Heathkit W-5M Guide

ASSEMBLING
AND USING
YOUR
HIGH FIDELITY
AMPLIFIER
MODEL W-5M

STANDARD COLOR CODE —RESISTORS AND CAPACITORS
AXIAL LEAD RESISTOR
Brawn —Insulated
Black —Nan-Ins uIated
o3T
Tolerance
Multiplier
1st and 2nd Significant Figures
Wire wound resistors have
1st digil band double width
insulated FIRST RING SECOND RING THIRD RING
UNINSULATED BQDV COLOR END COLOR DOT COLOR
Color First Figure Second Figure Multiplier
BLACK 00None
BROWN 1I0
RED 2200
ORANGE 33,000
YELLOW 440,000
GREEN 5 5 00,000
BLUE 66000,000
VIOLET 770,000,000
GRAY 8800,000,000
WHITE 9 9 000,000,000
DISC CERAMIC RMA CODE
5-Dot 3-Dot
Capacity
Multiplier
Tolerance
Temp. Coeft
RADIAL LEAD DOT RESISTOR
Multiplier
1st Figure
2nd Figure
5-DOT RADIAL LEAD CERAMIC CAPACITOR
•Capacity
Multiplier Tolerance
EXTENDED RANGE TC CERAMIC HICAP
Temp. CoeA. e, ./ C<*P«»Y
TC Multiplier Multiplier tolerance
RADIAL LEAD (BAND) RESISTOR
fMultiplier
““
BY-PASS COUPLING CERAMIC CAPACITOR
Tolerance Ht Figure
2nd Figure i/i 1? ili
Multiplier —3 *Tolerance
Voltage
(Opt.)
AXIAL LEAD CERAMIC CAPACITOR
Temp. Cooff. ——-,—.Capacity
ToleranceMultiplier
The standard color code provides all necessary information re-
quired to properly identify color coded resistors and capacitors.
Refer to the color code for numerical values and the zeroes or
multipliers assigned to the colors used. Afourth color band on
resistors determines tolerance rating as follows: Gold —5%,
silver =10%. Absence of the fourth band indicates a20%
tolerance rating. MOLDED MICA TYPE CAPACITORS
The physical size of carbon resistors is determined by their
wattage rating. Carbon resistors most commonly used in Heath-
kits are 34 watt, Higher wattage rated resistors when specified
are progressively larger in physical size. Small wire wound
resistors 34 watt, 1or 2 watt may be color coded t*ut the first
band will be double width.
White (RMA)
Black (JAN)
CURRENT STANDARD CODE
ignifkant Figure
Class
Multiplier
Tolerance
JAN A
1946
RMA
CODE
RMA 3-DOT (OBSOLETE)
RATED 500 W.V.D.C. ±20% TOL.
Multiplier
ISignificant Figure
BUTTON SILVER MICA
CAPACITOR
Class —
Tolerance
Multiplier
3rd digit
RMA (5-DOT OBSOLETE CODE)
|
Significant Figure Working -
Voltage
Multiplier
front
Working Voltage
Rear
Tolerance
Tolerance
1st 2nd
Working
Voltage
—Multiplier
Significant Figure
RMA 6-DOT (OBSOLETE)
*2nd ^Significant Figures
-3rd.)
-Multiplier
iTolerance
flank
RMA 4-DOT (OBSOLETE)
Working Voltage
-Multiplier
Tolerance
Working Voltage
—Multiplier
MOLDED PAPER TYPE CAPACITORS
TUBULAR CAPACITOR 1st
2nd [Significant Figure
Multiplier
MOLDED FLAT CAPACITOR
Commercial Code
!1'
Tolerance
Normally
stamped for
value
2nd
1st
A2digit voltage rating indicates more than 900 V.
Add 2zeros to end of 2digit number.
Significant
Voltage Figure
Working Volts
Multiplier
j- Significant Figure
IAN. CODE CAPACITOR
1st fSignificant
2nd fFigure
Silver
Multiplier
Cbaracier! Stic
Tolerance
The tolerance rating of capacitors is determined by the color
code. For example: red =2%, green =5%, etc. The voltage
rating of capacitors is obtained by multiplying the color value
by 100. For example: orange =3X100 or 300 volts. Blue =
6X100 or 600 volts
In the design of Healhkits, the temperature coefficient of ceramic
or mica capacitors is not generally acritical factor and there-
fore Heathkit manuals avoid reference to temperature coeffi-
cient specifications.
Courtesy of Central tab

THE HEATHKIT W-5M
HIGH FIDELITY AMPLIFIER
,* ••• ’>'“ ’v•-•
>H mSliSiSSS;- .i> ..V.-
"JUV-:
-i'r -
iiiigsss® fjf v...
jmmmrnmmtmmiimmm
IIKi^iiBiigBKiiilMlilgl #111111 ill ill
>. :
.
’iIf
iiiiil 1•:
•:#
r. v, .:r-
i--:""”' r-' ''
iM

