Heathkit SG-8 signal generator User manual

ASSEMBLY AND OPERATION OF THE
HEATHKIT SIGNAL GENERATOR
MODEL SG-8
=
4 a. mue =
cE ke,
2 =; To
a a a
Ei. $ ев к
A д de арта
EA PORTA A
TA ERA LT
+ "à CEE 4 ETA x Ш
ПОРН ВО Ро
a РОС с
vod E. O
RR NT
"ab: A : о"
“si A £ " OF "
2 + Os I
Fr... о RO E
Di ro x - . ля ‘
Hi = 5 - се Я
NE fon. а
h te . 7 . +, .
de NP Е
Ti кво РЕ
и E. | :
4 O J
; 7
SPECIFICATIONS
Frequency Range
Band A.....eoeoeocxecorocorosoorerococarcooos. 100 ke to 500 Ke
Вап@ В. .................................. 900 Кс 10 1600 Кс
Вап@ С... .................. г... .......... 1.65 тс to 6.0 ME
Band 2. .........)........................6.5 тс {10 25 тс
Band Е... .............. 2..2... 2.2... ....... 20 тс 0 110 тс
Calibrated Harmonics.................….........12°0 me to 220 mc
Radio Frequency Output........................In excess of 100,000 microvolts
Modulation Frequency............…............Approximately 400 cycles
Audio Output. .........e.e0ococereccesocccsrereeccoco: 2 103vVOIÉS
Audio Frequency Input......................... Approxiniately 5 v across 1 megohm
Tubes
12AUT. es ees 0000. .aaro0adacercecocaoo.. RE Oscillator-Buíffer
BC 4....._r.eoreccaoracocaranaeoccrvacac.s.e. Audio Oscillator or Audio Amplifier
Power RequirementS. ..........................105-125 v, 50/60 cycles
Cabinet SiZe. ..0...0.0000000000000000000040000011, 91/2 wice x 6 1/2 high x 5 deep
Shipping Weight. ...0..0.000000000000000000000040 4 +1 108.
1 1 8:95 13GOW
| = YMOLVYINIO 1VNOIS LIMHLVAH
| ,
7 ye
3 „”
и” —_— :
nn 0 (CO
E =.
034 | 132A
SdALS du (W) |
H314i103Y
WAIN3T13S
(J IXMOHI 4V
SHV
я
«ща
ni
2
Y
_ MEE — 20° ©
X 1 = || X т
8 у [+ || Л > |
_ 00! 102
O£E OO
s > | | ©
NTE) ани Т — 7 4)
\ / os coo' | I —
Un un an a en => в 2 BR O 10 —
NN | Ss CO
© WY V+ WA >—] \S | LNO 4Y
ANA Г HOLY M EE но’ 779 | _
- | 1081N03 | TI
A © | L ТВ | HILIMS Ooi e |
NOILYINOON |
¿no o" D и
„и
— _ &— + MAA, <)
009% NI +Y
Page 2
INTRODUCTION
The .Heathkit model SG-8 Signal Generator has been designed for simplicity of construction and
stability of operation. A little care taken during the process of construction will reward the kit
builder with a signal generator which will give excellent performance and will be both pleasant
and easy to use. This generator has been engineered so that it will be valuable to the radio re-
pairman, ham and experimenter over a wide range of uses, in addition to being a rugged and
highly dependable piece of test equipment. It is made with high quality parts, conservatively
rated, and will give long andefficient service. The model SG-8 Signal Generator utilizes factory
adjusted coils, thereby eliminating the necessity of having costly equipment available to cali-
brate the finished Kit.
CIRCUIT DESCRIPTION
The RF portion of the SG-8 Signal Generator consists of a 12AU7 twin triode tube. One triode
section of this tube is usedas a Colpitts oscillator. The other triode section is used in a cathode
follower type circuit and acts as a buffer between the oscillator and the output of the signal gen-
erator. Four inductances wound on forms comprise the coils for bands A, B, Cand D. Theyare
switched intothe circuit by means of the band switch. The E band coil is unique in its construc-
tion insofar that the heavy buswire of which it is composed actually forms the connections be-
tween the band switch and the tuning condenser for all of the lower frequency coils. When the
band switch is placed in E band position, a short is placed across the leads of the E band coils,
thereby making it a closed circuit inductance which is capable of tuning from 25 to 100 mega-
cycles.
In a Colpitts oscillator circuit, feedback necessary to maintain oscillations is obtained from a
capacitive reactance divider across the inductance of the frequency determining circuit. In the
model SG-8, a capacitive divider is obtained by the use of a split-stator condenser. The ad-
vantage of this will be made apparent from the following explanation. For example, take a ca-
pacitive divider composed of fixed capacities. А5 the frequency across the condensers is in-
creased, the reactance of the condensers is decreased. Therefore, using a fixed capacitive
divider, as the frequency is increased reactance would become lower until a point was reached
where oscillations could no longer be maintained. By the use.of a split-stator condenser for
both tuning and as the divider network as the frequency is increased, the capacity of the con-
denser dividing network is decreased. The reactance of a condenser for any given irequency 1s
inversely proportional tothe capacity. This tends to maintain the reactance of the network fair-
ly constant, thereby permitting oscillation over a wide range of frequency.
