Halp! WTF is this sound?

Discussion in 'Amps and Cabs' started by rollyfoster, Dec 8, 2016.

  1. rollyfoster

    rollyfoster Supporting Member

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    happens when I turn the amp on and kinda sounds like it's coming through the speaker. This example is with volume off and nothing plugged into the amp, though it happens when the whole rig is intact. Doesn't increase in volume when the volume knob is engaged. It's just....there. Ranges from a few seconds to a minute or longer.

     
    Last edited: Dec 8, 2016
  2. Humble Texan Fan

    Humble Texan Fan Member

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    Brand and model of amp, please?
     
  3. woof*

    woof* Member

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    Trem is bleeding?
     
  4. Hemlock

    Hemlock Member

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    sounds like a bad tube, power or preamp. Tap em all and see if it stops or gets worse.
     
  5. michael.e

    michael.e Supporting Member

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    Check tubes before anything.
     
  6. Agiknee

    Agiknee Member

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    Bad tube or fried grid resistor. My 5150 had bad grid resistors and made that same pulsating 60 cycle hum
     
  7. VaughnC

    VaughnC Supporting Member

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    Sounds like a microphonic tube or the circuit is unstable and on the edge of oscillation.
     
  8. rollyfoster

    rollyfoster Supporting Member

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    Yikes.

    The power tubes are new
    Suhr Bella. These are new sovtek power tubes, sent as replacements for JJs so noisy I couldn't play.

    I guess it may be a tube issue. I can tap on them with the volume off and hear it through the speaker. It also lessens if I hold my finger to the glass.

    But it would be really odd to me if 2 back to back sets had issues so I'm not sure if it's incredibly small odds of me getting 2 bum sets in a row or a symptom of a larger problem with the amp itself.
     
  9. BADHAK

    BADHAK Member

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    My 82 Marshall 4104 (50 watt 2x12 combo) does that. Im about to take it to a tech but I bet it's a microphonic preamp tube. I've had other amps do it previously and new tubes fixed it.
     
  10. michael.e

    michael.e Supporting Member

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    Pick up some of those tube damper rings from "Outtahere" here at TGP. They do wonders. I have them in my gainier amp and it really helps control the errant signal.
     
  11. Husky

    Husky Gold Supporting Member

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    Make sure you have a JJ 12AX7 in the effects loop spot.
    We will get the amp back though and give it a suhrtification.
     
  12. rollyfoster

    rollyfoster Supporting Member

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    Thanks John. I got that info to you in a PM.
     
  13. rollyfoster

    rollyfoster Supporting Member

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    Preamps are all the originals and don't seem to have any issues. I have a few spare 12ax7s I've swapped in to test out of curiosity and it still does it.
     
    BADHAK likes this.
  14. Husky

    Husky Gold Supporting Member

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    You will get the shipping label today or Monday. Thanks !
     
  15. Agiknee

    Agiknee Member

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    Now that's awesome service.
     
    TRGuy and rollyfoster like this.
  16. WhoJamFan

    WhoJamFan Supporting Member

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  17. rollyfoster

    rollyfoster Supporting Member

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    Probably the best I've ever dealt with!
     

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