The IG-102 Goes Transistor!

Julian ROS5'nick
1012 Tyson Aven ue
Philadelph ia PA J 911 1
The IG-102 Goes Transistor!
- tubeless portability for this Heath signal generator
T
he Heath IG-l 0 2 radi o
frequ e ncy signal gen erator is a versatile gene ralpurpose wide-ran ge inst rumen t o f co n ve n t io na l
vacuum-tube design which
ha s been catalogued fo r
several years. For those who
have acq uired the IG-l 0 2 in
the past and th ose who are
still looki ng for a good signal
generator at a mode ra te price,
th is article pro vides a simple,
economic, and fast mea ns of
co nversion for portability
w ith o ut sac r i f ici n g the
original qualities. Modifi cat io n of the IG·102 gives the
ins t rument new ca pabilities,
as foll ows :
1. Batt er y o pe r a ti o n
u t il izing either dry ce lls o r a
nic ke l ca d m ium rec hargeable
ba nk capable of su p plying 7
to 9 volts at a max im um
cu rrent o f 10 to 16 mA o
2. With t he use o f rec ha rgeable nic ke l ca d mi um
cells of approximately 1.2
volts per ce ll, 6 t o 8 cells are
su fficien t t o p rovide the req uired o pe rati ng supply vol t age. The basic radio frequency circuit will o perate
with a minimum of 4 volts
thr ou gh out its frequency
range . For c ha rging purposes,
a self-co n tained battery120
charging circuit is used whic h
employs the o rigina l compone nts (t hese can be d ispensed
with if d ry ce lls are installed) .*
3. All tube sec t ions a re
replaced b y four fi eld effec t
transisto rs, su ch as those
avai lable fro m Rad io Shac k #27 6-1623* * - or Catectro
- # K 4-634_
Procedure fo r Modificatio n
The followi ng ste p-by-step
instructions apply to c ha nges
and additi ons to the basic
IG-l 02 radio fre quency signal
generator. Accordingly, the
o riginal instruction manual
an d d rawings are used for
reference to detail th e modificat ion p ro cedu re . T his proce d u re invo lves sim p le
• Installa tion of the batte ry
supply is sim p le , si nce th er e is
a m ple c hassi s sp ace available t o
m ount batte ry brackets fo r accommodating the batt ery u ni ts.
•• So me o f th ese Rad io S hack
#27 6-1623 pac kages c o nt ain assort m e nts o f bo th rf and af field
eflect t ra nsistors. In testin g them ,
the af types w ill not oscillate. One
particula r type which responds
well a t radio fr equ enc ies is the
2 N59 5 1. The w hite-blac k t y pes
a re af and do no t oscilla te at radi o
freq ue nc ies; also, the metallic
types a re unsu ita ble .
changes, installati on o f ne w
compone nts , and constructio ns. Before u ndertaki ng the
modifications, 1 advise t hat
you s p e n d so me time
st udy ing and reviewing the
basic circuit and asse mbly to
be co me fam iliar wit h the
o ri ginal layou t . Add itio na ll y,
stu dy the detai ls o f th e fi eld
effect transistor connect ion
lead designat ions. In th e as
so rtment p ro vided in Rad io
Sh ac k's #2 76 -1 6 23, three
ty pes are referred to in the
designation of lead s. With
reaso nable ca re, th ere should
be no difficul ty using any of
the t ra nsisto r t ypes.
1. Re fer to Fig. 1, a copy
of th e o rigi nal circu it.
2. Remove all t ubes, if the
set has at ready been constructed.
3. Unsolder a nd d isco nnect power transformer connect ions (fila ment su p ply line
an d high-voltage rectifierfilter system), and recon nec t
the power su pply components as shown in Fig. 2,
usin g a dditi onal compo ne nts
as needed .
4 . So lder a 7 5-0hm,
Yl""Wa tt ca rbon resisto r ac ross
the R2 (33k, 2 W) decoupling
resisto r use d in the o riginal
circui t.
5. So l de r a 90·0 hm ,
Y}-Watt carbon resistor across
the R6 (4_9k, 2 W) decoupling resistor used in the
origi nal circui t.
