The Resistance-Coupled Amplifier

The routine problems of resistance-coupled amplifier design have been simplified and reduced to a set of graphs and convenient conversion charts. In the first section it is shown that the coupling circuit (Figure 1) can be replaced by a pair of equivalent resistance-capacitance circuits (Figure 3) so that it is easy to calculate an amplifier´s phase and amplitude-frequency characteristics. The design of a coupling circuit to give a specified band width and an acceptable loss has been simplified by the construction of curves of constant band width and peak-frequency loss (Figures 6, 7, 8). In the second section a method and charts (Fugures 9, 10) are presented for determining without the use of static characteristic curves a suitable operating point, electrode voltages, and plate or screen resistors for any vacuum tube operated class A. As the method given results in the tube being operated with proportionally reduced electrode voltages, its dynamic constants can be extrapolated from values furnished by the manufacturer. Charts facilitating the extrapolation are given (Figures 9, 11, 12, 13). A simple transconductance meter for measuring the mutual conductance and circuit transconductance (equation 24) of a tube operated with an external plate resistor is described in the final section. The gain of the tube and the equivalent plate-circuit resistance can be calculated easily from these two measurements. The dynamic constants ?? and r?? can be obtained also with an accuracy sufficient for most practical purposes.