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The Resistance-Capacitance-Coupled Amplifier

Author: E.E. Kimberly

If the amplifier circuit of Fig. 27-13 is to be used to excite the grid of a succeeding stage of amplification as indicated, a condenser C must be interposed to prevent flow of positive current to that grid from Ebb. To be certain that the grid of the succeeding stage remains negative, a grid leak resistor RI arid a negative bias voltage Ec must be added. The ratio of the grid voltage of the succeeding stage to the grid voltage on the tube shown in Fig. 27-13 is


The ratio Ka is the amplification factor of the tube and circuit and it obviously can never be quite so large as μ. It is important therefore that a tube having high μ be used in this type of circuit.

This type of amplifier has the merit that the coupling is independent of frequency as long as the condenser reactance is not so high as to be comparable with R1. If it is comparably great, the remaining voltage across R1 that is available to the following grid will be noticeably reduced below that across RL. At very high frequencies the grid-to-filament capacitance will provide a reactance that is small compared to R1 and the amplification factor will be reduced because the alternating-current plate circuit impedance is reduced.

Last Update: 2010-10-06