Heathkit IB 28 Manual

Page 2

TYPICAL COMPONENT TYPES

This chart Is a guide to commonly used types of elec- tions sham prove helpful in identifying most parts and
tronlc components. The symbols and related illusua- reading the schematic diagrams.
SSW CAPACITOR \\ mu
suPPazssoR
-IVI/\/\/\,- , -i (-- 23? was

CAYHUDE
/ FILAMENT

PN P cOLLEcoR
TRANSISTOR

[MITTEH
COLLECTOR

NPM EMITTER

ELECTROLYTIC

POTENTIOMETER . 0
'/ CAPACITOR

(CONTROL)

Q

RECTIFIER

I (DIODE)

TRANSFORMER
(IRON CORE)

TRANSFORMER
I | (ADJUSTABLE
POWDERED IRON
I I CORE) ARROW 358:
II INDICATES DIR<
ECTION or can
I I MOVEMENT To -

INCREASE FNDUCTA CE

.
TRANS FORMER "

(ADJUSTABLE
CORE)

ILLUMINATING
BULB

E METER
POWER pHONE
THANS- JAC K
FORMER °-\/
RECEPTACLE -
INDUCTOR SPST (SI-3&2?)
( co I L J .._

,1?
DPDT
.
PIEZOELECTRIC SWITCH r
CRYSTAL SPEAKER (ROTARY) §>Ilfl/)/éli
0-. I-O- O :3 fin
11'
0
o I
0.0
B'ND'NG MICROPHONE (I ~
@- POST : /- FUSE
L
CONDUCTORS
N477 EARTH GROUND
ANTENNA [1 1222:?
-_L NOT SHIELDED
GENERAL LOOP ? CHASS'S WOUND CONNECTED

CONNECTED

Page 19

Page 17

( ) After making the initial adjustments, install
the instrument in the cabinet and fastenwith
two #6 self tapping screWS through the rear
into the chassis, and with seven #6 screws
through the panel into the cabinet.

NOTE: The blue and white identification label
shows the Model Number and Production Series
Number of your kit. Refer to these numbers in

any communications with the Heath Company;
this assures you that you will receive the most
complete and up-to-date information in return.

( ) Carefully peel away the paper backingfrom
the blue and white identification label. Then
prese the label firmly into place on the rear
of the cabinet.

INITIAL ADJUSTMENTS

Plug the line cord into 50/60 cycles AC outlet of
the proper voltage. SERIOUS DAMAGE TO THE
TRANSFORMER WILL RESULT IF PLUGGED
INTO A DC SUPPLY. Turn on the power switch
on the GENERATOR LEVEL control.

CAUTION: The circuit ground and the case of
this instrument are both connected to the power
line ground through the green wire of the line
cord. Always connect the ground test lead of
this device to the chassis, or ground, of the
circuit being tested or measured.

The oscillator circuit is designed to operate
somewhere between 800 and 1200 cps. The actual
frequency will dependon the components. A trim-
mer condenser is provided So that thefrequency
may he set at approximately 1 kc by use of an
audio generator. The most convenient method is
to use an oseilloscope. Set the audio generator
at l kc and connect it to one set of plates of the
oscilloscotie. Connect the terminals on top of the
bridge to the other set of plates of the oscillos-
scope. Set the GENERATOR switch at AC
INTERNAL, the DETECTOR switch at AC IN-
TERNAL, the GENERATOR LEVEL control
clockwise, the FUNCTION switch at L-DQ andthe
RANGE switch at 1h. Adjust the trimmer untila
circle or ellipse appears on the oscilloscope, The
bridge generator frequency is then equal to the
frequency of the audio generator.

If an oscilloscope is not available, headphones
may be used. The output of the audio generator
and the bridge oscillator maybe fed into the ear-
phones and the trimmer adjusted until zero beat
is heard. The frequency of the bridge oscillator
will then equal the frequency of the audio oscil-
lator. The bridge may still be used even if an
audio oscillator is not available. Tighten the
trimmer condenser by turning the screw clock-
wise. Then turn the screw 1/2 turn counterclock-
wise. This will set the oscillator at approxi-
mately 1 kc. Later adjustment may be made
when, additional equipment is available.

The CRL control is set as follows. Check the zero
setting of the galvanometer. Set the FUNCTION
switch to B. Set the GENERATOR switch to DC
INTERNAL and the DETECTOR switch to DC
SHUNT. Set the RANGE switch to 100 Q on the
R scale. Set the ring of the CRL control to 5. .
Connect the 550 9 precision resistor supplied
for calibration across the terminals on the top
of the bridge. Rotate the knobof the CRL control
until the galvanometer does not move when the
DETECTOR switch is moved to DC METER
position. The switch is spring loaded in this
position so it will return to DC SHUNT position
when released. Now loosen the CRL control knob
and rotate it until it reads .5 on the stationary
pointer. The CRL dial now will read 5.5. Tighten
the CRL control knob and again checkto see that
the meter does not move when the DETECTOR
switch is moved to DC METER position. Repeat
the adjustment until the meter does not move. The
CRL control is now set and ready for uSE.

