient for the recording
enthusiast, since it is thus possible to
listen to one program while recording
another.
The i.f. amplifier is exceptionally selective with steep sided curves, permitting reception of adjacent -channel FM
stations without interference. Capture
ratio -the ability of the circuit to hold
onto one station without having a
stronger one on an adjacent channel pull
it away-is such as to reject signals with
intensities up to 80 per cent of the desired signal. Unit is wired to permit use
of a multiplex unit when such transmissions are available, and recorder feed is
selected by panel- mounted switch. Circuit arrangement is such as to feed both
AM and FM outputs through preamp-
which selects phono input and the two
positions of FM reception.
The second model in the Pilot line is
model AF -724, an AM -FM tuner with
sensitivity of 3.5 microvolts for 20 db
of quieting on FM, and a sensitivity of
5 microvolts on AM. This model uses an
r.f. stage common to both AM and FM,
mixer, two i.f. stages on FM and one on
AM, diode detector on AM and ratio
detector on FM, followed by an amplifier
stage and a cathode follower. Response
on AM is down 6 db at 9000 cps. A.f.c.
may be disabled when desired.
Model AF -825 utiliies a similar front
end for both AM and FM, but the second
FM i.f. stage is a transformer- coupled
Pedersen Model AFM -2.
Model AF1l -6 employs same tuner
circuitry combined with preamp- control
unit with input selector, four phono
equalization curves, microphone input;
bass, treble, loudness, and volume controls, and outputs for tape recorder and
multiplexing. Both units are the same
in. high, 14% in. long, and 8 in.
size
deep, and may be used in individual
cabinets or mounted on panels in any
desired cabinet.
-4
Pilot Radio Corporation, 37 -06 36th St.,
BT -14
Long Island City 1, N. Y.
Comprising five models of tuners and
one model combined with a 25 -watt amplifier, this line is one of the most complete available. The smallest model is
FM -607A, a compact FM -only tuner
with a sensitivity of 3.5 microvolts for
Pilot Model AF -850.
limiter which provides considerable amplification, and it is followed by another
limiter stage and a discriminator. In
addition. this model is equipped with a
preamplifier stage with five equalization
curves. and with tone and volume controls. Separate cathode followers are provided to feed the audio line and the
recorder line, the latter being connected
ahead of the tone controls. Sensitivity
is the sanie as for model AF -724.
Model AF -850 employs two i.f. stages
on both AM and FM, with variable bandwidth for AM. These are followed on
FM by two limiters and a discriminator,
with an audio amplifier stage and a cathode follower after the volume control. A
tuning meter is provided to aid in correct
tuning, and a 10-kc filter eliminates inter station whistles on FM, and in broad
position response is essentially flat to
9000 cps. Sensitivity on FM is 1.5 microvolts for 20 db quieting ; on AM, 2 microvolts. Phono input is provided which is
suitable for use with ceramic or crystal
pickups ; external preamp is required for
magnetic pickups. Cathode -follower output furnishes maximum audio signal of
10 volts.
Model AF -860 is identical in the tuner
section, but includes preamp with separate bass and treble equalization controls
-five positions on each -volume control
and separate bass and treble controls.
Separate cathode followers feed audio
line and recorder circuit, the latter ahead
of the controls. Sensitive tuning meter
indicates correct tuning point. Performance of AM and FM tuner section identical with AF -850. This tuner, in conjunction with a control -less power amplifier would serve as a complete control
center for a home music system.
AUDIO
34
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AmericanRadioHistory.Com
AUGUST, 1955
Radio Corporation of America, Engineering
Products Division, Front & Cooper Sts.,
Camden 2, N. J.
BT -15
Two tuners are available in the RCA
Intermatched High Fidelity line-ST -2.
as a basic tuner, and S\'T -1 which is
identical except for the addition of preamplifier and bass, treble. and volume
controls. Four positions of phonograph
equalization are provided in this model.
v
lowed IN two limiters and discriminator.
Audio amplifier stage and cathode fol lower provide output signal. R.f. stage
used on both AM and FM, with a.f.c. on
latter.
Model C1000 is top set in the line.
with cascode front end on FM, two i.f.
stages and two limiters, followed by discriminator and amplified a.f.c. circuit as
..,.
esi
M-860 AM -FM
-
PILOTUNER
The Ultimate in engineering skill
and sensitivity
symbolic of the
complete line of superb
Pilotuners.
Radio Craftsmen Model
RCA Model SVT
-l.
The tuner section of these models has
a sensitivity on FM of 5 microvolts for
20 db quieting; on AM, 5 microvolts for
0.5 -volt output. Separate r.f. amplifiers
are used, and FM section employs two
limiters and a discriminator. A single
audio amplifier stage is provided, and a
cathode follower feeds the signal out.
A.f.c. is provided to prevent drift and
simplify tuning.
The Radio Craftsmen, Inc., 4401 N.
Ravenswood Ave., Chicago 40, III.
BT -16
The Craftsmen line, now sold direct to
the user and therefore not to be found on
distributors' shelves, consists of three
AM-FM tuners and one FM model. The
latter is model C900, and offers a sensitivity of 1 microvolt for 20 db quieting.
It employs a cascode front end, three i.f.
stages, two limiters, and discriminator,
followed by an audio amplifier stage and
a cathode follower. Features amplified
a.f.c. which locks oscillator frequency
more closely than possible without this
circuit, it is claimed. Circuit operates at
i.f. of 20.6 me and has 250 -kc bandwidth
most tuners operate at 10.7 -mc intermediate frequency, but higher i.f. reduces
possibility of spurious images.
Model C10 is an AM -FM tuner with
fixed- turnover phono preamp, and bass
and treble tone controls, Sensitivity on
FM is 3.5 microvolts for 20 db quieting;
on AM. 5 microvolts for 0.5 volts output
signal. Circuit employs r.f. stage on both
AM and FM, with a.f.c, two i.f. stages
and two limiters and a discriminator on
FM. and one i.f. stage and a diode detector on AM. Two audio stages are provided to furnish sufficient gain for tone
controls and these are followed by cathode- follower output stage. Separate
12Aä7 serves as phono preamp.
Model C810 is a basic tuner with FM
sensitivity of 3 microvolts for 20 db
quieting. and an AM sensitivity of 5
microvolts for 1 -volt output. Employs
two i.f. stages on AM, three on FM fol-
Cl0
used in ('900. I'hono preamp has four
equalization curves, and selector switch
feeds cathode follower with output to
recorder feed circuit and to second cathode follower which drives tone-control
circuit. Third cathode follower feeds
audio signal out. Sensitivity on FM is 1
microvolt for 20 db quieting; on AM, 1
microvolt for 10 db signal -to -noise ratio.
With complete controls and phono pre amp, this unit serves as control center
for entire system.
AA -904 PILOTONE AMPLIFIER
World famous Ultra- linear Wil-
Radio Engineering Laboratories, Inc., 3640 37th St., Long Island City 1, N. Y.
BT -17
liamson circuit
an electronic triumph characteristic of the
wide range of Pilotone
Amplifiers.
Deluxe model, the "Precedent," which
has sensitivity of better than 1 microvolt
for 20 db quieting; specification claims
sensitivity of 2 microvolts for 40 db
signal -to-noise ratio. Two outputs are
provided -one for high impedance with
2 -volt output, and one for 600 -ohm line
with 0.2 -volt output. Two meters are
used, one to show signal strength and one
for tuning to center of discriminator
band.
PA -913 PILOTROL
Professional Preamplifier Equalizer, an innovation in audio
control -and other fine products,
including the portable Encore;
reflect the Pilot
;
AUDIO
-
"Standard of
Excellence."
FOR TECHNICAL DATA AND
BROCHURE, WRITE TO:
REL
"Precedent."
Circuit uses 15 tubes plus 10 germanium diodes, and utilizes cascode front
end, slug tuning of coils with dual -tuned
antenna and r.f. coils, five i.f. amplifier
stages, three pre -limiters, two limiters,
germanium diode discriminator rectifiers, two audio amplifier stages, and
cathode- follower output. "Thermocube"
design. which provides for air flow up
through large flue through center of set,
reduces drift clue to thermal changes to
an absolute minimum. No a.f.c. is provided, but stability is more than adequate
without it.
AUGUST, 1955
RADIO CORPORATION
37 -06 36th Street
Long Island Ctty, N. Y.
35
www.americanradiohistory.com
AmericanRadioHistory.Com
The Sargent -Rayment Co., 1401
Harbor Road, Oakland 20, Calif.
Radio Shack
"Realist" FM tuner.
Radio Shack Corporation, 167 Washington
BT -18
St., Boston 8, Mass.
Two small and compact tuners are
available in this line, one for AM and
one for FM. Both are of the same size,
and are available in wooden cabinets or
as chassis for installation as desired. The
AM tuner has a sensitivity of 5 microvolts, and employs an r.f. stage, mixer,
one i.f. stage, and a diode detector. The
FM model has a sensitivity of 3.5 microvolts for 20 db quieting, utilizes a tuned
r.f. stage, two i.f. stages, limiter, and
discriminator, with a.f.c. being applied
to the oscillator. Compactness of these
two models would permit installation
where most models would not fit.
Rauland -Borg Corporation, 3515 W. AddiBT -19
son St., Chicago 18, III.
The HF -155 "Golden Gate" tuner is
an AM -FM unit with sensitivity of 3.5
microvolts for 20 db quieting on FM,
and a sensitivity of 5 microvolts on AM
for 1.5 -volt output. Separate r.f. amplifier and mixers are employed in this
model, with one i.f. stage common to both
Middle
BT -20
Two AM -FM tuners comprise this
line, being somewhat similar in design
but differing in physical arrangement
and in the tone control section.
Model SR -707 employs a grounded grid booster stage on FM, followed by
a tuned r.f. stage which serves for both
AM and FM. Two stages of i.f. are used
on FM, followed by a ratio detector,
while one of the i.f. stages serves for
\M, and feeds a low-distortion AM detector. Phono preamp offers three equalization curves, and tone and volume controls are used. Sensitivity on both models
for FM is 3 microvolts for 20 db quieting; on AM, 5 microvolts.
Model SR -808 is electrically similar,
but AM and FM sections are completely
Hermon Hosmer Scott Model 311 -A.
bitted with 150 -kc steep -sided i.f. response provide high quality with ease in
tuning. Planetary dial drive on edge lighted lucite dial gives either quick or
vernier tuning. Sensitivity is 3 microvolts for 20 db quieting ; meter shows
both signal strength and correct tuning
point. Available as chassis only, or with
leather -finish plastic- covered cabinet.
Stromberg-Carbon Company, 1225 Clifford Ave., Rochester 21, N. Y. BT -22
Sargent Royment Model
SR -808.
independent of each other. Two i.f.
stages and two limiters are used in the
FM section, followed by a discriminator ;
AM section employs another version of
low -distortion detector, with resulting
high audio quality on AM. Three equalization curves are provided for the preamplifier, and the tone flexibility is remarkable. In addition to normal bass and
treble tone controls, there are four positions of low -pass filter action and there
is also a 50 -cps high -pass filter. Furthermore, the bass tone control has two positions of inflection-250 and 350 cps. The
250 -cps turnover point is preferable for
voice when some low- frequency boost is
considered desirable but the shape of the
curve should not introduce a boost in the
"chesty" region. For music the 350 -cps
turnover is most desirable.
Three models of tuners are available
from Stromberg- Carlson-one with tone
controls, phono preamp, and 10 -watt
power amplifier, and the other two as
basic tuners only.
Model SR -405 offers a combined
AM -FM tuner and audio amplifier all in
one unit, and has a sensitivity on FM of
3 microvolts for 20 db quieting ; on AM,
5 microvolts for a 1 -volt output. Phono
preamp provides two equalization
curves ; bass, treble, loudness, and volume controls are provided. Broadband
AM response extends to 7500 cps, with
whistle filter cutting response to - 29 db
at 10 kc.
Model SR-401 offers no tone controls,
but provides volume and a.f.c. controls
as well as selector switch for FM or wide
Hermon Hosmer Scott, Inc., 385 Putnam
BT -21
Ave., Cambridge 39, Mass.
Rauland -Borg
Model
11F -155.
\ \l and M, a second i.f. stage and two
limiters are used on FM. Cathode-follower output is provided, and a.f.c. may
be used or not, as desired. Particularly
interesting feature is provision for plugging in an external TV front end to feed
i.f. amplifier with FM signal from sound
carrier of VHF TV channels. This permits use of hi -fi system to reproduce
good quality sound with picture from
conventional TV set. Tuner is 4 in. high,
10 in. deep, and 13% in. wide, with perforated metal cabinet finished in marbleized charcoal black with brushed brass
control escutcheon. A.f.c. is particularly
effective on this model, and drift is sufficiently negligible that set can be left on
a chosen station for hours without retuning, and after cooling off overnight,
the same station reappears when the set
is turned on.
I
The Scott Model 310 -A FM tuner has
been on the market for over a year. and
no changes have been required, which
speaks well for the original design. The
circuit consists of a cascode front end,
pentode mixer, three i.f. stages, two
limiters, and a ratio detector. Squelch
and cathode follower stages complete the
line -up. Steep -sided i.f. pass band together with wide-band limiters and
detector result in minimum of distortion,
low capture ratio, (desirable), and minimum of effect of drift on quality. With
this type of circuitry, no a.f.c. is necessary. Sensitivity is 2 microvolts for 20
db quieting; maximum audio output is
4 volts for ± 75 kc carrier swing. Tuning
meter indicates signal strength as well
as showing correct tuning point.
Newest model just being introduced
is Type 311, lower in price but incorporating many of the same features. Wideband limiters and ratio detector com-
Stromberg- Carlson Model
www.americanradiohistory.com
AmericanRadioHistory.Com
-402.
volt output.
Newest model to be introduced this
Fall is SR -402, which provides for FM
reception with or without a.f.c. and for
either wide or narrow band AM reception. Sensitivity on FM is 3.5 microvolts
for 20 db quieting ; on AM, 5 microvolts
for 0.25 -volt output. Response on wide band AM is ±2 db from 20 to 7500 cps.
