'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. JD0x0

    JD0x0 Poster Extraordinaire

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    It could be the cap. Ceramics can do weird ****. That cap is 1000pF/1nF/.001uF but you could replace it with any common coupling cap values. Anything from 500pF to 100nF
    Larger values will feed more bass into the PI. Lower values will cut the low end into the PI.
     
  2. slider313

    slider313 Tele-Afflicted

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    Anything from .001 to .01 would work. I use a .005 in mine.
     
  3. lookah

    lookah Tele-Meister

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    Well, wasn't the cap. Moved on to probing the fiberboard and I measured up to .580V DC in one spot. Most of it is zero to .75V

    Is that enough to generate the noise and warrant a baking?
     
    Last edited: Aug 14, 2017
  4. jazzguitar

    jazzguitar Tele-Afflicted

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    Sounds like you have a bad board. The voltage as read directly from ground to any point of that cardboard should be below what your meter can read.
    Yes it is possible this is the cause. And then, maybe not.
    It appears you have bad luck, I see no reason why the faults should be connected.
     
  5. robrob

    robrob Poster Extraordinaire Ad Free Member

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  6. BobbyZ

    BobbyZ Doctor of Teleocity

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    Have you tried it with the verb/vib pedal and reverb cables disconnected?
     
  7. lookah

    lookah Tele-Meister

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    Yes
     
  8. lookah

    lookah Tele-Meister

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    I left it on overnight for ~8hrs. Seems that the crackling and popping is a bit tamed down. The only other clue is that turning the trem intensity knob up makes a whole lot of noise for a few seconds as though it's discharging some voltage. Furthermore if I subsequently insert my shorting plug into the Term pedal the ticking is unusually loud. There might be a connection... especially since my Term tube blew up yesterday inexplicably. The 100k & 10M resistors in the Term circuit have already been replaced. BTW what makes a tube go cloudy white inside. Is it a clue that it failed in that manner?
     
    Last edited: Aug 15, 2017
  9. BobbyZ

    BobbyZ Doctor of Teleocity

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    Cloudy white inside a tube means it's shot or will be pretty soon.
    All your grounds good ?
     
  10. Dacious

    Dacious Doctor of Teleocity

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    Cloudy white means outgassed. The white is the 'getter' absorbing oxygen. The tube is cracked, or developed a bad leak and may be partly the cause of your horrible noise. It sounds like the cap is an issue too.
     
    Last edited: Aug 15, 2017
  11. lookah

    lookah Tele-Meister

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    Thx. The failed tube happened yesterday while I was diagnosing the amp. I'd already tried swapping it out days ago and it's def not the cause of the noise. Plus noise is same now that there's a new tube in there.

    The intensity pot is really acting up now noise-wise. It's def scratchy when I turn it (so DC voltage is leaking there) and the thump when I activate the Trem is like none I've heard before...super loud!

    Same problem as crackly board? Different problem? Is the Intensity pot suspect or should look elsewhere in the Trem circuit first?

    Here's 2 audio files...1) the basic static noise and 2) the Intensity pot noise. Check out how loud the thump is when I active the trem half way thru. Sounds like a rave!!



     
  12. lookah

    lookah Tele-Meister

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    FIXED & SOLVED! The culprit...a .1 ceramic cap rated at only 50v connected to pin 6 of V4 and the 220k resitor at "Y" on the schematic. That cap gets fed ~200VDC so makes sense that it failed! Also makes sense that it was messing with the intensity pot and tremolo (nasty thump and scratchy/noisy Intensity pot are all gone). I'm thinking the previous owner put that low rated cap in by mistake (there are signs of major modding prior to my owning it). Or did Fender get it wrong? I think it's usually a higher rated orange-blob type cap, not a ceramic. Anyway...

    Thanks everyone for your patience and encouragement. It came down to isolating the problem by removing the various grid inputs and I was able to narrow it down. Saved myself a few hundred $ of tech fees for sure!

     
  13. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    FWIW - as rob *didn't* say..but sorta said. (lmao).

    Those board readings seem awfully high. Even if there isn't noise now...welll.....
     
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