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Aside from Mechanical parts the
followings are my policies regarding all semiconductors:
1) The only
transistor testers I accept result from are those that have been verified by
transistor (semiconductor) manufacturers.
2) The transistor testers have been recommended to authorized service centers in the past or recently by Audio, TV, and like manufacturers.
3) The transistor testers are fully capable of switching off (mute) base current to reduce unnecessary physical disconnect related spike at the base.
4) I reserve the right to request a clear picture be presented of the bench setup, instrument used, and gloves and grounding of the workbench as well as isolation of bench power.
Note: HFE/hfe (gain) and operating f specification have overtime changed as device manufacturers found different method of manufacturing such as epitaxial manufacturing process. Nevertheless many other power transistors originating from this era (1970~1985) cannot be assumed to have great high-frequency performance and there can be variation of open-loop gain and other specification when compared to modern transistors. Modern successors to early transistors (1970~1980) can be much more suitable in fast-switching circuits or high-end audio power amplifiers which enabled us to design amplifiers with specification of 15Hz~40Khz compared to older amplifiers 20Hz~20KHz. Why buy old transistors then. The group of transistors that work along the defective transistor you about to replace also originated about the same period. It simplifies job!. The reason is too long for this note.