The use of the cathode follower as a buffer stage has the following advantage: The characteris-
tics of a "cathode follower' are very low output impedance with an extremely high input imped-
ance. The extremely high input impedance produces little or no loading on the oscillator circuit.
The very low output impedance provides a very stable output from the signal generator. The
effect is such that a varying load on the output of the signal generator will produce little or no
frequency instability of the oscillator. The signal generator incorporates a step attenuator for
coarse control of radio frequency output afid a continuously variable attenuation circuit for fine
control of the radio frequency output.
The audio oscillator is also a Colpitts circuit. By the use of the large inductance of an iron-
core choke and relatively high capacity in the capacitive divider, it is made to oscillate at ap-
proximately 400 cycles. This type of oscillator was again chosen for its stability and purity of
waveform. With the modulation switch in the INT. position, 400 cycles audio voltage is ap-
plied through a resistance network to the grid of the cathode follower stage. This audio vo tage
is impressed as an amplitude modulated signal upon the RF output from the cathode follo ver.
At the same time the audio voltage is also applied to the external audio cc nne ‘tor marked CUT,
and may be used as an audio signal source for testing amplifiers, etc. Wich the modul ition
switch in the EXT. position, any external audio source of any frequency may be used to modu-
late the RF output of the signal generator. The 6C4 audio oscillator tube then becomes an am-
plifier stage for the external signal.
Page 3
The power upply consists of a transformer which furnishes filament voltage to the 6C4 and
12AU7 tubes and effectively isolates the instrument from the AC line. A selenium rectifier is
connected t¢ one winding of the transformer producing half-wave rectification. An RC filter
network cha ges the pulsed output from the rectifier to fairly pure DC. The 110 volt input has
both sides bypassed to minimize the signal feeding back through the power lines.
A unique de sign feature is the convenient AF IN-OUT control, which adjusts audio input if ex-
ternal modu ation is employed and likewise adjusts the AF output level when using the generator
as a source of audio output.
PRELIMINARY INSTRUCTIONS AND NOTES
The Heathki: model 3G-8 Signal Generator when constructed in accordance with the instructions
in this mam al, is a high-quality piece of test equipment, capable of years of trouble-free serv-
ice. We therefore urge you to take the necessary time to assemble and wire the kit carefully.
You will be rewarded with a neat appearing, well-built and dependable test oscillator.
This manual is supplied to assist you in every way to complete the signal generator with the
least possit le chance for error. We suggest that you take a few minutes now and read the en-
tire manual thr ugh before any work is begun. This will enable you to proc eed with the work
much faster wl en c »nstruction is started. The large, fold-in pictorials are handy to attach to
the wall above your work space. Their use will greatly simplify the construction of the kit.
These diagrams are repeated in smaller form within the manual. We suggest that you retain
the man ial in your files for future reference, both in the use of the signal generator and for its
mainten ince.
UNPAC]. THE KIT CAREFULLY AND CHECK EACH PART AGAINST THE PARTS LIST. In
so doing, ycu will become acquainted with each part. Refer to the charts and other information
shown on the inside covers of the manual to help you identify any parts about which there may be
a question. If some shortage is found inchecking the parts, please notify us promptly and return
the insp action slip with your letter to us. Hardware items are counted by weight, and if a few
are missing, please obtain them locally if at all possible.
Read the note on soldering on the inside of the backcover. Crimp all leads tightly to thetermi-
nal befcre soldering. Be sure both the lead and the terminal are free of wax, corrosion, Or
other Роге п substances. Use only the best rosin core solder, preferably a type containing the
new activat:d fluxes, such as Kester '"Resin-Five," Ersin "Multicore," or similar types.
NOT: ALL GUARANTEES ARE VOIDED AND WE WILL NOT REPAIR OR SERVICE
INSTRUMENTS IN WHICH ACID CORE SOLDER OR PASTE FLUXES HAVE BEEN
USED. WHEN IN DOUBT ABOUT SOLDER, IT IS RECOMMENDED THAT A NEW
ROL]. PLAINLY MARKED "ROSIN CORE RADIO SOLDER" BE PURCHASED.
Resistors and condensers generally have a tolerance rating of +20% unless otherwise stated in
the parts list. Therefore a 100 KQ resistor may test anywhere from 80 K2 to 120 K2. (The let-
ter K is coramonly used to designate a multiplier of 100.) Tolerances on condensers are gen-
erally even greater. Limits of +100% and -50% are common for electrolytic condensers. The
parts furnished with your Heathkit have been specified so they may not adversely atfect the op-
eration of the finished signal generator.
In order to expedite delivery to you, we are occasionally forced to make minor substitutions of
parts. Such substitutions are carefully checked before they are approved, and. the parts sup-
plied will work satisfactorily. By checking the parts list for resistors, for example, you may
find that a 2.2 megohm resistor has been supplied in place of a 2 megohm as shown in the parts
list. These changes are self-evident and are mention: d here only to prevent confusion in check-
ing the contents of your Kit.