Page 2
THE
HEATHKIT
W-5M
HIGH
FIDELITY
AMPLIFIER

SPECIFICATIONS
NOTE: There is, as yet, no general agreement for specifying amplifier performance. Acursory
review of specifications may easily give ahighly distorted picture of the characteristics of the
amplifier. In general, it may be assumed that the most important specifications are those which
are not shown.
At first glance, the specifications presented here may seem quite complex and possibly, con-
fusing. We feel that it is necessary to provide you with complete and factual information about
the Heathkit W-5M Amplifier. We urge your direct comparison of these figures against those for
competitive amplifiers. It is our intention to furnish you with enough information to point up the
fact that, in general, only the most optimistic technical information reaches the prospective
buyer of high fidelity amplifiers.
The specifications below have been taken with the most modern and accurate test equipment
available today. They are actual measurements taken on atypical amplifier, under carefully
controlled conditions; not to present the most favorable advertising information, but in strict
accordance with all generally accepted standard conditions. These conditions are listed at the
end of this specification.
Minor variations from these specifications may be encountered in kit-assembled amplifiers
.
Such factors as exact lead placement, component variations and tube characteristics are possible
sources of deviations. In ahighly stabilized amplifier, such as the W-5M, these variables may
be disregarded from aperformance point of view.
POWER OUTPUT:
Rated Power 25 watts
Maximum Average Power 32.5 watts
Peak Power 47.2 watts
Power Output Related to Frequency See Figure 1.
Please note that on the 15, 20 and 25 watt curves, portions of the characteristic have been bro-
ken. Power measurements cannot be considered valid in this region because they were made
with meters calibrated to RMS values. Waveform distortion in the broken areas was sufficient
to invalidate such readings.
On the power curves, asterisks have been used to designate overload points at both low and high
frequency limits.
ICPS IOCPS 100 CPS IKC 10 KC 100 KC
Figure 1Page 3

One of the outstanding features of the W-5M is the remarkable low frequency power response .
Observe that the 0.25 watt curve extends smoothly to 3cps and is only down 3db at this point
.
Also, note that it is possible to obtain 20 watts of power at 20 cps without overloading. In con-
ventional amplifiers, low frequency response at low levels has been sadly lacking. At high levels
these amplifiers tend to go into overload and block on heavy bass passages. Because of the unique
output transformer design featured in the W-5M, low frequency power response is greatly im-
proved. Special attention has been given to the problem of overload recovery. (See "Overload
Recovery” on Page 7.
)
FREQUENCY RESPONSE:
See Figure 2below. This curve was taken at 1watt reference output and may be considered as
the voltage response of the amplifier
ICPS 10 CPS IOO CPS 1KC 10 KC 100 KC
Figure 2HEATHKIT W-5M FREQUENCY RESPONSE (1WATT OUTPUT )
An outstanding characteristic of the W-5M amplifier is the complete absence of the rising res-
ponse at the low and high limits of the pass band which has been considered anecessary evil up to
the present time. Although outside the audible range, such humps add to the instability of the
amplifier and tend to create distortion in the audio range. This happens when low frequency trans-
ients, such as turntable rumble, line voltage surges or tuning thumps, drive the amplifier into
low-frequency overload. In the W-5M, these transients cannot create any audible distortion and
no hangover or "breathing" conditions are evident.
The curve in Figure 2, taken at 1watt output and the 5watt curve in Figure 1, represent aver-
age room listening levels. In this amplifier, aminimum of 500% reserve power is available to
accomodate heavy bass passages and to make up for the relative inefficiency of less expensive
speaker systems.
HARMONIC DISTORTION:
Figure 3below gives five curves which relate the total harmonic distortion to power output
throughout the frequency range. From these curves it becomes evident that specifying total har-
monic distortion at any power level without designating the test frequency can be very misleading.
)
Competent authorities seem to agree that atotal of 2% harmonic distortion is tolerable for mus-
ical reproduction through wide-range audio equipment. Harmonic distortion below 0.7% is com-
pletely imperceptible, even to highly trained critical observers. Curves showing the output ob-
tainable at these distortion levels throughout the frequency range have been included above.
Figure 4indicates the distortion versus frequency curves for several power levels.
Page 4
Figure 4HEATHKIT W-5M TOTAL HARMONIC DISTORTION (DETERMINANT: POWER OUTPUT )

INTERMODULATION DISTORTION:
Intermodulation distortion curves for three separate test conditions are plotted in Figure 5
.
Please observe that, again, the generally accepted limits for "extremely high fidelity" amplifiers
and "high fidelity amplifiers" have been added to the graph. The W-5M amplifier will supply
over 20 watts of power under any one of the three test conditions before its intermodulation dis-
tortion exceeds the "extremely high fidelity" requirements.
HEATHKITW-5M POWER OUTPUT (EQUIVALENT SINGLE FREQUENCY
POWER IN WATTS )
PHASE SHIFT: Figure 5
See Figure 6below, which is self-explanatory.
1CPS 10 CPS (00 CPS IKC 10 KC 100 KC IMC
HEATHKITW-5M PHASE SHIFT
Figure 6
Aphase shift of 75° occurs at 1.2 cps. It was impossible to locate the 90° leading point, since
it occurs below the pass-band of the amplifier. Note also that the phase shift occurs gradually
throughout the frequency range, rather than quite abruptly as is generally true of amplifiers
with heavy feedback. This contributes further to the stability of the amplifier.
Page 5