This model will employ cascode i.f. stage
on FM, with wide -band detector. AM
circuit to have whistle filter and temperature- compensated oscillator to prevent
drift
common practice in FM tuners,
but less often used in AM circuits. The
SR-402 is 12/ in. wide, 6% in. high,
in. deep
and 10 in. deep over all, or
behind panel.
-a
9/
AUDIO
36
SR
or narrow band A \I reception. Sensitivity on FM is 3.5 microvolts for 20 db
quieting ; on AM 5 microvolts for 0.25-
AUGUST, 1955
r
IDIFFERENTIATOR
B
PATENTS
B
I
I
(from page 2)
Figure 3 is the schematic of a practical
instrument for measuring amplifier linearity. The techniques of design involved are
new to many audio men but they are essentially simple and are common to those who
deal with pulse devices.
The step -wave generator itself is enclosed in dashed lines and comprises V,
through V,,; undoubtedly the number of
tubes may be decreased by using dual triodes in many cases. V, and V, are an unsymmetrical multivibrator which produces
a rectangular wave such as that of (D) in
Fig. 2, with relatively short negative pulses
occurring at the repetition rate desired for
the entire step wave. These negative pulses
appear at the plate of V,. Phase -reversed
positive pulses as at (E) appear at the
cathode of V. and the plate of V,.
V, is a blocking oscillator which is free running and whose frequency is controlled
by the variable resistor in its grid circuit.
The frequency at which it runs determines
the number of steps in each step wave. The
output is a series of steep-sided pulses which
we have shown for the sake of simplicity
at (F) in Fig. 2 as sine waves. The cathode
of multivibrator tube V, is connected to the
blocking oscillator cathode. The short positive pulse (E) from the multivibrator
cathode cuts off the operation of the blocking oscillator once per multivibrator cycle,
for a purpose we shall explain later.
The circuit which converts the blocking
oscillator pulses into step form begins with
the cathode- follower stage V, which applies
these pulses t6 capacitor C, through the left
section of the duo -diode V. On pulse alternations which are positive at the V, cathode, C, is charged ; on the other alternations
output goes through the right section of
V. to discharge the transfer capacitor, while
C, holds its charge. In this way, each succeeding positive pulse from V, adds to the
existing charge on C, so that the voltage
across C, builds up in a series of steps.
The step charging must not continue indefinitely, but only for a period corresponding to the desired step -wave repetition rate.
At the end of each period, therefore, C,
must be discharged so that it can begin
step -charging anew. The discharging is
done by diode V,. Amplifier tube V, is normally conducting and the d.c. voltage developed across its cathode resistor is normally more positive than the maximum
charge which C, will assume under operating conditions. Since the cathode of V. is
connected to that of V,, it is biased positive
and the diode cannot conduct and discharge
C,.
However, when the narrow multivibrator
(D), comes along, it is negative at the plate of V,. and this is coupled
to the grid of V,. V, is a cathode follower
and thereupon produces a negative pulse at
its cathode and at the cathode of V. Since
the latter is now temporarily much more
negative than its plate, there is a discharge
path for C,, which promptly dumps its
charge to ground through V.. After that
the multivibrator goes back into the long
portion of its cycle, V. no longer can conduct because its positive cathode bias is
restored, and C, begins to step- charge again.
This succession of events produces the wave
shown at (A) in Fig. 2.
The wave is applied to the grid of V., a
cathode follower provided for isolation; its
high input resistance prevents any inadvertent loading across C, which would inhibit
pulse, Fig. 2
AUDIO
e
V1?
C?
Vs
AMPL IF ERI- -H
TO BE
I
LIISIEP-I
T
SWEEP
GENER-
ATOC
V13
OSCILLOSCOPE
L
STEP -WAVE
J
GENERATOR
Fig. 3
the step- charging. Its output is applied to
the grid of V,., an amplifier with both
cathode and plate outputs. The cathode output is applied (through a potentiometer
which controls level) to cathode follower
V6, which provides step -wave Signal to the
amplifier being tested. The plate output of
V,. goes to the grid of cathode follower V,,,
the output of which provides a positive
voltage to the right diode plate of Vs. Ordinarily, as the charge on C, became more
positive, the left cathode of V, would assume a positive bias and less current would
flow through the left diode on each positive
alternation to charge C,; this would leave
a positive charge on C., which would bias
the right cathode of V. and prevent complete discharge of C, on negative alternations. Current flow "through" C. on positive
alternations would then be less and less, and
the steps of C, charge would decrease progressively in amplitude. To offset this, the
amplified increase of positive C, charge is
applied to the right diode plate, to keep
potential difference between plate and cathode constant and assure complete discharge
of C. on all negative output alternations of
V,. This is a linearizing effect which gives
a step wave of equal steps throughout.
The output of the tested amplifier is connected to a differentiator with a series capacitor and shunt resistor. Since the spikes
produced are caused by the vertical portions
of the steps, corresponding negative spikes
would then take hold on each spike. What
rectifier across the V. grid, which gives
a flat baseline as shown in (C) of Fig. 2.
This is not really necessary for the scope
display, since the positioning controls can
be operated to bring down the picture and
show only the upper spike tips. The spikes,
amplified by V,., are applied to the vertical
plates of the cathode -ray tube.
The sweep generator of the oscilloscope
cannot be synchronized internally by the
vertical input wave as is usual, for sync
would also be produced, were it not for the
should be shown is a complete succession
AUGUST, 1955
of spikes corresponding in time to one corn -
plete step wave as shown at (A) or (B)
in Fig. 2. Synchronizing voltage is therefore
fed to the sweep generator from the multivibrator. Narrow pulses of either polarity
could be used since most scopes have a sync
control which can be set for either polarity.
In the illustration the positive pulses from
the left plate are used since no other connection happens to be made there. Since
these narrow pulses occur at the step -wave
repetition rate, the sweep generator can
then be set with its own frequency controls
to show one or more complete step waves.
This patent specification or any other can
be obtained for 25 cents from The Commissioner of Patents, Washington 25, D. C.
2eyidie4
.. .
Positions Wanted and Positions Open are
listed here at no charge to industry nor to
individuals who are members of the Audio
Engineering Society. Positions Wanted
listings from non -members are handled at
a charge of $1.00, which must accompany
the request. For insertion in this column,
brief announcements should be sent to
AUDIO, P. O. Box 629, Mineola, N. Y. before the fifth of the month preceding the
date of issue.
YES, SIR. I'M YOUR MAN! Ten years'
diversified broadcasting experience in
operating ... maintaining ... and repairing broadcast studio consoles, tape recorders, and transmitter. Also, directing .
producing . . . and editing studio and
remote tape and live broadcasts; assisting
... directing and engineering foreign language programs. Seeking position with
future in audio field. Resume on request.
Ted Braunstein, 1165 West Farms Road,
Bronx 59, N. Y.
37
www.americanradiohistory.com
AmericanRadioHistory.Com
hum, from motors, power transformers and
sometimes just from nowhere -apparently
this in spite of ingenious and thorough -going attention to shielding. When
the final output to the amplifier is low and
you must turn up your volume control very
high, the hum problem is magnified.
So far, I haven't been able entirely to
clear up the underlying hum in my installation of this pickup and I'm ready to admit
that, as Dopey Canby, the trouble is my
fault. I've heard others just like mine playing away beautifully without a trace of that
annoying B- natural derived from 60 -cycle
AC. But I also found that even with the
tranformer, there was not enough output
from the pickup to drive a rather elderly
ten -watt amplifier that I use for emergencies-an amplifier that is very much like
a couple of million others now in use. The
cartridge drives my "big" amplifiers entirely adequately but the ten-watter gave
a half-hearted mezzo-forte at wide-open
volume, and there was some hum.
It seems that there is an excellent reason
for ultra -low output and transformers. Better sound quality, better pickup response.
This is one of those typical situations where
the engineers are faced with a pair of ugly
alternatives and must find ways to have
their cake and eat it too. If you want top
pickup response, as things now stand, you
must take very low output along with it.
There was a time, back seven or eight
years, when the present magnetics were
considered to have much too feeble an output for home practicality. The omnipresent
GE cartridge was often criticized at first
for too -low output. It is no longer. The
attendant problems have been conquered
in the great mass of home -type, medium cost equipment and the GE reigns supreme
-with the same old low output -the most
widely used and most inexpensive magnetic
-and
UD'
Pdward
INTERIM REPORTS
Shakedown
IT'S ALVAvs TIME for an interim report
in this department. It's not often that
I will ever get beyond the "interim"
stage, as a matter of fact, because, after
all, there is no ending to the sort of rough
and practical in -the -home test that seems
most useful here. An engineering report
(see our EQUIPMENT REPORT, almost any
issue) is something else again; there, the
concise and objective instrumental measurements of performance can be presented once
and for all (at least as far as the individual
part under test is concerned) and that is
that.
But this column knows its own business
and swings wide of engineering reporting.
Instead, my treatment is comparable to that
of the Shakedown, and a very good term
that is, too. Put the gadget to work -hard
-and just wait, to see what happens. Something always does. Like the brand new
amplifier that quietly went up in smoke on
me a few weeks back. Defective transformer But that, needless to say, is a freak
and unimportant since the amplifier maker
wasn't responsible for the defect. I'm interested in more routine happenings, in performance as measured by Mr. Average
Consumer (represented in fiendishly concentrated form by me), in features both
good and bad, as dopey Canby (deliberately
dopey) ignores the instruction sheets and
the printed warnings and plunges happily
ahead. (Who ever looks at instruction
sheets first? Maybe you do, but the average
buyer just can't resist plugging things together immediately-to see what happens.
Later on, especially if something goes
wrong, he gets around to the instructions
and the warnings.)
Just plug it in-and wait. That's what I
say. And if nothing happens-wait some
more. If after several months or maybe a
year or two nothing untoward has yet happened, by golly that product is good. And
the longer I wait the better it gets, so to
speak. Also, the better I get to know it in
actual working conditions, for its longterm quality, its convenience, its operation
in comparison to other items. So here goes
with a few interim items, in various stages
of interimity, if I may make up a pleasant
word.
!
Pickering.
Nope, not a new Pickering, though a new
one has, at this writing, been announced
to the trade and no doubt will shortly be
available. I'm thinking at the moment of the
1.
"old" Pickering phonograph cartridge, not
the ancient models, large -size, but the current miniatures, the 200 series, which come
in turnover double form and also in single
models. You see. I picked up one of the first
of these a couple of years ago (was it ?)
L
âtnall Canby
and that cartridge remains one of three
which seem to survive every temporary
inroad by constant new and lively competition. I try the others, and there are a number of them in various stages of interimity.
Some of them will never get to interim
first base, others are in operation, but not
too dependably. What strikes me about the
Pickering is its remarkable reliability. It
just keeps on working and it never makes
me any trouble.
The newer pickups now being introduced
are technically a good step ahead of anything we've previously had, as far as sheer
performance is concerned. But they bring
with them weighty problems for the home
user. Transformers that pick up hum most
devilishly (though of course "properly
mounted," they should not), odd shapes,
delicate innards, ultra -low output, damping
materials that prove unsatisfactory after
awhile, and so on. I suspect that the Pickering 200 will not quite match the newer
model that may soon supplement it, in absolute terms of ultra -high engineering performance. Possibly several of the newer
special jobs can also outperform it-in
the lab or ynder ideal conditions. But in
the home, no. There just isn't anything
much to go wrong in the Pickering, the performance is excellent and the voltage output is so high (for a magnetic) that hum
pickup is virtually impossible and the feeblest amplifier will be driven to its heart's
content.
Here's a pickup that has tremendous promise, not entirely fulfilled as
yet. Under ideal conditions, i.e. correctly
installed and used with good equipment, it
performs beautifully and offers several
pleasant features for the home user. The
tiny, lightweight arm is convenient and the
slip -on cartridges are easily handled. The
78 large- groove cartridge has, moreover,
an oval stylus instead of round, which,
though I haven't had a chance to experiment with it in detail, is intended to improve
the reproduction of old 78 records, especially near the inner grooves where loud
passages involve very steep and sharp corners for the stylus to tract. The oval point
slips around these with greater ease than
would a broad -beam standard round stylus
and so "fuzziness" is reduced, more music
comes through. An excellent idea and those
who value their 78's should investigate at
once. Any pickup that offers direct improvement in tracking the old -style discs
is a priceless hope for many ardent record
collectors. One important feature of the
cartridge is definitely worth mentioning
low output and the need for a transformer.
Low output is characteristic of a number
of new pickups and, though this offers no
real problem to the engineer and the advanced amateur, it should be pointed out
that in all such pickups there are inherent
characteristics that may prove embarrassing
to the amateur: Transformers do pick up
2. Ferranti.
-
cartridge.
Now we drop down again to a new and
greater low, speaking voltagewise. The
problems are back. But they may well be
conquered once more and. you can be sure.
the process has already begun. Bring the
mountain to Mohamet. Design the better
pickup, then make the rest of the equipment conform
But, for the time being, keep an ear out
for hum whenever you install a new ultra low- output job like the Ferranti, or the
Fairchild, the ESL, etcetc. They are the
excellent pickups, as to performance, but
they need race -horse treatment to win the
performance race.
!
3. AR -1.
I've had the new Acoustic Research speaker system in use for some time
now and I must admit that I am delighted
with it, so far. This is the speaker that.
uniquely, substitutes a springy pillow of
air for the stiffness in the usual speaker
cone. Its specially designed cone speaker is
limp and flabby, and would be entirely useless in any ordinary enclosure. But when
it is sealed tightly into the special AR -1
box, the infinite elasticity of air itself,
compressed behind the cone, provides a
virtually perfect springiness against which
the sound -motion of the voice coil can operate. A most ingenious idea.
The best thing about this new principle
is that the required body of air must be
small
cannot be large-and so the size
of the cabinet is necessarily small. It cannot
be large. Now this is something! All earlier
small speaker enclosures, including the R -J,
represent some sort of compromise, though
the compromise in the R-J models could
be said to be practically non-existent. But
here is a speaker system that is required
to be small and cannot be made large under
any circumstances. For that reason, the
-it
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38
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AUGUST, 1955
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t
makers are ready to compete against any doubling, for spurious big bass -indeed, the
speaker system, however large, in this, their bass from the AR -1 is reassuringly modest
first model. Other factors are involved in
and not overloud, a very good indication
of genuinely flat response, as opposed to
sound quality, of course, but as far as sheer
size is concerned, the AR -1's smallness is
tricked -up or faulty bass.
no impediment at all.