We strongly urge that you follow the wiring and parts layout shown in the manual. The position
age 4
TEST LEAD ASSEMBLY
—@ |
- lg bn ra _ CE = RE << M
Figure 11
| ен т.
| re a AE mur
Ой HN =e
| HAZ пана rr. 3
1 # м
CIC CT
“a. - "EEE EEE EEE
Po
The test lead is assembled as shown in Figure 11. One end of the shielded cable is connected to
the shielded plug; the other end has alligator clips mounted on it for connection to the equipment
under test. First, remove the spring cable guard from the connector plug by loosening the
screw in the side of the plug. Slide this spring over the shielded cable, with the small end of
the spring toward the end that is tobe connected tothe plug. The outside in:sulation onthe cable
is then cut back for a length of about 3/4", then flare the shield braiding at the end of the cable
so that it may be pushed back over the small end of the spring cable guard. The inner connector
is then stripped for a length of approximately 1 /8'"". The assembly at this point is slid back into
the connector so that the inner coaxial wire passes through the rivet in the insulated end of the
connector, the cable guard with the shielded braid flared over the end is pushed back into the
connector and the screw tightened to hold it in place. Solder the inner connector.
Quter covering removed
Shit lengthwise
7 4
7
Circular cul +
J Bend sharply and
Md MN separate shielding
# NY with smallscrew-
driver or knife
blade. Pull in-
ner wire out of
shielding.
Shielded test lead ready
tor connector.
Figure 12
On the other end of the shield cable, the outer insulation is cut back about 4' and the cable pre-
pared as shown in Figure 12. Solder alligiitor clips to both the inner conductor and the shield
braid.
ACCURACY
Any signal generator is designed as ‘a convenient and controllable source of modulated or unmod-
ulated signals. No signal generator is designed as a frequency standard. Expensi- e standard
signal generators have fairly accurate (3 to 20%) attenuators which control the ouiput voltage
and the calibration accu acy is rarely closer than 1%. The Heathkit Signal Generator may be
expected to fall within 2 to 3% of the frequency calibration, which is quite satisfactory for ser-
vice work and alignment. In receiver adjustment, the frequency at which the particular adjust-
ment is made is rarely critical but the adjustment itself for maximum signal output from the
Page 15
receiver is frequently quite critical. For accurate calibration of home built receivers or eq 11p-
ment, pr ‘ce>d as fcllo‘ss. Make a rough calibration with the signal generator. Then, with a
receiver, ture in W VV (Bureau of Standards) at 2.5, 5, or 10 mc. Set the signal generator to a
suitable sub-harmoic, such as 500 or 1000 kc, and adjust the generator for zero beat. Now
hirmonics of the si: nal generator occur every 500 kc or 1 megacycle, and these harmonics may
be used to give accurate calibrations at points 500 or 1000 kc apart, such as 2000 kc, 3000 kc,
3500 kc, 4000 kc, etc. These known frequency points can be marked on the dial of the equipment
being calibrated. Te object of the rough calibration is merely to furnish a means of identifying
for example, the 3(00 kc point from the 2500 kc or 3500 kc points. For calibration of higher
frequency equipmert, a choice of higher sub-harmonic will reduce the confusion between the
n ultitude of harmo ics and will also insure adequate signal strength. When checking the cali-
bration accuracy of the Heathkit Signal Generator, the most convenient standards of comparison
of sufficient accurac y are broadcast stations of known frequency. Crystaloscillators of standard
frequency when zero beat against WWV, are also convenient to use if available. The use of re-
c ’iver dial calibrations is frequently not of sufficient accuracy to warrant consideration.
Output Voltage: Th: RF signal strength going into the output control depends upon the strength
of oscillation of the 12A U7 oscillator. In all variable frequency oscillators the amplitude will
v:ry with the tunin; condenser setting. With ca. -eful design the variation may be minimized.
In the Heathkit Signe! Generator, the variation is kept down to a ratio of about 2 1/2 to 1 on each
band except band E, where the L/C (inductance to capacitance) ratio becomes sufficiently un-
favorable that oscillation may drop off rapidly in strength when the condenser is near maxi-
mum capacity. Hov ever, even on this band, the output of the SG-8 is in excess of 100,000 mi-
crovolts which is more than sufficient for the average application in which this generator. will
be used.
IN CASE OF DIFFICULTY
1. Recheck the en ire wiring. Follow each lead and color it on the pictorial with a colored
pencil. If possible, have a friend recheck the wiring for you. Most cases of difficulty re-
sult from wrong or reversed connections. In this unit, there is alsothe possibility of shorts
to the chassis o:curringon some of the bare wire connections from the coils. These wires
should be carefi lly spaced away from the chassis when the instrument is assembled.
à. Check the test l:ad with an ohmmeter to be sure there are no shorts between the inner and
outer conductor caused by overheating during the soldering process.
