A two-stage direct-coupled amplifier circuit with negative feedback which can be used for measuring small direct currents is described. The circuit details are given for a multi-range micromicroammeter which is compact and stable and operates from a.c. power. Through reduction of grid current in the input tube, which is a standard receiving type, it is possible to realize a high sensitivity approaching that of amplifiers using special electrometer tubes.
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Shepard Roberts (1939) studied this question.
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