maintenance
TROUBLE-SHOOTING PROCEDURES
Your amplifier should require little service except for
normal tube replacement. We recommend no substitutions
for the tube types used in this amplifier. The EL34 type
is distributed national ly by the Amperex Electronic Corp-
oration (230 Duffy Ave. ,Hicksville, L. I., N.Y. )and
Mullard Ltd. (International Electronics Corp. ,81 Spring
St., N.Y. 12, N.Y.) If necessary, replacements at any
time can be obtained directly from EICO.
To facilitate servicing, remedial and trouble-shooting
procedures have been provided in the TROUBLE-SHOOT-
ING CHART that follows. AVOLTAGE AND RESIST-
ANCE CHART is also provided as an aid in locating de-
fective components and to permit acareful, stage-by-
stage check of the amplifier. DC operating voltages are
given both at no signal and at asignal developing 35
watts output as well as the corresponding lkc signal volt-
ages.
To isolate the source of unusual hum or noise in your sys-
tem, first turnoff the AC power and then unplug the audio
cable connecting to the amplifier input. Then turn the AC
power on again and note whether hum or noise has de-
creased. If it has, the fault is in the preamplifier or
associated equipment and measures should be taken to
correct it as described in the service notes for these units.
If it is desired to provide agood building ground for your
entire system, run alead from under either speaker con-
nection terminal "G" to acold water pipe. Do notcon-
nectsucha ground wire to other components in the system.
If the trouble is no output or low output and the amplifier
is suspected, check AC signal voltages starting at the in-
put and work step-by-step toward the output, using a
sine-wave audio signal generator and aVTVM. Set the
inputsignal to.38volt. The corresponding grid and plate
signal voltages for this input are indicated on the voltage
chart. Repeat for the second channel. This procedure
should suffice to localize the defective stage.
If the trouble is an excessively distorted output, try tube
replacement, signal tracing, or proceed directlyto volt-
age and resistance measurements.
When the defective stage is localized, proceed to are-
sistance and voltage check of the stage, using the data
in the Voltage and Resistance chart. Disconnect the am-
plifierfromthe power line and discharge capacitors prior
to making any resistance check or removing the EL34out-
put tubes. Do not turn the amplifier on with any of the
output tubes removed. ~~ —— -—
CHECKING ATYPICAL TUBE STAGE
1. Check tube.
2. Check plate and cathode resistors.
3. Check coupling capacitors for leakage or short.
4. For output stage, check dc resistance of transformer
windings.
5. Check for open grid leak resistor.
6. Check cathode by-pass capacitors for short.
7. If no or lowB+ voltage on the tube, check decoupling
path for open or defectiveR31, R32or R35, filter capac-
itors C15, C16, C17 or C19, for short, or defective rec-
tifiers CR1 or CR2.
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 R31, R32 or R35.
SERVICE
If trouble develops in your instrument which you can not
remedy yourself, write to our service department listing
all possible indicationsthatmightbehelpful. Note num-
ber appearing in red under the word “Manual" on the front
cover. If there is no number, state this. If desired, you
may return the instrument to our factory where it will be
placed in operating condition for $8. 00 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, using
sufficient packing material (cotton, shredded newspaper,
or excelsior), to make the unit completely immovable
within the container. The original shipping carton is sat-
isfactory, providing the original inserts are usedor suffi-
cient packing material is inserted to keep the instrument
immovable. Shipby prepaid Rai Iway Express, if possible,
to Electronic Instrument Co. ,Inc., 33-00 Northern BIvd.
,
Long Is land City 1, N.Y. Return shipment will be made
by express collect. Note that acarrier cannot be held
liable for damages in transit if packing IN HIS OPINION,
is insufficient.
TRANSFORMER TEMPERATURE
The temperature of the trensformers used in theHF-87 run at less than 195°F despite the fact
that the safety limit is ata much higher 221°F. Although 195°F is cool for atransformer, it
is very hot to the touch. Transformers which seem too hot when touched with the hand, are
usually good aid are actually not overheating.
Output transformers usually run cooler than power transformers. Some output transformers
may appear hotter than others due to being located near hot components such as output and
power tubes and power transformers.
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