SENSITIVITY:
Figure 7below indicates voltage input required to drive the amplifier through its entire output
power range.
VOLTAGE OUTPUT (16.0.)
l0V 15V 20 V25V
5W IOW 15 W20 W25W
POWER OUTPUT
HEATHKIT W-5M INPUT REQUIREMENTS
Figure 7
The broken line has been plotted to show the linearity of the input-output voltage characteristic
of the amplifier.
HUM AND NOISE: 80.2 db below 250 milliwatts, unweighted. (General
average listening level.)
84.2 db below 5watts, unweighted. (Loud average
listening level.)
99 db below 25 watts, unweighted.
Anoise level of 60 db below 100% modulation for AM or FM broadcast stations is recognized as
acceptable by the Federal Communications Commission. Most stations exceed this figure to
some extent. Modern LP recordings seldom exceed 40 db below average program level. Broad-
cast quality tape recorders attain anoise level 60 db below full output. The extremely low noise
level of the W-5M exceeds these requirements comfortably, even at very low output levels where
noise is most noticeable.
OUTPUT TUBE BALANCE: Unique ”Bass-Bal" circuit, requires only simple volt-
meter for indication of exact balance.
FEEDBACK FACTOR: 18.1 db of feedback is applied around the entire am-
plifier and output transformer.
OUTPUT IMPEDANCES: 4, 8or 16 ohms, unbalanced.
DAMPING FACTOR: 40
Page 6

TRANSIENT RESPONSE: Square-wave response characteristics of the W-5M
are shown in the oscillograms below:
50 CYCLES 500 CYCLES 20 KC
NOTE: In all oscillograms used in these specifications, the upper trace represents the signal
applied to the input of the amplifier. The lower trace displays the output signal across a16O
load.
In Aabove, observe that the output wave shape, although "tilted" slightly, shows no evidence of
rounding, overshoot or instability. The tilt is caused by phase shift, which at this frequency is
approximately 5°.
In B, the input and output wave shapes are almost identical.
In C, made at 20,000 cps, overshoot and ringing characteristics are shown. Overshoot amounts
to approximately 15%. Ringing frequency is approximately 90 kc. Bear in mind that afunda-
mental square wave test at 20 kc will accurately predict the amplifier performance from that
frequency up to at least 200 kc. No known source of program material even remotely approaches
this rigorous test of high-frequency transient response.
OVERLOAD RECOVERY:
Particular attention has been given to this problem in theW-5M. Whereas high-frequency instab-
ility is generally blamed for many ills in ahigh fidelity amplifier, we feel that afar more im-
portant field is that of low-frequency overload and instability, for these defects are audible
,
even to the untrained observer. They are much more prevalent than is commonly believed, in
fact, most people listening to areally wide-range system with astable bass response charac-
teristic are immediately impressed by the tremendous sense of freedom and drive in the repro-
duced sound.
Overload is avery common condition, even in power amplifiers with considerable power output.
It may be caused by the sudden voltage "thump" developed by tuning an FM receiver through a
carrier, or by heavy bass passages in program material. Switching transients can develop tre-
mendous signal voltages, as can the connection of an input cable while power is applied to the
amplifier.
As afirst step to correction, the amplifier must overload symmetrically at any frequency. Os-
cillogram Dshows the overloaded or clipped output wave shape at 1kc with approximately 28
watts output. Note that the clipping is perfectly symmetrical.
c
c
c
cA'
oE——:
yu u wWVV..v
The amplifier must be capable of faithful reproduction of extremely low frequencies at normal
power levels. Oscillogram Eshows a5cycle sine wave output characteristic, taken at 1watt
level. No evidence of breakup or overload is present. No equipment was available to measure
harmonic distortion at this frequency; distortion is obviously quite low. Page 7

Power supply regulation, output transformer design and careful shaping of the overall frequency
response curve all play very important parts in the ability of the amplifier to recover quickly
when overloaded. There is no simple or easy way to specify the overload recovery capability
and the problem is made more complicated by the transient nature of the condition. In order to
present ameaningful specification, we have resorted to oscillograms of simulated conditions
which are known to create the condition. These are shown directly below.
The test signal shown in oscillogram Fis acomposite of three signals as defined in the sketch
below:
«50 MS
H-3MS*!
ThelOkc component represents normal mixed program material. The heavy 7millisecond rec-
tangular pulse simulates an overloading transient of sufficient length to show up any "ringing"
or "hangover" effect following the sharp rise in signal level. The short 200 microsecond pulse
follows this component after 3milliseconds. This pulse could be placed at any point on the wave-
form. Its purpose was to determine if overload recovery was sufficient to faithfully present a
short transient immediately following overload. The composite test signal is shown in oscillo-
gram F. (Again, remember that the upper trace is the input signal; the lower trace is the output
of the amplifier.) In order to show the critical portion of the cycle more clearly, oscillogram G
is a5times expansion of the trace. Vertical sensitivity of the lower trace of the oscilloscope
was 20 volts per centimeter or approximately 20 volts peak-to-peak. Under these conditions ,
the amplifier is operating safely below the overload point.
At H, the same test signal has been increased in amplitude; the amplifier is now trying to pro-
duce an output signal of some 40 volts peak-to-peak. Again, Jrepresents a5times expansion
of the same condition.
Observe at H, that the overloading transient has completely lost its identity because of output
limitation. However, the recovery of the amplifier is smooth and gradual, without hangover or
ringing. The short pulse is reproduced faithfully, even during the gradual recovery, which is
particularly important. This effect is shown quite plainly at J.
Page 8

