Heathkit HW 12A Manual

Page 1

Assembly
and
Operation

of the
HEATHKIT-

75-METER
SSB TRANSCEIVER

Model HW-12A

Scanned by WlATV

HEATH COMPANY

BENTON HARBOR.
MICHIGAN 4902 2

TABLE OF CONTENTS

IntrodlICtl-onua.IoonlanoIOIlIOI'IOll

PartsLiStI-QOIIIQOOOOIOIOIDID-I

Step-By-Step Assembly
Circuit Board Assembly. . . . . . .
Parts Mounting-Chassis. . . . . . .
Cable Assembly Wiring. . . . . . . .

Function Switch Wiring. . . . . . .
TOp Chassis And Front Panel

AssembIYO'aoaooolcIo-II-d§0
Final Wiring-Chassis Bottom. . . . ..
Final Wiring-Chassis Top. . . . . . . .

o
I
O
I

InitialTest.....................
Power Supply Connections. . . . . .. . . . .
Alignment And Adjustment. . . . ... . . . o
FinalASSemhly... ...............

Installation.....................

Noise Suppreasion Troubleshooting Chart. .

Operationovo-cnclooloiounorclot

In Case 01Difficulty,.............
Factczry Repair Service. . . . . . . . . . .
Troubleshooting Chart. . . . . . . . . . . . .
Specifications...-.............
Circuit Description. . . . .... . . . . . . . .

Chassis Photographs. , u I a... I o u I U I 0

Circuit Board X-Ray Views

(fold-out from page}. . . . . . . . . . . .

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

Schematic. . .(fold-out from page}. . . . .

18
20
2'?
28
30
32
33
36
39
42
45
49
5D
52

53

68

8'?

89

Page 2

Page 2

@

INTRODUCTION

The Heathklt Model HW-IZA Amateur Trans-
ceiver is a. 75~meter SSB {single-sideband)
tranSmitter and receiver designed for both mo-
bile and fixed station use. The receiver and
transmitter are locked together with a contin-
uously running VFO (variable frequency oscil-
lator) to insure that both sections operate at the
same frequency. The low frequency VFO is
temperature compensated to provide stable op-
eration.

Provisions have been made for both PTT (push-
to-tslk) and VOX (Voice operated transmitter)
operation. Other features include ALC (auto-
matic level control} to prevent the transmitter
from overloading, and AVC (automatic volume
control) to maintain consmnt receiver output
over a wide range of input signal strength.

An accessory socket is wired into the circuit
so the Heathldt plug-in Crystal Calibrator can
be used with the Transceiver to provide accu-

rate frequency checlcs at 100 kHz intervals.
A connection on the rear of the Transceiver
makes the Transceiver easily usable with linear
amplifiers. Power for the Transceiver canbe
obtained irom the Heathkit Model HP-13 (12
VDC) or Model PIP-23 (120 VAC Power Sup-
plies. Equivalent power supplies may also be
used.

NOTE: This Manual uses the newIEEE(Insiitute
of Electrical and Electronic Engineers) inter-
national standard term "hertz" as the basic unit
of frequency. The terms are used as follows:

Hz (hertz): cps (cycles per second).
kHz (kiloherts) = kc (mocycles per second).
MHz (megahertz) = mc (megacycles per second).

Refer to the "Kit Builders Guide" for complete
hirer-martian on unpacking, parts identification,

tools, wiring, soldering, and step-hy-step as-
sembly procedures.

Page 12

®

Page 35

Leg? POINT

RESISTANCE

I: ) Set FUNCTION switch to TUNE

( ) Tube socket V10 pin 1

( ) 'Ifiibe socket V2 pin 9

(

t

) 9 in section 2C

} MIC#2

2 megohm
0 9

0 to 20 K9 (varies
with setting of
TUNE LEVEL
control)

09

( I Set FUNCTION switch to PTT andthe Meter
switch to OPERATE TUNE

NOTE: Use the OHMS X100 range. Just touch
the test point and note that the 8 Meter de-
flects; do not attempt to measure the resistance.

(

A

A

n

} 13 in section 1B

8 Meter deflects
a small amount (di~
rection depends on
ohmmeter polar-
ity}

] Set FUNCTION switch to TUNE and use

OHMS X100 range

} 24 in section 4A

S Meter deflects

} Set FUNCTION switch to PTTandthe Meter
switch to BIAS SET. Use OHMS X1 range.

) 25 in section 50.

) SPKR socket

) POWER plug pin 11

Meter deflects
(opposite direction)

0.4 Q

Infinity, then press
relay for 0 fl

( )

TEST POINT
( ) ANT socket

( ) RCVR socket

RESISTANCE

0.4 Q, then press
relay for 10 KB

0.] 9

NOTE: Use the proper ohmmeter ranges for

each of the following tests.

( ) 1 in section 10

( ) 3 in section 43

( ) 27 in section 3C

( } G in section 30

( ) Tube socket V6 pin 3

( ) ALC socket

15 K9. then press
relay for 330 52

330 Q, then press
relay for 120 K0

0 to 22 KS} {varies
with setting of RF
ATTN control)

0 to 1 megohm
(varies with setting
of AF VOL control}

80 K9,press relay
for 70 K9

2.2 megohm (may
be 30 Kit with
ohmmeter leads
reversed)

This completes the Initial Tests.

( ) Install the tubes in their reapective sockets.

The tube numbers are lettered on the circuit
board. Support the circuit board from under-
neath with your finger while installing tubes
to prevent damage to the circuit board.

Install the pilot lamps in their sockets. Be

sure the one lamp does not touch the case

of the meter.

Page 26

TYPE OF NOiSE

Loud popping increasing
to buzz with increased
engine speed,

Ignition System,

Replace plugs with resistor type.

