Four 6L6GC Tubes 35 40 40 35 -- Balanced?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mbruffey, Mar 16, 2006.


  1. mbruffey

    mbruffey Member

    Messages:
    275
    Joined:
    May 22, 2005
    Location:
    Twin Cities
    Suppose I had 4 t6L6GC ubes, two drawing 35 ma and two drawing 40 at idle, 430 volts. If I arranged them in the following order, right to left, in the power amp, would the sections actually be balanced?

    35 40 40 35
    or
    35 40 35 40
    or
    40 35 35 40
    or
    40 35 40 35

    Would there be any noticable tonal difference with this kind of setup as opposed to a quad of 40 40 40 40?

    One more. TWO tubes, one 40 one 45 in a two tube output section. Can you hear the difference btw these and a 40/40 or 45/45/ pair?

    Just curious.

    Thanks, Mark
     
  2. JJman

    JJman Member

    Messages:
    990
    Joined:
    Mar 12, 2006
    Location:
    New Jersey
    All 4 schemes look balanced to me. At least from the OPT's point of view.
     
  3. mbruffey

    mbruffey Member

    Messages:
    275
    Joined:
    May 22, 2005
    Location:
    Twin Cities
    actually i'm running a 40/45 pair now; sounds good to me . . . .
     
  4. bob-i

    bob-i Member

    Messages:
    6,884
    Joined:
    Oct 16, 2005
    Location:
    Central NJ
    You're measuring the DC idle current, not the ability of the tube to amplify AC signals. You really can't measure DC and know if the AC will be balanced, you'd need to scope out the AC.

    It's pretty typical that an output xformer is unbalanced in DC resistance. I like to bias each tube on it's own so it can be balanced, but this has no effect on the AC amplification factors other than setting the bias point.
     
  5. mbruffey

    mbruffey Member

    Messages:
    275
    Joined:
    May 22, 2005
    Location:
    Twin Cities
    Does this (ignorance of the AC measurements/behavior) mean you could have two tubes that, say, are 20ma apart in current draw without any adverse effect on the tone? Obviously, one would have to remain within the safe dissipation limits of the hotter of the two, which could leave the cooler tube really really cold. If this is the case, matching isn't really all that big a deal, perhaps?
     
  6. rockon1

    rockon1 Member

    Messages:
    11,456
    Joined:
    Aug 12, 2005
    Location:
    Stamford CT

    I have read here that matching isnt a big deal

    FREQUENTLY ASKED QUESTIONS

    by Kevin O'Connor of [​IMG]



    Q: What's the deal with matched tubes? Some experts say they're very important, and these days it doesn't seem to be too expensive to get matched tubes. Then they talk about matched preamp tubes, and I don't know where to get those.
    A: You don't need matched tubes of any kind in your guitar amp. If you are trying to achieve vintage Fender, Marshall, Vox, Silvertone, Gibson et al. tones, then you simply plug in the tubes you have, check the bias and play. No manufacturer of musical instrument amps uses matched tubes, with the possible exception of Groove Tubes.
    As discussed in the TUT-series, matched tubes will drift out of balance over time due to electrical imbalances in the circuit and the different response of each individual tube to mechanical stimulus. Drop the amp and one tube may break while the other survives, even though they were electrically "matched" when you bought them.
    As discussed in this FAQ and in our books, asymmetries in the push-pull output stage, and in the handling of the signal throughout the signal path, contribute to the harmonic balance and thus the warmth of the tube amp's sound. You can build in specific asymmetries, or use unmatched tubes or even different tube types to play with asymmetry. Matched triode sections are often cited as "beneficial" in the Schmitt splitter used in most guitar power amps. The circuit is inherently out of balance and has skewed values to restore some semblance of output signal balance. Perfectly matched triodes would offer no actual benefit and would contribute to higher levels of odd-order harmonic distortion. These sound "crisp" in small quantities but are "harsh" in large levels.
     
  7. mbruffey

    mbruffey Member

    Messages:
    275
    Joined:
    May 22, 2005
    Location:
    Twin Cities
    OK, I have a single GE 6L6GC tube with side getter flashing. On this hypothesis, assuming it's a good tube, it would be perfectly sane to pick up a SINGLE good GE 6L6GC, plug in, bias and go! I might just do that! Thanks for all your input. This is really a great group of fellow audio lovers. Mark
     
  8. rockon1

    rockon1 Member

    Messages:
    11,456
    Joined:
    Aug 12, 2005
    Location:
    Stamford CT
    I guess Ive had good luck or maybe Sovtek are fairly rugged of the new manufacturers. In the last 15 years Ive only had 1 power tube fail(EL84) on me and I used Sovteks cause thats all I knew about until I got a computer a few years back.This is with 3 or 4 amps used fairly regularly.Never had a pre amp tube fail until recently when I had 2 JJ ECC803s's crap out on me within a couple of weeks of use.
     
  9. mbruffey

    mbruffey Member

    Messages:
    275
    Joined:
    May 22, 2005
    Location:
    Twin Cities
    All the Sovtek preamp tubes I have had experience with start with low output and go downhill from there . . . . I do think the Sovtek 5881WXT's (stock in my Fender Twin RI 15) sounded pretty good for the style I play (Chet) though. Mark
     
  10. mbruffey

    mbruffey Member

    Messages:
    275
    Joined:
    May 22, 2005
    Location:
    Twin Cities
    yuk! yuk! yuk!
     

Share This Page