STABILITY:
The W-5M may be operated with no load without damage to amplifier, output transformer or
tubes. Abuilt-in "Tweeter-Saver" prevents high-frequency oscillation under abnormal condi-
tions, which might destroy or overheat high-frequency drivers in multiple -speaker systems.
Shunt capacities of up to 0.05 pfd across speaker line cause no tendency toward instability or
oscillation.
Series inductance in speaker line causes no tendency toward instability or oscillation.
MECHANICAL PROTECTION:
Decorative top cover prevents contact to hot tube envelopes; keeps connecting cables from dam-
age by heat; "chiId -proofs” normally exposed portions of the equipment. Cover may be readily
removed without tools. Cover may be reversed, front to back, if desired. All controls, con-
nectors and fuses on one apron of the chassis.
FINISH: Chassis, satin gold enamel. Cover, satin-texture black.
MOUNTING PROVISIONS:
Must be mounted with KT-66 bases down. See template for space requirements. Heavy mar-
proof rubber mounting feet to protect mounting surface. Mounting bolts and T-nuts furnished;
can be mounted on any surface up to 7/8" thick.
POWER REQUIREMENTS: 105-125 volts 50-60 cycles, 140 watts
WEIGHT: 26.5 lbs. net
TEST CONDITIONS:
Output Impedance Dummy load, 16.43 ft (cold) resistive.
Line Voltage 117 volts, 60 cycles, regulated.
Accessories All measurements made while the amplifier was fur-
nishing power to a Heathkit WA-P2 Preamplifier.
Generators For harmonic distortion measurement, Krohn-Hite
model 440-A, inherent distortion less than 0.1%.
For frequency response measurements, Hewlett-Pack-
ard model 650-A test oscillator.
For square wave tests, Tektronix type 105 square wave
generator.
Distortion Total harmonic distortion measurements, Hewlett-
Packard model 330-B distortion analyzer.
Intermodulation distortion; Measurements Corporation
model 31 intermodulation meter, Heathkit AA-1 audio
analyzer.
Power Output Voltage measurements across 16.43 ft resistive load,
using Hewlett-Packard model 400-D vacuum tube volt-
meter.
Oscillograms Fairchild camera on Tektronix model 531 oscilloscope
with type 53 -C dual channel preamplifier.
Page 9

INTRODUCTION
The Heathkit Amplifier model W-5M was designed to fulfill the performance requirements of the
most critical audiophile, at the lowest possible cost. Up-to-the minute design techniques were
used throughout to reduce distortion and at the same time, increase power output, thus allowing
the connoisseur of music to enjoy a level of realism never before obtainable. The full dynamic
range of all types of audio material can be handled with ease because of the high peak power
handling capabilities of the W-5M.
Just afew years ago, tuners, phonograph pickups and speakers were considered as the stronger
links in the audio chain and the amplifier as the weakest. The audio field has advanced tremen-
dously in the past five years however, and now the positions are reversed. When the amplifier
is constructed and adjusted in accordance with the instructions, the Heathkit model W-5M Amplif-
ier will faithfully reproduce all program material fed to it, providing optimum performance from
all other parts of the high fidelity system.
It is logical to assume that best performance will be obtained with the highest possible quality
accessory components. The Heath Company cannot recommend specific components, but it is
suggested that reference be made to catalogs and magazines concerned with the audio field. In
general, the higher the price of the components, the higher the quality, but this is not necessarily
always true. Careful shopping will usually locate very satisfactory items at aprice to fit the
budget.
CIRCUIT DESCRIPTION
Thebasic circuit of the W-5M amplifier is straightforward and simple. Signal from the program
source is fed into the input jack, which is coupled to the grid of the input 12AU7 tube through a
.1 ju.fd condenser. Signal amplification takes place in the first half of this tube and the output is
directly coupled to the grid of the second half of the tube.
Phase splitting or signal inversion is accomplished in the second half of the first 12AU7, which
is asplit load type of inverter. Signal at the cathode of this stage follows the grid, while the
plate voltage will swing in the opposite direction. Coupling to the grids of the second 12AU7
push-pull driver stage is through .1 /Ltfd capacitors, one connected to the cathode and the other
to the plate of the phase inverter.
Amplification of the signal takes place once again in the 12AU7 driver stage and signal is taken
out through two 1jifd condensers, one connected to each plate of the driver. The opposite end
of these condensers is connected to the grids of the output tubes. Here, the signal voltage var-
iations are converted to large current changes in the output tubes and the output transformer
,
which is in the plate circuit. AC current variations in the high impedance primary of the trans-
former are passed to the low impedance secondary and to the speaker line connected at this point.
Feedback is applied from the secondary of the output transformer back to the cathode of the input
12AU7 stage to reduce distortion and lower the output resistance of the amplifier, thus improving
amplifier control over loudspeaker performance. Inverse feedback also improves the frequency
range of the amplifier.
In order to reduce harmonic distortion at low frequencies it is essential that the plate current of
the output tubes be balanced. An exclusive balancing circuit is incorporated in your Heathkit
amplifier to make the balancing operation easier and much more accurate. Precision balanced
resistors are connected in the cathode circuits of the power output tubes. When the current in
each tube is balanced, the voltage drop across each precision resistor will be the same and the
resultant potential will be zero if measured at both cathodes at the same time. Agreat advan-
tage is gained, since the current in both tubes is measured simultaneously instead of one at a
time.
Page 10

