Boxoffice-November.24.1951

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etc.
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WHEN TROUBLE
STRIKES
Continued Irom preceding page
half way, now gently tap first input
tube.
This should produce a thump in
monitor, indicating trouble may be in
input circuits. When I say trouble in the
j
input circuit, I mean you may have a dead
tube, faulty connection, shorted condenser,
If your tubes light up, this does not
mean that they are always okay. A positive
check on tubes is the tube checker,
of course. A check on circuits, condensers
and resistors is an ohmmeter. Voltages
should be as recommended by the manufacturer.
Replacement parts should be
same values as recommended by the manufacturer.
SOURCE OF SPEAKER TROUBLE
In general, trouble in stage speakers or
crossover will be evident by normal signal
from monitor 07ily. If your monitor and
stage speakers are all dead, your trouble is
in your amplifier or speech line going to
the amplifier and speakers, or in the crossover.
If a separate field supply is used for
speakers, it could be in the field supply.
Generally, PM speakers don't give you
trouble. The thing to do is to try to tie the
trouble down to some specific unit in the
system. Don't try to guess, as you will
waste time. A cool head and quick thinking
is needed when trouble occurs.
On many service calls I have found the
cause of low volume, distorted, fuzzy sound
due to oil and dirty sound lenses—in some
cases, the sound lens out of focus. In
some cases where oil got in the lens barrel,
the only cure was lens replacement and the
one with oil sent in to the factory. That
is why I have always emphasized in all my
writings that projectionists keep their
mechanism and soundheads clean and as
free of oil as possible. Don't drown your
soundhead or projector with oil. After
oiling, wipe all surplus oil off with a clean
rag.
TEST TUBES EACH MONTH
Tubes should be tested regularly if you
want good, sharp sound.
It is a good idea to
test tubes once a month, and if you find
one registering poor, replace it. Keep the
tube prongs clean and bright—see that
they fit snug in the socket. Take a small
orange stick and prod gently around the
wires, with the amplifier on, and if you
hear a cracking, you know you have hit
a poor connection.
In later articles in Modern Theatre, I
will tell you how to test condensers, resistors,
etc. I might say this right here,
to check an amplifier for a bad stage,
simply start with first tube by pulling it
in and out. You will hear a clock in the
monitor if the stage is all right, if you
don't, you know you have found a dead
stage. Don't pull your rectifier tube—check
it in a tube checker first before you start
checking the others.
If you find a dead or
defective stage, check the voltage first,
then the condensers, resistors, etc., until
you find the defect. More about this in
later
articles.
(Continued on page 70
6 6.
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BOXOFFICE 69