This circuit was found in an 80's General Electric documentation. The circuit uses uncommon components today like the PUT. Unijunction admits equivalent.
Using the name of varactor this circuit was found in the Radio Electronics magazine of July 1982....
We found this circuit in a 1960 Radioarama magazine. The instrument tests common general-purpose transistors...
This circuit uses an RCA module from the time. The circuit is from a Radio Electronics magazine from...