3. If the wiringis found tobe correctand the signal generator still refuses to work, try chang-
ing tubes. It is possible that one of the tubes is defective.
4. Check the voltages. A voltage chart is included showing the normal voltage to be expected
at the pins of the tube sockets. These voltages were measured with an 11 megohm input
vacuum tube voltmeter. A normal variation of +15% is to be expected. With regular volt-
meters, readings may be very much lower. All voltages are DC unless otherwise indicated.
5. If only one band onthe signal generator is inoperative, it is very likely that the coil associ-
ated with that band has become damaged. An ohm meter connected between the terminals of
the coil should show continuity. If it does not, one section of the winding is open.
VOLTAGE CHART
7 UBH Pinl | Pin2 | Pin3
12AU" | 78 * 2 to -15
Pin 5 Pin 6
6.3 AC | 6 3 AC | *75-85 3 to -30 0
65
Е:
*Dependent upon frequency.
NC - no connection. BIBLIOGRAPHY
Marcus and Levy; Elements of Radio Servicing
Kiver, Milton S.; How to Understand and Use TV Test Instruments
Johnson, J. Richard; How to Use Signal and Sweep Generators
Page 16
USE OF THE FF SIGNAL GENERATOR
This signal generator can be used to align ¡adio receivers. It furnishes a source of radio fre-
quency or modulated radio frequency by means of signal generator fundamental frequencies be-
tween 160 ke and 100 megacycles (1 megac: cle equals 1000 kilocycles) «nd useful harmonics of
the signal generator may be used to over 20:0 megacycles.
The RF Signal Generator will be found a most valuable aid to the radio service man as well as
the hobbyist. The day-to-day "bread and b itter"' job of the signal generator 1s receiver align-
ment. To save time and money, the service man or hobbyist should use a technique which can
be applied to the majority of sets encountered in normal work. After using the technique a few
times, it becomes virtually a matter of "second nature" and so easily used that the average set
may be completely aligned in a matter of minutes.
The majority of single band radio receivers have nowadays become quite standardized and there-
fore it is seldom necessary in alignment o receivers to refer to the specific manufacturer's
alignment instruction. In the average receiver, it is generally only necessary to take note of
the IF frequency (most home radios and aut ymobile radios employ a 455 KC IF frequency).
Figure 13 is a schematic diagram of a small, single-band superheterodyne radio receiver. The
majority of single-band sets use a circuit similar to this one. Variations likely to be found are
as follows:
(1) Use of an antenna coil rather than a rod-type or loop antenna.
(2) Use of a separate oscillator rather than a pentagrid converter.
(3) Trimmer tuning of IF and RF stages in place of iron core slugs.
(4) Use of an RF stage ahead of the mixer.
(5) More than one IF stage.
These variations do not appreciably affect the alignment technique and the following step-by-
step procedure may be used directly in most cases:
(1) Turn both the signal generator and the receiver on and allow severa minutes for both units
to reach normal operating temperature. (It is a good idea to leave the signal generator on
during all working hours.)
—_— 34 POINT "CT
12 AY B
2MD DETECTOR 4
IF AMP FIER | AUDIO AMPLIFIER
|
12 ВЕ ©
IST DETECTOR TS Ç
L OSCILLATOR | GREEW
ЗО
Ca
H
on
XT À
POWER Ya
F igur e 1 3 TRANSFORMER Ш
с Oo Му aC”
| ' GQ) | al. 47005. al: HM - 2 |
o [o do | &
‚ ® ©
3
IZBAD IZAYÉ
7
$ TUNER WIRING
7
{ЗА
Page 17
2) Connect an output indicator to the receiver. This may be an AC voltmeter connected di-
rectly across the loucspeaker voice coil; however, a VTVM connected to measure AVC vol-
tage 1s by far the most desirable method.
(3) Short ou the local oscillator tuning circuit temporarily. The simplest way to accomplish
this is merely by clipping a short piece of wire across the rotor and stator plates of the
oscillator section of the tuning condenser. Set the receiver dial to the low frequency end,
somewhere near 950 KC.
(4) Connect the signal generator to the antenna terminals of the receiver or if the receiver
employs a loopantenna or rod antenna, couple the output of the generator to the antenna sys-
tem through a one or two turn loop of wire around the antenna. In cases where an RF stage
is used ahead of the mixer, connect the signal generator to the injection grid of the mixer
stage. Set the signal generator to the IF value o: th: set. (455 KC is generally the accepted
standard.) Use a modulated signal if an AC voltmeter is employed as an output indicator.
An unmodulated signal is used provided the AVC voltage is used as an output indication.
(5) Using the lowest range of the output indicator, increase the output of the signal generator
until a reading can just be obtained.
{6) Adjust the IF transformers for maximum reading on the output indicator. Reduce the sig-
nal generator output as necessary to keep a low reading on the output indicator. Repeat the
adjustments at least once to correct for any interaction between primary and secondary
windings on the individual transformers. Interaction is most likely to occur in sets where
adjustment is by means of iron-core slugs rather than trimmer condensers.