Another excellent indication of quality
The AR -1 (how I wish it had a more in the bottom tonal range is, paradoxically,
vaguely
the
response of the system to the speaking
This
one
sounds
name!
euphonious
like a dog's growl. Arrrr !) costs in the male voice. It's a well -known principle
neighborhood of $185, complete. It is there- that a "boom -box" with resonant, peaky
fore a top -quality system, competing with bass will reproduce the voice in boomy
numerous fancy outfits most of which are fashion, whereas a really flat system brings
very much bulkier. The Acoustic Research it through cleanly and without added "bottom." That's the way the voice sounded
people will admit no restrictions at all on
quality of performance. They are quite on the AR -1. Sounded as though the bass
name
speaker weren't even working, which is
you
can
ready to meet any competition
head -on, no matter how elephantine. They just as it should be.
The AR -1 is small, but remarkably
have urged me to make any comparison I
heavy for its size as I found when I started
wish -but to date I haven't done it, not
to carry it around. It's still easily portable
because the AR -1 is inconvenient to handle
but because the competition is not generally
and has already travelled hundreds of miles
in the moveable category and I have a small
on the back seat of my car. But the iron
living room!
in that woofer must be plenty big, and the
woodwork in the cabinet is, for a fact,
Besides, I prefer to put a speaker to
enormously solid and thick, far beyond
work, as usual, under normal non -A -B
most cabinets. This is a necessity in order
conditions of use in the home. You'll learn
to provide the rigid support needed for that
as much that way, or more, than any set
internal air -spring behind the speaker cone.
of A -B tests can tell you. I did try AR-1
against a setup already present, involving But it's also highly desirable in any piece
of furniture that is supposed to last awhile
not
a 15 -inch bass reflex speaker, plus a
without warping or coming apart. Good.
so-new cellular -type 800-cycle tweeter. The
There is only one significant compromise
AR -1 outshone this system both on the botnecessary in the AR-l's general design. I
tom and on the top -though it also costs
didn't find it half as much a problem as I
a good deal more, to be sure. No doubt
had been led to expect. The speaker is inabout it, this little box is out after the big
efficient, necessarily. It doesn't make much
competition.
Let's get a better mental picture of this noise for a given input. I don't know how
piece of equipment. The AR -1 is an oblong it compares with "average" in terms of
box slightly larger of girth than the "book- db down, but the difference is certainly
shelf" type 8 -inch enclosures now so popu- noticeable. Yet with a good quality amplilar, but only by an inch or so. It could fier, I found, there is plenty of gain to fill
easily be mistaken for one of them several any large living room to bursting with volonlookers have been confused by the small ume. On a 20- watter I didn't come anywhere near to the full available volume besize. The box holds two speakers behind
the grill cloth. For the lows there is the fore my hands were in my ears.
The speaker is not recommended for use
special limp -cone job, ten inches in the outer
opening as you feel it with your fingers. with small ten -watt amplifiers, and soFor the highs -and this appeals greatly to natch-I immediately hooked it up to one
(the same elderly model mentioned above)
me -there is a 6 -inch cone speaker, the
familiar Altec 755, once Western Electric. to see what it would do. Shakedown system.
the
rear
I can describe the results easily. Indoors,
A tricky set of binding posts on
in a fair-sized living room, the ten -watter
allows for both 4 ohm and 8 ohm hook -up,
and also provides normal, increased and did all right with AR -1 at a moderate lisdecreased high response to compensate for tening volume. But I had the throttle advarying acoustical conditions. Good. ( Mine vanced a good ways up. Just for kicks, I
took the speaker outdoors on the lawn and
has, in addition, external means for contried listening to music as I mowed the
necting as a woofer alone, eliminating the
lawn. (A silent -type hand -push mower,
tweeter. I suspect this is not standard equipin
that merely produced a good, solid backment, but installed for my edification
ground of whirring white noise.) Well, that
making comparisons.)
How does it sound? Excellent! The fea- did it. Not many systems will sound "loud"
ture of the speaker is, of course, the unique outdoors, with nothing to reflect and plenty
system for propagating lows through the to absorb -tress and bushes and grass for
miles in all directions. So I revved up the
limp -cone infinite sealed baffle arrangement,
but I must quickly say that the highs im- ten -watter and got a listenable volume as
pressed me immediately as very lovely, long as the music stayed in the mezzo -forte
musical
(for range. But when it began to get real loud.
smooth, unprepossessing,
music) and unusually natural. No fancy the sound broke up badly. Too much for the
super -hi -fi screetch and scratch. Congrats, ten -watter.
Now nobody in his sane mind is going
here, to the Altec, which was chosen from
to use the AR -1, at $185. to accompany outnumerous tweeter possibilities as the best
door
lawn- mowing. And so I suggest that
sounding. I agree.
the inefficiency of the system is not very
As to the lows, I made no instrumental
measurements of course. (See the article important for most of us. The place where
it will show up most, of course, is in that
in Audio on this speaker, October, 1954,
salon
entitled "Revolutionary loudspeaker and utterly artificial situation, the sound
enclosure" for a technical account and, AB comparison. With the same signal inless loud
more recently, "Commercial acoustic sus- put the AR -1 will play noticeably
pension speaker," July, 1955.) But I was than many other speakers. To some, thereBut
anybody
good.
as
fore,
it
won't
sound
no end impressed, from the first time I ran
my finger over a pickup stylus and got who listens that foolishly, with nearly 200
a dope.
that hearty, wall- shaking thump that be- bucks in the balance, is worse than
tokens real bottom bass to the time when I Just equalize the volume levels on all the
fair
and
comparison,
for
a
speakers,
tests
had played records and tapes on the speaker
for some months on end. There are excel- you'll know what's what.
Nevertheless -you'd better hook up the
lent indications of good response in the
AR -1 to at least 20 watts or you'll have
sound. The bottom is clearly apparent and
(Continued on page 49)
there isn't much indication of frequency
AUDIO
40
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AUGUST, 1955
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DISCS
EDWARD TATNALL CANBY "`
covered in these
pages are clumped into convenient
categories, in whatever way seems interesting and useful, regardless of manufacturer or label. This is as it should be,
for the primary interest of most readers
is in the content of the new records, not
the color of their labels.
But in the long pull it turns out often
enough that for purely categorical reasons
a good many discs just don't get included
-they don't happen to fit in the scheme of- the -moment. And no matter how many
subjects I dream up, like "Audiosities" and
"Pot -Pourri," to take in as wide a choice
as possible, I still don't always keep up with
everything I'd like to. So, for a change, I'll
begin looking at a few labels this month,
brand by brand. Justice where justice is
due and, incidentally, an interesting new
slicing of the pie.
ORDINARILY THE RECORDS
M -G -M
This "classical" label, stemming from the
huge film enterprise, has made commendable
use of American-located talent, where
other labels have featured mainly Europeanrecorded material. The entire stack of
M -G -M records I have on hand from recent
months is American-performed.
This is commendable for, as we all know,
recording in this country has its problems,
not the least of which is the much greater
expense. But there are even more important problems, as far as engineering and
artistry are concerned. We have acoustic
troubles here. Too many of our engineers
are still attached to film and TV techniques
and to the dead, ultra -close -up sounds essential for that kind of work. M -G -M has
suffered for a long time from over -dead
studio recording.
A second problem is musical in nature.
Music costs money hereabouts and rehearsals are more often than not cut short. We
have plenty of expert musicians -too expert. They are perfectly capable of playing
really difficult music with scarcely a rehearsal, but the results, especially with unfamiliar music, are rarely as good as when
the music is intimately known after long
and careful rehearsal. At European rates
of pay, rehearsals generally can be longer
and more thoroughgoing, and, it seems, the
traditions over there are such that longer
rehearsals are more or less taken for
granted, as shorter practice is here. These
things are major problems for all who
try "classical" recording in the U.S.A. and
M -G -M has gleefully stuck its head into
a hornet's nest of them with its forthright
780 Greenwich St., New York 14, N. Y.
all- American policy. I think we can afford
to be understanding, then, though in the
interests of honest reporting the shortcomings (measured against European-recorded
competition) must be noted as they show up.
M -G -M has been singularly fortunate in
its solo piano department, notably in the
performances by Menahem Pressler, who
is one of the finest and most musical of the
younger pianists. The M -G -M stable is now
expanding with such names as William
Masselos, Marga Richter, Lenore Engdahl,
artists whose names are relatively new on
the scene and whose reputations will rise
along with M -G -M's as a result of their
records.
Other new forces are appearing at
M -G -M and there are good signs of a more
imaginative and competitive musical approach than has been evident in the past.
M -G -M does a superb job on piano recording and, aside from the prevalent dead studio acoustics, turns out excellent hi -fi in
its instrumental ensembles as well, though
pressing is a bit erratic here and there.
A special mention should be made of the
excellent and detailed jacket notes for
M -G -M by Edward Cole. They are so long
that the print is often microscopic but, if
your eyes can take it, they offer fresh and
original comments on the music in a most
readable essay form.
(P.S. I'd like to see a nice, new M -G -M
label to replace the present somewhat jaundiced yellow job -now that the M -G -M
albums have been dressed up with a shiny
finish. Adds dignity.)
Lambert: Concerto for Pianoforte and Nine
Players.
Lord Berners:
Piano
Music.
(Fragments
Psychologiques; Le Poisson d'Or; Three
Little Funeral Marches.) Menahem Pressler; ensemble cond. Theodore Bloomfield.
M -G -M E 3081
Constant Lambert, of the once -popular 'Rio
Grande" and a lot of other lightish British music,
here writes a serious piece of modernity dating
from 1933 that is probably a fairer representation
of Lambert's real aspirations than his easier stuff
ordinarily heard. It's a nicely colored piece combining a mild (for our advanced ears) jazziness
with a rather academic modernism, tinged still
with a trace of that unmistakable Elgar- Delius
elegance that still haunts British music even today.
Nice sonorites and the dry, close -to recording is
in this case musically appropriate.
Lord Berners was one of those musical amateurs of great talent who are to all intents and
purposes professional composers. Borodin was
another-his proper occupation being a doctor.
Lord Berners was a miniaturist. Like Satie (and
well after Satie) he turned out small, pungent
satires with tricky titles -his funeral marches
here are For a Canary, For a Rich Aunt, For a
Statesman; his Psychological Studies are only
seconds long and involve a Hate, a Laugh and a
Sigh -outward humor which, of course hides a
seriousness of purpose underneath. The music is
very dissonant, in a somewhat dated sort of way,
and rather too fragmentary for sustained listening
though well constructed.
A good "period" coupling, this record, and it
should be in every school and college music
library, along with-
Piano Music of Erik Satie. William Masselos.
M -G -M E 3154
Old goat-bearded Satie was the driving force,
the impishly persistent leader of the young radicals in France before the First War. He wrote
pieces with preposterous titles -"Piece in the
Shape of a Pear " -ripping the last remnants of
sentimental Romanticism to shreds, and thereby
vastly stimulating a whole generation of new composers, French and otherwise. Everybody in music
knows about Satie and most composers look up
to him, especially the French and the French.
trained Americans. But nobody ever hears him.
Now, if you can wish, you can decide for yourself just why, via this interesting collection, which
includes such items as a group of Veritable
Flabby Preludes for a Dog, Chapters Turned
every Whichway, Dessicated Embryos. An old
devil, this Satie.
But the reason Satie is talked about but not
often heard is fairly clear to me, at least. The
plain fact (blasphemy!) is that his music just
doesn't measure up to its saucy subject matter.
The man was undoubtedly a tremendous personality, what is usually called a "seminal influence,"
the sort that gets everybody else to going full
steam. But his own music is really ordinary, all
things considered. Nice and catchy, well written,
but with more than a touch of music -hall commonness to it and an over -all style not so different
(though less forceful) than much of the saucier
Debussy piano stuff.
Masselos plays forcefully and well and the piano
recording is tops. As I say, this one, too, should
be in every library. But it won't land in many
home collections, I predict.
Hindemith: Educational Music for Instrumental (string) Ensembles, op. 44. Maurice
M -G -M E 3161
Levine Sinfonietta.
Here's a remarkably interesting and listenable
disc that, on first glance, might seem bound for
the school study library too. Not at all!
Hindemith, you see, was a 20th century pioneer
in the revival of what is actually about the oldest
kind of music there is -music for use, composed
on specifications for a particular need.
There was no other kind, until Romanticism
came along and proclaimed that art was for art's
sake. Music, like other arts, has always been most
successful when a concrete goal has been in mind,
with a concrete and appreciative audience that
knows the rules and, indeed, creates the demand.
What would baseball be like if ball players suddenly became artists and demanded freedom to
make up their own rules! It's a wonder, I say,
that music survived at all under this sort of
Romanticizing. It still suffers a lot from it.
So- Hindemith wrote "practical" music and,
it happens, he was good at it, perhaps better at
it than at writing big, "important" pieces. Bach
AUDIO
42
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AUGUST, 1955
HEATHKIT
too, as witness the piano Inventions and
many another study piece. An etude, nominally
and often practically, is -3 study piece -but there
are some mighty fine etudes that are good for
listening, too.
These string pieces, many and short, date from
the late 20's when Hindemith was at the top
et his youthful maturity and possibly a better
cc mposer than he is now. (A fresher one, anyhow.)
lie starts with violin for beginners and the first
little piece, for two groups of fiddles or two fiddles
a.one, employs only two notes in each part. How
can you write music with two notes only? That's
tl e point! Beginning with such drastic limitations,
gradually adds more difficulties, more
-I indemith
notes and faster rhythms, for progressive violin
study. The audible spectacle of a first -class musical
tr nd doing stunts within such drastic limitations,
was,
"BUILD IT YOURSELF"
apIifier
k
1
1,Aiding little miracles out of almost nothing,
is
cite the most absorbing thing I've run into in
long period of record sampling.
The thirty pieces, in four groups, include a
's sole first side for violins only. After this long
a-.d intensely interesting exploitation of the violin
. - -.oir by itself, the appearance of the other stringed
instruments, on side two, has a remarkable impact of newness and drama. This is the essence
of real music- making, the principle that the great
early composers (beloved by Hindemith himself)
knew so well. After pages of simple diatonic
music with, say, all "white" notes, the old fellows
knew that the entrance of a single E -flat or A -flat,
a "black" note, could by sheer dramatic contrast
produce an extraordinary effect. Economy of
means! That's what we lack today.