Aload limiting device is built into the amplifier to provide high frequency and transient stability.
Rising impedance effects of speaker systems at higher frequencies will frequently cause oscill-
ation in afeedback type amplifier, since the amplifier fails to see areasonable load at these
frequencies. To counteract this, aresistor and condenser have been installed in series across
the output transformer secondary. The condenser is chosen to prevent the loading of the amp-
lifier throughtout the audible portion of the spectrum and still provide suitable loading above these
frequencies; thus assuring complete stability under all dynamic operating conditions.
Power for the amplifier is supplied by ahusky power transformer and ahigh current ruggedized
5R4GY rectifier. Output from the 5R4GY is very well filtered in an inductance-resistance-
capacity filter to keep noise and low frequency instability at aminimum. High capacity filter
sections are used throughout to reduce power supply impedance at low audio frequencies. Well
regulated high voltage at high current is available for the output stage, allowing high power out-
put at very low distortion.
Only the highest possible quality components have been incorporated in the Heathkit model W-5M
Amplifier. At no point have corners been cut to reduce cost at the expense of quality parts or
performance. All components are conservatively rated, giving assurance of trouble-free perfor-
mance for along time. An example of the conservative rating of parts is the 5R4GY rectifier
.
Another type of rectifier was considered and was actually used in the original development model.
While this tube was adequate for the purpose, it was operating near maximum ratings and so the
decision was made to use the more expensive and rugged 5R4GY instead. Ahigh safety factor
is used in the filter section of the power supply also. The electrolytic filter condensers are con-
nected in series with voltage balancing resistors across them, providing amaximum voltage
rating of 900 volts at the first two sections of the filter, where the operating voltage is in the
neighborhood of 500 volts and 700 volts at the output section, where the operating voltage is 470
volts. Special single section condensers could have been used, but it would be impossible to
employ them and provide the safety factor obtained by using series units. The amplifier cover
is another advantage, in that the appearance is improved and small children are protected from
severe burns since they cannot touch the output tubes and rectifier, which run quite hot.
NOTES ON ASSEMBLY AND WIRING
Your Heathkit Amplifier, model W-5M represents asubstantial outlay of money. In order to get
the high performance return for your investment it is extremely important that you take the time
to read the manual carefully before construction is started. Carefully read each step all of the
way through until it is completely understood. After you are thoroughly familiar with the pro-
cedure used, construction of the kit can be started. Care exercised in construction will be re-
warded with agreater sense of confidence, both in your amplifier and your own ability.
This manual is supplied to assist you in every way to complete the instrument with the least pos-
sible chance for error. The detailed instructions are specifically written to allow either the ex-
perienced or inexperienced constructor to construct the unit with a minimum of difficulty. Only
avery small percentage of Heathkit assemblers encounter any difficulty whatsoever in complet-
ing kits of this kind. Large fold-in pictorial diagrams are included in the manual for your con-
venience and are quite helpful if attached to the wall above your work space. The diagrams are
repeated in smaller 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 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 32. 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 leads 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.
Page 11

