Bugera 6260 infinium combo tube monitoring issue

Discussion in 'Amp Tech Center' started by Steve77, Sep 22, 2021.

  1. Steve77

    Steve77 TDPRI Member

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    So a friend of mine had this amp. It was giving him trouble so he took it in to a local shop several times. Nothing was achieved. He has since bought better amps and really gave up on this one.
    He has given it to me to fix or scavenge. A free Bugera, hmm well worth a shot at getting it going.
    It runs ok for a little. Then the tube monitoring on the back shows a problem with the number 1 power tube. It gets quite and sometimes no sound at all.
    I took all the power tubes out and swapped positions but I still get the number 1 power tube led lighting up.
    Has anyone encountered this problem?
    Could a bad preamp cause the light to come on?
     
    Last edited: Sep 22, 2021
  2. corliss1

    corliss1 Poster Extraordinaire Platinum Supporter

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    Nope. Good luck - this is a notoriously bad circuit and the little monitoring section is known to just not work well/go bad, with no spare parts available.

    I tried cutting traces on the board of one to try and work around it, but didn't get very far. Probably could have tried harder, but for the build quality of the amp it wasn't worth it to me.
     
  3. Steve77

    Steve77 TDPRI Member

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    I’m wondering if that’s what it’s gonna come to. Too much work for what it’s worth. It came with decent el34s and I can probably scavenge a little more from it.
     
  4. corliss1

    corliss1 Poster Extraordinaire Platinum Supporter

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    Even the knobs, while they look cool, are just a super cheap molded plastic.
     
  5. Steve77

    Steve77 TDPRI Member

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    Sigh.. bugera. Meh well at least it was free. Worst case I keep the power tubes and dump the rest.
     
  6. andrewRneumann

    andrewRneumann Tele-Holic

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    Does anyone know what the “tube monitoring” monitors? Some sort of overload protection / bias safety device?
     
  7. corliss1

    corliss1 Poster Extraordinaire Platinum Supporter

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    It's some type of bias detection thing.
     
  8. Gunny

    Gunny Tele-Holic

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    I'd be happy to get one of those amps for free. For a tech guy like me, I'd fix or eliminate the tube monitor stuff and just ensure all other parts were working properly - and if not, fix it.
    How bad (sounding) can this 100 Watt head be?
    Wish I lived closer; I'd buy it.
     
  9. Jon Snell

    Jon Snell Tele-Holic

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    As far as I am aware, 'tube monitoring' is not in these designs. Marshall brought out a version of bias monitoring that measured the cathode current at zero signal and set the bias voltage to the designed level.
    These were notorious when the EL34s got old!
    I have looked at the older versions and the newer versions of the 6260 and 6262. The output valve cathodes go to point F in all cases.
    Point F is a chassis point with no monitoring.
    The only thing that could be twisted to be called monitoring, is the test point that is set to -42v for the USA 5881 version.
     
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