Power Tube Types

Discussion in 'Amps and Cabs' started by voojo, Jan 2, 2008.


  1. voojo

    voojo Gold Supporting Member

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    Say you have an amp that isn't designed for any one specific type of power tube (let's say any octal type.) Using the same circuit & speakers, how big of a change sonically do you get just changing the power tubes? I know people generalize and say EL34s are the classic Marshall sound, 6L6s are usually associated with Fenders. Then you also hear people go from 6L6s to KT66s and say the differences are minor. What do you folks think?

    Seth
     
  2. Blue Strat

    Blue Strat Member

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    Generalizations are virtually worthless. Name a specific amp and 2 tube types.
     
  3. voojo

    voojo Gold Supporting Member

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    Fair enough. Though I have never played one, say a THD Flexi and EL34s vs. 6L6s, since those seem to be the most common.
     
  4. Roccaforte Amps

    Roccaforte Amps Member

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    Depending on the amp you may or may not notice
    the differences.
    For example,vintage 6L6 fenders still sound the same loaded with EL34's.
    Take a vintage Superlead and install 6L6 tubes and the amp will run cleaner,
    and be smoother on the bottom end. Very noticable.
    You can't assume anything, you have to try things to know for sure.
     
  5. voojo

    voojo Gold Supporting Member

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    Thanks for the response. Why I am asking is I have an amp on order (London Power Aurora FWIW) that can accept any type of octal power tube with a re-bias. I don't have a stock of tubes to play with, so I was thinking about buying a few different types of tubes to try, if it seems like it would be a somewhat noticeable change.

    I remember John Phillips stating that the tonal differences in a Bassman vs. JTM 45 were based more on circuit differences/amount of negative feedback and the speakers more than the tube type.

    Seth
     
  6. Laird_Williams

    Laird_Williams Member

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    There are so many variables in all this that it is hard to say.

    Bias voltage is certainly one variable and it tends to be nicely adjustable, as long as the amp does not have a self-bias circuit for its power tubes.

    An amp with EL34s at a relatively high plate voltage will sound different from one with EL34s at lower plate voltages. Both of these will sound different than 6L6's at high or low plate voltages.

    And you can say essentially the same for the screen voltage too.

    The net is, you really have to ask the question pretty specifically.

    What amp, what plate voltage, what grid voltage, what bias type, what bias voltage, which of these do you have the opportunity to adjust and which do you expect to keep set as-is?

    Oh yeah - and if you are putting EL34s into an amp that is designed for 6L6s, then double-check your available heater (filament) current, since the filaments on EL34s draw lots more current.
     
  7. Roccaforte Amps

    Roccaforte Amps Member

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    Why not ask London Power? He's a good guy he'll answer your questions.
     
  8. voojo

    voojo Gold Supporting Member

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    I could, he's on vacation right now, and I just thought it would be cool to get the opinions of some of the knowledgeable people on this board. More based on curiosity than anything. You are right though, Kevin is a nice guy and he has answered many questions for me.
     

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