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, a100 KO resistor may test anywhere from 80 K£2 to 120 KO and still be
acceptable. Tolerances on electrolytic condensers may be even wider and commonly run from
+100% tb -50%. The parts furnished with your Heathkit have been specified so as to meet the
performance specifications given.
In order to expedite 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
supplied will work satisfactorily in your kit. For example, if your kit is short a15Kfi resistor
and an 18 Kfi resistor is furnished which is not on 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.
STEP-BY-STEP ASSEMBLY INSTRUCTIONS
In assembling the kit, use lockwashers under all nuts, unless otherwise specified. Tube sockets
are mounted inside the chassis except for miniature 9-pin shielded sockets, which are mounted
on top. The insulated filter condenser mounting wafers are mounted on top of the chassis. Other
details of construction are included where pertinent in the instructions.
"()Place the chassis with the open side up in front of you on your workbench. Be sure that
the apron with the holes in it is nearest you. See Figure 8on Page 13.
'1'* )Mount a9-pin miniature tube socket at location VI, using 3-48 hardware with lockwashers.
Use the chart on Page 32 to identify hardware sizes if necessary. The body of the socket
should be outside the chassis, with the lugs extending up through the socket hole. Orient
the socket so the blank space is positioned as shown in Figure 8.
)In the same fashion, mount 9-pin miniature socket at V2.
NOTE: In the following steps, do NOT use the 6-32 x1/2" screws until called for.
Install an octal socket at V3, using 6-32 hardware. Be sure that a1-lug terminal strip is
mounted on one screw as shown in Figure 8. Position the keyway of this socket to the left
as shown.
( ) Similarly, install octal socket V4 and terminal strip F, with keyway oriented in the same
position.
)Mount octal socket V5. Note that the keyway for this socket is to the right. No terminal
strips are used on this socket.
()Outside the chassis, install insulated condenser mounting wafer at G, using 6-32 hardware.
Be sure that the wafer is mounted outside the chassis.
)In the same manner, mount asecond insulated condenser mounting wafer at location H. This
wafer also mounts outside the chassis.
%«- )Insert a3/8" rubber grommet in the chassis hole at R.
f)Insert a3/8" rubber grommet in the front apron of the chassis at FF.
()Insert 3/4" rubber grommets at locations Sand T.
()Mount a2-lug terminal strip Aand three dual-lug terminal strip B, using the hole to the
left of socket VI. Use 6-32 hardware.
()Mount three dual-lug terminal strip C, between sockets VI and V2, using 6-32 hardware.
( ) Mount 4-lug terminal strip Xdirectly below terminal strip C. Use 6-32 hardware.
Page 12

)Install three dual-lug terminal strip Jand 2-lug terminal strip Kbetween sockets V3 and
V4. Use 6-32 hardware.
()Install one dual-lug terminal strip Nas shown in Figure 8. Use 6-32 hardware.
()Directly above terminal strip N, there is astaggered row of four holes. Using the fourth
and smallest hole, mount 3-lug terminal strip P, using 6-32 hardware.
(- )in each corner of the chassis, you will find agroup of three holes. In these locations, Wl,
W2, W3 and W4, mount the four cover spring clips, using 4-40 pan head screws, lock-
washers and nuts.
(— )On the front apron of the chassis, mount the phono connector socket at location Y, being
sure that the ground lug is to the left, nearest the end of the chassis. Use 6-32 hardware.
(- )Cut four lengths of insulated sleeving (spaghetti) to alength of 3/8" each. Identify the mol-
ded 4-terminal speaker connector block. Slip alength of sleeving over each of the solder
lugs, so that 1/8" of the tip of the lug is exposed.
T)Mount the connector block at location Zusing the four 6-32 x1/2" screws.
)Mount the remaining octal socket at location AA on the front apron. Position the keyway
nearest the edge of the apron. Use 6-32 hardware.
<
(
C,
<)
i-J
Mount the dual tip jack strip BB, inside the chassis.
Install AC outlet CC nearest the bend, using 6-32 hardware.
Install AC outlet DD directly above in the same way.
Following Figure 9, mount the fuse holder at EE. Position
the contact lugs as shown in Figure 8. Install the fuse in the
holder.
Install the. 300 "Bass-Bal" control at D. Follow Figure 10
for assembly details and orient terminals as shown in Figure
8.
Identify the power transformer, the largest
of the three metal cased components. Note
that the leads come out in two groups, one
containing red, red-yellow and yellow wires;
the other containing black, green and green
-
yellow wires. Pass the red, red-yellow and
yellow wires through grommet Sand the
other group through grommet T. Secure the
transformer to the chassis, using six 8-32
screws, lockwashers and nuts.
CONTROL SOLDER
LUG OR LOCKWASHER
_-PANEL OR CHASSIS
FLAT WASHER
NUT
CONTROL MOUNTING Figure 10
()Identify the filter choke, the component with two wires coming through asingle bushing
.
Pass these wires through grommet Rand secure the choke in place with 8-32 hardware
through the four corner holes in the mounting flange.
( ) Now install 2-lug terminal strip Q, placing a6-32 screw through the choke flange, chassis
and strip bracket, as shown in Figure 8.
()The remaining metal cased component is the output transformer. Through one bushing ex-
tends agroup of five leads, color-coded red, brown, brown-white, blue and blue-white
.
Pass this group through hole Mand pass the group of four leads through hole L. Secure the
transformer to the chassis, using four 8-32 screws driven directly into the tapped inserts
of the transformer case. Use lockwashers under each screw head.
f)identify the 20-20-20 jxfd 450 volt filter condenser. This is the metal can with three termin-
als protruding through the insulating wafer at one end. Note that each terminal is identified
by asymbol punched through the insulator adjacent to the lug. Orient these terminals as
shown in Figure 8, slip the four mounting lugs through the slotted holes in the wafer at G
.
Then twist each lug approximately 45° to secure the condenser to the wafer. Be sure the
condenser is held firmly against the wafer while twisting the lugs.
()In the same way, mount the 40-40 fifd 450 volt filter condenser at H. Again, orient the lugs
as shown in Figure 8before twisting the mounting tabs.
This concludes the mechanical assembly of your Heathkit model W-5M Amplifier.
Page 14

