This circuit produces a pulse when the voltage in the regulator exceeds a certain value depending on the components. PUT is not a common component today. The circuit is from a 1970 EEE.
The operational amplifier used in this circuit is uncommon today, but the configuration can be...
This power stage with two transistors was found in Radio Electronics magazine from October 1963....
Suitable for operation with high impedance microphones, this circuit was found in American...