DECEMBER

j
SERVICING
AMPLIFIERS
I
S8IIPKK SKAPLITB
Continued from preceding page
in wattage carrying capacity, and becomes
carbonized, its resistance decreases in
value. If such decrease is very large it will
effect the operation of your amplifier.
w.
when you use
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Manufacturers of Many Types of
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Head
RESISTANCE CAPACITY
In most all modern amplifiers manufacturers
use very heavy duty resistors with
sufficient carrying capacity to prevent overheating.
Remember this: the smaller diameter,
the greater the resistance of a
resistor, and, naturally, the shorter the
resistor, the less resistance it will have.
Some times, in emergency cases, where the
resistor value is incorrect, you can raise the
resistance value by scraping a little of the
carbon from the body until the correct
value is obtained from the unit, but it is
not recommended for a permanent repair.
I have repaired wire-wound resistors, if
the wire near one end of the terminal was
broken. Simply remove the clamp, remove
a few turns of wire and carefully clean with
fine sandpaper, rewind carefully these few
turns of wire, replace the clamp over the
,
cleaned wire, and tighten clamp firmly so
it will make good contact. Don't try to re- I
pair wire-wound resistors if the break is in
the center as you cannot solder such a
break and secure satisfactory results. The
best procedure is to always replace resistors i
which have become defective with new ones
— exactly the same value and type as recommended
by the manufacturer.
CHECK CLAMPS FOR POOR CONTACT
In quite a few cases, when checking am-
I
plifiers, I have discovered that the terminal
clamps of wire-wound resistors had loosened
up, thereby causing poor contact, noise
and maybe an open circuit. Let me point
out here that loose connections or loose terminal
clamps making poor contact will
cause intermittent contact, and such poor
contacts will set up considerable trouble]
in any circuit. The remedy is to try toj
squeeze the clamp together so it will make'
good contact, but if the clamp cannot be
made to make a firm fit around the wire,;
immediately replace with a new one.
Grounds are often caused by clamps
touching the mounting bracket or chassis.
The cure for this trouble is to use a good
insulation material, such as fiber or a fiber
washer, which will prevent the clamp from
making contact. A good brand, with sufficient
carrying capacity, wire-wound resistor
seldom gives much trouble, but it
must be mounted firmly with all the clamps
electrically firm.
Let me emphasize here that emergency
repairs recommended in this department,
on sound equipment, are to be used in isolated
cases when a new part cannot be had
immediately, but the show must go on and
a repair must be made at once. Emergency
repair advices given herein are only those
that have been tried in practice and found
satisfactory. If you have to patch up a part
to keep your equipment operating, it Is
the only way out many times, but my advice
32
The MODERN THEATRE SECTION
f