Some Simple Amplifiers

Author: J.B. Hoag

A small input voltage, applied between the grid and filament of a triode, proves to be very effective in controlling the flow of current from a local battery in the plate circuit. Grid voltage changes are μ times as effective in changing the plate current as plate voltage changes, as explained in the preceding chapter. A triode, by itself, has a voltage gain of μ. But, in practical operation, it is necessary to use certain input and'output circuits in conjunction with the tube. The overall voltage amplification of the tube and its circuits is sometimes less and sometimes more than that of the tube alone.

Fig. 13 A. A simple resistance-capacitance-coupled single-stage triode amplifier

The stage-gain of the resistance-capacitance (R-C) coupled amplifier of Fig. 13 A is always less than μ, whereas that of the transformer-coupled amplifier of Fig. 13 B may be greater or may be less than μ. according to the step-up or step-down ratios of the transformers.

FiG. 13 B. A simple transformer-coupled single-stage triode amplifier