Loose crimped connections should be clean-
ed and soldered.

Place resistors in distributor system.

Whine; varies with
engine Speed.

Distinct but irregular
clicking noise.

Generator.

Voltage regulator.

0.1 aid coaxial-type capacitor in series
with the armature {"A" lead).

Clean commutator.

Replace brushes.

Ground generator shaft.

Parallel trap (#10 wire-coil and suitable
capacitor) in series with armature lead,
tuned to operating frequency.

0.1 ufd coaxial-type capacitor in series
with the battery (B) and armature (A) leads.
A series Combination of a .002 pic! mica
capacitor and a 4 9 carbon resistor to
ground from the field (F) terminal. All
components should be mounted as shown
in the diagram, close to the voltage reg-
ulator.

Same as above.

- H
Energy transfer to
primary system.

Install bypass capacitors as follows: 0.1
Md coaxial in the lead from the ignition
switch to the coil; 0.5 aid at the battery
lead to the ammeter; 0.5 ufd at the gas
gauge; 0.5 aid at the oil signal switch;
0.5 aid at the headlight and taillight leads;
0.5 aid at the accessory wiring from the
engine compartment.

l

Loud popping noise that
changes from one type
road to another. Most
pronounced on concrete.

Wheel static.

Install front wheel static collectors (avail-
able from most automotive distributors).
These should be checked every 5000 miles
for excessive wear.

-I
Same as above.

Tire static.

Injection of anti-static powder into tire
through valve stem.

4

Irregular popping noise
when on bumpy roads,

particularly at slow
speeds.

Body static.

If an extensive amount of suppression is re-
quired, the engine should be retimed and tuned

up at a reputable garage.

Tighten all loose screws.
Use heavy flexible braid and bond the en-
gine to the frame and fire wall. Bond the
control rods, Speedometer cable, exhaust
pipes, etc., to the frame.

Page 39

Page 81

amplifier V2B, which operates the relay. Ca-
pacitor 0105 and resistor R101 form a delay
network that establishes the time the relay
stays closed after being tripped. The length
of time is determined by the setting of the VOX
Delay control.

ANTLTRIP CIRCUIT

Because the VOX stages operate on both trans-
mit and receive, the speaker signals during
receive must be kept from tripping the relay
when receiving. This is done by taking aportion
of the audio signal from AF output stage V12A,
rectifying it with diode 0100 to produce a posi-
tive voltage, and feeding this voltage to the grid
of V10 from the VOX Sens control This voltage
tends to increase the plate current of V10; sig-
nals from the microphone {picked up from the
Speaker] tend to decrease the plate current.
Therefore with both signals present at the grid
of V10, the signals cancel each other, preventing
the Speaker from tripping the VOX circuit.
Speaking into the microphone produces signals
not present in the Speaker circuit, permitting the
VOX circuit to function normally. The VOX Sens
control not only adjusts for proper antl-trip
voltage, but also determines the sensitivity of the
VOX circuit.

PUSH-TO-TA LK CIRCUIT

With the Function switch in the PTT (push-to-
talk) position, V10 is disabled by grounding its
grid, and VZB is made to operate and close the
relay when its grid is grounded (shorting the
bias) by the push-to-talk switch in the micro-
phone. The Function switch, in the PTT posi-
tion, also makes the VOX delay' circuit inoper-
ative by removing C105 from ground. Push-to-
talk operation with the Motion switch in the
VOX position uses the VOX delay circuit, causing
the receiver to "delay" before coming on after
the microphone button is released. The Function
switch in the Tune position turns the transmitter
on by grounding the grid of V23.

RECEIVER SECTION

Radio Frequency Amplifier VGA And
Receiver Mixer V83

The incoming signal is connected to RF ampli-
fier V8A through coil L3. The amplified signal
from VSA is then coupled through coil L2 to

receiver mixer V88. During receiving, cutoff
bias is removed from the receiver section to per-
mit tubes VSA, V83, V9, and VIZA to operate.
V8A is controlled bybias from the AVG (autom at-
to volume control) circuit. AVC in the receiver is
similar to ALC in the transmitter, in that it
maintains a constant receiver output (gain)
even though the incoming signal level may vary
considerably. The cutofl voltage on the bias
line is controlled by section C of the relay.

The RF ATTN control varies the cathode bias
on RF amplifier V1, to permit receiver gain to
be reduced, to prevent overloading on very
strong signals. This reduction in RF gain will
also be reflected in lower meter indications.
Operating at a reduced RF gain, however, does
not disturb the AGC circuitry, nor will it cut
off the receiver completely. It simply reduces
strong signals to a level that can be handled by
the receiver to provide minimum Cross modu-
lation or desensitization.

Crystal Filter

The signal from mixer VBB is coupled to the
crystal filter through capacitor C80, which is
small in value to avoid upsetting the input im-
pedance of the filter. The crystal filter exhibits
the same characteristics in receiving as in trans-
mitting; it shapes the IF passband to have steep
sides, a flat top, and a narrow bandwidth. This
permits goad selectivity for SB reception in
crowded amateur bands.

Common IF A mplifier V3 And Receiver
IF Amplifier V9

Signals from the crystal filter are amplified by
common IF amplifier V3 and then fed to re-
ceiver IF amplifier V9. The cathode and screen
of tube V9 are connected directly to those of
tube VZA. The meter, which is connected inthis
circuit, indicates received signal strength in
S units, as the AVG voltage changes the current
in V9. The meter functions as an ALC indica-
tor when transmitting, without any switching.
The gain of V9 is controlled by the AVG voltage
applied through resistors 891 and R92.

Product Detector VllA And Audio
Frequency Amplifier VIZB.

The amplified signal from V9 is coupled through
IF transformer T3 to the grid of product de-