'66 Deluxe Reverb Crackle Pop & Static problem - not the tubes, sockets or plate resistors

Discussion in 'Amp Tech Center' started by lookah, Aug 13, 2017.

  1. lookah

    lookah Tele-Meister

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    Hi All. Need some help. I can't seem to figure out the culprit for the crackly noise from my DR. Main clue so far is that pulling the PI 12AT7 is the only thing that stops it. The amp has been working great for past few months. The issue started a few days ago as intermittent pops (~once an hour) and eventually the crackling and even some occasional whistling type noise joined in. Now happens as soon as amp goes off of standby. No guitar plugged in. All knobs on 0.

    -fresh set of new tubes that I've also dbl checked against other good tubes
    -deoxit on all tube sockets (and pots)
    -retensioned all sockets.
    -replaced PI 82k & 100k resistors
    -replaced all 100k plate load resistors
    -chopsticks test on every component - noise never goes away
    -grounding on brass plate was all redone
    -all filter & electrolytics caps are new

    Wasn't able to embed the audio file here but there's a link to how it sounds on my TGP post

    https://www.thegearpage.net/board/i...the-tubes-sockets-or-plate-resistors.1855817/

    Thanks!

    Luca
     
  2. Dacious

    Dacious Poster Extraordinaire

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    Does it do it with reverb cables unplugged?
     
  3. trouserpress

    trouserpress Tele-Holic

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    You could refresh the solder joints of the (said) tube socket(s). Sometimes chopsticking doesn't reveal a bad joint.
     
  4. lookah

    lookah Tele-Meister

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    Yes.
     
  5. lookah

    lookah Tele-Meister

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    I'll try that.
     
  6. JD0x0

    JD0x0 Poster Extraordinaire

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    Conductive Fiber board.
     
  7. lookah

    lookah Tele-Meister

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    Any solutions for that in case its the culprit? Humid Northeast weather is prob not helping. I lifted the board and cleaned the chassis, pots, brass plate etc months back when I was a chasing a different problem. Its a very clean amp inside.
     
  8. lookah

    lookah Tele-Meister

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    all solder joints on 12_7's retouched as well as on entire phase inverter circuit...any other ideas?
     
  9. D'tar

    D'tar Friend of Leo's

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    Dark room and watch for the light show. Lovely blue sparks. Speaker connections, wires, jacks.
     
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  10. Cleeve

    Cleeve Tele-Holic

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    Make sure there is no high voltage left in the caps then re-solder the whole circuit- paying close attention to the grommets that have resistors running parallel to the long dimension of the fiber board.
    Failing that, remove the power tubes and the pilot light, or tape over it, and in a darkened room with the amp on, look at the power tube sockets to see if any corona or arcing is going on from the high voltage pin recepticals.
    Also standby switches have a hard life.

    I've seen also carbon tracking on the fiberboard in the capacitor house, if the main caps were changed a time or two it may be a good idea to see what things look like between those fiberboards.
     
  11. jazzguitar

    jazzguitar Tele-Afflicted

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    A possibility is that same as the carbon resistors can go bad an crackle, the carbon trace of the control pots can do.
     
  12. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    Also check all pots - I went through a maddening time years ago on a customer's amp - turned out to be corrosion buildup between pots and chassis.
     
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  13. lookah

    lookah Tele-Meister

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    Thanks everyone. Will retouch everything and also try to see if there's a light show when I pull the power tubes. However isn't the clue that pulling the PI stops the noise mean it wouldn't be an issue in the power section?
     
  14. JD0x0

    JD0x0 Poster Extraordinaire

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    To check for board conductivity just put your meter on DCR and one probe to chassis ground, the other probe will poke around the board. Poke all around and see if there's voltage on the board. Since the issue seems to point more towards the preamp, pay more attention to those areas of the board.

    The conductive board true fix is a non fiber board, but to repair an original, clean the board, use a hair drier or heat gun to re melt the wax and evaporate the moisture. Some people recommend putting the board in an oven at low temp for 3 days.
     
  15. lookah

    lookah Tele-Meister

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    NEW CLUE! I replaced the 1M carbon comp resistor coming off the grid (pin 2) of my V6/PI and the crackling is gone! But I now have a,lost no volume. It sounds like the amp has been attenuated to 1/2 watt and I have to crank it to even hear something. Um...?
     
    Last edited: Aug 14, 2017
  16. trouserpress

    trouserpress Tele-Holic

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    One should think so. Maybe some flawed resistor or cap in the way of the PI. Let's hope it's not the power transformer - choking periodically on some insulation gone bad. Unfortunately I'm no real electronics buff and therefore ran out of clever ideas. Nevertheless I'll stay tuned as you work on further hints and wish you luck.
     
  17. lookah

    lookah Tele-Meister

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    Thanks for that info
     
  18. lookah

    lookah Tele-Meister

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    Meanwhile turns out that after that initial 1M swap, my brand new tremolo tube in V5 blew (turned cloudy white). The 10M resistor seemed suspect so i changed it out. Probably related? Whole lot of bad luck or is something cascading? Just rechecked (via swapping) all preamp tubes and power tubes. No change. Still low volume
     
  19. lookah

    lookah Tele-Meister

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    Good god..hold on. Turns out it wasn't the 1M resistor. .001 ceramic cap in the PI circuit had a broken leg. Reconnected it via alligator clips and crackling is back! Ugh. Now I just gotta find/order a .001 cap. Not the most common to have laying around. Could a bad cap be the culprit of the crackle?

    Thank you all for your time and patience with me.
     
  20. lookah

    lookah Tele-Meister

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    what value cap can i use instead of the .001 just to see if that's the what's causing the crackle?
     
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