(B) RCA PHOTOPHONE AMPLIFIERS

136. Voltage Amplifiers Used in PG-1 and PG-2 Equipments. - In Types PG-1 and PG-2 equipments the output of the projector circuits (photo-cell or magnetic pick-up) are transformer coupled to the grid of a UX-210 amplifier Radiotron. The plate circuit of this tube is transformer coupled to a UX-841 Radiotron, which has practically the same power capacity as the UX-210 but a much greater voltage amplifying ability. The characteristic of the tube which gives it its great voltage amplification also gives rise to another characteristic which renders it necessary to use either resistance or impedance coupling to the succeeding stage. In the voltage amplifier here described, the plate circuit of the UX-841 is resistance coupled into the grid circuit of another UX-210 Radiotron. The output of this tube is impedance coupled to the input transformer of the power amplifier.

Volume control is effected, in the case of the PG-1 voltage amplifier, by controlling the input to the UX841 Radiotron. In the case of the PG-2 voltage amplifier, volume control is effected by controlling the input to the second UX-210 Radiotron. All plate and filament voltages are supplied from the four unit motor-generator set described in section 36. Small dry batteries provide the necessary grid voltage.

The amplifier panels are provided with meters for reading current through the various circuits and the voltages across them. The use of the meters will be taken up in a later chapter on the operation of the equipment.

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