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The widespread use of the saturable-core transformer as a push-pull magnetic amplifier in servomechanism systems is well known. This amplifier is analyzed by the methods of Storm1 to obtain the basic performance equations and to gain a broad insight into the circuit operation. The analysis is predicated on the free flow of even harmonics, that is, low control-circuit impedance, and deals with the resistive load case. Under these conditions two modes of operation are found; further, the influence of core loss and primary resistance on gain becomes apparent. From this analysis ideal graphs are prepared which show the nature of circuit operation for changes in signal, line voltage, frequency, and loading. The resulting expressions for gain, together with the boundaries of circuit operation, form a useful background in component design, quality control, and system analysis.