Testing transistors!

davepinkham · Post by **davepinkham** » Wed Mar 30, 2011 12:01 pm

I'm learning how to test transistors, a step in my quest for electronics knowledge. I can't figure out what S, D, and G stand for as opposed to B, C, and E. Are they just different abbreviations for the same thing?

CurtZHP · Post by **CurtZHP** » Wed Mar 30, 2011 12:28 pm

S, D, and G stand for Source, Drain, and Gate. You will find these on FET's (Field Effect Transistors).

They are analogous to the Emitter, Collector, and Base on a standard bipolar transistor.

davepinkham · Post by **davepinkham** » Wed Mar 30, 2011 1:26 pm

much appreciated! I just noticed that the one i'm looking at has 4 legs as opposed to 3. could you explain this for me? thank you!

Scodiddly · Post by **Scodiddly** » Wed Mar 30, 2011 4:00 pm

Some FETs with a metal case have the 4th pin for case ground.

davepinkham · Post by **davepinkham** » Wed Mar 30, 2011 5:28 pm

cool, thanks!

cdixon6 · Post by **cdixon6** » Wed Mar 30, 2011 8:13 pm

BJT's and FET's are fundamentally different. But the math is pretty similar.

davepinkham · Post by **davepinkham** » Thu Mar 31, 2011 6:37 pm

Many thanks to everyone who has chimed in. Now I have another question. In the circuit I'm troubleshooting, one of the bipolar transistors seems to be testing bad. I'm pretty sure it says either 2N5085, 2N5086, or 2N5088, but the text is faded. Its definitely an NPN transistor. 2N5088 seems to be the only of the three readily available via Mouser. Should I go ahead and put the 2N5088 in? Could I be potentially messing stuff up by selecting the wrong transistor? I'm still treading unknown ground so please advise.

Thank you!

Nate Dort · Post by **Nate Dort** » Thu Mar 31, 2011 6:39 pm

you won't mess anything up by putting another NPN in there. if it's the wrong one, it probably just won't work. alternatively, it will work fine, even if it's the "wrong" one. it would be even better if you could figure out the pinout of the one you need. that may help narrow it down.

Scodiddly · Post by **Scodiddly** » Thu Mar 31, 2011 6:58 pm

Go to the NTE replacement semiconductor site and try the search function. Odds are decent that all three of those possibilities will point to the same NTE number.

davepinkham · Post by **davepinkham** » Thu Mar 31, 2011 9:13 pm

well, I checked out the NTE site and found the NTE96 to be the replacement for the 2N5005. They go for $39.68 apiece on Mouser so I'm assuming that's not the one. Gonna roll with the 2N5088, which are $0.37 apiece and see how it works.

Snarl 12/8 · Post by **Snarl 12/8** » Thu Mar 31, 2011 10:23 pm

Sometimes Transistors work in pairs in a circuit. I think of it as "push pull" but that could be entirely wrong. If that's the case, you might want to replace both at the same time.

I stress "might".

I know next to dick about the right way to do electronics even though I fuck around with it all the time.

davepinkham · Post by **davepinkham** » Thu Apr 07, 2011 1:32 pm

As a follow up: I fixed it by using the 2N5088. Thanks again for everyone's assistance! I now have spring reverb again, wooo!

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Testing transistors!

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