New tubes rebiased sounds like crap. Please help

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

  1. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    18,187
    Likes Received:
    12,196
    Location:
    Bio-Isolation Lock Down
    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.
     
    12AX7 likes this.
  2. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    24,657
    Likes Received:
    11,592
    Location:
    US of A
    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
    12AX7 likes this.
  3. tschrama

    tschrama Well-Known Member

    Joined:
    May 15, 2010
    Messages:
    1,135
    Likes Received:
    429
    Location:
    Netherlands
    Dont listen to them. Try 90mA and judge for yourself.
     
  4. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    18,187
    Likes Received:
    12,196
    Location:
    Bio-Isolation Lock Down
    You can run it low 90-100ma if you want but there's a lot of crossover distortion.
     
  5. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    24,657
    Likes Received:
    11,592
    Location:
    US of A
    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

    Joined:
    Apr 4, 2018
    Messages:
    249
    Likes Received:
    99
    AGAIN, tubes are a pain in the ass.
     
  7. Chris-in-LA

    Chris-in-LA Well-Known Member

    Joined:
    Jul 19, 2018
    Messages:
    1,038
    Likes Received:
    722
    Location:
    Los Angeles
    Really? They treat me just fine.
     
  8. Gunner64

    Gunner64 Well-Known Member Premium Member

    Joined:
    Nov 16, 2013
    Messages:
    6,041
    Likes Received:
    7,708
    Location:
    Midwest, USA
    You must be sitting in the wrong place..:D
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice