Heath Heathkit W4-AM Assembling And Using

PRICE

$1.00

WILLIAMSON TYPE

AMPLIFIER

MODEL W4-AM

HEATHKIT

WILLIAMSON-TYPE

AMPLIFIER

MODEL W4-AM

Phase Shift:

Intermodulation Distortion: See curve

below.

Sensitivity:

See curve below.

EQUIVALENT SINGLE

FREQUENCY

PQWER

Hum and Noise: 76.2 db below 0.25 watts

output.

95.2 db below 20 watts

output.

Feedback Factor:

Fixed; 22.6 db; independent

of output impedance.

Damping

Factor: Fixed;

28.5

to

1;

independent of output

impedance.

Output Impedances;

4, 8,

and 16 ohms.

Input Requirements:

105-125

volts,

50-60

cycles

AC,

115 watts at 117 volts.

Dimensions;

Single

unit;

15

1/4"

x

8

7/8" shelf

space,

7"

high.

Allow 1

1/2"

X

IS

1/4"

additional shelf space

for cables

and connections.

Weight:

Net: 23

1/4

lbs.

Shipping: 28 lbs.

TEST

CONDITIONS

Measurements taken at 117 volts line, with

WA-P2

preamplifier

connected.

Output

impedance

16.02 n resistive. For

harmonic distortion measurements; Krohn-Hite model

440-A

generator

(inherent distortion less than

0.1%),

Hewlett-Packard

330-B

distortion analyzer. For inter-

modulation distortion measurements; Measurements Corporation model 31 intermodulation

meter. For frequency response measurement,

Hewlett-Packard

model

650-A

test oscillator

.

For phase shift measurements, same oscillator with Tektronix 531 oscilloscope with

53-C

pre-

amplifier.

For

output

power,

voltage

measurements across

16.02

D

resistive

load,

taken

with

Hewlett-Packard model

400-D

vacuum tube voltmeter.

Measurements given are those taken on

a

representative amplifier under conditions stated.

Minor variations

from

these figures may be encountered in kit-assembled amplifiers because of

tube characteristics, component variations and

exact

lead placement. In

a

highly stabilized

amplifier such as the W-4AM, these variables may

be

disregarded from a performance point of

Page 3

INTRODUCTION

Most people are inclined to view the meteoric rise of the high

fidelity craze

as something which

has taken place in the last two years. Actually, public

acceptance of

home music reproduction

probably dates

from

the

summer and fall of 1948 when the Columbia "LP"

microgroove record-

ing techniques were introduced.

It is significant that a year earlier, there was

described in the British

publication "Wireless

World," an

amplifier

circuit

designed

by Mr.

D.

T.N.

Williamson which

culminated an extensive

search for what the author described as

a

perfect amplifier.

Within two years, the audio

world

had so

completely accepted the circuit that

it

became

a

standard for

comparison. After eight

years, the design still accounts for

by

far the greater percentage of

all high fidelity power am-

plifiers in use today.

Improvements have been

made,

faults have been discovered and corrected,

other circuits have

challenged the Williamson's

position,

but

still it stands as the basic high fidelity

amplifier.

Truly, the audio field owes Mr. Williamson

a

great debt.

In the

past

four years, literally

thousands of

people

have built and used Heathkit

Williamson-type

amplifiers. They represent a large majority of the

units of this type now in use

throughout the

audio-conscious

world. Your Heathkit model W-4AM Amplifier

incorporates all the

worthwhile

improvements and modifications resulting

from

this unequalled background.

If you are technically inclined, the

information contained in the preceding specifications will have

satisfied your questions as to the measured performance of the

amplifier.

If

you are

interested

primarily in how the amplifier will sound

,

your Heathkit W-4AMis

capable of placing the

burden

of proof on the most

elaborate and expensive speaker systems available today.

Unless you have,

or expect

to have, more than $300.00 to spend for a loud-speaker system, no significant im-

provement would

be

audible if the

W-4AM were replaced with any other

commercially available

power amplifier, regardless

of price. If more elaborate reproducers were used, some improve-

ment at extremely low frequencies

might be expected through the use of

amplifiers such

as

the

Heathkit W-5M.

In this discussion, we have

attempted to convince you that your

investment in the

W-4AM

kit

is

worthy of extreme care in construction and installation. Hurried or careless

construction can

only

lead

to trouble, either initially or after some period of satisfactory

performance.

TAKE

ENOUGH TIME TO DO THE JOB RIGHT THE FIRST TIME

and

you

will be repaid many times

in personal satisfaction and long, trouble-free

service.

If you

have

built Heathkits

before,

you

will

note a change in the usual

step-by-step procedure for

assembling and wiring. The new "all-on-one-drawing" plan used in this

manual

has been

devel-

oped to

make

your work even more enjoyable.

PLEASE

READ

THE

MANUAL ALL

THE WAY THROUGH

BEFORE ANY WORK IS STARTED.

Only a very small percentage of Heathkit assemblers encounter any

difficulty whatsoever in com-

pleting kits of this kind. Large fold-in pictorial diagrams are included

in

the

manual for your

convenience and are quite helpful if attached to the wall above your work space. The

diagrams

are repeated

in small form within the manual proper.

We

suggest that you retain the manual in

your

files for future reference in the use of the amplifier and for its

maintenance.

UNPACK THE KIT

CAREFULLY

AND CHECK EACH PART

AGAINST THE PARTS LIST. DO

NOT DISCARD ANY PACKING MATERIAL UNTIL THIS HAS BEEN

DONE.

In so doing, you

will become acquainted

with

each

part and

the chance of

accidentally throwing away

some

part

will be eliminated. Full size sketches of each of the parts categories

appear on Page 16.

Use

this in checking against the

parts

list

and

in identifying any

questionable components.