This 1-transistor circuit for currents up to 50 mA was found in the August 1974 Radio Electronics magazine. The transformer is 50 to 200 mA.
This circuit makes use of older operational amplifiers, but can be designed on the basis of modern...
Equivalent operational amplifiers can be used in this circuit of the 1990 Linear Databook,...
This switched, switched or PWM amplifier was obtained in the 1972 RCA linear integrated circuit...