66 Princeton reverb Troubleshoot

Discussion in 'Amp Tech Center' started by PooTwang, Dec 14, 2019.

  1. PooTwang

    PooTwang Tele-Meister

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    It just faded out like it lost a tube, no noise no smoke or smell. All tubes are lit, I rolled the pre amp tubes no result I can still hear some hiss when I roll up the volume but I got no signal coming out . I will pull Chassis and take a look inside it’s an old girl it’s output transformer was changed at one point in its life will see what we can find
    To be continued
     
  2. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Dead is usually the easiest to fix.

    It would be good to know if it's been recently serviced or not as it should be on it's third or fourth set of electrolytics by now. If there's no sound coming out though, tracing audio through a circuit would only take a minute to see where it's dying.
     
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  3. schmee

    schmee Poster Extraordinaire Silver Supporter

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    Try power tubes?
     
  4. D'tar

    D'tar Friend of Leo's

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    If volume pot has effect on noise I would assume all is good beyond that point. Try both inputs. Try another cable and guitar to rule that out. Swap in a known good tube for v1. You can use v2(reverb driver tube) for troubleshooting
     
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  5. D'tar

    D'tar Friend of Leo's

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    If you're going inside the chassis make up a voltage chart and observe any noises as you probe each pin. +1 on checking on the electrolytics
     
  6. PooTwang

    PooTwang Tele-Meister

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    All ready ruled out the cable ,speaker, pre amp tubes, Thats the plan start at the volume pot chase the signal path
     
  7. PooTwang

    PooTwang Tele-Meister

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    A quick look over of the chassis everything looked ok , popped it back together. And it works
    Better lucky than good! may have been a loose tube
     
  8. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    I was thinking loose power tube as well. My 68 did that when I first bought it.
     
  9. BobbyZ

    BobbyZ Doctor of Teleocity

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    Have to be two loose power tubes to kill it completely. One can fall out completely and it'll still sorta work. The volume drops and it's forced to run single ended instead of in push pull, not a real good thing, but it'll still "work" like that.
    Old amp trick for finding out if one tube is weak or to see if one side of things is wonky. Trying a two tube amp with just one.
    Not a good idea on cathode biased amps with a shared cathode resister!

    Anyway I think your trouble is else where and if you're like me, it'll happen again.
     
  10. PooTwang

    PooTwang Tele-Meister

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    BobbyZ you called it , she quit on me again.
     
  11. BobbyZ

    BobbyZ Doctor of Teleocity

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    Did it start working again or stay dead?
    It's easier it they stay dead. But you could get lucky and see something loose inside. Spend some time looking at every solder joint, sometimes you'll see it.
     
  12. PooTwang

    PooTwang Tele-Meister

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    The DR. Found a bad bypass cap on V1 to be the culprit , very odd the sprauge dated 2006 gave up weird thing is it tested ok but still passed to much voltage go figure
     
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