Two Range Transistor Tester


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Two Range Transistor Tester

The original transistor tester from Wayne Green’s book was a very cheap and useful means of checking germanium transistors that were around in the sixties and seventies. The original circuit could still have a use for checking old germanium transistors that are intended for use in Fuzz boxes, but has a limited range of checking transistor gain (β) up to a maximum of 150.

This is a modified version that allows a very wide range of modern silicon and germanium devices to be checked with two ranges, 0 – 250 and 0 – 1000.



The original potentiometer of 150k though still available from some suppliers is not as readily available as a 1M potentiometer so this value has been used instead. The range switches a different value of emitter resistor and changes the operating current IE accordingly. Two 1k resistors are put in parallel to obtain the 500 ohms resistor and two 1k resistors are put in series to obtain the 2k ohms resistor.

For the less fussy constructor simply use a 470R and a 2k2 without that much loss of accuracy, this is only a qualitative test after all.

I used a plastic box measuring 5 inches by 2½ inches or for those of you who prefer metric measurements 128 x 67 millimetres. That is about the minimum size you can use in order to accommodate the potentiometer scale. The potentiometer knob used was an old fashioned pointer knob.

A transistor socket could be purchased or simply use a cannibalised chip socket like I did.

Two scales are needed on the meter and are shown below with a suggested front panel layout.


What's New?

Fuzz Box 2