Bassman Head Crackling

Discussion in 'Amps and Cabs' started by jonlarsen002, Feb 4, 2008.

  1. jonlarsen002

    jonlarsen002 Member

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    HELP!!!.....So here is an updated list of all the issues my Fender Bassman 1966 Blackface amp head has:

    1) Subtle and sometimes louder crackling noise that goes on even with no guitar plugged in. Usually responds increases or decreases with volume knob.
    2) Sometimes crackle and fuzz builds up then makes a pop and goes away, only to build up and pop and cut out again.
    3) The Bass channel did this wierd thing where everything sounds detuned.
    4) If you dig in and play with attack, the signal cuts off and then will come back on a few seconds later.

    Any experience with this? I'm assuming it could be the tubes, but any other ideas before I throw down the money and change them?
     
  2. hogy

    hogy Member

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    With 95% certainty it's the plate load resistors. They are carbon comp types, essentially pressed carbon dust. As they age and go through thousands of heating and cooling cycles, microscopic cracks develop that cause the crackling sound as the resistor expands with heat.

    Easy fix, you need to replace them, but change the preamp tubes first, they too can cause similar noises.
     
  3. sickboy79

    sickboy79 Member

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    Agree with Hogy - start with your tubes - preamp, and I also wouldn't rule out power tubes. I had a set of EL34s making crackling/popping noises on me once.
     
  4. Trotter

    Trotter Supporting Member

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    I bought a 1966 Bassman that started doing almost the same thing... turned out to be a bad pre-amp tube! Easy fix.
     
  5. jonlarsen002

    jonlarsen002 Member

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    Updated list of issues... please help!
     
  6. alivegy

    alivegy Member

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    Did you try the preamp tubes? Always start with the easiest solution and work your way down.
     
  7. FleaRadical

    FleaRadical Member

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    Try the tubes and plate load resistors first. The crackle build-up and pop sounds like it could also be a capacitor (or a breakfast cereal). You can try lightly tapping some of the caps on the main board with a wooden stick. If you get any pops or other noise through the speaker when you tap on a specific component, it most likely will need replacing or possibly re-soldering. BE EXTREMELY CAREFUL AND DON'T TOUCH ANYTHING WITH YOUR BODY!!! IT'S A LIVE CIRCUIT AND CAN KILL YOU!!! IF YOU ARE NOT FAMILIAR WITH THIS TYPE OF WORK, TAKE IT TO AN AMP PRO.
     
  8. Blue Strat

    Blue Strat Member

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    As others have said, preamp tubes and/or plate load resistors are probably causing the random noise.

    The detuned sounding bass channel is likely caused by failing filter caps. If the amp hasn't had a cap job in the last 15 years, it's time.

    Many of these amps produce "ghost notes" at higher volumes even with updated filter caps.
     
  9. Guitarman3366

    Guitarman3366 Member

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    I have a '66 Bassman now, and have owned others in the past. The one I had before the one I have now had similar problems. I found it to be a preamp tube. I have MESA tubes in the one I have now, but I liked the JJ's I have used in the past much better.
     

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