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Transistors

Discussion in 'General Electronics Discussion' started by ALFRED, Dec 7, 2015.

  1. ALFRED

    ALFRED

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    Jul 1, 2010
    i am working on vintage amp from 60,s. Stereo. One side works good the other low. After about 15 min. She starts to hum and 2 of the transistors get very hot ( it has 8 transistors) is it normal for them to get very hot? Thanks Al
     
  2. Martaine2005

    Martaine2005

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    May 12, 2015
    Hi ALFRED,
    I would check capacitors before anything else.
    Is it a tube amp? If so, wait for the veterans here!!
    Transistors do and can get hot but noticabley different to the other channel would suggest a fault.
    You have a direct advantage by having a stereo amp, check each stage for any difference!

    Martin
     
  3. shrtrnd

    shrtrnd

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    Jan 15, 2010
    Are they the big TO-3 Metal Can Packaged transistors? They can get hot.
    I'd help us help you if you tell us the make and model so somebody can check the schematic.
    For your general information, the first things to go on the old sets are the big electrolytic capacitors. They dry out and don't work efficiently,
    if you keep running them, you'll damage other components in the circuit.
    What are the numbers on the transistors?
     
    Martaine2005 likes this.
  4. ALFRED

    ALFRED

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    Jul 1, 2010
    Four 2n2429,s and four 2n2431,s. It is a Dynovox
     

    Attached Files:

  5. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Martaine2005 likes this.
  6. ALFRED

    ALFRED

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    Jul 1, 2010
    No luck. I can't find SAMs listing. Thanks Al
     
  7. cjdelphi

    cjdelphi

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    Oct 26, 2011
    The 2 that get very hot...

    Either they're damaged (got info on them? )

    Or whatever is firing them off is damaged?

    I'd pull them out and measure the diode drop/test for shorts (as suggested already you have working ones to compare against)
     
  8. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    Check and see if there is a bias potentiometer near these transistors. The bias adjustment sets the bias such that the output stage run s in the linear part of the output curve. If this gets out of adjustment the transistors can run hot and destroy themselves.

    I recently worked on an amplifier with this problem. In most cases a coupling capacitor gets leaky and causes the bias to change. In my case, the potentiometer became dirty and intermittent. Just touching it corrected my problem. I gave it a shot of cleaner and it was good to go. We should always be this lucky.
     
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  9. ALFRED

    ALFRED

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    Jul 1, 2010
    Just checking if I got this correct:
    When identifying legs on transistor,the base will have common resistance with emmiter and collector. The higher of the two is the emmiter. The resistance between E & C should be high. Am I good so far...
     
  10. duke37

    duke37

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    Jan 9, 2011
    I do not think that you will see much difference between the two junctions.
    Leakage between collector and emitter should be low but may be significant with old germanium transistors.

    Most digital meters have a socket for testing transistors. If you find the base and test the gain, then with the transistor the wrong way round, the gain will be low, if you then test the other way, the gain should be high.

    One of my analog meters uses 3V to test resistance. I use this with a 100k resistor to get a rough idea of gain. For an even rougher measurement I use my thumb instead of the resistor.
     
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