TROUBLE-SHOOTING PROCEDURES
Connect aphonograph and speaker to the amplifier as de-
scribed in "Electrical Connections" and set controls for
phono listening. Play aknown high quality LP recording
on the phonograph. If there is no output to the speaker
or if the output is low or audibly distorted, procede to the
checks for those symptoms. If there is excessive hum in
the output, disconnect the phono input cable from the
amplifier and short the phono input jack to chassis. If the
hum disappears, the trouble is not in the amplifier but in
the phonograph or in the connection to the amplifier.
The cause of phonograph hum maybe ametal pick—up arm
not grounded to the cable shield (try agood single ground
connection to the cable shield from turntable frame, pick-
up arm, and cartridge case), direct hum pick-up by the
magnetic cartridge from the record player motor (try using
arubber mat on the turntable to Increase the separation of
the pick-up from the motor), or pick-up from apower trans-
former or other magnetic field in the vicinity (try moving
phonograph away from suspected source). Check also that
the phono input cable shielding is grounded to the ampli-
fier chassis atone pointonly, through the skirt of the input
connector where it plugs into the amplifier. Finally, try
agood building ground such as aconnection from acold
water pipe terminated under speaker terminal "G" on the
amplifier. Do not connect such aground wire to other
components in the system.
Excessive hum on other inputs maybe checked in asimilar
manner. Disconnect the input cable in question and short
the particular input jack to the chassis, if the hum dis-
appears, the trouble is external to the amplifier. Note
that on all inputs, the braid of the input cable should con-
nect to the amplifier only through the skirt of the input
connector. The cause and remedies for the following symp-
toms are then based on the assumption that checks made in
the manner described above have eliminated the possibility
of the trouble being external to the amplifier.
If the trouble is no output or low output, check AC signal
voltages and DC operating voltages starting at the Input
and working step-by-step toward the output. Set the
VOLUME iLOUDNESS controls to maximum (10), the
BASS and TREBLE controls to their mid-points (0),and the
SCRATCH &RUMBLE filters to OFF. Use a1000 cycle
sinewave signal, such as supplied by theEiCO 377 Sine &
Square Wave Audio Generator, In addition, use apre-
cision 100:1 attenuator to permit obtaining alevel of
0.005 volt fed into MAG. PHONO from an audio gen-
erator output of 0.5 volt, which can easily be measured
on the lowest AC volts range of your VTVM (also improves
signal to hum from generator). Use ahigh Input impedance
VTVMforall AC signal voltage measurements and aVTVM
or 20, 000 0/volt VOM for DC voltage measurements.
If the trouble is an excessively distorted output, try tube
replacement, signal tracing, or procede directly to voltage
and resistance measurements.
When the defective stage is localized, procede to aresist-
ance and voltage check of the stage, using the data In the
VOLTAGE and RESISTANCE chart. Disconnect the ampli-
fier from the power line and discharge capacitors prior to
making any resistance check and prior to removing any or
all of the EL84 output tubes. Do not turn the amplifier or\
with any of the output tubes removed .
CHECKING ATYPICAL TUBE STAGE
1. Check tube.
2. Check plate and cathode resistor.
3. Check couf^lng capacitors for leakage or short.
4. For output stage, check dc resistance of transformer
windings.
5. Check grid leak resistor for open.
6. Check cathode by-pass capacitors for short.
7. If no or low B+ voltage on tube, check decoupling
path for open or defective R40, R41, R42 and filter capac-
itor C31 or C32.
8. If wiring and circuit components including the tube
check O.K. and B+ voltage is excessive, check the de-
coupling path for short or defective R40, R41, R42.
Suspected trouble in the equalization, tone, filter, and
volume or loudness controls and networks should lead to
specific resistance and capacitance checks to localize the
trouble. In general, if the user suspects poor frequency
response, defective equalization, or defective operation
of the tone controls or filter circuits, the amplifier should
be tested thoroughly with audio generator, vtvm, and scope.
SERVICE
If trouble developes in your instrument which you can not
remedy yourself, write to our service department listing
all possible indications that might be helpful. If desired
you may return the instrument to our factory where it will
be placed In operating condition for $9,50 plus the cost
of parts replaced due to their being damaged in the course
of construction. NOTE: Before returning this unit, be
sure all parts are securely mounted. Attach atag to the
instrument, giving your home address and the trouble with
the unit. Pack very carefully In arugged container, us-
ing sufficient packing material (cotton, shredded news-
paper, or excelsior), to make the unit completely immov-
able within the container. The original shipping carton
is satisfactory, providing the original inserts are used or
sufficient packing material inserted to keep the instru-
ment immovable. Ship by prepaid Railway Express, if
possible, to Electronic Instrument Co. ,Inc. ,33 “00 North-
ern Blvd., Long Island City 1, New York. Return ship-
ment will be made by express collect. Note that acarrier
cannot be held liable for damages in transit if packing
IN HIS OPINION, is insufficient.
