Heathkit IT 18 Manual

Page 1

Assembly
and
Operation
of the

@

IN-CIRCUIT/

TABLE OF CONTENTS

Introduction.....................
Parts List....................

Step-By-Step Assembly
Parts Mounting. . . . .........._.

OUT-OFC'RCUIT Chassis Wiring...............

TRANSISTOR TESTER Adjustments. . . . . . . . .

MODEL IT-18

Knoblnstallation..............

FinalAssembly.................
Operation.....................
InCase0fDifficulty........-.....

Troubleshooting Chart. . . . . . . . . . . . .
Specification. . . . . . . .

Circuit Description. . . . . . . . . . . . . .
Emotional Parts List. . . . . . . . . . . . . .
Chassis Photograph. . . . . . . . . . . . . . .
Schematic. . . .(fold-out from page). . . .

Replacement Parts Price List. . . . . . . .

Factory Repair Service. . .(fold-out from
page). . . .

HEATH COMPANY
BENTON HARBOR, MICHIGAN 49022

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18
18

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20
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23

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24

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Page 2

Page 2

INTRODUCTION

The Heathkit Model lT-18 In-Cireuit/Out-Of-
Circuit Transistor Tester is a quality instrument
for testing of transistors or diodes. Its low in-
ternal impedance and handy test leads enable you
to check transistors without removing the tran-
sistors from the circuit. A test Socket is also
provided for checking lowpower transistors that
are removed from the circuit.

The large, easy-to-read meter permits direct
reading of DC Beta (gain) on two ranges. The
Transistor Tester also enables you to make
leakage measurements for transistors and di-
odes, and to make a positive identification of
NPN or PNP type transistors.

The self-contained power supply, which consists
of a single 1-1/2 volt D cell, makes the instru-
ment fully portable. This low voltage will not
damage a transistor or diode that is incorrectly
connected to the Tester. Since no battery current
is drawn unless a transistor or diode is being
tested, long battery life is assured.

The rugged circuit construction and durable
shock-resistant case combined with convenient
easy-to-use operation provides you with a, test
instrument of fine quality and long dependable
service.

Refer to the "Kit Builders Guide" for complete
information on unpacking, parts identification,
tools, wiring, soldering, and step-by-step as-
sembly procedures.

PARTS LIST

To order replacement parts, refer to the
Replacement Parts Price List and use the Parts
Order Form furnished with this kit.

PART PARTS
No. Per Kit

RESISTORS (1/2 WWI-CAPACITOR

DESCRIPTION

(l3)252-15 4

PART PARTS
No. Per Kit

DESCRIPTION

Hardware I cont' d.)
4-40 nut

(1)1-112 1 180 n resistor (brown-gray- (14)252-7 3 Control nut
brown) (15)253-10 3 Control flat washer
(2)2-250 1 11.8 52 precision resistor (16)254-4 3 Control lockwasher
2-251 1 25 9 precision resistor (l7)254-7 2 #3 lock-washer
2-252 1 225 n precision resistor (18)254-9 4 #4 lockwasher
(3)21-51 1 .005 F disc capacitor (19)255-15 4 #6 x 1/2" spacer
CONTROLS-SWITCHES
(mo-201 1 10 kn control WIRE
(5)10-254 1 500 k9 control
(6)60-24 1 SPST rocker switch 344-59 1 Hookup wire
(7)60-43 l DPDT rocker switch 347-7 1 4-conductor cable
(8)63-493 1 Rotary switch
63-494 1 Rotary switch(spring return)
HARDWARE KNOBS
(9)250-175 2 2-56 x 3/8" screw (20)462-246 1 Large knob
(10)250-206 4 632 x 11/16" screw (21)462-249 1 Small knob
(11)250-52 4 4-40 x 1/4" screw 462-250 1 Small knob with white
(12)Z52-51 2 2- 56 nut marker

Page 20

Page 19

SPECIFICATIONS

DC BETA ........................

Out-Of-Circuit Accuracy .................

