Twin Reverb Amplifier squealing really load when I turn reverb past 5.

Discussion in 'Amp Tech Center' started by harleyman5, Oct 27, 2021.

  1. harleyman5

    harleyman5 TDPRI Member

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    Hi, Everyone, I was on here a few weeks ago and never had a chance to get back on here. Now I do. I am not sure of the year but the volume knob does pull out as someone asked me to check. I just had a little crackle now and then so I thought I would take it in for a tune up. Well Randy here in Fargo ND is the only guy that works on amps around here so I dropped it off and he recaped it and cleaned it. I took it home and never tried it out. I got in a bad Motorcycle accident when this woman pulled in my lane and we hit head on. I was layed up for over a year and finally wanted to play guitar one day. When I turn the reverb past five it sueal's so load its unreal. Called Randy and took it back in and he said he can't find the problem and told me to pick it up. I was not happy and let him know. Anyone got any ideas what it could be. The amp is like new and never had much use and no repairs done at all till now. Could sure use some help. Thankyou to all.
     
  2. Sea Devil

    Sea Devil Friend of Leo's

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    If it's a squeal rather than a hum, I'm not sure what would cause that other than a microphonic tube, possibly a bad ceramic cap. It could also just be a bad reverb pan. Hum, on the other hand, can be the result of the reverb pan's proximity to a transformer or speaker magnet, or just vibration from being in the same cabinet as the speaker.

    Try disconnecting the pan and turning up the reverb. If it stills makes the noise, that eliminates the pan as the source of the problem. If it persists, it's inside the amp. If it doesn't make the noise, reconnect the pan; try new cables and new reverb output and take-up tubes.

    If none of this workds, you're kind of SOL. It's unlikely that your guy has suddenly learned more and will be able to fix it when he couldn't before. Your only option would be to pull the chassis and ship it to someone with more experience.
     
    Last edited: Oct 27, 2021
  3. G.Rotten

    G.Rotten Friend of Leo's

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    Bad tube?

    I'm no expert. I've had similar and that possibility comes up.

    The Tech should have but possibly didn't do a tap test on the tubes and went straight to re-capping (which did likely need to be done).
     
  4. harleyman5

    harleyman5 TDPRI Member

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  5. harleyman5

    harleyman5 TDPRI Member

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    Thanks a lot for your help. It does make the noise even when I unplug the reverb tank.
     
  6. mojavedesert

    mojavedesert Tele-Meister

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    OK done.
     
    Last edited: Oct 28, 2021
  7. Sea Devil

    Sea Devil Friend of Leo's

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    Edited post above for clarity, in case OP is getting alerts to new posts in this thread
     
  8. harleyman5

    harleyman5 TDPRI Member

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    someone said start pulling tubes. Can I do this with the amp powered up? If the noise quits its that tube then. Just want to be sure I don't want to mess anything else up.
     
  9. corliss1

    corliss1 Poster Extraordinaire Platinum Supporter

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    Yes, you can pull the preamp tubes with the amp powered up. They'll be hot, but not super crazy hot like power tubes are.

    Looking at the back of the amp, the reverb tubes would be the 3rd and 4th tubes from the right. You can try a different tube if that stops the noise (it likely will). If a new tube causes the same problem, you at least know what section of the amp has an issue.

    No other techs in the area? Vintage Fender is the easiest stuff to work on of all time, so if he couldn't track that down I'd be leary of the work in general.
     
  10. Peegoo

    Peegoo Doctor of Teleocity

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    Another cause for this symptom can be as simple as a dirty control pot.

    Shoot some Deoxit into the reverb control pots and vigorously rotate the knobs through their entire travel. Also make sure the pots' mounting surfaces and hardware are clean and tight.
     
  11. Sea Devil

    Sea Devil Friend of Leo's

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    DeOxit can remove the white paint from the knobs. Take 'em off first. Works 100X better from inside the amp.
    Keep a paper towel handy and blot, don't wipe, any excess off of the faceplate; the print on that may come off, too.
     
  12. tubedude

    tubedude Tele-Holic Silver Supporter

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    Use that on the RCA connectors while you're at it.
     
  13. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I am going to go out on a limb here because the squeal happens when the reverb is turned past 5...

    Imo, Randy would have tried most of the remedies mentioned on his second attempt so, I am gonna make a WAG...

    I can envision Randy replacing the resistors on the power tubes on his first repair. If he accidentally switched the positions of the signal wires the negative feedback would now be positive feedback. It is possible and I don't think Randy would look for it on the second attempt.
     
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