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CHAPTER IX

INPUT CONTROLS

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:

Type No.
(New)
Type No.
(Old)
Type of
Fader
Location of
Class
No.
Fader
Control
Volume
Control
Exciter Lamp
Rheostat
PG 1 & 2
A&B (MG)
Relay
Projector
Amplifier
Amplifier
I
PG 3 & 4
C & D
Potentio-
meter
Input Con-
trol Panel
Input Con-
trol Panel
Input Con-
trol Panel
II
PG 6, 7, 8
B (SPU)
C-1, D-1
Potentio-
meter
Input Con-
trol Panel
Amplifier
Input Con-
trol Panel
III
PG 10 & 13
F & G
Relay
Projector
Amplifier
Projector
IV

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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