Transistors, unlike vacuum tubes, are very rugged because they can tolerate
vibration and shock.
Under normal operating conditions a transistor provides a
long period of dependable operation. Transistors may fail when subjected to minor
You can use various test methods to determine the condition of a
In many cases you can substitute a transistor of known good quality
for a questionable one. This method is highly accurate and sometimes expeditious.
You should avoid indiscriminate substitution.
When transistors are soldered into
equipment, substitution is impractical because the transistor may be damaged during
In this case, it is generally desirable to test the
transistor in the circuit if a tester with this capability is available.
Since certain fundamental characteristics are indicative of the condition of
a transistor, test equipment is made to test these characteristics with the
transistor either in or out of the circuit.
Although triode testers are
commercially available, as are diode testers, you may have to make your own.
Figure 3-16 shows the schematic diagram of a typical transistor tester and Figure
3-17 shows a locally made transistor tester.
Figure 3-16. Transistor tester
Figure 3-17. Locally manufactured