help making a amplfyer?

I was going to build a amplfyer from this instructable but had no BC548 or 2N3904 transistors. I did a google search to find out what could also work. I found a website stating simmalar transistors. On this website, at the related transistors section it states a few simmalar transistors. What transistors could I use instead of the BC548 or the 2N3904?

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lemonie6 years ago

What transistors do you have then?

David97 (author)  lemonie6 years ago
I have a few but dont have any BC548 or 2N3904. I usaly scanvange them off old eletronics. So having a list of what would work would help. I will check what I have in the list tomorow.
lemonie David976 years ago

Spot the ones you have most of, they'll probably be "general purpose" NPN, and after that PNP.

David97 (author)  lemonie6 years ago
So your saying that most NPN transistors will work?
Yes, most transistors will work, as long as they are general purpose and the same type (NPN or PNP). Make sure it isn't a power transistor ot a high frequency one or something. Also, I would recommend getting some 2N3904s, BC548, and BFY51, they are very common, useful transistors (especially the 2N3904). However, assuming the hFE is the same or higher, it should work fine.
lemonie6 years ago

Thanks for the best answer.
If you strip e.g. a stereo system and you've got at least 4 of the same, you'll find they are "general" and useful for lots of things, cheap-o general transistors.
If you want to shift a lot of power you'll find that audio amplifiers tend to be single-package ICs, but an old TV is usually quite good for heat-sunk transistors and similar.

David97 (author)  lemonie6 years ago
I will remeber that... Just got a new tv but threw out the old one.......opps
Yes, substituting transistors for simple projects is pretty easy.

Look at the maximum collector current and use a transistor that can handle the same or more - usually for high power switching projects.

Look particularly in audio projects for "Hfe", the gain - higher is better. Look at the MINIMUM Hfe, and make sure THAT is at least as high as the minimum Hfe for the original transistor.

Also check that VceMax is higher or equal to the original transistor

Substitution isn't always that simple though.

David97 (author)  steveastrouk6 years ago
My dad works on heat pumps so I can ask him to pull a few old boards out of the skip (thats where our heat pump came from, LOL). I think it shouldn't be to hard to find the right transistor.