CHAPTER XIII
RCA PHOTOPHONE EQUIPMENTS
164. Introduction. -An RCA Photophone equipment consists of sound head attachments for the
projectors, voltage amplifiers, power amplifiers, loudspeakers, voltage supply and control apparatus.
Synchronous disc attachments (turntables) are supplied with most of these equipments.
The separate units used, except the compensator panels which are described below, have been
described in the previous chapters. The purpose of this chapter is to enumerate and describe the
arrangement of the units used, to discuss their inter-relation, and to give operating instructions for the
amplifier equipment.
For convenience of discussion this chapter is divided into three parts. The first part will take up the PG-1 and PG-2 equipments, which are motor-generator operated. The second part takes up the PG-3, 4, 6, 7,
8 and 10 equipments, which are partially socket power operated. The third part describes the PG-13, a
small theatre equipment using a motor-generator set.
165. Compensator Panels. -Due to the number of recording systems in use and the number of different
producers using each system with the consequent differences in recording methods, wide variations in
the quality of recording occur. In order to equalize the reproductions of sound from recordings made by
different producers, some adjustment is necessary when the sound is reproduced.
This adjustment is termed "compensation" and is made by means of a "compensator" control knob on
the amplifier rack.
The control knob is used to compensate for the ill effects of poor recording. It has been pointed out in
Chapter I that the proper reproduction of the human voice requires the presence of the higher
frequencies much more than that of the lower frequencies. If the recording was not properly done and
some of the higher frequencies were not sufficiently recorded, or if the lower frequencies were
over-recorded, the blurred effect in the reproduction which results may often be eliminated by turning
the control knob counter-clockwise to strengthen the effect of the high frequencies by reducing the
amount of low frequencies present. Music, on the other hand, requires the presence of all frequencies
for its proper reproduction, and may often be improved by turning the control knob clockwise to
increase the amount of low frequencies present.
If the recording was properly done, however, constant manipulation of the compensator knob is
unnecessary, and its normal setting is at the point of best reproduction of the average picture.
1
