Found in a 1967 documentation this circuit can be applied to any operational amplifier. Components without values determine the frequency to which the circuit is tuned.
This interesting adjustable power supply uses the transistors themselves as controllers and...
This alarm from an old 1978 publication uses PNP transistors and driver and output transformers that are...
This is a typical source of the time (1989) using the well-known regulator integrated circuit 723....