If, for some reason, you can’t get an exact replacement for transistor that you want to replace, you can refer to one of transistor substitution guides or book, and try to identify a “near replacement”. Beware, however. A substitution guide will sometimes list a replacement for your part, even though two parts are not very similar. The most commonly used transistor substitution guides is Philips ECG semiconductors Master Replacement Guide. Selecting right transistor parameters or specifications for equipment you repair will avoid callbacks from customers. Callbacks or repeated repairs due to wrong transistor substitution will cost you extra money and a waste of time.
Some important transistor parameters are:
Maximum collector-to-base voltage (VCBO) – The replacement part should have a VCBO rating equal to or higher than original.
Maximum collector-to-emitter voltage (VCEO) – The replacement part should have a VCEO rating equal to or higher than original.
Maximum emitter-to-base voltage (VEBO) – The replacement part should have a VEBO rating equal to or greater than original.
Maximum collector current (IC) – The replacement part should be able to handle as much (or more) collector current as original.
Power dissipation (PD Watts) – The replacement part should be able to dissipate as much (or more) power as original part.