Simple circuit measures breakdown voltages of most types of small-signal and power transistors, reverse breakdown voltages of small power diodes, and zener diodevoltages. Two small 90V batteries in series provide power. R1 biases upper transistor into conduction. When voltage is applied to diode or transistor iunction under test, junction breaks down and current flows through R2. This makes lower transistor conduct, thereby dropping base voltage of upper transistor. R2 may be used to set breakdown current over wide range. Voltmeter reads breakdown voltage of junction, since drop across R2 is negligibly smalL-J. W. Brown, Simple Breakdown Voltage Meter, Wireless World, July 1973, p 337.
Required Field 
