AA763 Reverb sqeals and whistles

Discussion in 'Amp Central Station' started by heave1, Jun 9, 2021 at 12:48 PM.

  1. heave1

    heave1 TDPRI Member

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    Just finished a MT AA763 Deluxe reverb amp kit and the reverb seems to squeal after adjusting above 4-5. New tubes and reverb tank. Reverb works great until it reaches that certain point.
    Any advice is welcome.
     
  2. schmee

    schmee Doctor of Teleocity Ad Free Member

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    -Try swapping other tubes in V3, maybe V4. What make of tubes are those?
    -Make sure the "grippers" on the reverb cables are tight on the jacks on the back of the amp and tank. Get it squealing a bit and try gripping/rotating those cable ends to see if it stops. Many modern RCA cables dont grip well at all. The old style "all metal" grip tightly.
     
    uriah1 likes this.
  3. wabashslim

    wabashslim Friend of Leo's

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    There's a 4.7M or a 3.3M bypassed by a 10pF cap that isolates the reverb input from the output. Make sure those are right or you'll get feedback through the reverb circuit.
     
  4. Roger66

    Roger66 Tele-Meister

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    You need to buy another guitar.
     
  5. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    I'm not sure PFB causes squeal related to the verb, but it can cause a lot of funky behavior. If simple reverb-sector fixes don't do it, you might swap OT primaries. (Or secondaries. Just not both.)
     
  6. 11 Gauge

    11 Gauge Doctor of Teleocity

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    I had a '79 DR that did this at some point, and it turned out to be an issue with a cathode bypass cap that wasn't properly connected. I can't remember if it was the one for the 12AT7 driver tube, or the recovery triode right after it, but it was one of those two.

    After I got the cap properly reconnected, I could max out the reverb with no more squealing.
     
  7. heave1

    heave1 TDPRI Member

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    I had the reverb tank too close to the chassis. When I moved it to it's proper orientation, no squeal. I found this out on a post here on TDPRI. Thanks for the help.
     
    BobbyZ, King Fan and schmee like this.
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