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AA1164 Princeton Reverb build BUZZ

Discussion in 'Shock Brother's DIY Amps' started by Paul Strat, Jan 11, 2019 at 3:29 PM.

  1. symbiotic

    symbiotic TDPRI Member

    Did you mean you've added another filter cap in parallel? Adding a cap in series will double the voltage handling but halve the capacitance, right?
     
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  2. schmee

    schmee Friend of Leo's

    Jun 2, 2003
    northwest
    " I changed the output tube socket wiring to allow me to try 6L6 tubes"
    No wiring changes are required for that. What did you change?

    a couple thoughts:
    -Not fond of the wire rail grounding scheme near the pots, but it may be fine. I built a tweed amp like that and had to remove it due to buzzing.
    -Just remove your extra filter cap for now while debugging as it's of minimal use anyway. I have tried various filter "upgrades" in Princetons and 6L6 Princetons with minimal change.
    -No choke needed. I have built them with Super Reverb trannies and no chokes.
    -Try twisting those Reverb Tranny wires and keep them clear of anything else as much as possible.
    -There's a wire end off the resistor on the pot shown in pic 4... is it close to the chassis? I cant tell.
    -In the last picture near the center the heater wires are close to the nut that holds the tube socket... cant tell if they are too close...?
     
    Last edited: Jan 12, 2019 at 12:00 PM
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  3. Paul Strat

    Paul Strat Tele-Meister

    139
    Apr 7, 2017
    Muscle Shoals, AL
    The Mojotone layout had had no resistors between pins 4 and 6 on the output tube sockets, and had the leads going to 4. Also didn’t have the resistors between 5 and 1. Pics of the sockets below.
    Also removed the extra filter cap.
     
  4. bwacke

    bwacke Tele-Meister Gold Supporter

    360
    Oct 28, 2007
    Toledo, OH
    V2 kills the buzz? The 12AT7? That's the reverb driver. You may have a bad reverb transformer, or a problem with the power supply connection wiring to the transformer primary. Or a bad 12AT7 for that matter...
     
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  5. schmee

    schmee Friend of Leo's

    Jun 2, 2003
    northwest
    I see, yeah I always put those resistors on 6V6 or 6L6 sockets. I guess the stock PR didnt have them. Although the DR's do.
     
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  6. Paul Strat

    Paul Strat Tele-Meister

    139
    Apr 7, 2017
    Muscle Shoals, AL
    I wondered about the transformer. I’ve tried different tubes.
     
  7. Paul Strat

    Paul Strat Tele-Meister

    139
    Apr 7, 2017
    Muscle Shoals, AL
    Unfortunately that app is only for Android. I did try a couple of apps and it appears to be 60hz
     
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  8. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    So 60Hz is likely a grounding issue of some sort. Double check *all the things* around v2
     
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  9. bwacke

    bwacke Tele-Meister Gold Supporter

    360
    Oct 28, 2007
    Toledo, OH
    What is the voltage reading across the 2200 ohm cathode resistor on V2? It should be around 8 volts. Also, what is the voltage from pin 6 and pin 1 (plates) to ground?
     
  10. Paul Strat

    Paul Strat Tele-Meister

    139
    Apr 7, 2017
    Muscle Shoals, AL
    This CE can cap has 4 ground lugs but they are all connected to the base and f the can. Is there a way to isolate the preamp section of the can?
     
  11. aerhed

    aerhed Tele-Afflicted

    Age:
    59
    Dec 24, 2016
    Boulder, WY
    Yes. By wiring a separate cap(s) for B+. I usually use 40uF on the first stage for these. It's fine with a GZ rectifier, but don't go higher.
     
  12. Paul Strat

    Paul Strat Tele-Meister

    139
    Apr 7, 2017
    Muscle Shoals, AL
    Cathode resistor is 8.8
    Pin 1 392
    Pin6 393
     
  13. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    On pin 1 and 6, what voltages to you get on both sides of the plate resistor? So, you've already measured at the pin, but what about the other side of the 100K resistors?
     
  14. Paul Strat

    Paul Strat Tele-Meister

    139
    Apr 7, 2017
    Muscle Shoals, AL
    On v2?
    It comes straight from the reverb transformer.
     
  15. Paul Strat

    Paul Strat Tele-Meister

    139
    Apr 7, 2017
    Muscle Shoals, AL
    But apparently I can’t count. It’s V3 that kills the buzz when pulled.
     
  16. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    Oh....bah.....yup :D

    And counting is important :D

    What if you ground pins 2 or 7? That effectively cuts of any signal going into that half of the tube as those are the grids. As there is no voltage there, it's safe to just ground it out with a clip lead. You don't have to do it right at the pins either as that might be hard to get to. Does doing that change anything? If so, that might help you narrow down the issue to half a tube instead of a whole tube.
     
  17. Paul Strat

    Paul Strat Tele-Meister

    139
    Apr 7, 2017
    Muscle Shoals, AL
    Grounding either 2 or 7 on v3 kills the noise.
     
  18. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    I'd focus on pin 2 since that's the reverb side of things. Killing 7 would kill both halves of that tube anyway really, since it's the second half of that reverb recovery.

    So....there's not a whole heck of a lot on pin 2 - a resistor to ground and your rca jack from the reverb. Do you measure 220K to ground from pin2?

    Disconnect each of those things and I bet your noise stops, since no signal would be coming into the tube.
     
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