Differential-feedback magnetic amplifiers

In push-pull TYPE magnetic amplifiers with two single-ended external-feedback or self-saturating circuits in back-to-back connection, each of these circuits has its own positive-feedback component which reduces or nearly nullifies the intrinsic negative feedback of the ordinary saturable reactor (transductor). As a result of this fact, the individual quiescent currents of these circuits vary considerably with large changes in supply voltage, frequency, and ambient temperature. Therefore, the characteristics of the magnetic-core and rectifier elements have to be carefully matched over a large part of the working range to avoid excessive asymmetry zero-drift errors. This necessity becomes particularly important in low-level d-c signal applications in the realm of instrumentation, control engineering, and analog computer technique.