Behavior of a Balanced D.C. Amplifier

Abstract

A study of the Barth balanced circuit employing the FP‐54 electrometer tube disclosed several new properties of the circuit. (1) The value of the filament current at which a balance is obtained usually shifts when the potential of the control grid is changed, thus throwing the circuit out of balance. This shift may be eliminated by suitable adjustments of the circuit resistances. (2) A balance usually exists at two or more values of the filament current, and these may be moved together by adjusting the circuit resistances so as to form a broad plateau. (3) Tubes with low plate current were difficult to balance until after their plate current was increased by ``flashing.'' The new balance, necessitating changes in circuit resistances, resulted in an increased range of balance.