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Are these safe B+ voltages (SF Champ)

Discussion in 'Shock Brother's DIY Amps' started by grobe, Jul 26, 2009.

  1. grobe

    grobe TDPRI Member

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    Hi there. Newbie to this board. :p

    Just did a complete rebuild of my '70 champ and did some voltage readings before actually 'plugging in'. The only original part in the current build is the power transformer. I'm getting around 500v at the 5Y3 and Cap-can, around 475v at the 6V6 anode, and around 450v at 12AX7 anode. I'm using a cheap VOM so those readings could be off a bit. These are obviously WAY higher than what is printed on the schematics, and I'm a little scared to start using the amp.

    Are these normal voltages? Why the huge difference?
     
  2. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    Are the tubes in?
     
  3. RomanS

    RomanS Poster Extraordinaire

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    They seem to be a bit high...
    As JC already asked: did you measure with the tubes in (without tubes, voltages are higher!).
    What kind of 5y3 are you using? The modern Sovtek "5Y3"s aren't really 5Y3s and drop too little voltage, if you've got one of those, try to find a NOS 5Y3 for lower voltages!
     
  4. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    Good call RomanS, I forgot to ask about these new 5Y3's...
     
  5. grobe

    grobe TDPRI Member

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    Yup. All tubes are in and I've tried some different tubes. Same result.
     
  6. grobe

    grobe TDPRI Member

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    All tubes are various Vintage/NOS -Mazda's, RCA's, Sylvania's, etc.
     
  7. grobe

    grobe TDPRI Member

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    Thanks for the replies.
     
    Last edited: Jul 26, 2009
  8. grobe

    grobe TDPRI Member

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    Aha! I think I found the problem and I can't believe I didn't pick up on this before. The lamp and filaments aren't getting any power. I just thought that it was the lamp bulb. Would that explain the high voltages at tubes? I wonder if that part of the power transformer got burned out. Hopefully I didn't damage the tubes.
     
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