(7) Next, remove the short across the local oscillator and tune the receiver to its ‘highest fre-
quenc/ setting (s mmewhere around 1600 KC). Set the signal generator to the same frequency
and adjust the oscillator trimmer for maximum outout.
(8) Now tune the recciver and signal generator to 1400 KCand adjust the RF trimmer for max-
rx imum output.
(9) Turn che signal generator to 600 KC and tune the receiver to the low frequency end of the
dial. Yow "rock" the receiver tuning condenser while at the same time adjusting the trim-
“mer condenser for maximum output. In sets using especially shaped plates inthe oscillator
„Section of the tuning condenser, generally no trimmer condenser will be found. Also, in
- some sets, the lcw frequency oscillator adjustment will be through means of an iron-core
slug in the oscilletor coil rather than a trimmer condenser.
(10) Steps 7, 8 and 9 should be repeated if it was found necessary to readjust the trimmer con-
dense (or iron-core slug) as directed in Step 9.
The alignment proced: re for multi-band AM superheterodyne receivers is essentially the same
as outlined above for a single-band set. First the IF stages are aligned using the same technique
as given in Steps 1 through 6. Next, each RF band is aligned separately, starting with the high-
est frequer cy band an! working towards the lowest. The technique given may be used but with
corresponcing frequercy settings for each band.
If the oscillator and I F trimmer condensers for the different bands are not well identified, a
simple technique may be employed to locate the proper adjustment screws. Turn the receiver
band switch to the higlest frequency band and tune in a signal, using a short-wave station or a
signal from the RF generator. Using an insulated alignment tool, try compressing the different
oscillator trimmers until one is found that changes the tuning of the signal. Do not compress
the oscillator trimmer condensers by turning the adjustment screws, just press the leaves of
the condenser together temporarily. This method will identify the trimmers for each band with-
out drastically changir g their original setting. After identifying the oscillator trimmer for the
band in this manner, -'epeat the technique to identify the RF trimmer. Turn to the next band
and reneat the method being careful not to touch the trimmers already identified.
Page 18
Should the oscillator trimmer of the short-wave band have a wide tuning range, 1t may »e pos-
sible to pick up and "peak" a signal with two different settings of the trimmer. Shculd his the
the case, use the setting with the least capacity to insure that the oscillator is tuned al ve the
incoming signal.
FM RECEIVER ALIGNMENT
It is the standard practice to align the IF amplifier of an FM receiver (tuner) before aligning; the
RF and oscillator sections just as in AM receivers. However, the exact technique of aligmaent
depends on whether a limiter discriminator or a ratio detector is used. Where a limiter and
discriminator are used, usual practice is to align the IF section up to the input of the limiter
first. Then align the discriminator as a separate step. When aligning the I)¥, RF and osc la -
tor sections, the grid current of the limiter may be used as an output ir dicator. Althoug! the
voltage across a limiter grid resistor, measured with a VTVM, willserye in many ca ses, it is
not an ideal indication. A typical limiter and discriminator stage is shown in Figure . 4. ?ro-
per alignment technique for the complete FM receiver is as follows:
(1)
(2)
LIMITER
Coso DISCRIMINATOR
=
e |
|
|
|
O ©
eo AUDI)
Figure 14
Connect an output indicator by (1) attaching a VTVM across the limiter grid resistor; or
(2) breaking the circuit at the grid of the limiter and inserting a microammeter with a max-
imum range of around 150 microamps. If this method is used, be sure and bypass the meter
with a .05 ufi condenser to ground. See point X in Figure 14.
Connect a signal generator to the input of the mixer stage and turn on both the signal gen-
erator and the receiver. A sufficient warm-up time must be allowed to permit both tie re-
ceiver and the generator to reach their normal operating temperature. In the case of FM
receivers this is usually 15 to 20 minutes before complete stabilization can be ob ained.
Adjust the signal generator to the IF value of the set. This is usually 10.7 mc. Ihe un-
modulated RF output of the signal generator is used.
Peak all IF trimmers for maximum meter readings. If the IF is considerably out ¢ align-
ment so that very little meter reading is obtained, it may be necessary to connect tae s1g-
nal generator to t ie last IF stage and align this portion of the circuit first. Then wo-~khack
toward the mixer stage, rechecking previous IF adjustments at each point.
Connect a VTVM »etween point 1 and ground as shown in Figure 14. Adjust the trim ner or
slug "J" for max aum reading using a low VTVM range.
Transfer the VI M connection to point 2 and adjust trimmer "H''for a minimum voi meter
reading.
Fage 19
(6) Transfer the signal generator lead to the antenna terminals and align the RF and oscillator
trimmers, using essentially the same technique as is outlined for AM receiver adjustment,
except the frequency settings will fall between 88 mc and 108 mc. The output indicator for
this adjustment is the same as discussed in Step 1. Lastly, adjust the antenna trimmer for
maxirium indication or volume using the receiver's own antenna and at its permanent loca-
tion. N
RATIO DETECTORS
The following technique may be used for alignment of ratio detector FM receiver circuits. Re-
fer to Figı re 15. LAST IF
RATIO DETECTOR
pr == == o re тн Ч)
AUDIO
1 |
a nod
mfp A
Чин = a.
