Boxoffice-April.07.1958

I
condensers
How to Locate and Correct Trouble in Sound Systems • Part 1
FIVE MOST COMMON TROUBLEMAKERS IN SOUND
DUE TO SIMPLE CAUSES AND EASILY CORRECTED
Preventive Maintenance Is
an Important Factor for Good Results
By
'
WESLEY TROUT
*5
\JvR MAIL
brings requests for
simplified ins:
ructions on servicing
leading makes of
theatre sound systems.
In view of the
fact that many theatres
do not liave regular
sound service, we
present some instructions
on general
Wesley Trout
maintenance which
should prove helpful in better operation
and better quality in sound reproduction,
moreover, it will help you locate components
which may cause trouble.
TECHNICAL TERMS AVOIDED
We have dispensed with too highly technical
terms that might prove more confusing
than helpful. In most any technical
discussion, some technical terms are necessary,
of course.
Let us start off by pointing out that when
sound trouble does develop, some defect in
the circuit, such as a resistor, condenser,
transformer or choke has become defective
and not the entire circuit or components.
Pin your trouble down, if possible, by observation
of various parts. If a short has
developed, smell to see if some component
has burned out. or if there is a short somewhere,
etc. Keep a cool head but work as
swiftly as possible. When checking for
trouble, the use of a multimeter cannot be
beat. !7i most cases. An elaborate array of
electronic equipment is not always necessary
to find and correct trouble in the
sound system. However, when tuning up a
sound system, some special equipment is
necessary.
SHOULD STUDY EQUIPMENT
We do want to emphasize the importance
of making a very careful study of your
complete sound system—a complete understanding
of the function of each unit and
its location. All manufacturers supply some
instructions on operating and maintenance
of their equipment, but seldom is this infonnation
complete enough for good maintenance
of any equipment. One needs to
know the correct voltages necessary at the
tube elements, the values of resistors, condensers,
etc., in order to do a tip-top job
of maintenance. You must have a schematic
of the amplifiers, either from the
manufacturer or draw one, but the latter
is quite a task. Most leading manufacturers Checking some of our inspection sheets,
will furnish schematics free.
over a period of years, we find the second
While there is an almost infinite variety troublemakers on our list are capacitors
of things that can go wrong with electromechanical
equipment as complex as a greater amount of failures than any other
Capacitors account for a
I .
modern theatre sound system, the great component. There are some amplifiers using
plug-in capacitors, but in most cases
majority, we have found from experience,
are troubles due to simple causes, and can they are soldered in. A capacitor can be
be just as simply corrected once located. A checked with an ohmmeter, but one end of
working knowledge of your equipment is a it must be unsoldered. For testing condensers
or resistors in the circuit, there is
"must." Understand the function of each
part: namely, resistors, condensers, chokes available a checker in kit form or factorywired.
R-om radio supply houses they can
and transformers. Check each component
by using your schematic or parts catalog. be purchased from $20 up. However, for
the projection room, usually a
Our many good ohmmeter
will suffice.
years of experience in the field
of servicing have shown that more troubles
involve failures in vacuum tubes than any
of the other components, the exception
OTHER TROUBLE CAUSES
being
condensers. That is the reason tubes The other components that may cause
still remain in the plug-in class for quick trouble are resistors, chokes and transformers.
In order to check a resistor, it
replacement. Good sound reproduction,
sufficient power, depend upon tubes in will be necessary to unfasten one end. Resistors
are very important in securing the
first-class condition, and they should be a
well-known brand for long service. Moreover,
tubes must fit snugly in their sockets plifier, in conjunction with capacitors and
correct voltages and operation of your am-
and the prongs be kept clean for good contact.
elements are absolutely necessary if the
transformers. Correct voltages at the tube
amplifier is to function efficiently. Always
use exact duplicate when replacing resistors
or capacitors.
We can honestly say the above five classifications
include the large percentage of
amplifier components which may cause
trouble, and we have listed them in their
importance. These components are important
in the proper operation of the amplifier
or amplifiers, likewise important in
good quality sound reproduction in any
make or type of sound equipment.
These components are generally rated
far above lin voltage safety) capacity then
absolutely necessary, but this is a safety
Most 0/ the leading makes of amplHiers have meter precaution. Sometimes a condenser requires
a peak voltage capacity of only 500,
or meters for check'mg tubes and operation of the
push-pull stage. A continuous check on the functioning
of the push-pull output stage is afforded
but generally it is 600-volt i>eak capacity.
by the front panel plate milliameter and associated
ANOTHER SOURCE OF TROUBLE
buttons or suitable switching arrangement as shown
above. This gives the projectionist a good check One frequent source of trouble is electrolytic
capacitors. All manufacturers try to
on the tubes. Simplex equipment has a meter for
checking all the tubes by indicating the condition eliminate any defects in their manufacture,
but occasionally you get one that is
of the tube when the meter pointer is in a certain
"block"—green and red blocks. Instructions are
defective, or will give very short service.
sent on the correct usage of the tube check. Motiogroph,
and some of the other leading equipment Always purchase capacitors, particularly
indicate operation with a milliameter, using buttons
and rotating switch. A meter on amplifiers brand. There are a number of cheap elec-
those in critical circuits, of well-known
gives the projectionist a daily check on his equipment
and its functioning. A check on the output
trolytic capacitors on the market that give
inferior performance and short service, if
stage is very important and most meters will show
they are overloaded. Of course, one should
how nearly "matched" the output tubes are. In
push-pull stages, output tubes should be purchase the correct capacity when making
carefully
matched for maximum performance.— Ampex photo. replacements so that it will not be over
42 The MODERN THEATRE SECTION