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view B, a colored dot, usually red, indicates the collector. If the transistor is round, as in view C, a red
line indicates the collector, and the emitter lead is the shortest lead. In view D the leads are in a triangular
arrangement that is offset from the center of the transistor. The lead opposite the blank quadrant in this
scheme is the base lead. When viewed from the bottom, the collector is the first lead clockwise from the
base. The leads in view E are arranged in the same manner as those is view D except that a tap is used to
identify the leads. When viewed from the bottom in a clockwise direction, the first lead following the tab
is the emitter, followed by the base and collector.
Figure 2-17.—Transistor lead identification.
In a conventional power transistor as shown in views F and G, the collector lead is usually connected
to the mounting base. For further identification, the base lead in view F is covered with green sleeving.
While the leads in view G are identified by viewing the transistor from the bottom in a clockwise
direction (with mounting holes occupying 3 o'clock and 9 o'clock positions), the emitter lead will be
either at the 5 o'clock or 11 o'clock position. The other lead is the base lead.
TRANSISTOR TESTING
There are several different ways of testing transistors. They can be tested while in the circuit, by the
substitution method mentioned, or with a transistor tester or ohmmeter.
