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Blues Junior keeps blowing F1 Fuse

Discussion in 'Amp Central Station' started by DougF, Oct 18, 2009.

  1. DougF

    DougF Tele-Meister

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    When I turn my Blues Junior on it hums for about two seconds than blows the F1 fuse. Any suggestions as to where to start with troubleshooting? It does have the BillM presence control and a Celestion 30, but is otherwise stock. Any advise would be appreciated.
     
  2. Al Watsky

    Al Watsky Tele-Afflicted

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    Power tubes would be my first try. Install a new set and hit the on switch and see what happens.
     
  3. tele_jas

    tele_jas Tele-Afflicted

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    If not a power tube, probably a Rectifier... If none of those, you'd probably need to take it to an amp tech.

    I kept blowing fuses in my Dr Z when my Rectifier tube was going out.
     
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  5. Billm

    Billm Friend of Leo's

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    The rectifier is solid state. I have yet to see a Blues Junior blow a diode, but anything is possible. I'd suspect output tubes, too. It's fairly common for EL84 screen grids to fail and short out to some other part of the tube.

    There have also been problems with leaky filter caps. One could short out internally, which would blow the fuse right quick:

    [​IMG]

    More info about this on my site:

    http://billmaudio.com/wp/?page_id=267
     
  6. DougF

    DougF Tele-Meister

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    Bill, you nailed it on the head. I noticed one of my Mullards had a black spot on the glass and when I swapped it out the amp worked fine. Does it hurt to have two different makes of output tubes? I noticed the other Mullard has a blue ring on the top its grid while the new Electro Harmonics looks fine.
     
  7. Billm

    Billm Friend of Leo's

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    Your output tubes should be a matched pair for best performance. When the tubes have different current draw and thus run at different levels of amplification, their ability to cancel out common mode hum is diminished. They also produce more harmonic distortion.

    Fender recommends that the output tubes be within 20 percent of one another.
     
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