DECEMBER

PROJEQION AND SOUND
00
Easy-To-Foliow
Directions
For Servicing Amplifiers
by WESLEY TROUT
%m KT S TAKE UP
in this issue, and the
next several issues of
Modern Theatre,
step-by-step simplified
amplifier servicing
data. Audio amplifiers
are not so
complex that you will
have a hard time understanding
the cir-
(.u.:^ \\'c will ^t.ut with an amplifier circuit
using not so many tube elements and
advance, later, into more complex circuits
of the modern theatre amplifier. With a
little study of text books on the subject,
such as radio and audio amplifiers servicing,
and data that will be presented in this
department, I am sure you will obtain a
good working knowledge of theatre sound
systems.
KEEP COOL AND THINK
Trouble-shooting requires ordinary Intelligent
thinking, keeping cool and working
systematically. A thorough understanding
of his equipment is a "must" for every
projectionist desiring knowledge on general
maintenance of sound and projection
equipment. A competent projectionist, in
my opinion, is one mentally alert, eager to
learn more about good sound and projection,
how to service such equipment. Regardless
of whether the theatre has sound
service or not—he must be prepared for
trouble and know fairly well what to do!
If sound goes off suddenly or volume suddenly
decreases, there is not too much time
for prolonged reflection—the show must go
on as quickly as possible. Don't entirely
depend on your service engineer for many
minor troubles, because he may be several
hundred miles from your city and it would
take time to get there. If you have a fair
knowledge of servicing sound and still can't
clear the trouble up completely, you can
'phone him, and he will tell you what the
cause may be. You can, by acquiring servicing
knowledge in this department and
text books, more intelligently understand
his instructions and quickly clear up the
trouble.
GOOD TEST INSTRUMENTS IMPORTANT
The modern theatre amplifier is ruggedly
buUt, contains components well constructed,
having plenty of capacity to carry
voltages, etc. It is a very fine, delicate
piece of equipment. Don't use cheap test
instruments for trouble shooting—they are
practically useless for checking circuits as
most of them draw too much current. Buy
your equipment from a reliable source so
it will give dependable service and true
readings. Indispensable Is a good, high Internul-resl.stance,
multlple-ranKe, combination
voltmeter-miUlammcler; next hlKh
quality, high-resistance hciidi)honps. If you
don't have the nece.s.sary equipment for
checklnR circuits, it may take you hours to
find an open or short, defective condenser,
resistor or choke. Good voltmeter is absolutely
necessary for checking your power
supply. Power supply and tubes should
always be checked first! A good tube checker
is of paramount importance in any projection
room.
USE
HIGHEST RANGE
Next In importance is to take care of this
equipment so it wlU always be ready for
instant use. Always use the highest range
on meter, if you don't know how high the
voltage is in the circuit you are testing
it will be safer and avoid damaging your
Instrument.
An output meter is very useful for testing
focus of sound lens and running transmission
tests. The unit of power output of
: •
•: ."' Ut-clbeh or
uay umpiiticr i.-> in' >
watLn, but engine*-! li-clxb a.s the
more convfiilenl unit for .vjund m'-a^urfmi-nl-H
Moat muHl-ranKi- voltmi-t'r.\ have
drclUU on the scale. U th«y mrt quality
Instruments.
A reel of good musical recording Is excellent
for testing the system, from time to
time, for quality reproduction, a general
check on all frequencies. A number of sixfoot
test loops for checking sound lens
focus, lateral guide adjustment and a
•buzz" track loop. A few good frequency
test records are excellent, but I favor a
reel with various lest frequencies to the
records, I find pluno recordings best for
checklns flutter in a sound head.
SERVICING AUDIO AMPLIFIERS
It generally doe.s not pay to try to repair
resistors as they are inexpensive and
not worth the time expended—such repairs
should only be made for emergency purposes.
Molded-carbon and metallized fixed
resistors should be replaced with new ones
when they become defective as they can
seldom be repaired to give permanent service.
Some times carbon resistors, if overheated
for a long period of time, become
carbonized, and they should be replaced
immediately with a new resistor of similar
resistance but with a much higher wattage
rating, so it will not overheat. Bear in mind
when such component Is not heavy enough
POWERSTAT
PROVIDE
BIG
TIME
LIGHTING CONTROL
ON A SMALL T
IPS
Modtm light dimming wjuipmtnt n»«d not b«
•xp«niiv«. Thi» wo» conclujivtiv d«monitrat«d
by Lawr«nc« Voii, a m«mber ot th» faculty
ot Southern Illinois Univtrjity, wh«n h« built
o 25,000 watt, pr«s«t, proporiional dimming,
completely flexible, portable switchboard ot o
moterioli cost of opproximotely $1,200. Ma>t«f
dimming is achieved by foyr 5,000 watt
POWERSTAT Dimmers. The flexibility, th« consistent
performance, the unusual economy of
POWERSTAT Dimming Equipment put big lime
ghting control within lh» reach of very
mited budgets.
Write for the complet* tloryj tofl«»h»f ¥Hth
pictures and drowingt, of In* iwitchbeord
built by Mr. Voss.
2/22 DfMfRS AVENUE, BRISTOL. CONN
m SUPERIOR ELECTRIC co.
Continued on tollowing page
BOXOFnCE December 8, 1863 31
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