EL34 tube type selection

Discussion in 'The Workbench' started by Deepstone, Aug 8, 2012.

  1. Deepstone

    Deepstone New Member

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    Hi I have a Marshall 2558 that uses 2 EL34 tubes and I need a new set. the last time it was biased it looks like they set it around 37.8 ...would that be low, med or high type EL34's? not sure what to buy. MF also has a color code for some. Please advise ..also what is a good brand for a fat blues rockin tone!! Thanks!!:thumb:
     
    Last edited: Aug 8, 2012
  2. plexifier

    plexifier Active Member

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    Bias must (or at least should) be adjusted in fixed-bias amps like yours when you replace power tubes, in spite of what Groove Tubes, Musician's Friend or others may claim.

    Tubes can vary a lot, even within so-called "matched sets" or those with rating numbers like GT uses.
     
    Last edited: Aug 8, 2012
  3. Deepstone

    Deepstone New Member

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    Thanks...:dude:
     
  4. LBKENNEDY

    LBKENNEDY New Member

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    probably sling a cat to the city limits of knoxvil
    seriously deepstone there are several factors to be considered before
    using some arbitrary value recommended by somebody's cousin.
    there is an official factory value determined by marshall at build.
    by all accounts it is now incorrect, since modern tubes must be derated.
    the math is all over the internet, my friend unless you can afford
    a pickup full of vacuum tubes, studying this issue and then deciding.
    at the very least this should tell you the kind of amp tech your looking for,
    a good one
    lbk
     
  5. LBKENNEDY

    LBKENNEDY New Member

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    hey folks make sure you listen to further on up the road and
    on deepstones reverbnation link. pretty good stuff. lbk
     
  6. Wilder Amplification

    Wilder Amplification New Member

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    There is no such thing as "official factory values" when it comes to biasing and even if there was, it would be invalid.

    Anyone who understands the operation of amplifiers can easily calculate the setting.

    That being said, in Class AB amplifiers you can go no higher than 70% of the rated plate dissipation of the valve provided the amp was designed with the proper plate loading in mind (which most Marshall amps were).

    For the type of tone the OP is looking for I would recommend a set of JJ E34L valves. Nice fat mids and tight lows...very responsive and musical sounding valve with lots of clarity.
     
    zenfly likes this.
  7. peterichardz

    peterichardz Well-Known Member

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    What Jon says!!!!!!
     
  8. LBKENNEDY

    LBKENNEDY New Member

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    official might br the wrong word mr wilder,but there are many documents
    out there saying that 45mv was originally used, which as you have pointed
    out is not ideal.

    aint eyes wonderful, mouths not so much.

    regards lbk
     

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