We know how transistor works but some of us doesn't really know how to test the component itself. Nowadays, most Digital Multimeters have sockets provided to test them, but what will you do if you have those old Analog/Needletype ones? This is a simple way to do it.
Step 1: Basic Configuration
Bipolar transistors has 3 pins, The Emitter(E), Base (B) and the Collector (C) which is usually connected to the casing for most Power transistors (TO-3 casing). It can be categorized into two, NPN and PNP configuration, see figure 2. This test is based on the theory that a transistor is like two diodes connected together, see figure 1.