LL =
(1) Connect a VTVM or high resistance DC voltmeter across RC.
(2) As before, both receiver and signal generator should be allowed to warm up. The receiver
-dial should be set to the low frequency end (88 mc) and the signal generator adjusted togive
an unmodulated signal at the receiver IF. Connect the signal generator to the input of the
mixer stage as before.
(3) Adjust all IF trimmers (or slugs) for a maximum reading on the meter, using a low range
and the least signal generator output possible. Repeat the adjustments at least twice to cor-
rect for any interaction. Be sure slug N is accurately adjusted.
(4) Connect two 100,000 © 1/2 watt resistorsacross RC (RA and RB) and connect the voltmeter
as shown in Point V in Figure 10.
(5) Adjust the trimmer (or slug) M for a zero output indication on the meter.
(6) Align the RF and oscillator stages using the techniques previously described, measuring
the voltage across RC as an output indication.
SERVICING BY SIGNAL INJECTION
THE AUDIO AMPLIFIER
‘The block diagram for a typical audio amplifier is shown in Figure 16. Let us assume, for the
moment, that the amplifier is "dead" due to a defective second audio stage.
A
OUTPUT
Las D C
x IST 2ND PHASE
2 AUDIO AUDIO INVERTER
о
z SPEAKER
O
т.
a.
POWER
SUPPLY 2 [PVTRYT Figure 16
Page 20
In servicing the equipment, the first step, of course, is to check for obvio 1s defects such as
lack of B plus, defective tubes and so forth. After these preliminary tests hi.ve keern made, the
Heathkit RF Signal Generator is used as an audio signal souice by plugging the ouipu:: cable into
the "AF-OUT" jack. The level of the audio tone obtained is adjusted by the ' AF [N-OU1 con-
trol. The MODULATION control should be set in the "INT. ' position.
Check the operation of the output stages by connecting the ground lead of the >utpat cable to the
chassis of the amplifier or circuit ground and touching the ' hot" lead of the >utput cable to the
orid of first one output tube Point À in Figure 16 then to the >ther output tube Point B in Figure
16. All of these tests must be made through a .05 ufd condenser. In this fashion the opzration
of each output stage is checked individually. As each grid is touched, a clear audio tone should
be heard in the loudspeaker.
Next, the operation of the phase inverter stage can be check=d by transferrii g the hot lead (to-
gether with a .05 ufd condenser) tothe input of this stage (Point Cin Figure 3 6). Again, à clear
signal should be heard from the loudspeaker. The tone should be louder than | efore. If tco loud,
the volume can be reduced, using the "AF IN-OUT" control.
The second audio stage is now checked by transferring the hot signal generator lead to the input
of this stage, Point D in Figure 13. If this stage is dead, no more tone will be heard in the loud-
speaker. Having isolated the trouble to a specific stage, it is now a simple matte r to check DC
operating voltages and parts until the defective component is found.
As each amplifier stage is checked, work back towards the input stage (first aucio), a clefinite
increase in volume should have been noted. It ray even be necessary to reduc: th: volum: using
the control mentioned. This, then, provides an additional test technique. A weak stage can be
identified if little or no increase in volume is heard as the "hot" lead is tr.nsferred past the
stage. Be careful when interpreting the results of this test, for overloading 1 st::ge may cause
apparent loss in volume even when the stage itself is in good condition. Th:refre, when at-
tempting to isolate a "weak" stage, be sure to keep the signal level at a reas nal le point.
AN OPEN COUPLING CONDENSER may be isc lated using this signal injection technique. Refer
to Figure 17, which is part of a conventional r:sistance coupled amplifier. I co pling conden-
ser C-1 should open, little or no signal would he transferred between stages. To heck tae con-
dition of the coupling condenser, it is first necessary to connect a small blockin ' condenser in
series with the "hot" lead of the signal generator. The condenser may have : va ue of .05 ufd.
The exact value is not atall critical. The block--
ing condenser permits the ""hot'' lead to be placed
on the plate of a tube without danger of the DC
voltage present injuring circuits within the gen-
erator.
F E
|
Ca
If a clear tone is heard when the "hot" lead is
touched to Point E but not when touched to Point
F, we are reasonably sure Condenser C-1 is
open.
Figure 17
B+ =
RADIO RECEIVER
Referring to the block diagram for a typical small AM rece:ver, Figure 18, again the technique
of signal injection, is essentially the same as that used inthe case of the audio amplifier. That
is, a substitute signal is injected into each stai;e starting at a convenient point and working back
towards the "front" of the equipment. In the (ase of the audio amplifier, we work towards the
input jack of the amplifie:. In the case of the radio receiver, we work towaids he anteni 2.
