Heath Heathkit W4-AM Guide

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" x87/8" shelf space, 7" high.
Allow 11/2" XIS 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 nresistive. 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 Dresistive load, taken with
Hewlett-Packard model 400-D vacuum tube voltmeter.
Measurements given are those taken on arepresentative 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 ahighly stabilized
amplifier such as the W-4AM, these variables may be disregarded from aperformance 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 ayear 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 aperfect amplifier. Within two years, the audio world
had so completely accepted the circuit that it became astandard 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 agreat debt.
In the past four years, literally thousands of people have built and used Heathkit Williamson-type
amplifiers. They represent alarge 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 aloud-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 achange 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 avery 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.

Components with wire pigtail leads can be conveniently sorted by inserting one of the ieads into
the corrugated edge of the shipping carton flap. It may be helpful to mark the value of the com-
ponent on the flap so the part may be readily located when needed.
If some shortage is found in checking the parts, please notify us promptly and return the inspec-
tion slip with your letter to us. Hardware items are counted by weight. An occasional shortage
occurs and if this is true in your kit, please obtain the missing parts locally if at all possible.
Resistors and controls generally have atolerance rating of ±20% unless otherwise stated in the
parts list. Therefore, a 100 Kfl resistor may test anywhere from 80 KH to 120 Kfl and still be
acceptable. Tolerances on electrolytic condensers may be even wider and commonly run from
±100% to -50%. The parts furnished with your Heathkit have been specified so as to meet the
performance specifications given.
In order to e^qjedite delivery to you, we are occasionally forced to make minor substitutions of
parts. Such substitutions are very carefully checked before they are approved and the parts sup-
plied will work satisfactorily in your kit. For example, if your kit is short a15 K(2 resistor
and an 18 K£J resistor is furnished which is not in the parts list, you will understand that such
asubstitution has been made. This fact is mentioned here only to prevent any confusion in check-
ing the contents of your kit.
CAUTION: We strongly urge that you follow the wiring and parts layout shown in this manual.
The position of leads and parts is quite critical in the instrument and changes may seriously
affect the characteristics of the circuit. We do not represent that the circuit or layout of the
instrument cannot be improved; however the methods shown in this manual are the result of many
experimental models and unless the constructor has access to full laboratory facilities, we rec-
ommend that they be followed very closely.
Actual construction of the amplifier consists of three phases, each of which is covered by asingle
drawing containing all pertinent information necessary for completion:
Phase I-Assembly of parts to chassis.
Phase n-Preliminary wiring.
Phase HI -Final wiring.
These three drawings appear on the following pages of the manual. They 'are also reproduced in
much larger form as fold-in inserts included with this manual. The large drawings should be
mounted on the wall above your work space where they may be referred to readily.
Notice that each phase consists of asequence of operations, which are contained in numbered
boxes surrounding the drawing. When anote is referred to, the note will be found near the oper-
ation box where it is first applicable. At the end of each operation, asmall space is provided
(). Use this to check off each operation as it is completed. Then, if your work is interrupted
,
possibility of skipping an operation is minimized.
Start Phase Iwith operation 1, in the upper left hand corner of the drawing. Follow the steps
in numerical sequence.
Page 5

NOTES ON WIRING
Before proceeding with actual wiring of yourW-4AM kit, the following notes should be read care-
fully.
1. Notice that on the Phase II drawing, each contact of the terminal strips and other parts has
been identified by anumber. No numbering is shown for tube sockets since markings are
molded on each socket, as shown in the sketch under Step 1.
This system of numbering terminals is used to simplify wiring instructions. For example,
when an instruction reads, "Connect yellow lead to J1 (NS), "it will be understood that the
yellow lead is to be connected to terminal number 1on terminal strip J.
2. The abbreviation (NS) is used to indicate that other connections will be made to that terminal
later and the connection should not be soldered yet. When the last connection has been made
to aterminal, the abbreviation (S) in inserted indicating that the connection should be sol-
dered.
3. The term "dress" appears several times in the instructions. This means to place the cable
or lead so that it reaches to and remains near the terminal indicated. It may be necessary
to form or bend the cable slightly so that it stays in position without undue strain on the
connections.
4. "Stripand tin" means that the insulation on the lead should be removed, usuallyfor adistance
of 3/8" or so. Then twist the exposed bare strands of wire together and coat with hot solder
so the wire may be easily pushed through terminal holes without fraying out.
5. To avoid possibility of error, each color coded component is described quite completely in
the wiring instructions. On most resistors, agold or silver band will be found in addition
to the three colors called out. This fourth color may be disregarded, since it indicates only
the resistance tolerance.
6. On electrolytic condensers of the tubular type, one of the leads will be marked "positive"
by means of a+sign or other method. The instructions plainly indicate to which terminal
the positive lead is to be connected. It is very important that the condenser be connected
exactly as called out, otherwise it will be destroyed and may possibly damage other com-
ponents as well.
7. On paper dielectric condensers, usually of the molded paper type, aband or other marking
sometimes appears to designate the outside foil of the condenser. Such markings are not
significant in the W-4AM and may be disregarded entirely.
8. Before doing any soldering, read the note on the inside rear cover of this manual.
NOTE: ALL GUARANTEES ARE VOIDED AND WE WILL NOT REPAIR OR SERVICE
INSTRUMENTS IN WHICH ACID CORE SOLDER OR PASTE FLUXES HAVE BEEN
USED. WHEN mDOUBT ABOUT SOLDER, IT IS RECOMMENDED THAT A NEW
ROLL PLAINLY MARKED "ROSIN CORE RADIO SOLDER" BE PURCHASED.
9. Unless otherwise indicated, all wire used is insulated. Wherever there is apossibility of
bare leads on components shorting to other metallic objects, the leads should be protected
by useof insulated sleeving. This is indicatedin the instructions by the term "use sleeving."
10. Leads on most components are longer than they need to be. Excess lead length should be cut
off before the part is wired in place. This will not only give aneater appearance to the job,
but actually improve the operation of the equipment.
Page 7