Page 20

Page 18

If greater accuracy of the DQ control calibration
is desired (more than that obtainable by simply
zero-setting the knob), proceed in the following
manner:

1. Set up the controls as outlined for the CRL
calibration. Remove the 550 Qprecision re-
sistor from the terminals on top of the
bridge,

2. Disconnect the end of the wire connectinglug
2 of the rear section of the DQ control to lug
6 on the rear deck of function switch FS at
the switch.

3. Temporarily connect a jumper wire (clip-
leads will suffice, if available) betWeen lugl
of the rear section of the DQ control and lug
1 of terminal strip TS on top of the bridge.
Connect another lead between lug 2 of the
same rear section and lug 2 of the binding

HEATHKIT

post strip (the red post). Turn on the power.
Set the CRL controls to read 160 [Z and ad-
just the DQ control to bring the meter to
zero (this will occur near the 0.1 mark on
the DQ knob). Verify this adjustment by turn-
ing the DETECTOR switch to DC METER. No
pointer movement is noticeable at exact
zero. The adjustment is critical, so use care.

When the bridge has been balanced, notethe
position of the 0.1 mark on the DQ dial with
respect to the pointer. Correct the knob set-
ting to read exactly 0.1 and rebalance the
bridge to check. A double check may be made
by turning the RANGE switch to 1000 $2. The
bridge should balance at 1.0 on the DQdial.

When calibratiOn is complete, remove the
jumpers and reconnect the proper leads to
the control and the switch FS.

OPERATION

CAUTION: The circuit ground and the case of
this instrument are both connected to the power
line ground through the green wire of the line
cord. Always connect the ground test lead of this
device to the chassis, or ground, of the circuit
being tested or measured.

DC Resistance Measurements

1. Plug in the cord and turn on the switch
mounted on the GENERATOR LEVEL con-
trol.

2. Check the zero setting of the galvanometer.

3. Connect the unknown resistance to the
terminals on top of the bridge.

4, Set the FUNCTION switch to R.

5. Set the GENERATOR switch to DC INTER-
NAL.

6. Set the DETECTOR switch to DC SHUNT.

7. Set the CRL DIAL to zero.

For greater indicating accuracy of DC resist-
ance measurements, external batteries may be
used as follows:

Provided the CRL dial is not turned below 1, the
following external battery voltages in series with
additional resistance may be used:

0n multipliers

not more than

in series with

0.1 o, 1.0 o, 10 o, 100 9..
10m,1oum,1Megohm,,

67l/2V,
135V.........
2021/2V......

not less than 1500 ohms.
not less than 4000 ohms.
not less than 8500 ohms.

shoot.

Page 23

HEAT-HKIT

Page 2 1

IN CASE OF DIFFICULTY

1. Check the wiring by following each wire on
the pictorial and in the instrument, inspect-
ing the soldered connections on each end. and
then checking off that wire on the pictorial
with a colored pencil. This will reveal mis-
takes and omissions in wiring, which is the
most frequent cause of difficulties. Oiten
having a friend check the wiring will reveal
a mistake consistently overlooked.

2. Check the position of the switches on the
panel and be sure they are in the proper
position.

3. Check the tubes.

4. Check the voltages between tube socket
terminals and chassis, The readings should
come reasonably close to the values tabu-
lated below, if a vacuum tube voltmeter with
11 megohm input resistance is used. Other
type meters may give considerably lower
readings. If a voltage reading fails to check
with the tabulation, investigate the portion
of the circuit involved by checking the re-
sistors and condensers.

Refer to the Kit Builders Guide for Service and
Warranty information.

VOLTAGE CHART

GENERATOR

F 45-50 0 1.4-1.45

2.4-2.6

H 100-110 1.4-1.45

DETECTOR
N 35-40 0

1.4-1.45

S 1.4-1.45 100-110 1.4-1.45 2.4-2.6

* - Negative with respect to chassis.
NC - No connection.
NS - Not significant.

All measurements made with GENERATOR
LEVEL control set at maximum, GENERATOR
switch at AC INTERNAL, DETECTOR switch at

AC INTERNAL, FUNCTION and RANGE switches
in maximum clockwise position.

Unless otherwise indicated, all voltages are
positive and measured to chassis.

Line voltage - 115 volts, 60 cycles.

BIBLIOGRAPHY

Hague, B_, "Alternating-Current Bridge Meth-
ods," Sir Isaac Pitman and Sons, Ltd,, London

Terman, F. E., "Radio Engineers' Handbook,"
section 13, McGraw-Hill Book Co., New York

Stout, M. 8., "Basic Electrical Measurements,"
ch, 9, 13, Prentice-Hall, Inc., New York

Harris, F. K., "Electrical Measurements," ch. '7,
15, John Wiley and Sons, New York