The Levine strings play Hindemith most symlathetically and the recording is excellent, the
not -so -live acoustics entirely appropriate for the
music. I heartily recommend this disc for straight through listening, as a basic experience in the
growth of music out of the simplest beginnings
into complexity. I'll eat my hat if, after one or
maybe three playings, you don't feel its cumulative
power.
1111i14
q
a
mostly under Iz-
dead muffled
studio type, has been equally at
ault.
This disc would seem to be transitional. The
-ecording is the same close -up type but at least
t is not hopelessly out of place in this fairly intimate type of music. Yet other competing versions
the same music feature gorgeous resonant
liveness that for most ears is bound to seem more
attractive and natural. Ultra -dry acoustics always
make for tough listening, in any music.
I'd feel happier if I thought M -G -M really
believed in this dry, close sound as appropriate
to Mozart. But, instead, I suspect it was merely
automatic and a happenstance, indicating a lack
:,f imagination somewhere along the production
f
line.
The playing of the Mozart is curiously uneven.
Some pasages, notably by the oboe, are produced
with great beauty and sensitivity, but the whole
impression, nevertheless, is one of lumpiness, too rigid rhythm and no poetry. There is, again, that
indefinable sense of routine, the "we'll play anything you give us" attitude of the professional
musician doing a job. This is not a "dedicated"
Mozart performance with heart and soul put into
it by all participants, and it should be.
For these happen to be two of the finest works
in the Mozart repertory, both extraordinarily vivid
and intense, and the competition, on other LP
abels, is formidable with excellent recordings of
the same music from Vox, Westminster, and
others. Has M -G -M heard them?
Hovhannes: "Khaldis" and other works.
Wm. Masselos, piano, with Chamb. Ens.
cond. Izler Solomon.
M -G -M E 3160
Hovhannes is a curious composer -an Armenian- American whose formal musical education was
strictly Boston -made, whose first thousand works,
many in a vaguely Sibelius -like style (we are told),
were destroyed when the composer set out to com-
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Until recently M -G -M's instrumental ensemble
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AUGUST, 1955
EMATICill
43
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!1
fundamental Armenian orientalisms with
Western techniques, for Western instruments.
He's been at it now for some years and the Hoybrume- stamp is unmistakable and inimitable, as
abundantly illustrated by these works for variously
colored instrumental combinations.
This is oddly un- Western music. It does not,
like other Western music, rise to climaxes, fall
into hills and valleys of emotional force, it has
no fixed center, no very conclusive beginning or
ending, it simply is, in a hypnotic, repetitive but
endlessly interesting way. As Virgil Thomson
said, this music is like a long roll of hand -made
wall paper, no two designs just alike but with a
compelling sense of dynamic motionlessness.
Unique!
The "Khaldis" concerto features piano, four
trumpets and percussion but it is unlike any concerto you can imagine. The piano writing is the
typically liquid, plunking, oriental sort Hovhannes
has developed. most effectively ; the trumpets play
fascinating silvery repetitive counterpoints among
themselves for minutes at a time, then fade gently
away; the percussion makes irregular background
rhythms that pulse, but never march. And the
"key," the "harmony," mostly modal in a rather
beautiful way, stands still for long periods, supporting lovely, sensitive, flowing, dynamically
static melody. like the monotonous flow of fountains.
On side 2 there are exotic new sounds, piano
solo, beginning with a strange piece played in
part with a rubber mallet inside the instrument,
for long, slow, ominous rumbles of musical distant thunder, which seem to grow without percussion, defying the laws of piano tone -production.
A good deal more effective music and much less
pretentious than the piano experiments of John
Cage, I'd say. Later on we hear a mandolin sound,
via a soft plectrum that picks at the piano strings.
And throughout, there is that same, hypnotic,
dreamy oriental mood that is so characteristic of
Hovhannes. Most interesting to hear.
I'm inclined to feel that it really doesn't matter
whether we classify this sound as "good music"
or bad, or even whether it is music at all. Like
Varese's "Deserts" (see "AUDIO, ETC.,"
July), you'll find this of interest simply as
Organized Sound, sound in patterns that are perceived by the ear and the emotions.
The performance is, so to speak. from the
horse's mouth; Masselos has been closely associated with Hovhannes since the beginnings of his
oriental style and is, indeed, about the only Hovhannes pianist available who really has absorbed
the music to the hilt.
Gorgeous recording, particularly nice in the
trumpets and in the piano. The dreamy quality
of the music seems oddly to create its own liveness; there is no problem at all here in the actual
acoustics though the recording is not particularly
bine
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Hovhannes: Incidental Music to "The
Flowering Peach" ( 1954) ; Suite From the
Ballet "Is There Survival?" (King Vahaken) (1950- 1955) , Orbit No. 1. Various
instr. ensembles conducted by the CornM -G -M- E 3164
poser.
Ïi
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An interesting sequel to the above, for here
Hovhannes travels the time- honored road from
"pure" music to music on Broadway. In a sense
the "Flowering Peach" represents commercial
music. The show was a vast success in a big way.
But, as you'll quickly hear, the compromise is
very slight, if there can be said to be any at all.
Yet there is a difference, in the "Peach," perhaps simply the latest constructive advance in the
prolific Hovhannes technique. Least important,
though first to be noticed, is the use of the more
conventional theatre instruments -alto sax, harp
and the like. More interesting is the beginning of
motion. For here, though the dreamy, exotic atmosphere remains, there is a change which may
represent a new consolidation of the timeless East
and the dynamic West in Mr. Hovhannes' fertile
East -West mind. Somehow, ever so intangibly,
these melodies move onward a bit, Western- style,
and the fascinating hypnosis is lifted a trace.
The "Survival" score, rewritten in 1955 from
a 1950 ballet, combines audibly the two eras. At
the beginning there are the same trumpets as in
"Khaldis," here composed originally a few months
earlier, and the same hypnotic repetition without
motion. But there are other parts that move outward, more like "Peach," and these must be in
part the 1955 revision -expansion. Highly colored
again (and nicely hi -fi to match), with strangely
used celesta, sax, percussion, harp and what -not.
Exceptionally good sound quality throughout with
excellent, imaginative microphoning. This is the
New Order at M -G -M, I should guess, and it
rates a hi -fi double star.
Piano Music for Children by Modern American Composers. (Copland, Cowell, Diamond, Hovhannes, Harold Lawrence, Per sichetti, Marga Richter, Alan Skelly, Virgil
Thomson, Stanley Wolfe). Marga Richter,
piano.
M -G -M E 3147
M -G -M has been issuing, intermittently, an excellent series of documentary piano recordings,
so to speak, spreading forth a vast repertory of
modern pieces for children's piano study -playing,
not listening -by many composers of today. Notable in the catalogue are Manahem Pressler's sensitive playings of the immortal Bartok "For Children" (E 3009, E 3047), (though several other
equally good readings exist also on LP) and
another disc that includes Malhaud, Bloch, and the
rather dull Shostakovitch "Six Children's Pieces"
as well as the ineffably beautiful and moving
"Music for Children" ( "Summer Day Suite," in
the orchestral version) by Prokofieff.
Here, Marga Richter plays a sympathetic host
to a mixed group of moderns, all writing as well
as they are able for children, and from their various viewpoints towards the needs and emotional
abilities of the childish fingers and mind. Too
much to describe in detail -and the listening is
tough, too, since the order of the pieces is different on the record and in the album commentary and so you must stop the disc at the end of
every band to see what comes next.
My general comment is that, though these are
generally a bit either too cute or too sophistcated
for kids' minds (missing the bull's eye on both
aides), they are on the whole very well put together, reasonably expressive and well within the
graded categories that are conveniently provided
(also the publishers) for teachers' use. Yet few of
them, it seems of me, really approach the high
plane of communion in simplicity that really first rate children's music must have. Children are not
dopes, nor are they incapable of emotion -far
from it. A genuine sympathy for children's unlimited musical intuition, as in the case of
Prokofieff, is as rare in music as the same thing
in the field of children's books.
Still -when you think back to the utter dishwater that is ordinarily served up to kids for
their piano practice in the early stages (will I
ever forget "Fun, Fun, O what fun, Music Lessons have begun !"), these many little pieces are
superb in comparison. The classics, yes -Bach
and Mozart and the rest. But let's have at least
a bit of today in our kid's training. These pieces
will do the job nicely, especially (as my ear
caught them), the "Little Piano Book" of Vincent Persichetti and the short items by Harold
Lawrence. out of Prokofieff.
Note: A sequel, "Piano Music for Children by
Modern Composers," including Hindemith, Satie,
Hovhannes, Surinach and Toch (E 3181), is worth
investigating thoroughly if you are interested. I'm
putting it aside for later digestion when I've
caught up with the ten composers and the dozens
of individual pieces in the first volume, above.
Milhaud: Saudades do Brazil.
Villa- Lobos: Saudades das Selvas Brasileiras
and other piano works. Lenore Engdahl,
piano.
M -G -M E 3158
A logical pairing, I admit, and fine for those
who are interested. But, after four or five of the
Milhaud evocations of Brazil from the early 20's,
in that slightly Latin -American, smart-aleck, dissonant style of his, I get entirely bored, though
each one in itself is piquant and pleasantly acid.
Too much of one not very important good thing.
The Villa -Lobos just goes in one ear and out
the other, try as I will to concentrate. I'm afraid
I hear V -L about as he composes -as endlessly
as a babbling brook that never stops. He seldom
does, and I seldom can keep my attention on him.
A personal reaction and if you feel otherwise
you'll find Miss Engdahl a powerful pianist with
a vast dynamic range, from smooth and lyric to
trip- hammer double - forte. Not exactly a poetic
or sensitive pianist here, but perhaps that isn't
her fault but V -L's. Excellent piano recording.
ultra -natural,
AUDIO
44
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AUGUST, 1955
SOUND TRUCK RESTRICTIONS
froid paye
li
)
of police. He stands athwart the channels of communication as an obstruction
which can be removed only after criminal trial and conviction and lengthy appeal. A more effective previous restraint
is difficult to imagine.
"Loudspeakers are today indispensable instruments of public speech. The
sound truck has become an accepted
method of political campaigning. It is
the way people are reached. Must a
candidate for governor or the Congress
depend on the whim or caprice of the
chief of police in order to use his sound
truck for campaigning? Must he prove
to the satisfaction of that official that
his noise will not be annoying to people?
"The present ordinance would be a
dangerous weapon if it were allowed to
get a hold on our public life. The highways and places of public discussion can
be controlled. But to allow the police to
bar the use of loudspeakers because
their use can be abused is like barring
radios because they too make a noise.
"The police need not be given the
power to deny a man the use of his radio
in order to protect a neighbor against
sleepless nights. Any abuse which loudspeakers create can be controlled by
narrowly drawn statutes. Courts must
balance the various community interests
in passing on the constitutionality of
local regulations of the character involved here. But in that process they
should be mindful to keep the freedoms
of the First Amendment in a preferred
position."
Loudspeaker Uses Limited
Six months later in a controversy involving a similar ordinance of Trenton,
New Jersey, which prohibited the use
of an amplifier "which emits therefrom
loud and raucous noises," the court set
the boundaries to the use of loud-
speakers.3
"If enforced, freedom of speech in
disregard of the rights of others would
he harsh and arbitrary in itself. That
more people may be more easily and
cheaply reached by sound trucks, perhaps barred from some zealous supporter, is not enough to call forth constitutional protection for what those
charged with public welfare think an
annoyance, when easy means of publicity are open. This ordinance bars
sound trucks from broadcasting in a
loud and raucous manner in the streets.
"There is no restriction on the communication of ideas or discussion of
ideas by the human voice, by newspapers, by pamphlets, by dodgers. We
think that the need for reasonable protection in the homes or business houses
from the distracting noises of vehicles
with such sound amplifying devices,
justifies the ordinance."
3 Kovacs v. Cooper, 52 A.2d 806, aff'd.
336 U.S. 77, New Jersey.
AUDIO
Let's Get EFFICIENCY Straight
THE experienced engineer understands that
high efficiency in any piece of audio equipment
implies high sensitivity over a limited working range.
But many laymen have come to believe that
high efficiency indicates greater audio quality
in a music system. Speaker A sounds louder than
Speaker B at the same amplifier-gain setting:
therefore, Speaker A is thought to he the better.
-
High efficiency, in this sense of greater loudness,
is the result of a pot- bellied middle
that is,
great power in the middle frequencies to which
the ear is most sensitive.
with a weak or absent bass and upper treble.
In a quality music system. where the response from
30 to 20,0011 cycles must he deal and balanced,
the controlling factor in loudness. and in
overall efficiency, is low -frequency power, which
is the most difficult kind of power to develop.
And the mid -range and treble must be properly
proportioned to this bass foundation. with
distortions at a minimum.
Regardless of size and price. no other driver
delivers as much bass- output per Watt -input
as the Bozak B -í 99A. In no other speaker systems
is the entire audible spectrum tailored so faithfully
to the bass as it is in the Bozaks. No other
speaker systems can boast such vanishingly -low
distortions, such clean transient response,
so much listening ease.
The experienced engineer will find that
the Bozaks are unsurpassed for overall efficiency ...
the perceptive listener. accustomed to the sound
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With a fine music system there is no question
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45
AUGUST, 1955
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General Radio R -C Oscillator. In addition to two sine -wave outputs, the new
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B -11
46
and turning down the bass tone control of
the equipment. This provides an improved
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annoyance of induced hum pickup. Although the microphone can be set to amplify the lowest piano notes when desired,
its sharp cut -off characteristics below 40
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B -13
AUDIO
www.americanradiohistory.com
AmericanRadioHistory.Com
AUGUST, 1955
4'g HARVEY
the House of Audio
The NEW
The NEW
Mc INTOSH
BOGEN
te
Model MC -60
AUDIO
60 WATT
AMPLIFIER
CONTROL
Model PR100
Designed to meet the most exacting demands of advanced high fidelity
systems, the PR100 preampcontrol offers the ultimate control flexibility
and reproduction quality. frequency coverage is from 5 to 150,000 cycles
±0.5db.