STEP-BY-STEP WIRING INSTRUCTIONS
Pictorial 1represents acompletely wired W-5M amplifier. We again suggest that before you
start wiring, you attach the large fold-in version of this pictorial to the wall above your work
space, so that it may be conveniently referred to as the work progresses.
Read the note on the inside rear cover concerning wiring and soldering.
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 IN DOUBT ABOUT SOLDER, IT IS RECOMMENDED THAT ANEW
ROLL PLAINLY MARKED "ROSIN CORE RADIO SOLDER" BE PURCHASED.
In Pictorial 1, note that each component part has been given acode designation which corres-
ponds with the identification used during the assembly of the kit. In addition, each terminal on
each part has been assigned anumber.
When the instructions read, "Connect one end of a1jufd condenser to V2-6 (NS)," it will be under-
stood that the connection is to be made to contact pin 6on socket V2. The abbreviation "NS"
indicates that the connections should not be soldered as yet, as other leads will be added to the
same terminal later. When the last wire is connected, the terminal should be soldered and the
abbreviation "S" is used to indicate this.
Unless otherwise indicated, all wire used is insulated. Wherever there is apossibility of the
bare leads on resistors and condensers shorting to other parts or to chassis, the leads should be
covered with insulated sleeving. This is indicated in the instructions by the phrase "use sleev-
ing. "Bare wire is used where the lead lengths are short and the possibility of short circuits
non-existent. Use small diameter ba-re wire except where otherwise specified.
Leads on resistors, condensers and transformers are generally much longer than they need to
be to make the indicated connections. In these cases, the excess leads should be cut off before
the part is added to the chassis. In general, the leads should be just long enough to reach their
terminating points. Not only does this make the wiring much neater, but in many instances the
excessively long leads will actually interfere with proper operation of the instrument.
The pictorials indicate actual chassis wiring, designate values of the component parts and show
color coding of leads where pertinent. We very strongly urge that the chassis layout, lead place-
ment and grounding connections be followed exactly as shown. While the arrangement shown is
probably not the only satisfactory layout, it is the result of considerable experimentation and
trial. If followed carefully, it will result in astable instrument operating at ahigh degree of
dependability.
(,) Twist together the two green leads coming through grommet T. Place them to reach socket
V4 and cut one lead to length sufficient to reach V4-2. Cut the other lead to length to reach
V4-7. Save the cut-off leads. Strip and tin the leads. Connect either lead to V4-2 (NS) and
the other to V4-7 (NS). (See Figure 12 for tube socket contact numbering.)
(^Twist together the two black leads coming through grommet T. Dress this pair to socket
AA, using the route shown in Pictorial 1on Page 16. Cut one lead to reach AA7 and the
other lead to reach AA8. Strip and tin the ends.
(’ )Cut alength of Spirashield (the spring-like flexible tube) to alength of 43/4" and slip this
over the twisted black leads. Following Pictorial 1carefully, dress the shielded leads to
the left of terminal strips Eand F.
()Cut a11/2" length of bare wire and fold it in half to form ahairpin. Push the open end
through the hole in the bracket for terminal strip F. Let the closed end extend horizontally
to the left of the bracket and solder the hairpin in place.
()Similarly, connect ahairpin to the bracket for terminal strip Eand solder it in place.
Page 15

Page 16
PICTORIAL
1

()Now dress the shielded pair tightly against the two terminal strip brackets, form the two
bare wires over the shield and solder them to the shield. When properly completed, this
procedure will secure the shield tightly against the chassis and the two terminal strip brack-
ets. Refer to Figure 11 for details.
KEYWAY
Figure 12 9— PI N
SOCKET
()At the apron end of this pair, connect either wire toAA7 (NS) and the other wire to AA8(NS).
( ) Pass the free end of the green-yellow wire coming through grommet T, up through hole Ul
temporarily. Hole Ul is at the left end of the chassis. Further instructions concerning
this lead will appear later.
t)Twist together the two yellow and two red wires coming through grommet Sand dress the
cable up to the rear apron and along the bend of the chassis to socket V5. Cut either red
wire to length to reach V5-4 and the other red wire to reach V5-6. Cut either yellow wire
to reach V5-2 and the other yellow wire to reach V5-8. Strip and tin all four ends. (See
Figure 12 for tube socket numbering details.)
()Connect the first red wire to V5-4 (S).
()Connect the second red wire to V5-6 (S).
^)Connect the first yellow wire to V5-2 (NS).
(' )Connect the second yellow wire to V5-8 (S).
()Using diagonal cutters, cut anotch in mounting lug G4 Figure 13
on condenser G. See Figure 13.
()Dress the red-yellow wire coming through grommet Sto condenser ground lug G4, strip and
tin and connect to G4 (NS). The notch in this terminal is used in subsequent wiring.
()Dress the red wire coming through grommet Mon the output transformer along the bend in
the chassis and to terminal strip P. Cut the lead to length to reach PI, strip, tin and con-
nect the wire to Pi (NS). Be sure that this lead is dressed into the bend of the chassis as
shown in Pictorial 1.
X)- Twist together the blue and blue-white wires coming through grommet Mand dress them to-
ward socket V4. Cut the blue wire to length to reach V4-3 and the blue-white wire to V4-6.
Strip and tin both leads. Connect the blue wire to V4-3 (S) and the blue-white wire to V4-6
(NS).
X* )Twist together the brown and brown-white wires coming through grommet Mand dress them
toward socket V3. Cut the brown wire to length sufficient to reach V3-3 and the brown-white
wire to length to reach V3-6. Strip and tin both leads and connect the brown lead to V3-3
(S). Connect the brown-white lead to V3-6 (NS).
("'*) Carefully dress the two pair of leads just connected so that they lie snugly against the chas-
sis. These leads will carry the highest signal voltages in the amplifier and it is important
that they be kept as close to the chassis as possible.
(OTwist together the four leads coming through grommet L. As shown in Pictorial 1, dress
the cable along the front bend of the chassis toward speaker terminal block Z. Cut the green
lead to length to reach Zl, yellow lead to reach Z2, brown lead to reach Z3 and black lead
to reach Z4. Strip and tin all four leads. Connect the green lead to Zl (NS). Connect the
yellow lead to Z2 (S). Connect the brown lead to Z3 (S). Connect the black to Z4 (NS).
(•»-.) At the filter choke, dress the red wire coming through grommet Rto terminal strip P. Cut
and strip the lead and connect it to P3 (NS). Connect the black lead to PI (NS).
Page 17

