109. General Classification.-Under this heading are included the various pieces of apparatus
used for the purpose of controlling the circuits between projectors and amplifiers on
Photophone equipments. These devices contain the necessary switches and controls for
operating exciter lamps, for changing, or "fading," sound output from one projector to the
other, and for controlling volume.
These controls come under three classifications; the control for the exciter lamp current, for
the sound output circuits from projectors to amplifier, and for volume of output.
On some equipments all of these controls are grouped together in one unit, called the input
control panel. On others the locations vary, so that the fader itself, for instance, may be in one
place, and its actuating switch in another, so that even though the apparatus described in this
chapter is closely related as to function, it is not unified as to location. However, since the
subject of circuit controls is of prime importance during the running of the show, it is important
that a complete description of the equipment used for this purpose, and its construction and
operation, be grouped together and presented as in this chapter.
The following table shows just what devices are used, together with their location on different
types of equipment:
The Class numbers are used for reference purposes only. It will be seen that there are two
quite different types of fader switches in use, whereas the other differences shown in the
table are for the most part differences of location only. All these controls, with the exception
of the relay type of fader, used on the PG-1, 2, 10 and 13, operate through the use of two
special type of resistors, the rheostat and the potentiometer.
110. Input Control Panels.-A reference to the table will show that on PG-3 and 4 equipments
all the controls mentioned are mounted on the input control panel. Types PG-6, 7 and 8 also
use an input control panel, similar in all respects to the other, except that it has no volume
control. Both types are illustrated in Figure 74. Figure 79 shows a rear view of one type.
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