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Phase Reversal

Author: J.B. Hoag

Suppose that, for a moment, the input signal should make the grid of tube 1 in Fig. 13 G less negative than its static value. Then the plate current would increase and the potential drop across R would increase. The steady-state value was such as to make the top of R negative. Hence an increase in current makes this end still more negative. This change of voltage, feeding through the condenser Cg to the grid of tube 2, will be negative at the upper terminal (with respect to the filament), the reverse of the positive voltage fed onto the grid of tube 1. In other words, there is a 180° phase reversal in each stage of an R-C coupled amplifier.

Fig. 13 G. Resistance-capacitance coupling

Last Update: 2009-11-01