This circuit is from a Radio Electronics from July 1965. The circuit uses components from the time also controlling a servo from the time. The power supply is 28 V.
This is the power supply for the amplifier in the previous circuit. We found it in the same Radio...
We found this circuit in a 1990 documentation. It is totally up to date by the components it uses...
This circuit was found in a 1970s General Electric documentation. Transistors are uncommon today....