)Select the two lengths of green transformer lead cut in the first step of the wiring instruc-
tions. Cut each lead to alength of 41/2" and strip and tin all four ends. Offset the ends
about 3/4" and twist the two leads together. (See Figure 14.)
'sjf-s )At one end of this pair, connect the longer lead to V4-2 (S).
...( )Connect the adjacent lead to V4-7 (S).
O)At the other end of this pair, connect the shorter lead to V3-2 (NS).
"‘t-O Connect the adjacent lead to V3-7 (NS).
C)Cut apair of 6" lengths of hookup wire, strip all four ends and twist the two leads firmly
together.
'~~( ")At one end of this pair, connect either lead to V3-2 (S) and the adjacent lead to V3-7 (S).
(~ )Dress the pair along the chassis bend, under socket AA and up the left side of AA. Connect
either lead to AA1 (NS) and the adjacent lead to AA2 (NS).
'""f-. )In the same fashion, form a7" long twisted pair of hookup wire. Strip all four ends. At
one end of this pair, connect either lead to AA1 (S) and the adjacent lead to AA2 (S).
()Dress this pair down along the left side of socket AA to the chassis, along the chassis bend
to the left and directly up to socket V2. At the socket, connect either lead to V2-9 (NS).
Connect the other lead through V2-4 (NS) to V2-5 (S).
t'") Cut and strip apair of 31/2" lengths of hookup wire. Offset the ends about 3/4" and twist
the two leads together as before. (See Figure 14.) At one end of this pair, connect the lon-
ger lead to V2-9 (S) and the adjacent shorter lead to V2-4 (S).
At the other end of this pair, connect the shorter wire to VI -9 (S).
Connect the adjacent longer lead through VI -5 (NS) to VI -4 (S).
Now solder VI -5.
'T )Connect awire from socket AA7 (S) to AC outlet DD2 (S).
)Connect awire from AA8 (S) to AC outlet CC1 (NS).
X" )Connect ashort bare wire from CC1 (NS) to DDl (S).
"f~) Using bare wire and sleeving, connect CC2 (NS) to fuse holder Figure 14
EEl (S).
'( )Connect awire from AA6 (S) to EE2 (S).
~(~ )Connect awire from AA5 (S) to V5-5 (NS). Dress this wire under the Spirashield and the
green twisted pair, as shown in Pictorial 1
.
//(/ )Similarly, run- awire from AA4 (S) to G(NS).
~f )Connect abare wire from AA3 (NS) to Z4 (NS).
()Connect awire from Z4 (S) to the phono connector Y2 (NS).
“(-)Connect one lead of a0.1 pfd 200 volt condenser to AA3 (S) (use sleeving). Connect the other
lead of this condenser to terminal strip X4 (NS).
NOTE: Some condenser manufacturers use amarking to identify the "outside foil" of aconden-
ser. Usually this appears as aband around the body of the component, near one end. In this
instrument, this distinction is not important. Therefore, the outside foil markings may be dis-
regarded or if the constructor has apreference, he may use his own judgment. IMPORTANT:
THIS DOES NOT REFER TO MARKINGS ON ELECTROLYTIC CONDENSERS WHERE POLAR-
ITY IS CRITICAL.
)Connect awire from G*(NS) on the filter condenser to terminal strip B2 (S). Dress this
lead against the chassis.
T"') Connect awire from G(NS) on the filter condenser to terminal strip C2 (NS). Dress this
lead against the chassis.
()Connect awire from Ga(NS) on the filter condenser to terminal strip C6 (NS). Dress this
lead against the chassis.
)Using bare wire and sleeving, connect alead from P3 (NS) to V5-2 (NS). Sleeving is used
on this lead for maximum voltage breakdown protection,
f•- )Connect awire from V5-3 (NS) to terminal strip Q2 (NS).
()Connect awire from filter condenser Ha(NS) to P2 (NS).
Page 18