The circuit shown was found in an American documentation from 1964. The circuit uses transistors of the time and the indicators are small lamps.
This circuit was found in a 1967 EEE. The transistors are from the time and can be tested...
With this circuit it is possible to obtain a higher voltage from a zener diode. The circuit is from...
This circuit for the experimenter of the 60s allowed testing the most common transistors in the...