Pulling tubes

Discussion in 'Amps and Cabs' started by edcat, Jan 14, 2015.

  1. edcat

    edcat Supporting Member

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    I've read that some people actually pull a power tube in some amps to decrease volume . I think I read a post that this could be done with a Fender Twin. Is this true and would damage be done to the amp in doing so?
     
  2. wyatt

    wyatt Member

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    You can not pull ONE power tube, you need to pull a pair, they work as a push-pull arrangement.

    So, yes, you can do it with quad-tubed Twin Reverb (But not a twin-tubed Super Reverb, Pro Reverb, Deluxe, Reverb, etc.). You also disconnect one speaker to get the impedance to match. Though must people will tell you the drop in perceived volume is relatively insignificant; if you are hoping for a big difference, you'll probably have to find a different solution.
     
  3. Mikeishness

    Mikeishness Member

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    Most tube amps are Class A/B, which means that two power tubes work as a pair. In that case it would be a very bad idea to remove one of the power tubes. However some amps like the Fender Twin have four power tubes - two pairs working in tandem. In that case it is possible to remove two of the tubes, as long as you remove ones that leave the remaining two working as a pair.

    I'm not sure how good an idea this is, or whether you need to rebias the amp after doing this. But it is possible on an amp like a Twin assuming you pull the right tubes.
     
  4. jonnytexas

    jonnytexas Supporting Member

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    My amp sounded funny at a gig recently, breaking up too early, less headroom, ect (haha) but got me through the gig. Turns out 1 6L6 had fallen out. Its a super reverb.
     
  5. swiveltung

    swiveltung Member

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    Yes, pull every other tube on the Twin. The speaker matching impedance changes though. You might not notice on the twin however....
     
  6. Blue Strat

    Blue Strat Member

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    Pulling 2 of 4 power tubes gives you a 50% POWER reduction which produces a barely noticeable volume reduction.
     
  7. C-4

    C-4 Member

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    I've done the tube pulling thing. Another possible suggestion is to use 4 Yellow Jackets.
     
  8. mcknigs

    mcknigs Supporting Member

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    On a Twin, pull the inner two or outer two (the former provides for better cooling of the tubes). This will change the ideal impedance from 4ohms to 8ohms. You could disconnect a speaker, change speakers to a pair that can be wired for 8ohms, or live with the mismatch. Theoretically, you should rebias. Practically, that might not be necessary.
     
  9. edcat

    edcat Supporting Member

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    Aha! Good thing I asked, I have a two power tube amp. Thanks guys.
     
  10. davebc

    davebc Member

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    I've never tried it, Because the impedance thing threw me.
    I thought it was either the 2 outside or 2 inside that got pulled?
    That's not correct?
     
  11. zenas

    zenas Member

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    Yeah a two tube amp will work like that BUT (really big but here) what happens is the amp goes from runing two tubes in push pull class AB to one tube in single ended class A.
    The amp will run like that but not well and for how long is anybody's guess. I'd quess the output transformer would be the first thing to go but I've never pulled one tube from my Super Reverb to see how long it would run or what goes up in smoke first. :)

    In short don't do it !
     
  12. woof*

    woof* Member

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    Yes, either the two outside or two inside.
     
  13. Blue Strat

    Blue Strat Member

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    That'll work. In reality, it's either one from the left pair PLUS either one from the right pair.

    Regarding impedance mismatch, if lower volume is your goal...the mismatch is preferable.
     
  14. mcknigs

    mcknigs Supporting Member

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    OTOH, if lower volume is your goal, fewer speakers is also helpful. ;)
     
  15. Blue Strat

    Blue Strat Member

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    There's that too! Both ways should be tried. ;)
     
  16. jonnytexas

    jonnytexas Supporting Member

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    Won't do it again. Thanks for the heads up.....it sounded kinda cool, though
     
  17. davebc

    davebc Member

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    I've never tried pulling a pair of tubes. I always heard it didn't make for a noticeable volume drop..
    I guess what's the point then? :dunno
     
  18. zenas

    zenas Member

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    Cuts the cost of power tubes in half.
     
  19. davebc

    davebc Member

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    Ohhh:roll that makes perfect cents.
     

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