Six input channels with individual level adjustments ore fed through a
push -button selector and permit its use with tuner, phono, monaural tape,
binaural tape, TV, etc. Three outputs ore provided for main amplifier, tope
reproduction. Separate Turnover and Rolloff conrecorder and for bi
trols, each with 6 positions, permit any record equalisation characteristics
to be set. In addition, there are separate boss and treble controls for 15 db
cut and boost at 50 and 15,000 cycles, respectively.
Sharp cut -off filters provide 5 positions or frequencies at which abrupt
attenuation can be introduced te cut -off any low frequency noise or high
frequency distortion originating in the signal source. There is o normal
volume or level control, os well os Loudness Contour Selector. All control
knobs are of the dual -purpose, coaxial type.
$9950
._.
Complete with tubes and mounting front panel
In Cabinet (specify mahogany or blonde)
I
Employing the famous McIntosh-exclusive circuit with unity coupling, the
new Model MC60 provides performance within .4% of theoretical perpower made available by its 60 watt
fection. The tremend
output, gives the MC.60 a distinct advantage in handling transients and
other sudden surges without overloading or distortion and contributes
immeasurably to the realism of reproduction.
There is less than .5y of harmonic distortion from 20 to 20,000 cycles
even at full 60 -watt output. Frequency response extends from 10 to 100,000
cycles ±1.0db; 16 to 60,000 cycles ±.5db; and 20 to 30,000 cycles
±.1db. Intermodulation distortion, under 120 watts peak, is less thon .5%.
Socket terminals ore provided for powering McIntosh and other preqmps,
and there are two inputs for .5 volts and 2.5 volts, respectively. Output
terminals have the following impedances: 4, 8, 16 and 32 ohms. The
McIntosh MC -60 employs the new T
6550 output tubes in push -pull.
1
Complete with
The
_
The NEW
GARRARD
TURNTABLE
Professional Model
301
unit designed specifically for discriminating listeners and owners of
home sound systems. The turntable itself is a 71/z lb. disc, precisely
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specially developed by Garrard for use in this unit. Armature is dynamically balanced and the rotor set in self- centering phosphor bronze
bushings. A newly designed motor mounting technique, employing counter
balanced springs, absorbs virtually oll vibration.
Intended for all 3 speeds: 331/z, 45 and 78 rpm, the 301 features an eddy
current speed control for making fine adjustments. Speeds cannot be changed
ting any possible jamming of the
unless the unit is shut off, thus pr
idlers. Other features include: built -in lubricating system, R/C switch network to eliminate 'on /off' clicks, shutoff brake, and a rubber mat to
prevent slippage of records.
A
Model301
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BELL
and PLAYBACK Unit
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o depth of only 33/e" the D123 is the most compact 12 -inch speaker
in the field. It con actually be wall- mounted flush with the surface and
between studding. In o properly designed reflex or horn - loaded enclosure,
the usable frequency response extends from 30 to 15,000 cycles.
Power handling capacity is 20 watts; impedances 16 ohms; and funda.
mental resonance, 35 cycles. The diameter of the voice coil is 3 inches.
With
-
The New
GRAY
Viscous -Damped
High Fidelity ARM
Model 108C
fluid suspension provides automatic regulation of both the vertical
and lateral movements of the arm. Improves tracking and minimizes groove
jumping and skidding. Protects records because arm will not drop suddenly.
Mechanical resonance is virtually eliminated. Simple slidein feature per.
wits instant interchange of cartridges. Handles records up to 16" diameter.
Has adjustments for viscosity and stylus pressure.
$3995
Model 108C_ _..
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this handy coupon
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NOTES Prices Net, F.O.B., N.Y.C.
HARVEY
Subject to change without notice
ESTABLISHED 1927
RADIO COMPANY, INC.
103 W. 43rd Street, New York 36
JU 2 -1500
I enclose
check 0 money order for $ ---- _..._._...._.._ including estimated
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A single control lever permits operation of this unit at either 1.875 ips for
lectures, meetings, etc., with a frequency response from 50 to 4000 cycles
at 3.75 ips for general recording purposes with a frequency
±6db
or at 7.5 ips for high fidelity
from 50 to 6500 cycles ±3db
res
with
frequency response from 50 to 12,000 cycles ±3db. Correct equal.
ixalion is automatically introduced with each speed change. Dual track
ding permits 4 hours of sound on a 7" reel at 1.875 ips.
Push -button controls are provided for both fast- forward and fastrewind.
There are two microphone inputs, one for crystal and one for dynamic or
ceramic
plus inputs for radio, phono and other high level program
material. Microphone and high level channels can be recorded simulta.
neously. Playback is provided by means of a built -in amplifier and 6 e 9"
oval, wideronge snooker. There are two outputs: 3.2 ohms for external
speaker and 500 ohms for line. A high impedance output is also provided
for feeding o high fidelity system. The entire unit is contained in a portable
case measuring only 16% x 15 x 91/s" and weighing 35 lbs.
Complete with microphone, red of tape, tokeup reel.
_..
tubes, and instructions
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AUGUST, 1955
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47
www.americanradiohistory.com
AmericanRadioHistory.Com
sheer
musical
magic
HAROLD LAWRENCE'
Watts in Salzburg
SIMMER. from the end of July, tu
the end of August, hundreds of musicians converge on the little Austrian
town of Salzburg to take part in a music
festival which, for variety of repertoire,
calibre of performance, roster of internationally known artists, and magnificent surroundings, is unsurpassed. Shuttling back
and forth from the Festspielhaus to the
Mozarteum (with occasional stops elsewhere), audiences are being entertained
this year by conductors George Szell,
Charles Munch, George Solti, Karl Böhm,
Rafael Kubelik, Hans Knappertsbusch, and
Eugene Ormandy ; soloists Nathan Milstein, Geza Anda, Clifford Curzon, Edwin
Fischer ; the Strasbourg and Salzburg
Cathedral Choirs, the Vienna Philharmonic,
the Scarlatta Orchestra of Naples, and the
Mozarteum Orchestra ; and several chamber groups including the Barylli Quartet,
Vienna Octet, Juilliard Quartet, and the
Boccherini Quintet. In addition, there are
plays by Molière, Hofmannsthal and Schiller, ballet performances by the Vienna State
Opera Ballet, and all of five operas in
lavish productions.
For months before Festival time, nearly
everyone in Salzburg is busier than the
violin section of an orchestra involved in
Paganini s Moto Perpetuo. Artists have to
be contacted, programs built. sets designed,
accommodations reserved-not to mention
rehearsals, which, in the case of a four hour opera like Pfitzner's Palestrina with
a cast of 22 soloists, can be a prolonged
affair. Present at virtually every performance are staff members of the local radio
station, under whose auspices programs are
broadcast and recorded simultaneously. In
charge of these and all other activities of
Radio Salzburg is Dr. Paul Becker, who
visited the United States last June at the
invitation of tl.e State Department. One
of the purposes of Dr. Becker's trip was to
make available to good music broadcasters
tapes of the Salzburg Festival. Over a
lunch on a hot and humid June 17th, amiable soft -spoken Dr. Becker went into great
detail on the operations of Radio Salzburg
where 'live' music is the order of the day
and the long -playing record nearly as obsolete as the Edison cylinder.
Like the British Broadcasting Corporation, Radio Salzburg sends out more than
one 'program.' Two are AM signals of 1
and 10 kw respectively, the third FM of
1 kw power. Again as in the case of their
London counterpart, the Third Program is
of a more serious nature : concerts, lectures,
plays, documentaries, etc. The AM programs are devoted to popular and light
music, news, community items and DJ's.
With the exception of popular music, the
recorded musical fare is on tape.
The long -playing record, so popular with
good music broadcasters in the United
States, failed to gain a foothold in European radio. There are a number of reasons
for this : (1) highly vulnerable plastic surfaces make for a short life span (clicks,
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swishes, pops, and crackles), (2) the disk
seldom matches the quality of the original
tape recording, (3) other defects such as
pre -echo, off- center pressings, end -of-side
distortion. This does not mean that the
latest record releases are not performed on
European air- waves. Many stations, particularly in West Germany and Austria,
have arrangements with the major recording companies whereby master tapes are
loaned to the station for copying, even before they are processed for transfer to disk.
At Radio Salzburg, however, recorded
music plays a smaller role in classical programming than at most other radio stations. Of course, it cannot be said that
musicians outnumber non -musicians in
Austria, but there is decidedly a performer
surplus in this country of seven million.
The results are extremely beneficial to
radio since so many artists are available
at all seasons, not only during the summer
months. In addition, Mozart's native city
boasts a world famous music school (also
a museum and library), the Mozarteum,
which maintains a permanent orchestra.
Although not in a class with the Vienna
Philharmonic or the Vienna Symphony.
it is a thoroughly competent organization
and has become what amounts to Radio
Salzburg's house orchestra. (The Salzburg
Mozarteum, incidentally, will be touring
the United States next spring as part of the
Mozart Bicentennial celebrations. Its itinerary will consist mainly of universities.')
From this group of musicians are drawn
smaller ensembles and soloists. Dr. Becker
and his staff plan an entire season's concerts with the Mozarteum, and that includes
operatic productions. As for summer programming, Dr. Becker coordinates his efforts with those of the Salzburg Festival
Committee to avoid duplications.
FM broadcasting is still a relatively new
development in Austria. World War II
stifled any progress along these lines. Later
the Soviet occupation authorities forbade
ultra -short wave transmission until two
years ago. Despite the ban, Austrian stations secretly built transmitters and made
their tests, ready to go into operation the
moment the word was given. Like the
B.B.C., Radio Salzburg derives its principal
income from listeners' license fees. In both
cases, the postman is the authorized tax
collector. England's annual fee for sound
broadcasting is f 1, Salzburg's, $3.60. The
discrepency is accounted for, obviously, by
difference in audience size. At the end of
1950 there were nearly 12 million set owners
in the British Isles, 200 times the entire
population of Salzburg. According to Dr.
Becker, the tax is not enough to keep pace
with Radio Salzburg's ambitious plans.
Therefore, to supplement income, the station devotes certain segments of its schedule
to "commercials." Fully aware that Salzburgians love to hear their names mentioned on the air, three-hour periods on
Saints' Days are sold to friends and relatives of Peters, Pauls, and Matthews, who
record birthday or anniversary greetings.
After each greeting, the announcer introduces the next selection, a favorite piece
of the recipient (mostly by Mozart, nat-
AUDIO
48
www.americanradiohistory.com
AmericanRadioHistory.Com
AUGUST, 1955
orally). The station has little trouble sellthese three-hour 'shows' although.
.ighed Dr. Becker, it still needs more
.nosey. But, for that matter, what director
f any enterprise would not like to have
ing
larger budget?
Next January marks the 200th anniversary of Mozart's birth. We need no crystal gazer to tell us that in 1956 the air will be
as filled with Mozartian melody as a Christmas day resounds with carols. Festivals
a
have been planned years in advance. Scores
.)f books on the Salzburg composer will
no doubt be published on or around January 27th. Recording companies have also
gotten into the act. No less than four different versions of Così fan hate. for example, will be issued this fall and winter, not
to mention the two sets of Mozart piano
works on Haydn Society and Angel which
have already been released (Haydn Society
still has a few volumes to bring out). Salzburg will join in the festivities with a ten day celebration including a pair of operas
and featuring such stellar performers as
Wilhelm Backhaus, Edwin Fischer, Irmgard Seefried, Herbert von Karajan, and
Karl Böhm.
Radio Salzburg obtains special permission
to record Festival performances on the condition that the tapes are erased at the end
of each year. Thus, unfortunately, some
superb recordings are lost forever. However, a performance of Don Giovanni, conducted by Furtwängler, was filmed in color
during the 1954 Festival and will be released here shortly. Although the sound
track is technically not up to the latest
standards (as a recent showing at the Royal
Festival Hall in London indicated) the performance is excellent. Through this film.
Radio Salzburg's tapes, and the Mozarteum
Orchestra, Mozart and Salzburg will reach
their largest audience during the Bicentennial Year.
AUDIO ETC.
it mot paq.
the manufacturer
And anyhow, this
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after you with a whip.
is a top -quality system
doing it justice unless
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A final word, or rather a question : is the
AR -1 principle -limp cone and air- springapplicable to less expensive systems? I have
no official word and we'll have to wait for
a hypothetical AR -2 to find out. But I can
do some speculation, of an elemental sort.
A speaker system using this principle must
have an unusually solid and well -built cabinet, sealed tight. This costs money in any
size. If you're going to build a quality
cabinet you might as well put quality inside
it too-so there you are. I personally doubt
that the AR principle will be introduced
in really low- priced systems, unless a revolutionary cabinet-say of plastic -is invented to go with it.
Meanwhile the presently available AR-1
makes a unique high -quality speaker outfit
for installation wherever space is limited
but quality must be tops. The speaker marks
an important step along the way towards
bigger bass in smaller space, as well as a
major advance in speaker design.
(Note: The AR -1 comes in an unfinished
cabinet, too, for about $145 and is also
available with woofer alone, minus tweeter
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complete outfit, either finished or unfinished.
A wise policy of versatility.)
4. ATR for Tape. After an unconscionable
but unavoidable delay of a year or so I'm
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Here are some of the feature advantages:
Hysteresis synchronous constant speed motor
Cast aluminum turntable lathe-turned with extra -heavy
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Single ball pivot bearing suspension
Instantaneous selection of record speeds:
331/x, 45 and 78 rpm
Built-in, retractable 45 rpm record hub Attains
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Speed regulation well within
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15% -inch turntable diameter allows VI inch overhang for cueing
Fits most existing
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49
AUGUST, 1955
www.americanradiohistory.com
AmericanRadioHistory.Com
bound and set to offer an interim report on
a project that I happily conceived last sum-
C2-100
Net price, $4.50
The highest
overtones of
the piccolo
mer and then never got the time to cornplete. Better late than never. The project:
How well will a standard inverter (6- or
12-volt d.c. to 110 -volt 60 -cps a.c.) work
on a tape recorder, for casual in- the -field
sobs, of a semi -amateur sort? How about,
in particular, that vital matter, exact pitch,
or frequency?
