Simple Transistor Tester

00 While experimenting with electronic circuits, it will often be necessary to rap- idly test bipolar transistors and FETs before they are fitted in the circuit, or when they have been removed from the circuit when a malfunction is suspected. More specifically, constructors will need to know whether a transistor of known type and make is sound or not, and also whether an unknown device is a particular type of FET, or a bipolar transistor (PNP or NPN). This tester can be built from parts found in the junk-box. When the transistor under test (TUT) is OK. and correctly connected, the circuit will oscillate dur- ing half the period time of the alter- nating supply voltage (50 or 60 Hz). Red LED D2 lights when the TUT is OK and of the NPN type. The function of green LED Di is similar for PNP TUTS. The TUT OK/not OK indication is obtained with Sz set to the centre position, and Si opened as shown in the circuit diagram. The LEDs will indicate that the oscilator amplitude is significantl...