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kalamazoo model one

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  • kalamazoo model one

    I have a record player amp that used a 6au6 el84 and a 6x4. PT is putting out 332 on pin1 and 332 on pin 6 of 6x4 with a rectified voltage of 447. C4a is a 40uf versus the 20uf listed on schematic getting 443 volts c4b is 10uf getting 440volts and c4c is 10uf getting 401 volts. To me this seems awfully high for a el84 even though that's what originally was in it. These voltages are with the rectifier only, have not put in 12ax7 or el84 yet. What could i do to bring voltage down or will it come down once other tubes are in?

    Thanks,
    JasonClick image for larger version

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    soldering stuff that's broken, breaking stuff that works, Yeah!

  • #2
    Load it up with tubes.
    Then remeasure it.

    It's not the voltage that will get you, it's the current.

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    • #3
      It would help A LOT if we had a schem of the original amp to bounce those voltages off of. I'll assume that because it was an old record player that the PT primary was 110V. I think R.G. has a nifty device made from a 12V Rat Shack transformer wired in conjunction with the PT primary that will get you closer to vintage voltage. This would be especially important to the filament circuits. A recent thread here revealed that tube life is shortened dramatically over 10% of spec for filaments. It certainly wouldn't hurt the EL84 either being that anything over 350V would be high for class A on that tube. Nudging up to 390Vp (where you'll probably land) is really high. I've done it. It greatly reduces tube life also.
      "Take two placebos, works twice as well." Enzo

      "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

      "If you're not interested in opinions and the experience of others, why even start a thread?
      You can't just expect consent." Helmholtz

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      • #4
        Having worked on those old single ended phono amps, all that I can say is the voltages will be fine.

        They had to squeak every watt out of that EL84 that they could.
        Which isn't much.

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        • #5
          Originally posted by Jazz P Bass View Post
          Having worked on those old single ended phono amps, all that I can say is the voltages will be fine.

          They had to squeak every watt out of that EL84 that they could.
          Which isn't much.
          Fair enough. But the designers :

          1) had better tubes to abuse
          2) didn't expect 40V extra or more on the tube
          3) wouldn't dream that it might one day be used cranked up into a square wave most of the time

          So I suppose it depends on how this new incarnation of the amp will be used/abused to some degree. I still think getting the voltage down to stock would be a good idea.
          "Take two placebos, works twice as well." Enzo

          "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

          "If you're not interested in opinions and the experience of others, why even start a thread?
          You can't just expect consent." Helmholtz

          Comment


          • #6
            Gotten this amp going now will have to post pics and voltages tomorrow. For an exercise in true point to point I'd have to say Lead Dress if done without much thought will drive you nuts.

            jason
            soldering stuff that's broken, breaking stuff that works, Yeah!

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