Halfwave bridge-type magnetic servoamplifiers, which have been widely used for instrumentation and control problems, have been improved by adding biased rectifiers in the control circuit. It has been shown that such amplifiers give higher gain than the conventional type of halfwave amplifier and maintain the large input impedance required by the synchrocontrol transformer output.The paper gives a systematic mathematical analysis of d.c. and fundamental-frequency gain of halfwave magnetic servoamplifiers with biased-rectifier control, considering resistive and capacitive loads. Graphical illustrations have been added to mathematical analysis wherever necessary. The result of the analysis shows good correspondence with experimental values.