We found this test circuit in a March 1967 Radio Electronics. The circuit uses a zener-regulated supply and analog indicator.
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....