There is one important dit erence between using the signal injection technique >n' n audioaiipli-
fier and using the same technique on a receiver. In the case of the amplifier as we have : een,
the audio output signal ob iined from the signal generator was used exclusive ly; however, vhen
trouble-shooting a receiver, it becomes necessary toswitchto an RF signal wl 2n « hecking stages
Page 21
ahead of the second ¢ tector. In addition, the frequer cy of the RF signal will have to be changed
to match the operatir : frequency of the stages being checked. A rather common receiver com-
plaint is that the "set is dead". When such a complaint 3 caused bya defective local oscillator,
the trouble n.ay prov. somewhat difficult to isolate.
As before, the first step inservicing the equipment is to check for the obvious defects. A quick
check with a DC voltn eter will indicate whether or not the power supply is operating.
To isolate the trouble to a stage as rapidly as possible, a technique which experienced service
men often employ may be used. Instead of stage-by-stage testing, the set is considered to con-
sist of major sections and primarily isolation of the trouble may be made on ‘his basis. The
audio signal obtained from the Heathkit RF signal generator may be used to inject a signal at the
input of the first audio stage (Point H in Figure 18). If a loud clear tone is heard, we know im-
mediately that the entire audio section of the receiver is operating and can forget about these
stages for the time being.
Shift the outp: t c:ble of the signal generator to the RF OUT jack and adjust the controis to give
a modulated :F signal at the IF value for the receiver. (In most cases this will be 455 KC).
Using a 50 д; Г с ndenser in series with the "hot" lead inject the signal at the input of the IF
stage (Point . in “igure 18). The use of a small couplin;; condenser in this case is to minimize
detuning of th: II and RF stages for the signal generato lead. If a tone is once again heardin
the loudspeak :r, we know that the IF stage, under test, is in satisfactory operation.
Repeat the sig 1al injection tests until the defective stage in the receiver has een located. From
this point on, the), it is a simple matter to isolate the defective components causing the re-
ceiver to be ii ope rative.
Var ations of a si rnal injection technique may be used for servicing FM and TV receivers as
well as the he ‘ein discussed AM receivers and audio amplifiers.
B 2ND
ge en La fe a de
SPEAKER
POWER
SUPPLY Figure 18
REPLACEMENTS
Material supplied with Heathkits has been carefully selected to meet design requirements and
ordinarily will fulfill its function without difficulty. Occasionally improper instrument opera-
tion can be traced to a faulty tube or component. Should inspection reveal the necessity {or re-
placement, write to the Heath Company and supply all of the following information:
A. Thoroughly identify the part in question by using the part number and desc ription found in
the manual parts list.
B. Identify the type and model number of kit in which it is used.
С. Mention the order number and date of purchase.
D. Describe the nature of defect or reason for requesting replacement.
The Heath Company will promptly supply the necessary replacement. Please do not return the
original component until specifically requested to do so. Do not dismantle the component in
Page 22
question as this will void the guarantee. I! tubes are to be returned, pack them carefully to
prevent breakage in shipment as broken tubes are not eligible for replacement. This replace-
ment policy does not cover the free replacement of parts that may have been broken or damaged
through carelessness on the part of the Kit builder.
SERVICE
In event continued operational difficulties of the completed instrument are experienced, the fa-
cilities of the Heath Company Service Department are at your disposul. Your instrument may
be returned for inspection and repair for a service charge of $3.00 plus the cost of any additional
material that may be required. THIS SERVICE POLICY APPLIES ONLY TO COMPLETED
INSTRUMENTS CONSTRUCTED IN ACCORDANCE WITH THE INSTRUCTIONS AS STATED
IN THE MANUAL. Instruments that are not entirely completedor instruments that are modified
in design wi'l not be accepted for repair. Instruments showing evidence of acid core solder or
paste fluxes will be returned not repaired.
The Heath Company is willing to offer its full cooperation to assist you in obtaining the specified
performance level in your instrument. Factory repair service 1s aviilable for a period of one
vear from the date of purchase or you may contact the Engineering Consultation Department by
mail. For information regarding possible modification of existing kits, it is suggested that you
refer to any one or more of the many publications thatare available on all phases of electronics.
They can be obtained at or through your loca! library, as well as at ary electronic outlet store.
Although the Heath Company sincerely welcoines all comments and suggestions, it would be im-
possible to design, test, evaluate and assume responsibility for proposed circuit changes for
specific purposes. Therefore, such modifications must be made at the discretion of the kit buil-
der according toinformation which will be much more readily available from some local source.
SHIPPING INSTRUCTIONS
Before returning a unit for service, be sure that all parts are secure!y mounted.
ATTACH A TAG TO THE INSTRUMENT GIVING
NAME, ADDRESS AND TROUBLE EXPERIENCED.
Pack in a rugged container, preferably wood, using at least three inches of shredded newspaper
or excelsior on all sides. DO NOT SHIP IN T HE ORIGINAL KIT CARTON AS THIS CARTON IS
NOT CONSIDERED ADEQUATE FOR SAFE SHIPMENT OF THE COMPLETED INSTRUMENT.
