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i84 SOUND MOTION PICTURES
cloth, such as linen saturated with carbon-tetrachloride. It is best to turn the machine by hand while doing this.
B. Optical System
Two special io-volt, 5-ampere prefocussed lamps are used in each optical system. Before each show these lamps should be inspected. Any one that shows evidence of a sagging filament or discolouration should be replaced with a new one. Both lamps must be checked, since one of these is a spare to be thrown into position should the other fail. Do not replace an old lamp while still hot, since the hot lamp may loosen the bulb. With the lamp in good condition a clear image of the main section of the lamp filament should be seen on a white card held vertically in the hollow of the drum in the sound head.
To compensate for difference in volume between the two projectors run the same short test reel of sound film through each projector. With the amplifier in normal operating condition adjust the lamp current (1LAX1 or 1LBX1) of each projector so that the output voltage of the amplifier, as measured on the meter marked "Special Current," is the same when either machine is run.
The lamp current for each optical system is dependent upon the sensitivity of the photo-cell for the particular machine and should be between the limits of 4.8 to 5.25 amperes. If the difference in volume cannot be adjusted make a compensation test, as described, with spare photo-cells, matching the volume of different combinations of cells.
C. Amplifier
Start the amplifier, using the procedure given under "Operation-Amplifier Preparation, " and check the meter readings with those given in the Meter Reading Table.
D. Loudspeakers The daily check may be obtained in the following manner: With the amplifier in normal operating condition, with all switches on the sectionalizing panel in "Off"