In-Circuit Accuracy

Collector-To-Emitter Leakage, ICEO ' ,,,,,,,,,,,

Collector-To-Base LeakageJ (:30

Diode Testing ......................

Out of circuit only.

X1 range: 2 to 100.
X10 range: 20 to 1000.

25%.

Indicates good or bad.

0-5 mA (midscale = 1000 #A).

0-5 m (midscale = 1000 ILA).

III-circuit or out-of-chcuit tests.

Meter Indication shows that diode is either
good, shorted, or open.

One 1-1/2 volt size D cell.

9-3/8" wide x 5-3/ " high x 9 deep.
Beige panel and cabinet.

2-1/4 lbs.

The Heath Company reserves the right to discontinue
instruments and to change specifications at any time without
incurring any obligation to incorporate new features in

instruments previously sold.

Page 21

Page 20

-HEATHKIT!

CIRCUIT DESCRIPTION

Refer to the Schematic Diagram (fold-out from
Page 23) while reading the Circuit Description.

The In-Circuit/Out-Ot-Circuit Transistor Test-
er measures beta (gain) andleakage. The circuit
of the Transistor Tester is basically a low-
impedance, common-emitter amplifier without
a transistor; the transistor being tested com-
pletes the circuit. Note on the Schematic that
the emitter of the transistor being tested
(the emitter o! the test socket and test lead)
is connected through lugs 1 and 12 of the Func-
tion switch and lugs 5 and 3 of the Polarity
switch to -l.5 volts. The base of the transistor
(as now shown) is connected through lugs 11 and
10 of the Function switch, the Beta Cal control,
the Beta Test switch, resistor R2, and lugs 7
and 6 of the Polarity switch to +1.5 volts. The
collector (as now shown) is connected to +1.5
volts through two parallel paths: one path goes
through R4 and lugs 8 and 9 of the Function
switch; the other path goes through the Beta
Test switch, lugs 1 and Z of the Polarity switch,
the meter, lugs 5 and 6 of the function switch,
and lugs 9, 7, and 6 of the Polarity switch.

At current levels through the meter that are be-
low 200 HA, diode D1 does not conduct. As the
current through the meter increases, D1 con-
ducts and by-passes current in excess of 200 A
around the meter. This provides protection for
the meter.

Power is supplied by a 1-1/2 volt flashlight
battery (size D cell). The five sections of the
Polarity switch, in the Off position, disconnect
the battery and meter circuits, and placeashort
across the meter terminals for dynamic damping
of the meter movement during transit. In the N PN
and PNP positions, this switch removes the short
from the meter and applies voltage of the cor-
rect polarity to the circuit.

It is possible to check transistors without remov-
ing them from a circuit because the resistances
in the Transistor Tester are considerably low-
er than those encountered in most transistor
circuits. This means that any parallel current
paths around the Transistor being tested will not
draw enough current to cause any appreciable
error in the beta reading on the Transistor
Tester.

BETA (GA IN) TEST

The collector current of a transistor depends on
and is proportional to its base current. There-
fore, transistor Beta (gain) is equal to the ratio
of these currents.

collector current I;

Beta = base current I5

The gain of any transistor can therefore be
determined by carefully measuring these two
currents and dividing the collector current by the
base current.

In this circuit, Beta Cal control R3 is in series
with the base of the transistor and it controls
the base current. The base current in turn, con-
trols the collector current by varying the forward
bias applied to the transistor. Collector current

'passes through shunt resistor R4 and through the

Beta Test switch to the meter circuit.

The collector current is adjusted by the Beta
Cal control to a 4 mA reference point (the cali-
bration point on the meter scale). This first
condition, where the collector current is meas-
ured and the Beta Test switch is in the Cal
position, is shown in the simplified schematic
of Figure 5A.

®

CALIBRATION

R2 MEIER DI g Re

1.5»:
+ BATTERY

5F-

TRANSISTOR
UNDER TEST

.5

stunsr z g" g

TRANSISTOR
Ll NDER TEST

Figure 5