6. Spot so lder o ne radi o
frequency field effec t transistor ac ross tube socket
V1B, te rminals 1-2 -3 , using
the lead referen ces given in
t he tr ansistor package tnstructio n shee t. However, if tran sistors are selected from the
Bctranslstor assortment given
i n Rad io Shac k's packet
#2 76 -16 23, t hen lead orie ntation should be foll owed as
pe r t he drawing supplied in
t he pac ke t.
To mou n t the t ra nsisto r
o n the tube soc ket, do th e
followi ng: Hold each lead
wit h long-nose pliers (fo r a
heat sink) as solder is ap plied.
Use a 35- to 4 0-Wa tt pe ncil
iro n with a small bla de tip
1/ 8 " wide, and sol der alloy
60-40. Apply a small dro p of
solder to the e nd of each
lead. Afte r thinning the leads,
spread th em to matc h th e
spaci ng o f the Jugs on the
tu be socket. Ap ply eac h lead
to th e required tube socket
term inal , as designa ted above
( t o facilitate con nection s,
also ap ply fresh so lder to the
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Fig. 7. OriginallG-702 circuit.
tube-soc ket terminals).
In spreading the transistor
leads, a slight bend on the
wi re ends will help in making
surface-to-surface contact fo r
solde ring. With the pliers,
hold each lead against t he
surface of the required tubesocket terminal , and apply
th e iron to the opposite side
of t he terminal until solder
flows well t o form a good
spo t - s olde r joint. No
m echanical co nnect io n is
necessary to co mplicate the
procedure. Once the first
transi stor lead is so lde red, it
will make t he tra nsist o r selfsuppo rt ing, a nd the remaining
solder operation wi ll be easily
handled and completed.
Rem ember to use the longno se pliers as a heat sink for
" pushing" t he transistor leads
aga inst the tube socket ter-
minals when soldering. Care
in so ldering and applying t he
transistor leads wi ll insure
success and avoid thermal o r
me chanical damage to the
components.
7 . Foll o wing the sa me
technique for soldering as
explained in step #6, apply
and connect another rf field
effec t transistor across "the
tube socket 1A, t erminals 6,
7, and 8.
8. Apply and con nect t he
t hird rf field t ransist o r to
tube socket 2B, terminals 6,
8, a nd 9.
9. Apply the fourth field
effect transi stor to tube
socket 2A, terminals', 2, and
3 . ( If another type of
FET t ransistor is used, make
certain t hat t he proper tran sistor leads are used to make
connections.) Again, it may
be more convenient for
making connections t o turn
the transistor over (rou nd
side up ) a nd cross the D an d
G leads ( u se insulated
sleeving).
Step #9 completes t he
modif icat io n conversion of
the basic IG-' 02 rf signal
generator. Additionally, I installed rear t ip jacks with the
circui t connect ion leads to
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permit external testing of the
battery supply (+) and (-).
Test, Operation, and Adju stme nt
1. Before applying battery
power to the circu it, check
the positive-to-ground resista nce to make certain t hat
there is no short c ircuit or
abnormally low resistance
readi ng due to a defective
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Fig. 3. Modified I G- I 02 circuit. TlA , TlB, T2A, and T28 -
fourrf FE Ts equi valen t to Radio Shack package #276-1623 or
Calectro #K 4-634.
component or wiring co ndition. Rotate the bands witc h
while checking t he resistance
to ground (which should be
several hundred Oh ms, at
least).
2. Insert a milliammeter
in series with the battery, and
check the direct current on
all bands, which should be 7
to 15 mAo Switching in the
audio to ne oscillator-modu lator will increase it about 1
rn A.
3. Rf out put. A diode
detect or rf volt meter a pplied
to the high end of t he fine
atte nuator cont rol (turne d
co untercloc kwise for minimum rf out put ) should indicate about 1 t o 1.25 volts on
band "A" (low-freque ncy
en d), and, on each successive
band, it will drop off pro-
m
gresstvelv. Never th eless, rf
out put should be detectabl e
on all bands.
Vary the tuning on each
band fro m low t o high en d the rf voltage should vary
smoothly (usually decreasing)
wit hout t he sudden jumps or
falloff usually assoc iated with
parasi tic absorption conditions.
4 . Audio tone oscilla tor
modulator. The ac output of
the audio tone oscillator , as
measu red across t he audio
ou tpu t control , should be 1
to 2 volts. Check th e tone
frequency with a pai r of
headphones co nnected t o a
0 .1 uF co upling capacitor.