Now the boys who do professional recording from stationwagonsful of "portable"
tape equipment know all about the problems
of portable a.c. and have long since met
them in their own various ways, mostly
expensive. I'm talking, rather, about the
ordinary guy (or doll) who has a tape recorder, wants to make it work in places
where the car goes but power -line a.c.
doesn't. Campfire singing, mountain-top
picnics, outdoor concerts. Frivolous pursuits, perhaps, but then sometimes they can
be important, and there are times when
semi-professional work can be done in this
way, folk song documentation for example,
that might be invaluable
a good recorder were used, Magnecord, Presto, Ampex 600 or equivalent, and if (a) pitch
came out correctly and (b) hash and inverter noise were low or inaudible.
So I got me a 12 -volt inverter to try on
my car (12 -volt system) and then-didn't
get around to it. But I did make one test
which I pass on to you for what it is worth.
I took the time one day to hook up a Columbia 360 table phonograph to the inverter, try
a record for pitch, then rush the machine to
a nearby power line outlet and play the
same record. AB comparison.
The ATR people had been a bit afraid
of hash trouble and had sent me a special
capacitor to hook in if there was too much
noise. There was some, but not really
enough to be objectionable, except perhaps
in highly professional work. I assume that
a similarly modest noise level would get
through into an Ampex or a Magnetorder,
or a Crestwood or what-have -you, operated
from the inverter. Not enough to be objectionable in anything short of strictly professional work.
So much for noise. I suspect that there is
always some if it in any inverter -type system for producing a.c. and I've heard dreadful buzzes emitted by other inverters, presumably over -age and overworked. But this
one purred discreetly, no more.
Pitch? Ah, there's the rub! Now the ATR
inverter I used, Type 12 RHF (there is an
equivalent for 6 volts) was a heavy -duty
model, intended to take on a full -sized professional tape recorder, in case I wanted
to try one. It may be that the Columbia
360 underloaded it. But the fact is that
there was almost a half-step difference in
pitch between the music as played via the
inverter and via the power line. Too high.
I.e., the inverter buzzed too fast. The three position frequency adjustment made a difference, but not enough to bring the pitch
down to its correct level, in this particular
situation.
The test is still unfinished, I hasten to
say -because it is now up to me to load
that inverter down with enough equipment
to let it work at its rated and proper wattage. It's quite possible that with a Magnecorder hooked in the circuit the inverter's
pitch will be correct. But even so, I think
we have some useful and legitimate information which will help potential users of
this sort of equipment.
We must never underestimate the power
of the ear when it comes to pitch accuracy
You may think you have no musical ear
at all, but beware -you have. An instrumental record played a mere half -step too
-if
The deepest tones
of the bass tuba
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AUDIO
50
www.americanradiohistory.com
AmericanRadioHistory.Com
AUGUST, 1955
igh or too low sounds definitely odd to
Almost anybody, especially if the music is
familiar. A vocal record sounds just plain
ludicrous with a half -step worth of inacl
curacy either way. We require extreme
exactitude in pitch reproduction for all
orts of recording, whoever we are.
As you can understand, a tape recording
made at a too -fast speed will play back perfectly on the same current -but will come
net too slow when played on regular line
current, and vice- versa. If you want to
.day your tapes forever on the auto battery
.aid never bring them into the house-fine.
But if not, then when you acquire an inverter try it out immediately for pitch and
consult the dealer if in your particular situ ation it is not exactly the same as power line pitch.
The difference between American 60 -cps
and European 50 -cps incidentally, amounts
to a major third in pitch, enough to hike the
C Major Symphony of Schubert up to E
major and make Lily Pons squeal like a
,tuck pig.
ATR, by the way, now sells a special
inverter specifically designed to operate
with the Ampex 600 portable tape recorder,
which includes a storage battery (ultra lightweight, I trust I) in order to make that
machine "really portable." With this gadget
you can walk your Ampex right into the
woods and fields or the jungles of IndoChina and come out with records. If this
inverter is really accurate as to pitch (and
we can assume ATR has spent a while on
this problem, unless their engineers have
real tin ears) it should be a useful gadget
for professionals who must have hi -fi of
top quality but cannot depend on a car
battery.
Just lead an idea. I've got me a 50 -foot
extension cable for a.c. power. Tomorrow
I'll run my car up on the front lawn, hook
in the inverter and haul the cable through
the window into my tape studio where my
present Magnecorder
is more or less built in and not exactly portable. Then I can
switch like a flash from inverter to power
line -and we'll sec what's what, for fair.
I've got my fingers crossed, and I apologize
to ATR for the delay in crossing them. Report can he expected soon, and I trust it
will he entirely favorable.
Acclaimed Coast to Coast!
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SOLDERING TIPS
llruut ¡'aye 13)
The golden rule which must be observed in soldering electronic equipment
is to ensure that the solder wire is applied to the heated components as in
Fig. 2, not to the soldering tool. The
reason for this rule is that since the flux
is contained in the solder wire, it is
essential that the flux be applied to the
components that are to be joined in
order to remove the surface oxides and
prevent them from forming again (luring
the soldering operation. Probably 90 per
cent of the trouble that is experienced
in undertaking soldering jobs is due to
the fact that the solder was applied to
the iron or gun and the tool was then
applied to the components. Consequently,
the flux was just wasted.
Some of the soldering jobs which will
be carried out by the audio enthusiast
will be soldering shielded and unshielded
wires to pins of plugs. Many of these
jobs can often be made easier by fixing
the iron in a vise as shown in Fig. 3,
rather than by holding the tool in the
AUDIO
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Contest closes at midnight, September 30, 1955.
Get Full LEONARD RADIO, INC.
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51
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Fig. 2. Always apply the solder to the work,
not to the iron. If it is touched to the iron, the
flux in the cores becomes vaporized and does
not clean the work.
hands. The wires and plugs can be applied to the solder bit with one hand and
the solder wire with the other. When
wires are to be connected to lugs. it is
a good plan to follow the professional
practice of passing the wire through the
hole in the lug and making a good mechanical joint before soldering.
Another golden rule of soldering is
cleanliness. Although modern noncorrosive fluxes will remove surface oxides,
it is not intended that they should remove dirt. Consequently, if old wires are
being soldered. or joints are being made
to lugs of components which have been
in use or in storage for a long time, it
may be necessary to remove dirt by
cleaning with a file, or even a knife.
If the solder does not run very easily
although it is of good quality and, if
possible. 60/40 alloy, this is a sure indication that insufficient heat is being applied. This may be due to too cold a
soldering tool. Generally, this deficiency
is the result of one of two causes. Either
the heating element in the soldering iron
is worn out or the whole design of the
iron is too small for the job. For example, for joining wires to lugs in an amplifier a soldering iron of small physical
size is an advantage. On the other hand,
this type of soldering iron is quite un-
suitable for soldering a wire to the
ground lug of a large metal chassis.
While it is possible to get unsatisfactory
joints because too much heat is applied.
many more faulty joints are made from
applying too little heat. Even when undertaking soldering jobs in which low melting -point insulation is used, it is
Jeep informed-read
ELECTRONIC
MUS/[AL
INSTRUMENTS
Fig. 3. Clamping the iron in o vise often lends
an extra hand for "three- handed" jobs.
invariably advantageous to apply a lot
of heat for a short time rather than a
little heat for a long time. When soldering shielded cable to plugs. some initial
difficulty may occasionally be experienced due to the insulation between the
wire and the shielding being melted away
and thus causing a short. If, however.
the soldering job is undertaken quickly
with soldering tools of sufficient bit temperature, this trouble should not occur.
In some circumstances, it is advantageous to use a thermal shunt to conduct
the excessive heat away quickly. A simple form of thermal shunt is a pair of
pliers.
There is considerable fascination in
doing a good soldering job. If the audio
enthusiast invests in a good soldering
tool with sufficiently high bit temperature, always remembers to clean dirty
surfaces before attempting to join them.
and purchases a good- quality cored
solder, preferably 60/40 alloy, he should
have no difficulty in undertaking any
of the soldering jobs which give a high
fidelity installation truly professional
performance and appearance.
HOLLYWOOD BOWL
(porn ru,/,. /a
By
Richard H. Dorf
In one big volume, you can now learn all about the intricacies of
commercial electronic organs, including the Allen, Baldwin,
Connsonata, Hammond, Minshall - Estey, Lowrey Organo, and
others, together with many smaller instruments. Constructional
details on the author's Electronorgan and the simpler Thyratone
show you how to build one of these fascinating instruments for
yourself. A compilation in book form of the author's articles in
Radio Electronics, brought up to date and with many additions.
Price $7.50 (Foreign,
$8.00).
is to dealers and distributors
Customary di
RADIO MAGAZINES, INC., Book Division
P.
Please send me
0. Box 629, Mineola, N. Y.
copies of Dorf's ELECTRONIC MUSICAL INSTRUenclose check
money order
for $7.50 each
MENTS.
(Foreign, $8.00).
I
culties were discovered and isolated, and
by the time the 1955 season closes, the
system should be complete and finished.
Far more difficult than the designing,
building, and installing of some $50,000
worth of components, is the task of overcoming echos, traffic and aircraft noises,
sound losses in the open air, humidity
and other weather conditions, feedback,
and the innumerable other situations
noticeable only after the equipment has
been installed. Truly, sound reinforcement has moved to the status of science
from its early position of a trial -and-
error art.
In addition to the others named above,
Name
Address
City
i
nel has been about 7 watts, 1 /10 of the
total power available. As a result, any
one of the stereophonic sound channel,
could handle the entire audience area
with ease if need be. Only one microphone on each stereo channel is used on
regular symphony orchestra pickups.
During the 1954 season, the first for
the new sound system, most of the diffi-
Zone
State
thanks go to Mr. William Severns, manager of the Bowl, for his cooperation
and for the many courtesies he extended
for .the preparation of this article.
AUDIO
52
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AmericanRadioHistory.Com
AUGUST, 1955
CARE OF JACKS AND PATCH
CORDS
(front page 20)
Failure to observe polarity will ground
out the high side of unbalanced circuits.
[t may also throw microphones out of
phase in a multiple mike setup, with re;tilting partial or complete cancellation
if outputs. And speaking of polarity, reiember when making up new cords or
eplacing plugs on old ones to pole the
;dugs consistently at both ends.
Never store cords coiled up. Hang
-hem up vertically to avoid unnecessary
-trains. Avoid using unnecessarily long
cords; they may hang in front of important controls lower down in the rack
or dangle in strong hum fields from
power supplies. Too short a cord may
suffer severe strains from the resulting
sharp bend at the plugs. It is customary
to have a supply of cords on hand in
various lengths differing by increments
of two feet.
Some cords are made with the shield
grounded to the plug body at both ends.
However, modern practice is to ground
the shield at one end only to avoid
ground loops.3 If the cords in your plant
are grounded at both ends, this can be
one possible cause of noise and hum.
3
Oliver Read, "Recording And Reproduction Of Sound," 2nd Ed., Howard W.
Sams & Co., Inc., p. 613.
Fig. 3. This test fixture checks patch cords for
continuity and shorts.
THE LANGUAD EXPERT
ra,,; IQ)
respect to frequency and what ?"
I had to think a minute. "With respect to frequency and intensity !" I
cried.
"And." said George, "since it features
selective recreation of the disparate bass
tones and since it captures every minute
tonal variation, we are safe in saying
that it is the finest system manufactured
"The finest system manufactured regardless of price!" we finished in unison.
By this time I was feeling all warm
and comfortable inside again and sensing
that I liad reached by level of normal
befuddlement. I turned to go. As I
skirted a large stack of AUDIO copies
on my way to the door, I noticed a small
.
mahogany-grained
plastic cabinet
perched on one corner of George's desk.
It looked vaguely familiar and as I
stepped forward for a closer look I
experienced the audiophile's sudden
shock of loathing upon being confronted
with a ( ugh !) commercial radio I
hastily
phonograph combination.
averted my eyes from the hated object
and, taking a moment to assume the
approved stance of righteous indignation, demanded of my friend. "What.
may I ask, is that thing doing here ?"
"Oh, that," replied George with a
patronizing smile. "That is what I
listen to. After all, it is unconditionally
guaranteed to perform as well as the
most expensive system available."
with BEAM
AMPLIFIERS*
* "For applications requiring up to 30 watts...
this unit should satisfy the most critical."
-Audio Equipment Report
The outstanding audio achievement of
recent years, the superb QUAD II system
provides unparalleled audio reproduction
plus complete flexibility of control. Add
high efficiency, harmonic filtering, pushbutton equalization and channel selection,
exact pick-up matching, balanced feedback throughout, precision made 13 -section output transformer, low distortion,
superb British craftsmanship, and the
smartest styling in high fidelity today
and you see why QUAD is the recognized world leader in high quality audio
Hear it at your earliest
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-
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1
RESPONSE:
QC II Control Unit:
QUAD
II
10- 60,000: 0.5db
Amplifier: 20-20,000 cps, fiat
Total Distortion, QC II: 0.02%
Less than
Total Distortion, QUAD II:
1
/10ío
Full complement of controls, including filter slope, bass, treble, 3 channel selection
and record compensation.
OC II Control Unit
$120.00
$130.00
Quad II Amplifier
System Complete
$237.50
For detailed specifications on the Beam
QUAD AMPLIFIER, and literature on Beam
Stentorian Speakers from 8" to 12" sizes,
5 and 15 watt super tweeters, woofers,
matching crossovers, 10" and 12" Duplex
(Twin Concentrics), and Beam enclosures,
write:
BEAM
INSTRUMENTS CORPORATION
Empire State Building
350 FIFTH AVENUE
NEW YORK, N. Y.
Charter Members
Institute of High Fidelity Manufacturers, Inc.
AUDIO
AUGUST, 1955
53
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AmericanRadioHistory.Com
ELECTROACOUSTICS
RETTINGER
The keynote of the book is UTILITY in a practical coverage of the
rapidly developing field of electroacoustics.
Electroacoustics is presented in
the light of the most recent developments. The modern methods and devices discussed in the book are those
used at present in radio, sound -film
recording, and allied arts.
Special emphasis is placed on the
relatively new and promising field
of magnetic recording.
Many tables and curves show at
a glance the required quantities, reducing calculations to a minimum.
