New tubes rebiased sounds like crap. Please help

Discussion in 'The Workbench' started by 12AX7, Feb 4, 2020.

  1. ampmadscientist

    ampmadscientist Well-Known Member

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    100ma would make the tubes last forever but it would sound like doo doo.
    They might set it that way when it's under warranty, just to make sure the tubes won't wear out.
    Well yes eurotubes is correct at 180 ma.
    With 180 reading, the actual plate current is around 40 ma per tube or 160ma plate all 4 tubes.
    The other 20 ma is being used by preamp tubes, screen grids, and slight leakage of filter caps etc.
     
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  2. mickeydg5

    mickeydg5 Well-Known Member

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    100mA is incorrect. Do not follow this instruction. There is a lack of information. This amplifier can operate with 6L6/5881.
     
    Last edited: Feb 6, 2020
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  3. tschrama

    tschrama Well-Known Member

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    Dont listen to them. Try 90mA and judge for yourself.
     
  4. ampmadscientist

    ampmadscientist Well-Known Member

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    You can run it low 90-100ma if you want but there's a lot of crossover distortion.
     
  5. mickeydg5

    mickeydg5 Well-Known Member

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    My biggest point was that the instruction indicating 100mA did not specify the power tube type.
    6L6/5881 may be nice at 25mA per power tube but I would not care for 6CA7/EL34 at that idle.
    I also do not think it mentioned pulling preamp tubes or how much current the rest of amplifier will draw.
    If you subtract that from the 100 then its way low for 4 power tubes.
     
  6. J E H

    J E H Active Member

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    AGAIN, tubes are a pain in the ass.
     
  7. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Really? They treat me just fine.
     
  8. Gunner64

    Gunner64 Emotional Support Animal Gold Supporting Member

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    You must be sitting in the wrong place..:D
     

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