Page 
2 
INTRODUCTION  
The Heathkit Model IT -3120 FET /Transistor Tester 
is 
a quality 
instrument for quick,  accurate tests of  conventional (bipolar) 
transistors,  diodes,  FET's,  SCR's,  triacs.  and  unijunction 
transistors.  Gain  (DC  Beta),  transconductance  (Gm),  and 
leakage  values  are  read  directly 
on 
the  large  easy-to-read 
meter. 
You 
can 
quickly 
and  easily  test devices  either in-circuit 
or 
out-of-circu it.  The  Tester  provides  special 
circuitry 
to 
balance 
out 
in-circuit  impedances. 
Use 
either  the 
color 
coded 
leads 
for 
in-circuit tests 
or 
the 
built-in 
transistor and 
FET sockets 
for 
out-of-circuit tests. 
Five current 
ranges 
permit 
leakage measurements 
as 
low 
as 
1 
microampere  and  collector  currents 
as 
high 
as 
1 ampere. 
Pushbutton 
type 
range,  mode, and 
function 
switches 
assure 
easy, 
consistent operation. 
A  special  battery testing 
circuit 
provides a meter indication 
of 
the 
condition 
of 
the 
self-contained  power  supply. 
Another  convenience 
of 
this  portable  instrument 
is 
the 
two-color 
front 
panel  design,  black  lettering 
for 
conventional  (bipolar)  transistors  and 
red 
lettering 
for 
FET's.  Also,  separate,  brief  operating  instructions 
are 
printed on the rear panel. 
Refer 
to 
the 
"Kit 
Builders 
Guide
" 
for 
information 
on tools, 
wiring, 
soldering, 
resistors
, 
and 
capacitors. 
PARTS 
LIST  
Check 
each 
part against 
the 
following 
list. The key numbers 
correspond 
to 
the  numbers  on the 
Parts 
Pictorial 
(fold-out 
from 
Page 
5) . 
Any 
part 
that 
is 
packaged in 
an 
envelope 
with 
a 
part 
number 
on 
it 
should 
be 
placed  back  in  its  envelope  after 
it 
is 
identified 
until 
that 
part 
is 
called 
for 
in a step. 
KEY 
HEATH  
No.  Part No.  
RESISTORS 
1/2-Watt 
A1 
1-129 
A1 
H05 
A1 
6-1509 
PARTS  DESCRIPTION 
Per 
Kit 
3  
4.7 
n, 
10% (yellow-
violet-gold) 
10 
kn, 
5% 
(brown-
black-orange) 
15 
n. 1% (brown 
green-black-gold) 
1/4-Watt, 
1% 
Precision 
A2  6-1
660-12 
2 
166 n 
(brown-blue-
blue-black) 
A2 
6-3600-12 
360 
n 
(orange-blue 
black-black) 
A2 
6-1501-
12 
1500 
n 
(brown-green-
black-brown) 
Other 
A3  2-11-2 
1.5 
n, 
2-watt, precision 
A4  3-13-3 
.15 
n. 
3-watt, 
To 
order  a  replacement  part, 
use 
the  Parts  Order  Form 
furn
i
shed 
with 
this 
kit
. 
If 
one 
is 
not 
available, 
see 
"Replacement  Parts"  inside  the  rear  cover 
of 
the  Manual. 
For pricing  information, refer to separate  "Heath Parts Price 
List." 
KEY 
HEATH 
PARTS 
DESCRIPTION 
No.  Part No. 
Per 
Kit 
CAPACITORS-DIODE-CONTROLS 
81
' 
82 
83 
84 
85 
21-57 
57-65 
10-934 
10-926 
14-
11 
2 
.005 
J-lF 
disc capacitor 
1 N4002 silicon diode 
750 n  control 
15 
kn 
control 
250 
kn/5000 
n  (5 
k) 
control 
HARDWARE 
#2 
Hardware 
C1 
C2 
C3 
250-1'75 
252-51 
254-7 
10 
10 
10 
2-56 x 
3/8" 
screw 
2-
56 
nut 
#2 
lockwasher 
#4 
C4 
C5 
C6 
Hardware 
250-52 
252-2 
254-9 
8 
8 
8 
4-40 x 
1/4" 
screw 
4-40 
nut 
#4 
lockwasher