Ship by prepaid express if possible. Return shipment will be made by express collect. Note that
a carrier cannot be held liable for damage intransit if packing, in HIS OPINION, is insufficient.
SPECIFICATIONS
All prices are subject to change without notice. The Heath Company :eserves the right to dis-
continue instruments and to change specifications at any time without incurring any obligation
to incorporate new features in instruments previously sold.
mor x УР т Y
a | il; "9 nN J A
Ah | x 7
¿ |
b
WARITANTY
Heath Company warrants that for a periodof t! ee months from the date of shipment, all Heati:kit
parts shall be free of defects in materials and workmanship under normal use and service «nd ‘
that in fulfillment of any breach of such warraaty, Heath Company shall replace such defective у
parts upon the return of the same to its factory. The foregoing warranty shall apply only to the
original buyer, and is and shall be in lieu of all other warranties, whether express or implied J
and of all other obligations or liabilities on the part of I ‘ath Company and in no event shall |
Heath Company be liable for any anticipated profits, « nseq ential damages, loss of time or other A
losses incurred by the buyer in connection witl the purchas :, assembly or operation of Heathkits
or components thereof. No replacemer shall be made oi parts damaged by the buyer in .he
course of handling or assembling Heathl t equipment.
NOTE: The foregoing warranty is comp :tely void and we will not replace, repair or serv ce
instruments or parts thereof in which ac 1 core solder or paste fluxes have been used.
NW о О РСА Е ОС TDR RE
НЕАТН СОМРАМУ A
sao
— 1-26
PART PAI TS
_ №. Per Kit
Resistors
1-1
1-4
1-7
1-9
1-3A
1-18
1-21
1-2
4
1-32
1-33
Condensers
21-3
21-7
21-11
21-16
21-21
23-8
23-28
25-7
26-17
pod pb ND bed fd dk 8 he ND вай NN
bod já Ja jar pk CT) ph 5 ed
Controls-Swi ches
10-32 1
19-18 1
63-67 1
53-69 1
03-70 1
DESCRIPTION
Mi
47 Q € |
330 7
680 Q: >
1 Ко
3.3 КО 1 watt
5600 Q
15 Ко o
33 KQ |
100 KQ
390 KQ
470 KQ
10 vuf (.00001 ufd)
33 uv uf (.000033 uíd)
и
Lo
„”
>
150 uuf (.00015 uf и
.01 ‚ıfd 489
‚005 ufd (5000 uuf)—
‚02 ufd [= T
1 ud ——
20-20 ufd 150 v LL.
450 ци! dual tuning +
rr
1 megohm control Lo
1 KC control with switch?
9 position band switch --
2 position modulation switeHClips- Plugs-Wire
PART PARTS
Per Kit
No.
Sockets-Knobs-Jacks
100-M19
432-3
434-15
434-16
434-22
462-18
462-19
Hardware
200-2
200-7
290-8
200-9
290-13
290-19
250-63
251-1
202-1
202-3
292-7
203-10
253-22
204-1
294-4
209-1
‘3 position attenuator switch4 89-1
Coils-Chokes Transformers
Oscillator coil band A —
Oscillator coil band B
Oscillator coil band C
Oscillator coil band D
Oscillator coil band E
40-47A 1
10-47B
40-477C
10-47D
10-47E
16-1
4-2
pa ja jr fea una
AF choke L-~
Power transformer Da
l'ubes-Lamps -Rectifiers
Selenium rectifier
7-2 1
411-4 1
411-290 1
412-1 1
6C4 tube —
12AU7 tube
Grommets-Feet-Terminal Strips
73-1 6
261-1 4
131-2 2
2
431-3
Page 24
LA
3/8 grommet D
Rubber feet
#4" pilot light и
-
2-lug terminal strip “
3-lug terminal strip -
207-3
260-1
340-2
343-3
344-1
345-1
346-1
432-1
295-73
1
3
1
1
1
1
о
pub pi pt pt pas HA д нь ны
1
1
1
1
1
1
pure
NN WT ANN HH TON WA
DESCRIPTION
E
Indicator assembly “7
Shielded connector ;
7-pin miniature socket +7
9-pin miniature cle
Pilot light socket :-
Skirtless knob#
Skirted knob «+
3-48 x 1/4 screw
6-32 x 3/16 screw
#6 x 3/8 sheet metal screw
6-32 x 3/8 screw
6-32 x 1 screw
8-32 x 1/8 set screw
#10 x 1/2 handle screw
6-32 spade bolt
3-48 nut
6-32 nut
Control nut
Control nickel washer
3/4 flat washer
#6 lockwasher
Control lockwasher
#6 solder lug
Line cord и
1/8" cable clamp _-
Alligator clip —
length #20 bare wire
length Shielded test lead
roll Hookup wire '—”
length Shield braid
length Spaghetti (sleeving) vd
Shielded piug
Chassis-Panel-Manual
90-14
200-M54
200-M55
203-26F67
211-4
Cabinet
Chassis
Sub-chassis
Panel
Handle A |
Instruction Manual ”
и
">