amp squeal! 5e3

Discussion in 'Amps and Cabs' started by dad gad, Feb 15, 2008.

  1. dad gad

    dad gad Member

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    I just recieved my 5e3 combo and when i turn everything up all the way, i get a squealing sound. if i lower the tone or primary volume, it goes away, so only at extreme volume. seems to be linked with the tone control. any ideas?
     
  2. hasserl

    hasserl Member

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    Microphonic V1 tube. Tap the top of the amp with it powered on and Volume up about half way, can you hear the tube making noise as you tap?
     
  3. dad gad

    dad gad Member

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    I am gonna check that when i get home.thanks for heads up!
     
  4. dad gad

    dad gad Member

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    Ok, so I swapped tubes and the same thing. Then I swapped from a 12ax7 to a 12au7 in v1 and it went away. Any reason why a ax7 won't work? I know that the original tube is a 12ay7, but I have heard dozens of folks that use a ax7 and have no problems. Any ideas?
     
  5. hasserl

    hasserl Member

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    There is something in the circuit, possibly just the lead dress, that has the amp on the verge of instability. The added gain of the 12AX7 pushes the amp into a hf oscillation due to that instability. The lower gain of the 12AU7 doesn't quite push it hard enough, so it remains stable and the oscillation does not occur..

    Stick a 12AY7 in it and see how it goes, if all is well you're good to go. If it doesn't send it back to the builder and tell him to fix it.

    On the other hand, how often do you crank everything up all the way? It's not really very useful like that anyway, is it?
     
  6. go7

    go7 Member

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    Hasserl, I`m with ya. Go back to the 12ay7 in V1. Good Luck!
     

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