Wide-Band D-C Amplifier Stabilized for Gain and for Zero

Previous technical literature has described direct-coupled d-c amplifiers having a wide frequency pass band but with appreciable zero drift,^1,2 and also has described contact-modulated d-c amplifiers having a relatively stable zero but with a narrow pass band.³ This paper describes an arrangement of a direct-coupled amplifier together with a contact-modulated amplifier. This arrangement retains the wide band of the former and the zero stability of the latter. Block diagrams are used for explanation, and schematic circuits are given for an experimental setup. Records from a fast recorder and from an oscillograph disclose the results achieved, such as rapid response to a step input and greatly reduced, nonpermanent output disturbances following large, unbalanced changes of heater voltage.