Reverb Feedback....

Discussion in 'Glowing Bottle Tube Amp Forum' started by Joe M, Jan 20, 2020.

  1. Joe M

    Joe M Super Moderator Staff Member

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    Just brought home a Fender Fudge Brownie PRRI. Way different sounding than the "regular" model with the ceramic speaker. Problem is, if I turn the reverb up past 2.5 or so, huge feedback roars out of the amp, even with nothing plugged in. I've had a ton of Fender amps, both vintage and reissue, and have never had this problem. Before I lug the amp back to the store (50 mile round trip) I'd like to ask the collective wisdom of the group here. My first guess is that it's a pre-amp tube. Which one should I try swapping first? If that doesn't work, any other guesses as to what the problem may be?

    Thanks for any help.
     
  2. Wally

    Wally Telefied Ad Free Member

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    V2 should be a 12AT7 and is the reverb driver. V3, a 12AX7, has one triode as a gain stage and one triode that is the reverb return.
     
  3. Joe M

    Joe M Super Moderator Staff Member

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    Thanks, Wally, I'll give those a swap later today.
     
  4. Wally

    Wally Telefied Ad Free Member

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    If the tube change doesn’t stop the squeal, try pressing the top of the reverb tank. If the squealing stops, one could go into installing some vibration insulation. But....with a new amp this is troubling to have this problem, imho. If it is used, then one can do what one wants eliminate the feedback. Foam rubber strips, tank bag....
     
  5. Joe M

    Joe M Super Moderator Staff Member

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    Ok, squealing gone, but with a kind of weird solution.....changed out V2, squeal still there; changed out V3, squeal still not gone; moved the amp from my work place back to it's stand, tried it one more time before taking it back and, no more squeal. The only other variable I can see was unplugging and plugging the footswitch, which I can't believe could have been the problem. Anyway, I really don't care, it's working the way it should, so I'm a happy camper.

    Thanks again, Wally, for pointing me to the right tubes.
     
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  6. Wally

    Wally Telefied Ad Free Member

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    You may have had a slightly oxidized connection there...or there may be a bad connection in the footswitch cable that corrected itself during the process.
     
  7. Joe M

    Joe M Super Moderator Staff Member

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    Wait, are you saying that the footswitch connection could have been the problem all along????
     
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  8. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Yup - there is signal on the footswitch, which is why it's shielded.
     
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  9. Joe M

    Joe M Super Moderator Staff Member

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    Color me stupid, if that's the reason.....:oops:
     
  10. bumnote

    bumnote Tele-Meister Ad Free Member

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    I have that exact same PRRI...I liked that speaker even better after a break-in.
    Anyway...my foot-switch crapped out close to a year out. First the trem was never entirely off....then that button stopped functioning. I could probably fix it...but haven't tried. At some point I'll replace it will a good foot-switch, but honestly don't need to anytime soon.
    Other than that I love the amp.
     
  11. aerhed

    aerhed Friend of Leo's

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    If you really really want to solve that I have a wireless footswitch for you.
     
  12. Wally

    Wally Telefied Ad Free Member

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    nah...that does not establish stupidity. It is merely one of many reasons why a squeal could happen. Checking the simple stuff first eliminates possibilities.
     
  13. Joe M

    Joe M Super Moderator Staff Member

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    I've always subscribed to that theory myself; look for the simple things first. Never crossed my mind that the switch could be the problem, I thought that a bad tube would be the simplest fix. Anyway, as I said, doesn't matter, it works now. I'm not even gonna put the original tubes back in, let sleeping dogs lie....

    Thanks again for the help guys....
     
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  14. Switchy

    Switchy Tele-Holic

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    Do not most people use a pedal reverb instead of the built in reverb? Just curious.
    My little crappy Frontman has reverb, but I don't use it at all. I use my Oceans 11.
     
  15. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    The whole point of Fender amps is the onboard reverb :D :D
     
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  16. Joe M

    Joe M Super Moderator Staff Member

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    ^^^^This
     
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