A Stable d.c. Amplifier Using 7567A Tubes

Abstract
Two single‐tube d.c. amplifiers with 7567A tubes have been constructed which are extremely stable in operation. Following the design of DuBridge and Brown, a modified balanced bridge circuit is described wherein the drifts are not due to fluctuations in battery potentials or changes in filament emission. Data on the determination of circuit constants necessary for the elimination of drifts are given. Currents of 3×10−15 ampere give galvanometer deflections of one cm and readings can be obtained every 15 seconds.

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