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 resistor	C1 = Input (coupling, blocking) condenser
R2 = Cathode resistor	C2 = C-bias (cathode) bypass condenser
R3 = Screen resistor	C3 = Screen bypass condenser
R4 = Plate resistor	C4 = Plate bypass condenser
R5 = Plate decoupling resistor	C5 = 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.