Found in an Electronics World of 1966, this circuit makes use of FETs of the time. Modern equivalents can be used. The high voltage supply suggests its use with tube amplifiers.
This interesting circuit for testing NPN and PNP transistors for general use and medium power was...
We found this circuit in a 1986 documentation. It uses only LEDs, batteries, resistors and the...
Published in Radio Electronics in January 1963, this circuit uses 5 transistors of the time. The...