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Single Transistor Amplifier Circuit Help

Discussion in 'Electronic Basics' started by trevor, Mar 8, 2006.

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  1. trevor

    trevor Guest

    Hi,

    I am working on a High school Physics project, and we are trying to set
    up the second circuit found at:
    http://www.pbs.org/transistor/teach/teacherguide_html/lesson4.html

    I am having trouble with this circuit--when we set it up, it just makes
    a "static clicking" noise when we rub the leads together. Does anyone
    have any experience with single transistor amplifier circuits--or any
    suggestions on where I can find another one, or have any ideas about
    this circuit. I've been searching Google for alternatives and found a
    few, but I cant get those to work either....maybe I'm doing something
    trivial wrong.

    Thanks
    Trevor
     
  2. Pooh Bear

    Pooh Bear Guest

    No surprise. It's not the cleverest experiment I've ever seen.

    Graham
     
  3. I take it you are talking about the second circuit, with an output
    transformer.

    Are you using a transformer that has worked before, or did you
    purchase one new, for this experiment?

    Are you sure you have the leads on the transistor correctly sorted out?

    Have you checked that you don't have the two resistors switched?

    Same question but about the capacitors.

    Have you seen the note about what the dots mean where two lines cross?
     
  4. trevor

    trevor Guest

    Thanks for your suggestions...I bought new transformers.

    I actually have a question about the transformer. There are three leads
    going in and three going out...but on the circuit diagram, there are
    only two output gates. Is this normal...if so, which outputs should i
    use...I've been using the top and the bottom one, disregarding the
    middle one. Should I tie that to the ground....or am i doing something
    wrong.

    I'll recheck the capicators and resistors....

    but does this circuit look like it should work?


    thanks,

    Trevor
     
  5. This worries me. Since the transformer should have been designed for
    a speaker on the output side, I'm wondering if this transformer is the
    right one. I gather from the schematic that they want a 1k primary
    and an 8 ohm secondary for audio frequencies:

    : http://www.radioshack.com/product/index.jsp?productId=2103254&cp
    : http://www.radioshack.com/product/index.jsp?cp=&productId=2103254&tab=features

    I looked at the picture there and, looking closely, it appears to only
    have 5 wires. The red and white should be your audio 8 ohm side and
    the green, black, and blue should be your audio 1k ohm side. Further,
    the second link above shows:

    Frequency response: 300Hz to 10kHz
    1,000-ohm center-tapped primary
    8-ohm secondary

    Note that they don't mention the phrase "center-tapped" in the case of
    the secondary.

    I think you got the wrong part. The page you mentioned lists the
    Radio Shack part #273-1380. Are you sure you got that one?

    Jon
     
  6. Transformers can be made in almost infinite variety, with the windings
    turn count the main variation. The circuit you are building needs a
    transformer with at least one center tapped winding, that is made to
    connect to a 1k source, in order to make the positive feedback work in
    the audio range. The second winding has to have many fewer turns, to
    drive a speaker without loading the transformer so much that the
    oscillation stalls out. If your transformer has 3 leads at both ends,
    I am doubtful that it has one end designed to drive a speaker. Do you
    have any specs on the transformers you have, so far?
    It is very similar to the very first transistor circuit I built about
    45 years ago. I learned to produce Morse code with it.

    It is a fairly forgiving circuit, if you have a transformer that even
    comes close to what is specified. Back in the days when 5 transistor
    radios were in everyone's shirt pocket, it was easy to pull the output
    transformer out of one and build this circuit. The center tapped
    primary (for a 2 transistor push pull stage) to speaker output
    transformers are harder to find, today. Where are you getting yours?
     
  7. trevor

    trevor Guest


    I got mine at RSR electronics...thanks for the suggestions--I'm going
    to go and buy that transformer and try it in the circuit.
     
  8. Check the website at http://www.scitoys.com

    He has some fantastic simple amplifier circuits that are tested and
    will work great. Also,

    http://www.techlib.com

    has some fun stuff for you to build (and also all circuits tested and
    work fine)
     
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