Found in an Electronics World of 1966, this circuit makes use of FETs of the time. Modern equivalents can be used. The high voltage supply suggests its use with tube amplifiers.
Agostgo 2016 - Mouser Electronics is already providing the new TPS3890 voltage supervisors from...
This configuration can be applied to other operational amplifiers to increase the current...
This PWM control circuit was found in an old documentation, but appears elsewhere on this site...