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R-C Coupled Amplifiers

Author: J.B. Hoag

The principle of operation of the resistance-capacitance coupled amplifier was discussed in Sec. 13.5. These amplifiers are characterized:

  1. by being relatively inexpensive,

  2. by good fidelity over comparatively wide frequency ranges,

  3. by freedom from picking up undesired currents from the a.c. heater leads (since there are no coils to pick them up).

  4. They are especially suited to pentode and high-μ triodes.

A typical circuit is shown in Fig. 25 A, together with the names of the various parts.

Fig. 25 A. A typical resistance capacitance coupled amplifier

R1 = Grid resistorC1 = Input (coupling, blocking) condenser
R2 = Cathode resistorC2 = C-bias (cathode) bypass condenser
R3 = Screen resistorC3 = Screen bypass condenser
R4 = Plate resistorC4 = Plate bypass condenser
R5 = Plate decoupling resistorC5 = Output coupling condenser
R6 = Second stage grid resistor

Let us first trace the various circuits. The d.c. grid circuit is G, R1 R2, K. The a.c. grid circuit is G, R1, C2, K. The d.c. screen circuit is Sc, R3 R5, B-Bat., Grd., R2, K. The a.c. screen circuit is Sc, C3, C2, K. The d.c. plate circuit is P1, R4, R5, B-Bat., Grd., R2, K. The a.c. plate circuit is P, R4, C4, Grd., C2, K.

Last Update: 2010-11-27