Finally , use an allb and receiver or grid-di p meter , if
available, t o check th e rf out pu t frequency. The frequency
response in each band shoul d
be wit hin a few percent an d
not need any alignment or
tuning adjustments.
Het erodyn ing with broadcast stations will show excellent frequency stability. On
band " F", use an identifiable
FM station to spot check the
frequency calibration in t he
88 to 108 MHz range. I found
it necessary to "squeeze" the
rf co il to a bout one-half its
origi nal length to get good
frequ ency alignment. Use the
long-nose pliers to squeeze
t urns. To check against an
FM sta t ion, turn t he audio
modulation on, connect the
rf cable, an d bri ng it near the
FM receiver's vert ical antenna. A good clean modu lation note shou ld be heard
when the signal gene rator
passes t hrough an FM station.
Conclusion
I modified the original errcult by converting to the
battery-operated solid state
design, as described. In addition, a t hree-crystal oscillator
frequency-spotting standard
was installed with a product
detector and audio amplifier
speaker section. This co mbination provides freq uency
chec k intervals of 100 kHz,
1.0 MHz, and 10 MHz, for
s pot-chec king the inte rna l
six-band vfo or for externa l
testing. Usin g the crystal stand ard , h e t erod y ne testing
showed excellent frequency
tr ac kin g a n d calib rat ion
t hrough the six bands. Si nce
there is ample chassis space
available, the three-crystal
frequen cy spot circuit is left
optional and is merely suggested to you. For t his purpose, in a more extended
project, three crystals and
oscillator design data can be
obtained from Jan Crystals,
2400 Crystal Drive, Ft.
M y ers FL 339 0 1. A ddi tionally, a dual-gate MOSF ET
pr oduct detector, a 250 mW
integrate d audio power am plifi er, a m in iature volume con trol, and a 2%" lou dspeaker
can be com bined to prov ide
the desi re d freq uencyspo tting funct ion.
Fig. 4 shows a circuit
which in corporates t he addi tional features just described
- a th ree-crysta l osci lla tor
frequenc y section with a
product detector and an
audio power amplifi er for
monitoring the heterodyne
reacti ons betw een crystal frequencies and the vfo spectrum. T he entire unit can be
easi ly and c onv enientl y
mounted in the rf signal generato r chassis assembly or
sep ar at el y assembled ex-
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Fig. 4. TR4-TR10 - Radio Shack #2 76-2039 or equivalent; TRI I - auat-oate MOSFET; cn
- Area 309 padder; CT2 - Area 306 padder; CT4 - Area 465 trimmer; L1 and L2 - d e; L3 20 turns #30 enamel wire on 2 W, lOOk resistor.
t ernall y as a subun it.
Heterodyne activity can be
detected up to the 50th harmonic . With addi t ional wave-
shaping am pli fi ers, the harmonic order could be exten ded considerably, but , un fortunately , that w oul d in-
volve high input current levels
which would place excessive
de mands on the battery
power su pply , •
New Products
f rom page 60
($15.95) way of quickly learning
and appreciati ng the advantages of the solderless breadboarding approach.
The PB-6 Proto-Board Kit
comes complete with a preass em bl ed br eadb oard ing
soc ket , tw o pre assem ble d
solderless bus strips, four flveway binding posts, a metal
ground base plat e, non-marring
feet, and all required hardware.
When complete,l ts si x hundred
thirty tie-points permit fl exible
configu rations of as many as
six 14-pln DIP ICs.
Despite its low cost, the PB-6
pro vi des a ver y co nfi d ent
breadboarding base. Of the
l our binding post s, one Is
grounded to the ground base
pla t e,
per mittin g
h igh
The Palomar PTR-130K transceiver.
d istributed capac itance and
low distributed inductance for
enhanced high·speed ci rc ui t
operation. The three remaining
fi ve-way binding posts can be
used to interconnect t he c ircuit
on the PB-6 to power and signal
lines and the outside world .
Follow ing the easy assembly
instructions enclosed, uSing
only pliers and a screwdriver,
assemb ly time for th e PB-6 Is
less t han ten minutes .
For further information, conta ct Continental Sp ecialties
esc Proto -Board 6.
Corporation. 70 Fulton Terrace,
Ne w Haven ';T 06509.
123