modell

I'm new here and am trying to learn electronic stuff in my spare time. I find it frustrating but fun at the same time. Once I figure stuff out it seems so simple but then another roadblock. I guess thats how you learn. Anyway to my question, I'm trying to build some simple circuits like a signal tracer/injector and small guitar amps and things like that. I have alot of old circuit boards I rob alot of parts from with all sorts of transistors and ic with different numbers and I've searched for data sheets and got alot of info and I was wondering if its alright to put like a 2n904 in place of a bc547 and 2n906 in place of a bc557 I think there both basically the same but the data sheets show slightly differnt numbers I also have many other transistors I could use that have close specifications. I guess what I'm getting at is do things have to match exactly or can you substitute things with similar specs. Or does it depend on the circuit. Thanks for your help. Also can you use mylar capacitors (most of the ones I have are green) in place of ceramics and vice versa.While asking about capasitors alot of the circuit boards have small blue capasitors I think they are called multi layered with the same numbers as the mylar and ceramic can they be used in the place of the mylar and ceramic ones or does this once again have to do with circuit application?

Sceadwian

You can always substitute, but it's going to alter performance and may require you to change other parts of the circuit as well, not usually adviseable to someone that's learning, unless you don't mind a lot of smoke. A simulator such as LTspice will help you a bit in understanding the circuits you're playing with without haveing to build them and can do some really amazing analytical things as well. You can change the paramaters of a transistor and see the results in a graph on the screen.

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3v0

Try this site
Transistor Cross Reference Database

3v0

modell

thanks alot for the info and the data base link. Ive seen some sites explaining how to use the spice program but never really read much about it I'll have to check that out.Oh yeah I don't mind the smoke so much but I was messing around with a power supply and had the transistor in backwards and that thing popped and the plastic flew scared me to death from then on I ducked when I powered it on.

Hero999

Please post the schematics.

It's quite possibly that most small transistors will do but it's totally impossible for use to know unless we can see the schematics.

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audioguru

I don't know why European semiconductor manufacturers make the BC547 and BC557 transistors, American manufacturers make 2N3904 and 2N3906 transistors and Japanese manufacturers make 2SCxxx transistors when they are nearly the same except for the pins layout and the American ones don't have as high a range for gain.

The European BC series can be purchased with the current-gain range pre-selected in groups. A BC547A has low gain, a BC547B has medium gain and a BC547C has high gain.

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Uncle $crooge

hotwaterwizard

http://www.ee.washington.edu/circuit...rts/cross.html

Nice Link very useful Thanks

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