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

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HIGH FIDELITY AMPLIFIER
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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