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I have to replace a faulty BFY51 Transistor. I could not find one in the market since they have been discontinued. What is a suitable replacement?

BFY51 NPN Transistor

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    $\begingroup$ I'm voting to close this question as off-topic because it belongs to Electronics / Electrical Engineering $\endgroup$ – Edwin van Mierlo Aug 2 '17 at 12:50
  • $\begingroup$ by the way, after using my favorite search engine, it seems that some shops still stock this $\endgroup$ – Edwin van Mierlo Aug 2 '17 at 12:53
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    $\begingroup$ @EdwinvanMierlo A question being on-topic elsewhere does not make it off-topic here. That said, this question could be improved by explaining what, presumably, radio it is used in (which would narrow down what possible substitutions could be made). $\endgroup$ – Kevin Reid AG6YO Aug 2 '17 at 15:05
  • $\begingroup$ I know this is an old post but I need a few BFY51’s for a current project. Futurlec.com still carries them. $\endgroup$ – Brock R. Wood Apr 16 at 4:48
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Searching Mouser for:

  • NPN, BJT discrete transistors
  • max collector-base voltage >= 60 V
  • max collector current >= 1 A
  • gain-bandwidth product >= 50 MHz
  • TO-39 package

yields 13 results. 2N3019, the cheapest and most available result, seems like a reasonable replacement. Of course without knowing the precise details of the circuit it's impossible to say for sure if it will work.

If this is in any sort of push-pull amplifier, you should probably replace all the transistors and not just the faulty one to maintain symmetry in the circuit.

There seems to be nothing special about BFY51 besides the TO-39 package which isn't very common. Using a similar search at your favorite parts source I bet you can find some other replacements which are cheap and available in your area.

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  • $\begingroup$ Note that as Phil said, you'll be replacing multiple components in your circuit – and it's far from unlikely you'll also have to change a few bias resistors to keep the same performance. It might be worth a) to share your whole circuit, not just one component of it and b) actually reconsider the whole circuit. As Phil pointed out, there's a lot of transistors that are at least as good as yours, but it's very likely yours wouldn't be the component of choice in your application in this day and age;but making a better device using better components might imply a (partial) redesign of your circuit $\endgroup$ – Marcus Müller Aug 2 '17 at 22:16
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It's also worth trying to see if you can dig up the datasheet on the BFY 51 and compare it's applicable characteristics to the replacement you are considering.

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