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Modulation of a Pentode Amplifier

Author: J.B. Hoag

Pentode and beam-tetrode tubes can be used in a Class C plate-modulated amplifier if the audio frequency modulation voltage is applied in series with both the plate and screen grids, as in Fig. 28 C.

Fig. 28 C. Plate and screen modulation of a pentode amplifier

Here, the value of the resistor R is chosen in the usual way so as to establish the screen grid at its normal d.c. voltage. In computing the power input to the amplifiers, use the sum of the d.c. screen and plate currents. The plate and screen-grid bypass condensers C1 and C2 (0.002 μfd. or less) must both have high reactance for audio frequencies to provide both tube safety and good modulation.

Last Update: 2009-11-01