Specifications

amplifier and the Heathkit WA-P2. Should other units
with different power plug wiring be used the takeoff
socket may be rewired to suit requirements. The wire
jumper between lugs #2 and #3 of the 5 lug terminal
may have to be cut depending on the type of preamp
to be used. This jumper should be cut for use when
powering a
Dynakit PAM-l preamplifier or Heath-
kit WA-P2 or any other preamplifier which requires
power from a "floating" or ungrounded heater sup-
ply. The jumper should not be cut when using any
preamplifier which has its own, or a separate, power
supply.
PROTECTIVE COVER
The protective cover supplied with the MARK IV
has been designed to be both functional and attrac-
tive. In normal home usage the cover should always
be used; although the voltage at the top of the printed
circuit is not lethal, an unpleasant shock can be ex-
perienced,
plus the fact that the tubes in normal
operation run hot enough to produce a minor burn if
touched.
The amplifier should be located where there is am-
ple ventilation-at least one foot of space above it
and several inches all around. The amplifier can be
located away from other elements of your system so
there is no need to place it in a confined area. Never
place anything directly on the cover which might
limit the ventilation. It is always advisable to operate
the amplifier in its normal vertical position.
The cover and bottom plate are attached at the
same time. Place the amplifier on the bottom plate,
then lower the cover over the unit, the tabs on the
cover will fit between the ends of the bottom plate
and the chassis. The three pieces are fastened simul-
taneously with sheet metal screws through the sides.
IN CASE OF TROUBLE
Your Dynakit MARK IV has been conservatively
designed to be as trouble free as possible. Error in
assembly
or possibly a defective component may
affect performance or render it inoperative. Here are
some suggestions which may help. First of all the wir-
ing
and assembly should be doubly checked, by some-
one other than the constructor if possible.
The tubes should light a few seconds after the unit
is turned on. If not, miswiring or a blown fuse will
probably be the answer. Replace a blown fuse only
with the type (2 ampere) originally supplied.
If the fuse blows when all tubes are removed from
sockets a defective power
transformer or miswiring is
indicated.
If one or the pair of EL-34 output tubes glow a cherry
red after warm-up, it is possible that a tube is defec-
tive,
or there may be a fault in the bias supply
which controls the current flow of the output tubes.
When the biaset reading is 1.56 volts the bias voltage
at the grids (pins 5) of the output tubes should be
within 20% of 34 volts NEGATIVE. A VTVM or
high impedance meter must be used here. If the volt-
age at each of the grids is not exactly the same, one
of the
.1 mfd coupling capacitors on the printed cir-
cuit board may be at fault. If one tube has no negative
voltage at pin #5, an open circuit exists between the
tube and bias supply.
If no meter is available and one tube glows, inter-
changing the two tubes will help indicate the fault. If
the same tube glows in the other socket, the tube is at
fault. If the other tube glows in the original socket
position
then wiring or components are at fault.
The output tubes supplied with your MARK IV
are carefully matched at the factory. When replacing
output tubes a matched pair should be used, or a new
one should be rna tched to the remaining good one.
In emergencies, substitution of tubes can be made.
Type 5881 or KT66 may be used in place of EL-34's
provided the bias is readjusted for these tubes. Type
5U4 or 5U4GB can be substituted for the GZ-34/
5AR4 rectifier.
Either of these substitutions will re-
sult in somewhat lowered power output, however.
There is at present no substitute for the 7199 tube.
No Signal
If the momentary insertion of a small screw driver
in the input socket causes a loud hum, the trouble is
probably in the associated equipment. If the ampli-
fier is at fault, testing or substitution of tubes may
help. Voltages may be checked in accordance with
the voltage chart provided in the instructions.
Hum and Noise
If excessive hum or noise is apparent, it is essential
to determine whether the disturbance is from the
power amplifier or associated equipment. Power am-
plifiers are often blamed for noise coming from the
preamp. The quick and simple way to determine this
is to remove all but the speaker from the amplifier. If
the hum or noise disappears, the noise comes from
other than the amplifier; if it persists, it can safely be
assumed it is in the unit.
Sizzling
sounds may be caused by poor solder con-
nections
and occasionally by a defective resistor.
Loud cracking or popping sounds are generally caused
by loose tube elements and in rare cases a defective
quad section filter capacitor.
In the event that the trouble cannot be found, fac-
tory consultation is available at no charge and service
at moderate fees.
FACTORY SERVICE AND GUARANTEE
The MARK IV is designed to provide good service
for a long time.
It is intended for operation at the
conventional 117 volt line voltage supply to most
homes and may be operated at up to 125 volts with-
out problems. Operation with line voltage above 125
volts will
shorten tube and component life, and is not
covered by the guarantee.
All parts in the MARK IV are guaranteed for a
period of one fuB year from purchase date with the
exception of the tubes which are covered by the stand-
ard EIA guarantee of 90 days. Defective parts will be
replaced
at no charge if they are returned prepaid di-
rectly to the factory or through the dealer from whom
the kit was purchased. Many DYNACO dealers stock
parts for convenience of replacement. After the guar-
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