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PRRI Reverb Issue. Help?

Discussion in 'Amp Tech Center' started by DennisM, Feb 10, 2019.

  1. DennisM

    DennisM Tele-Meister

    154
    Nov 18, 2013
    Nevada
    My PRRI developed a hum in the reverb. Reverb works, but the higher I go on the pot the louder it gets. Sounds like an open ground in the circuit. I checked the tank, the cables, the tank position and V2. Everything seems fine externally. So, I opened it up this morning and took the meter to it. Seems the right footswitch jack (as pictured from the inside) might be the culprit. I get continuity all the way from the left (red) through the orange cap looking resistor to the left leg of the right resistor. No continuity through the resistor on the right. I guess that would the open ground. My question is, what kind of resistor is this? It's labeled Y5P, 221K 500V. By chance could I put a regular 220K resistor there? If not, where the hell could I get on like this?


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    Last edited: Feb 10, 2019
  2. Nickfl

    Nickfl Tele-Afflicted

    May 24, 2016
    Florida
    Thats not a resistor its a cap, 221k = 220pf. The one you are getting no continuity through is normal, you are getting continuity across the other one because it is connected to one end of the secondary of the reverb transformer (the other end is connected to ground and it has low resistance). So both those caps are reading the way I would expect and your problem lies elsewhere.
     
    flyswatter likes this.
  3. DennisM

    DennisM Tele-Meister

    154
    Nov 18, 2013
    Nevada
    Thanks. Red faced. I guess I'm not as smart as I thought I was. The search continues.
     
  4. LudwigvonBirk

    LudwigvonBirk Tele-Holic

    Age:
    117
    640
    Aug 26, 2017
    Madison
    V3 is Reverb Recovery and Reverb Mix. Try swapping V3 out?
     
  5. DennisM

    DennisM Tele-Meister

    154
    Nov 18, 2013
    Nevada
    Yes I did. Thanks. Since it's a PCB (I hate PCBs) I did the best I could looking for obvious causes i.e. bad solders loose wires etc. I moved a few wires away from the heater wires. I put it back together and it seems to be some better. I play at about 3 to 4 on the knob and it's acceptable I guess.
     
  6. Snfoilhat

    Snfoilhat Tele-Holic

    Age:
    37
    807
    Apr 8, 2016
    Oakland, CA
    Can you describe how you did the tests? Plugged the PR's reverb pan and cables into a different known-good amp? Plugged a known-good reverb pan and cables into your noisy PR? Plugged in known-good cables with your reverb pan? Plugged in a known-good pan with your cables? :eek:

    Your ears may have gotten it right from the beginning - a noise like a missing ground - and just not looked in the right place. Are you using the amp with the reverb foot switch plugged in? Fender's vintage reverb switching system with no electrical relays turns the entire reverb foot switch and cable into an antenna plugged straight into the grid of the reverb recovery stage.

    The spring reverb tray itself (4AB3C1B) needs to be grounded through it's connection to the chassis on the output side (the red RCA jack). If the little bead of solder inside the pan that connects common/ground to the pan's shell is messed up, or if the shield/sleeve of the RCA cable on the reverb output doesn't connect to the amp chassis correctly, then the reverb tray won't be held at ground potential.

    I hope this helps. I'm no expert, but rather have come up against some reverb gremlin in nearly every amp I've built and find it interesting if also frustrating. Good luck
     
    DennisM likes this.
  7. DennisM

    DennisM Tele-Meister

    154
    Nov 18, 2013
    Nevada
    The PRRI is the only reverb amp I have. I don't have another pan to try. I did try different cables to no avail. I tried different positions of the pan and ended up with it upside down with the jacks pointed outward. That seemed to improve the sound but not the hum. I'll have a closer look at the grounding on the pan. Every suggestion helps! Thanks!

    Edit to say I do play with the footswitch plugged in. I'll try unplugging it.
     
  8. LudwigvonBirk

    LudwigvonBirk Tele-Holic

    Age:
    117
    640
    Aug 26, 2017
    Madison
    jfyi, on a PR, Reverb and Trem are both ON when the footswitch is unplugged. Unplugging is still worth a try in case the switch/cable have something wrong with them.
     
  9. DennisM

    DennisM Tele-Meister

    154
    Nov 18, 2013
    Nevada
    Yes, thanks! I just turn down effects to zero. I did try it and there was no change. The good news is that whatever wires I moved might have helped. It's not really audible when I'm playing on 4, and when I turn it all the way up, there's a hum but it's not as bad. I guess I'm calling it good. :)
     
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