The diagrams in the book are useful
not only for lessening figure work
but also for checking calculations
and illustrating relationships.
CONTENTS
FOREWORD.
MceaoraoNes: Anecdotal
History of Microphones -General Aspects
Types of Microphone
Microphone
Technique. LOUDSPEAKERS: Direct -Radiator Loudspeaker- Loudspeaker En-
-
-
closures- Loudspeaker Cabinets -Corner
Cabinet for Loudspeakers-Horn Loudspeakers- Directional Radiation-Damping Loudspeaker-Cabinet Panels -Speaker
Measurements- Speaker Distortion. Cut-
-
Constant -Resistance Crossover
Networks
Impedance- Measuring Networks- Mixers. MAGNETIC STRUCTURES:
General Aspects
Permanent Magnets.
Pow-lc-Amass SvsTEMS: General Aspects
Outdoor Loudspeaker OutputPower Requirements
Specifications
Testing Public- Address System Installations -The Hollywood Bowl Sound-Reinforcement System- Loudspeaker Matching. VIBRATIONS: Transients -Vibration
Isolation.
ARCHITECTURAL
AcousTIcs:
Dynamic Symmetry
Convex Wood
Splays for Broadcast and Motion -Picture
Studios-Recording Studios-Television
Studios
Home Acoustics
Sound -Absorptivity Measurements-Acoustic Measurement Facilities. MAGNETIC RECORDING:
Ring -Type Magnetic- Recording and Reproducing Heads -Front Gap -Back Gap
CUITS
-
-
-
-
-
-
-
-
- -
-Alternating -Current Magnetic
271 pages
1955
full output. It may be necesary to change
the polarity of the power line to reduce
hum.
These amplifiers are suitable for home
use where all that is needed is an amplifier capable of delivering 2 watts undistorted at 60 cps with a flat response from
20 to 20,000 cps. (Below 60 cps there is
very little program material and most
loudspeakers produce a great deal of
harmonic distortion.) As a matter of
fact, with the present higher -efficiency
loudspeakers and loudspeaker housings
an input to the loudspeaker of 2 watts
bass is more than enough to reproduce
symphony music in the average living
room ; and continuous operation at this
level is sure to make the neighbors complain.
Although it was not tried, it is very
probable that by raising the plate voltage
in the circuit of Fig. 5 to 135, better than
5 watts undistorted power output can be
obtained at 60 cps. If a transformer
supplying 6.3 volts is available for the
filaments, 6Y6's can be substituted for
the 50L6's. The cathode-bias resistor
of the output stage R. should then be in
creased to 120 ohms. A B supply of 135
volts is shown in Fig. 6.
Several amplifiers were constructed
in accordance with the circuits in Fig 4,
in which the following transformers
were used with excellent results : Stancor
A -3825 ; Thordarson T22S60. A Thordarson 22S74 (costing about $5.00) was
used in the circuit of Fig. 5 with 6L6's
and the following changes : B+, 285
volts ; primary impedance, 5000 ohms ;
R,e, 125 ohms ; R., R,., 400,000 ohms.
With these changes the undistorted
power output at 60 cps on the oscilloscope was 11 watts. A Stancor A-3830
was also used in a similar amplifier with
the additional change of substituting a
12AX7 for the 12SL7. With the 12AX7
it was found necessary to remove the
output transformer, which was not
shielded, from the chassis and mount
it on the loudspeaker frame, and also to
connect a 100 -µµf capacitor from the
plate of the input half of the 12AX7 to
ground to cut out high- frequency oscillation. Despite this, there was a subtle
difference in "feel" between the 12AX7
and the 12SL7 in favor of the former.
Erase
Frequency Response
Experimental Results. APPENDIX: Octaves
Decibels, Volume Units, Dbm versus
Watts -Dbm versus Voltage- Bibliography- Index.
Heads
104 per word per Insertion for noneommerelal
advertisements: 25e per word for commercial Aber.
tisements. Rates are net, and no discounts will be
allowed. Copy must he accompanied by remittance In
Rates:
(from page 12)
practical
M.
CLASSIFIED
AMPLIFIER USES
Simplify design and
calculation
8
10/2w.
RI
CI
C2
.01
30/150
Hy, 150 ma.
.
$10.00
Order your copy today from
CA
100/350
SELENIUM
C3
RECTIF IERS
150 ma.
40/350
full,
and
most
reach
the
P. O. Box
629
Mineola, N. Y.
Fig. 6. A 135 -volt power supply for the push -
pull amplifier.
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office
by
the
25 -50% DISCOUNT. Factory -fresh guaranteed LP records, 690 and up ; send 200 for
catalogue. SOUTHWEST RECORD SALES,
Dept. A, 1108 Winbern, Houston, Texas.
SALES-SWAP-SERVICE
all types of new and used audio equipment.
AItGUS SERVICE COMPANY
235 Lyons Avenue
Newark, N. J.
WAverly 3-3025
on
IIIGII- FIDELITY SPEAKERS REPAIRED
\mprite Speaker Service,
Iork 7, N. Y. BA 7 -2580
70 Vesey St.. New
A NI PLI FIERS
-III -FI
45% off 40,000-cycle amplifiers, recorders,
pianos, organs, accordions, typewriters, movie
equipment. binoculars. Amazing bargains!
A ELMART, 466 Belmont, Paterson 2, N. J.
6- Element Broad Band FM antennas. All
aluminum. $10.95 ppd. Wholesale
Supply Co., Lunenburg 10, Mass.
seamless
VARITYPING Composition, DSJ, IBM.
paste -up, ruled forms, advertising layout and
technical matter in English and foreign languages. Catherine Rein, 874 Broadway at 18th
St., New York. GRamercy 7 -5720.
WANTED: Cutters, RCA MI-4887 recording
heads, upright type, any condition. Also Altec
21 -C, prefer 150-A base, and Edison cylinder
records. George Somes, 1247 Savoy St., San
Diego 7, California.
CONCERTONE portable tape recorder with
amplifier, speaker, and ALL accessories in 501
portable case. In precise mechanical and
electronic alignment. Low (and high) impedance inputs, new heads and silent fan. $325
or best offer. Write for complete specifications.
Pete Helffrich, Wescoesville R #1, Pa.
RARE QUALITY AUDIO ITEMS
Pickering model 165 -L studio -quality phono
equalizer with separate power supply; usual
net around $165 ; express prepaid for $90.
Proctor Multi -Speed studio -quality phono
16-inch turntable, providing any speed from
20 to 90 rpm ; with long arm ((.,ray) and
slide -in clips ; excellent condition ; $135 exprepaid to you.
Ipress
f you are a Proctor owner and need parts
or service, write
ADOLPH HOEFER
Clayton
8330 Kingsbury Blvd.,
24, Mo.
BROOK AMPLIFIERS- famous all -triode
model 12A. Guaranteed, Brand New ; closing
out for only $99.00. Craig Audio Lab, 12
Vine St., Rochester 7, N. Y.
CONCERTONE 1502D, hysteresis drive
motor, dual track, used 150 hours, excellent
condition, reel adapters included, $275 (cost
$450 new). Norman Tetenman, 2350 East
27th St., Brooklyn 29, N. Y.
AMPEX 400 -A Tape Recorder, $750. AltecLansing M-11 capacitor Microphone system,
Electro-Voice 635
extra 25 -ft cable. $175
Dynamic Microphone, $35; Private owner,
excellent condition, priced f.o.b. V. R. Hein,
Illinois.
BARGAIN : Two famous Telefunken ConMicrophones, $295 each. Complete,
Guaranteed. 9 Edgehill Road, Winchester,
Mass.
denser
AUDIO
54
York
date of Issue.
THE AUDIO ESt'l1ANt;Is h:w the largest
selection of new and fully guaranteed used
equipment. Catalog of used equipment on
request. Audio Exchange, Dept. AE, 159 -19
Hillside Ave., Jamaica 32, N. Y. OL 8 -0445.
418 Gregory, Rockford,
AUDIO
New
first of the month preceding the
AUGUST, 1955
PROFESSIONAL
DIRECTORY
eesti4uce4c44 Since 1944
HOLLYWOOD ELECTRONICS
First
Pettple
901414141441
Notwithstanding the East's most severe
heat wave in years, energetic Irving
Greene, sales promotion manager for University Loudspeakers, Inc., added to his
normal duties the chores of furnishing
speakers for the Newport Jazz Festival,
delivering a number of lectures before
New England civic groups, and engaging
in promotional activities for his recently
published "New High Fidelity Handbook"
Another doubler-in -brass is Dan Cavalier, Washington, D. C., representative for
A. R. F. Products, Inc., who also heads up
Washington's annual High Fidelity Fair;
he is already setting up preliminary organizational plans for the Fair scheduled
for next Spring.
Mort Lee, sales executive with British
Industries Corporation, New York, escaped
torrid temperatures with a vacation in
England
Personnel promotions at
Fairchild Recording Equipment Company
include Ruben E. Carlson, who has been
appointed Ina ii r of the high -fidelity
division, :tint Robert G. Bach who has been
named 1...g. -r f Innmotion and distribution ... Roy G. True has been appointed
executive vice- president and Richard C.
Hoch chief engineer of I.D.E.A., Inc.,
according to recent announcement by Edward C. Tudor, president
E. S. Seeley,
chief engineer of Altec Service Corporation, New York, has been named director
of engineering for Altee Lansing Corp.
Arthur L. Poster is newly -appointed
sales promotion manager of the Strom berg -Carlson sound equipment division
he will also be responsible for all advertising, working directly with A. G. Soldlino, vice- president
Allied Radio
Corporation has appointed L. M. Burchett
as manager of the firm's stores in the
Chicago area -he has been with Allied
for a number of years as personnel training director ... Phillip L. Gundy, manager
of the audio division of Ampex Corporation, has been appointed a director.
Larry S. Racine, president of Chicago
Standard Transformer Corporation, has
taken an indefinite leave of absence due to
III health. William J. Shea, chairman of the
board, will assume the office of president,
and Donald Schwenneeen, vice -president
in charge of engineering, will add sales to
Richard C. (Dick)
his responsibilities
Wells, widely known announcer and broadcast engineering specialist, is director of
the industrial sound department recently
established by Newark Electric Company,
Chicago ... Acro Products Company, Philadelphia, has undergone complete reorganization and is now under the sole ownership of Herbert I. Heroes. A new program
of sales planning is being developed by
Jack Snyderman, who has been named
sales malinger.
things
last!
.
IICLUSIVILS
746
11/11t. Ave
Loa
Angeles 4b,ColifWFbster 3.8208
.
'HIGH -FIDELITY HOUSE
Most complete stock of Audio
components in the West
536
S.
.
Phone: RYan 1 -8171
Fair Oaks, Pasadena 1, Calif.
...
"EVERYTHING IN HIGH FIDELITY"
From Primary Components
to Completed Custom Audio Equipment
KIE
F
Los Angeles 15, Calif.
ZEnith 0271
CANADA
High Fidelity Equipment
t'omplete Linea
Complete Service
Hb FI Records
Component.
and Acceeaorlee
-
SOUND SYSTEMS
TORONTO,
DUNOAS ST. WEST.
CANADA.
FIDELIVOX
RECORDED TAPES
THE L- O- N- G -E -5 -T HOUR OF
SOOTHING
CATHEDRAL ORGAN BACKGROUND MUSIC
Moderate Cost
Mail Order
Free Details
ELECTROSONIC, 7230 Clinton, Upper Darby3.
Please
Pa.
IF YOU ARE MOVING
notify our Circulation Department
at least 5 weeks in advance. The Post
Office does not forward magazines sent
to wrong destinations unless you pay additional postage, and we can NOT duplicate copies sent to you once. To save
yourself, us, and the Post Office a headache, won't you please cooperate? When
notifying us, please give your old address and your new address.
Circulation Department
RADIO MAGAZINES, INC.
P. O. Box 629 Mineola N. Y.
AUDIO
.
.
reproducing equipment.
.
&LECTRO-UO10E
141
-
.
Sound Corp.
820 West Olympic Blvd.
Richmond 7.0211
s_
We freely confess that when we began
planning the Tannoy high -fidelity
Domestic Sound System, we did not
contemplate designing and manufacturing
our own phono- cartridge. After all,
there were several excellent cartridges
already on the market.
We changed our minds when the first
power amplifiers and 'Autograph'
pre -amplifiers began to emerge from the
assembly lines. It was evident that
the almost uncanny faithfulness of the
amplifying chain, ending with the now
world- famous Dual Concentric Speaker,
justified the use of a cartridge of more
than ordinary ' freedom'.
Our engineers therefore set about the task
of designing a cartridge which was free
to extract and pass on, everything from
the recorded groove without any spurious
effects or blanketing resonances. The
result is the Tannoy Variluctance
Cartridge... a precision transducer which
would be completely wasted on any but
the very finest of high -fidelity
Atoka,
Advanced degrees in electronics engineering at Stanford University are available to outstanding electrical engineering
graduates on a work -study basis through
the Honors Cooperative Program of Ampex
Corporation and Stanford University,
George I. Long, Ampex president, announced recently. Under the program participants may obtain a graduate degree
at Stanford while earning a living income
as employees of Ampex. To qualify a candidate must be a graduating senior with
a major in electrical engineering or physics in the top 10 per cent of his class,
desire a career in electronics, and be an
American citizen able to obtain government clearance.
Three snore independent record companies are entering the recorded -tape field,
according to a recent announcement by
Livingston Electronics Corporation, Livingston, N. J., recorded tape manufacturers and distributors. Boston Records,
Lyrichord Discs, and Polymusic Records
have concluded arrangements with Livingston for tapes of material which has so
far been available on disc only.
AUGUST, 1955
TECHNICAL SPECIFICATION
Every cartridge hand-made and laboratory tested.
Upper frequem.r limit > 16,000 cps.
No resonant peaks.
No undamped resunanres in sub -supersonic range.
Simple turn-over mechanism.
Stylus assemblies completely independent.
Instantaneous replacement of styli without use
of
tools.
Optimum lateral to vertical compliance ratio.
Very low effective dynamic mass.
Output: 20 mV at 12 cm per second.
Termination load : 50,000 ohms.
Tracking weight : 6 grams for all discs.
