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CHECKING A
TYPICAL TUBE STAGE
1. Check
tube.
2. Check
plate and cathode resistor.
3. Check
coupl ing 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 R60,
R61, R62, R63 and fiI ter
capacitor C37, C38 or C39.
8. . If wiring and circuit components including the tube
check O. K. and B+
voltage is excessive)' check the de-
coupl ing path for short or
defective R60, R61,
R62and R63.
Suspected trouble in the
equalization)' tone, focus, and
volume controls and networks should lead to specific
re-
sistance and capacitance checks to localize the trouble.
In general, if the user
suspects poor frequency response,
defective equal
ization)' or defective operation of the tone
controls, the amplifier should be tested thoroughly
with
audio generator, vtvm, and scope.
SPEAKER PHASING
IMPORTANT NOTE ON
SPEAKER PHASING: The two
loudspeaker systems must be
connected so that they operate.
in phase, meaning that corresponding cones or diaphragms
in the systems move in and out together when
actuated by
the same or similar signals. A simple method of checking
this is to
playa
conventional monophonic (lateral)
record-
ing having considerable bass program material, setting the
FUNCTION SELECTOR
at MONAURAL. After listening
for a few minutes, reverse the connections of the speaker
leads at only one of the speaker
systems
- not both
- and
listen again to the same
program material. Normally, you
wi II noti ce that one of
these connections seems to give
bass re-
inforcement and the other bass cancellation. The
connection that gives bass re- inforcement is the in-
phase
connection and should be used.
Another criterion for the in-
phase connection is that of
blending, which can be best applied if the speaker systems
are identical or at
least have similar middle
and high
frequency range
reproducers. With the in-
phase con-
nection and both speakers operating at approximately the
same volume level, a monophonic
source will appear to be
emanating from a point mid-
way between and the two
speakers will blend. With the out-of-
phase connection,
the two sources will appear to remain separate.
SERVICE
If trouble developes in your instrument which
you can;.,t
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 wi
be placed in operating condition for $12.
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 a tag to the
instrument, giving your home address and the trouble with
the unit. Pack very carefully in a rugged
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 I,
New York.
Return ship-
mentwill be made byexpress collect. Note that a
carrier
cannot be held liable for damages in transit if packing
IN HIS OPINION)' is insufficient.
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Troubleshooting
