An analysis is presented of a 3-phase magnetic amplifier with bridge-connected output circuit and any number of series-connected and parallel-connected control windings. Approximate output difference equations are derived for two modes of operation representing one-half to minimum output and one-half to full output. These output difference equations express the dynamic relationship of the sixth-cycle average input and outputvoltages in terms of a core function and the control circuit resistances. The importance of a feedback factor associated with the fraction of the voltage from a gating core which appears across the cores in a position to be reset is demonstrated. Approximate gain and time constant expressions appropriate for a simplified dynamic representation are derived from the difference equations and a more complicated block diagram representation.