I'm building a small (about 500 mW) class AB amp for my office. Currently, I'm using the BC639/638 transistors pairs in the push-pull section. I've seen that SS8050/8550 pairs can handle more power in a TO-92 package than practically any other TO-92 transistor. I've also seen very few references or user stories about the SS8050/8550. Why is that? Are they particularly bad? Or just not well known?
The S series of transistors were low cost, high volume products developed by National Semiconductor for mass produced portable consumer devices in Malaysia many years ago. They were used by the pallet load in personal radios, tape players, boom boxes, portable TVs and other battery operated consumer gadgets.
Now they appear to be produced by several unidentified manufacturers and even reputable ones like Taiwanese manufacturers Unisonic and Wingshing. They could even be other products which roughly fit the spec. but have been regraded and marked as they now appear. The point being, that like so many generic products, if they don't have a definite identifiable manufacturing source, documentation and quality that you can rely on, you need to test samples of each lot for yourself rather than assume that the flaky datasheets have any relevance to what you bought.
For guaranteed performance, use BC328/338 or BC327/337 instead. BC639/40 are actually good for up to 1A, if you are looking for the highest all-round ratings but all these will get just as hot and their cases are an insulator - not the best for cooling and reliability from any transistor. The maximum current ratings for S8850/8050 are actually 0.5A which is a bit less than the comparable BC types referred to.
Now they appear to be produced by several unidentified manufacturers and even reputable ones like Taiwanese manufacturers Unisonic and Wingshing. They could even be other products which roughly fit the spec. but have been regraded and marked as they now appear. The point being, that like so many generic products, if they don't have a definite identifiable manufacturing source, documentation and quality that you can rely on, you need to test samples of each lot for yourself rather than assume that the flaky datasheets have any relevance to what you bought.
For guaranteed performance, use BC328/338 or BC327/337 instead. BC639/40 are actually good for up to 1A, if you are looking for the highest all-round ratings but all these will get just as hot and their cases are an insulator - not the best for cooling and reliability from any transistor. The maximum current ratings for S8850/8050 are actually 0.5A which is a bit less than the comparable BC types referred to.
Many thanks, what a fantastic and informative answer.
Wish you happy new year as well.
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