T,aNNOY
VA
Rh
UClA N
CE
Phono -Cartridge
For service in the United States
call New York WHitehall 3 -7060
TANNOY (CANADA) LTD
36 Wellington St. East, Toronto
1,
-
Ontario, Canada
55
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INDEX
111 um
Ill
$43.75
NET
Acro
Products Co.
33
Audak
40
Co.
Corporation
Belden Mfg.
FILTER
installation
Variable Filter and 4201
Program Equalizer are now available
in component form, as illustrated, for
the custom builder.
In addition to the flexibility of
installation, all the features and char.
acteristics of the standard models are
retained.
The high and low sections of either
model moy be obtained separately.
Complete wiring instructions included.
The 4200
Send for Bulletin TB -4
50
Allied Radio Corp.
Audiogersh
simplify
custom
design
Type T/CFB
also available
$47 net
The
51
Co.
PARTRIDGE (1"B
Audio Transformer
5
Gell Telephone Laboratories
10
Bozak, R. T. Co.
45
British Industries Corporation facing p.
1,
Built to the arr, highest standards the Partridge Type
(:FB reproduce,. full A.F. range with lowest distortion.
Series leakage inductance IOn,R. D.C. resistance per
half prima... 88 ohm.. Power up to 60$1. from 22 ea,
to 30 kris. Distort'on less than I
u V.F.B. T. CFB
is similar in performance to above but with each half
primer, brought out to terminals as a separate winding
and tapped al 43 of turn..
3
Carter Motor Co.
2
Ccntralab, Division of Globe -Union
50
Classified
54
Ads
Electrosonic
"
For specifications and prices of Partridge Transformers and name of local distributor write to:
Partridge Transformers Ltd.,
cfo British Electronics Sales Co. Inc.,
23 -0:1 .15th Road, Long laland City, I, N.Y.
55
Electro- Voice,
Inc.
Cover 4,
ALSO AVAILABLE
TYPE U.L.2. :f p.p. Transformer of "C" Core design,
specially designed for really high quality A.F. reprodoting equipment. Power up to 50 runes. S26.30 NET.
TYPE W.W.F.B. Built to the famous Williamson
apeciffration and available in a wide range of impedances. Power rating I6 antes roni,nao,,, steady mar.
I
Electro -Voice Sound Systems
55
Fisher Radio Corp.
29
Harman- Kardon, Inc.
22
Harvey Radio Co., Inc.
47
Heath Co.
43
High- Fidelity House
55
Hollywood Electronics
55
0
Iiiiiik
Hughes Research and Development
Laboratories
Hycor Co.,
1
Inc.
P
A
R
T
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D G
E
TRANSFORMERS LTD.
TOL W ORTH SURREY ENGLAND
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.....
BOUND VOLUMES
Kierulff Sound Corporation
L
627.75
eonard Radio, Inc.
1954 ISSUES AUDIO MAGAZINE
Minnesota Mining and Mfg. Co.
r'artridge Transformers, Ltd.
Model 4200 Variable Filter
(Send for Bulletin S)
9
Pilot Radio Corp.
.
Presto Recording Corporation
. s'
Professional
x
now available
Sc
Pickering & Company, Inc.
3T.
4'
Directory
$10.00 each postpaid.
,toad Amplifiers
Sp
Radio
3
U. S. Delivery only.
Model 4201, Program Equalizer
(Send for Bulletin E)
Shack Corporation
PPauland -Borg
Corporation
41
Rek -O -Kut Company
Representatives in
Principal Cities
Send order
49
ockbar Corporation
Cover
R
and remittance today.
,chober Organ Corporation
Scott,
Tannoy
Herman Hosmer, Inc.
ICanadal
.
Box CF 4.
Limited
Technical Tape Corporation
AUDIO
Triad Transformer Corp.
Subsidiary of
International Resistance Company
11423 VANOWEN STREET
NORTH HOLLYWOOD 3, CALIF.
P.
Unicut Transformer
Co.
Cover
O. Box
629, Mineola, N. Y.
2
1
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
AUDIO
56
www.americanradiohistory.com
AmericanRadioHistory.Com
AUGUST, 1955
SIMPLE AS
A
IB
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To make it just as easy as possible for AUDIO's readers to subscribe, order books, get
further information about the new products and the new literature mentioned in the pages
of the magazine, or to get catalog sheets and brochures describing articles advertised, we
provide herewith three cards. We know that many readers are loath to cut coupons from
the pages of their favorite magazine because they have told us so. And we know that many
times one would like to have complete and thorough data about something he sees in these
pages, yet he considers it too much trouble to hunt up paper and envelope -not to
mention the stomp -and write a long letter detailing what he wants
to know. This is just as simple as we know how to make
it with the exception of stenciling each subscriber's name
and address on each of the postcards -an operation
which would be highly impractical from the printing
standpoint. But from now on, when you want more
information about something you have seen advertised
or mentioned in AUDIO you need only indicate it on
the appropriate card, print your name and address, and
drop it in the nearest postbox. We pay the postage, and it goes
without saying that we wouldn't include these cards if we didn't welcome your
use of them. And, for the first time, you can enter your subscription without sending a penny
with your order -we'll bill you later. For books, we'll have to ask for the money in advance,
but only for books.
z
O
N
ó
u-
Readers have told us that they often want to
know more about some of the items mentioned in the New Products and New Literature pages of the magazine, but that they
do not want to take the time and effort to
write to each one of the sources individually
to get all the information they need. As a
matter of fact, in an average issue there
are usually ten items in the New Literature
column, and between ten and fifteen on
the New Products pages. It is conceivable
that the average reader might want information on at least ten of these items, since
they are selected with the interests of most of
AUDIO's readers in mind. Thus one would
have to have ten envelopes, ten sheets of
paper, and ten three -cent stamps, together
with the need for writing the ten letters
and inscribing each with name and address.
We do it all for you, assuming that you are
willing to circle the items about which more
information is desired and to write your nome
and address once. We will forward your
inquiries to the organization involved, and
you will receive the data you want with only
one inquiry. Isn't that as simple as A B C?
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ú
a
z
Postage
No
Will be Paid
Postage Stamp
Neoeerq
by
u wiled in the
Addressee
United States
BUSINESS REPLY ENVELOPE
First Class Permit No. 142, Mineola, N. Y.
AUDIO
P.
O. Box
629
Mineola, N. Y.
ttttfttttlo
No
Postage Stamp
Necessary
If Mailed in the
United States
In just the same way you can get more information about any product that is advertised in the pages of AUDIO. But there is
a little more work involved
in this, since
you must indicate the item in which you are
interested and the name of the manufacturer.
However, you still have to write your name
and address only once for all the information you want about advertised items from
a single issue-unless you want to know all
about everything. If your cards indicate that
this is likely to be the case, we will make
them larger to fit your requirements. In the
meantime, if you do need more space, you
might subscribe to two copies.
BUSINESS REPLY ENVELOPE
First
Class Permit No. 142, Mineola, N. Y.
AUDIO
P.
O. Box
629
Mineola, N. Y.
www.americanradiohistory.com
AmericanRadioHistory.Com
BOOK ORDER
below,
send me the books checked
money order
postage paid. I enclose check
in full payment.
for S
Please
the 2nd audio anthology
Board cover, $3.00
the 2nd audio anthology
Paper cover, $2.00
aC
O
co
7
Electronic Musical Instruments
Dorf. $7.50 (Foreign $5.00)
Wear and Care of Records and Styli,
Weiler. $1.00
O
X
n
lJ
To start receiving Audio monthly without
any effort on your part to locate one
on the newsstands or at your jobber's,
mark the appropriate boxes with crosses,
tear out the card, and drop it into a
handy postbox. If you are one of those
who always pays in advance, we will
accept your check or money order -we
do not recommend cash to be sent
through the mails -enclose the card in
an envelope, and mail. This will cost
you an extra three cents, so if you wait
until we send you a bill, we'll enclose a
business reply envelope for your convenience. We try to make it as easy for
you as we know how.
Unfortunately, we do have to have money
with your order in the case of books, for
many of those our readers order are those
which we must purchase from other
sources. And even with our own publications, we do have to pay the printer if
we expect to have him print the next
book we put out. But we can help in
this fashion
you want any book from
any publisher, just list the name of the
book and the author and we'll get It for
you. It helps if you know the name of
the publisher, but that isn't necessary.
If you aren't sure about the price, make
a good guess and enclose that amount
we'll mail the book COD for the differ-
-if
-
NAME
[
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ó
IIIIIIIlIIIIIIII
AUDIO,
P.
0.
9
ZONE
CITY
further information on the items circled
B
B
1
8
B
B
2
9
B
3
B
10
B
B
4
11
B
5
B
12
6
B
3
BT
4
9
BT 10
BT
11
BT
12
BT 13
BT 14
BT 17
BT 18
BT
19
BT 20
BT 21
BT 22
BT
5
6
BT
7
BT 15
BT
8
BT 16
We'll do the rest, and you may
-
-
-
-STATE
ZONE
CITY
be sure
that we'll be prompt because we are just
as anxious for your inquiries to get to
their destination as you are -and besides, we don't have room enough
around the office to accumulate a lot of
cards. Circle one item, if you wish, or
all of them -we'll carry on from there.
This whole system breaks down if there
is a charge for the New Literature described, so if you can suggest any improvements in this service, we would
NAME
ADDRESS
At the end of each item of New Literature or New Products you will notice a
letter and a number -the letter indicates
the month and the number indicates
which item it is. All you have to do to
get full information about the product or
to get the literature described is to circle
the appropriate number, add your name
and address -printed if possible, so the
information doesn't end up in the Post
Office at Washington -and mail it to us.
B
13
B
BT
BT
BT
BT
listed in New Products and New Literature
as
2
1
STATE
Box 629, Mineola, N. Y.
Please send me
BT
ence, or we will refund the overpayment
if you are too generous. In any case, we
pay the postage on the book, although
you will have to pay the postage on the
envelope you use to send us the order
card. Try it once and see how easy it is!
ADDRESS
6
appreciate hearing about them.
B
AUDIOabout-
We can't think of any way to simplify
this card without actually listing every
product mentioned throughout the magazine, and this becomes an impossibility
we don't always get the ads sufficiently
far in advance of printing time to make
it possible to plan such an elaborate card.
So if you want to know more about any
product advertised -except from the
Classified section -just write down the
product and the name of the advertiser as
well as your own name and address. We
can't promise that no salesman will call,
but we think it highly unlikely, because
very few manufacturers have enough
salesmen to answer all the inquiries individually in person. But we are sure
that each manufacturer will be glad to
send you the information you want without any obligation. If we find that this
card doesn't have enough room for all the
information you want, we will have to
enlarge it, but let's try this one for size.
Please send me complete information
advertised
-
by-
NAME
ADDRESS
CITY
ZONE
STATE
www.americanradiohistory.com
AmericanRadioHistory.Com
Overwhelming
THE
CcUctievRC-54
The Automatic Record Changer
That First Introduced
Overwhelming is the word
- because
...
the very features offered you by the Collaro RC -54:
smooth, quiet operation
inter -mixing of all size
RC-54. In the past 4 months, more RC-54s have been
records at all speeds without presetting-3 -speed opera-
sold than in any other similar period. And it looks
tion: 331/2, 45 and 78 rpm
like this record is well on its way to being broken.
cycle regardless of record speed
-
wow and flutter
that you would recognize this fact so soon. It appears
then that what you have been really looking for arc
Sold by Leading Sound Dealers.
A
R
C
O
R P
O
R
A
T I
O N
2
1
5
1
-
- fast (7 seconds) change
- minimum rumble,
-
gentle handling of records jam proof operation- smaller mounting deck, and all the
other convenient advantages of the RC -54. But above
all, it appears that what you want in home music repro duction is fidelity ... Just Plain Fidelity
M A
Write for complete specifications to Debt
O C K B
Just Plain Fidelity
that's just what the reaction has been to the new Collaro
Of course, we knew all along that the RC -54 was
worthy of such popularity, but we didn't quite realize
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Slightly high..
3 7
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Street, New York
www.americanradiohistory.com
AmericanRadioHistory.Com
W.,l el
1
6,
N.Y.
ReeMie,
gleCZY01.0
you are invited by
to...
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LIFETIME
CONTEST STARTS AUGUST
As always, Electro -Voice is FIRST! Now
E -V sponsors this unique and exciting
contest, that you might hear (perhaps
win) today's finest matched high fidelity
sound systems. For a lifetime after this
i
ll=;-
OF
llllllll
HIGH
1955
1,
í
1111111
III
FI DELI T l' MUSICi
glorious listening experience, you will judge
music reproduction equipment by its ability
to approach the perfection already achieved
by E -V matched high fidelity components and
loudspeaker systems!
WIN this "double- size" first PRIZE!
0
o
WEEK -END WITH HIGH FIDELITY ALL -EXPENSE -PAID week -end trip
for two ... from wherever you enter the contest to Electro- Voice -the Home
of High Fidelity! See hi -fi equipment take form before your eyes! Take part in
the assembly of your own wonderful prize, if you wish.
LIFETIME OF HIGH FIDELITY MUSIC with your own incomparable Patrician 4 -way audio reproducer and the beautiful Peerage console complete with
all equipment!
and LOOK...9 more PRIZES, wonderful to WIN!
WIN the incomparable Patrician 4 -way audio reproducer! Choice
of Korina Blonde or Mahogany cabinet,
four speakers, three level controls and 4 -way
crossover!
3
...
magnificent E -V 15TRX 15-in.
three -way speakers!
3 Third Prizes
outstanding E -V 12TRX
12 -in. three -way speakers!
3 Fourth Prizes
powerful E -V
Second Prizes
...
...
12TRXB
WIN the beautiful Peerage console plus 30 -watt ampli-
12
-in. three -way
speakers!
fier, pre -amplifier, remote control and FM tuner and
record changer or turntable of your choice!
ELECTRO- VOICE, INC., BUCHANAN, MICH.
Gentlemen:
Please send
I
wont
me
a chance
to win a r'Wook -End with High Fidelity."
the names of nearest participating
Address
ELECTRO -VOICE, INC., BUCHANAN, MICHIGAN
City
My nearest large trading center
www.americanradiohistory.com
AmericanRadioHistory.Com
Zone
is
E -V
Distributors.
c .
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