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Transistors Replacements

Discussion in 'Electronic Basics' started by BobG, Mar 29, 2005.

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  1. BobG

    BobG Guest

    Looks like any ol transisitor that will handle 12V and 2 A will work.
  2. Chretien

    Chretien Guest

    I'm trying to build a circuit that calls for these three Transistors.
    My local guy does not have them. I would rather buy from him than some place
    I have to have them shipped into, added cost etc.

    Who knows they may be obsolete?

    Does anyone have a book or something where they can look up replacements for
    these that might be more available.


    The circuit would like to build is at :

  3. Chris

    Chris Guest

    Hi, Chretien. If you can't find the specified parts for a hobbyist
    project, you might want to try NTE replacement semiconductors. They're
    made for repair and engineering prototype stuff. Their cross-reference
    page is$$Search?OpenForm

    You can frequently find what you need there.

    I did a quick search on their cross-reference page, and came up with
    the following:


    If you can't find NTE parts locally, you can always get them out of the
    Mouser catalog

    (By the way, please wear eye protection when you use your NiCd zapper
    circuit. Also, try using a 12V automotive bulb as a load when checking
    out your circuit, before you try a battery.)

    Good luck
  4. Chretien

    Chretien Guest


    I am a novice and tend to slavishly follow schematics. However I know that
    many circuits can use as you say any old transistor. I don't always
    understand why, accept to say that I suppose the circuits are so heavy
    handed and non specific that almost anything will do so long as the are NPN
    or PNP.

    Thanks again.
  5. BobG

    BobG Guest

    I am a novice and tend to slavishly follow schematics. However I know
    The rule of thumb is that the transistor needs to withstand the voltage
    and current from the circuit, so over spec-ing the transistor just
    hurts your wallet. Same with caps... you can use a 50v cap in a 5v
    circuit, but not vice-versa
  6. In the well known electronics magazine Elektor they use the acronyms tun
    and tup to mean transistor universal npn(pnp).

    The requirements for these transistor are something like this:
    Max collector voltage min 30V, hFE min 200, max current min 100mA.

    Thousands, if not millions, of small signal transistors meet these
    requirements, and you can use any of them in most circuits.
    Elektor use those basic types in many of their circuits.

    In your circuit 3 are such small signal transistors and there is no
    special requirements as far as I can see. The power source is
    12 Volt, and practically all transistors ever made can be used when we
    consider the maximum voltage alone.

    The BD type is a power transistor which need to be able to handle 2Amp

    There are circuits where other parameters mean a lot, like in an audio
    preamp if it says BC109c it means a low noise transistor with a hFE above
    500 or so. But your circuit does not seem to need any special types. Take
    what you have and it will probably work just as well as with the named

    A well known tun is BC107 (108,109), a well known tup is BC177 (178,179).
    The numbers ending in 9 in these series denote low noise types, but they
    can take less maximum voltage. (30V instead of 60V for the 107 and 108
    types) If there is a letter at the end it shows the hFE value.

    BC107b = General purpose npn small signal transistor with medium amplification
    factor, hFE = 300-500 or so.

    All numbers above are approximative, different manufacturers have
    slightly different values.

    Check out these links:
  7. Chretien

    Chretien Guest

    Hey thanks thats that will be a great help in the future.
  8. Chretien

    Chretien Guest


    Thanks for the tutorial it was extremely helpful. Here and I thought all
    those letters where just manf codes.
    I'm printing off your message and will keep it in my transistor file for
    future reference. The web links were very useful also. I have actually made
    a few of Mr Toons projects but somehow didn't see those links.

    I have to say this newsgroup is one of the most helpful I have ever used. I
    always seem to get some help when I need it.

    Thanks again.
  9. Jamie

    Jamie Guest

    those are generic type PNP and NPN signal transistors.
    from what i can see.
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