A Veritable Almanac!
This tester requires a digital multimeter to check the d.c. gain of transistors. The dial is adjusted till the D.M.M. reads 2 volts. The gain of the transistor is then indicated on the scale.
The original circuit is from a book edited by Wayne Green - "Solid State Projects for the Experimenter"
This circuit is ok for testing old Germanium transistors where the gain rarely exceeds 150 and there was a significant possibility of leakage.
In case of difficulties in obtaining the 150k lin pot, some possible alternatives:-
Use (1) 1M lin pot with a 3k3 emitter resistor RE - gain will be tested at Ic = 0.6 mA instead of 4mA.
or (2) 100k lin pot with a 330R emitter resistor RE - gain will be tested at Ic = 6mA instead of 4mA.
***Note! The value of Ic can affect the current gain of a transistor significantly***