Balanced triode?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by joek86, Feb 3, 2006.

  1. joek86

    joek86 Supporting Member

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    I have a Tophat Club Royale, I am going to try all Tung Sol pre tubes, should V#3 be balanced? What is the difference?

    Joe
     
  2. K-man

    K-man Member

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    From what I've heard, the only preamp tube that you will benefit from being balanced is the driver tube (the last preamp tube), and only if your amp is a Class AB (push-pull) amp.
     
  3. VintageJon

    VintageJon Member

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    The benefit is subtle. I have gone to excessive measures to balance the Phase Inverter and can hear very little difference. (Of course after 40+ years of Rock and Blues I don't hear that well!)

    Often the Phase Inverter is not balanced by design anyway...

    -Jon
     
  4. K-man

    K-man Member

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    That's what I've heard as well. Theoretically all of the resistors and caps in each side of the driver circuit would have to be exactly the same, which is next to impossible when they have a 10-20% tolerance and drift in value over time.
     
  5. scottosan

    scottosan Supporting Member

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    There is no benefit to the drive tube being balanced. The driver stage in that amp is self balancing. The only folks that will tell you you "need" a balanced tube would be those who benefit from you purchasing one from them.
     
  6. VintageJon

    VintageJon Member

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    Well, actually you can, but you have to test parts until you find them, and it rakes a lot of parts! (I test everything I sell.)

    The Priceton Reverb Phase Inverter balance is so popular that I've tested and labeled 500 of the 56K and 1K resistors and labeled them so I can just pick them out, having already spent the time to test them...

    -Jon
     
  7. Blue Strat

    Blue Strat Member

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    Jon: Have you checked DC balance (the only tester I know of that does this is the VTV) as opposed to AC balance (what most testers give you)?.

    I haven't spent the time yet, but plan to in my spare time (laughs) someday.

    Balanced DC triodes do seem to make a difference in the resulting plate voltages on the PI. As most of us know, if one half of the signal clips sooner than the other, which is the result of unbalanced plate voltages, the amp will break up sooner. Not to say that this is necessarly "bad" since some ears may prefer this.

    Simply repeating the mantra that "the phase inverter is self balancing" is lame. When someone has test results I'd like to see them.

    Note that I don't advocate tubes with balanced triodes, but if someone is convinced they want them, I do provide them. I'm not an evangelist, but I'm also not stupid enough to argue with customers.
     
  8. scottosan

    scottosan Supporting Member

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    No more or less lame than the statements made about the neccessity or benefits on having a balanced triode in the PI spot. I'm sure Hendrix, SRV, Santana, Clapton, etc.. were only able to get the tones they did with a balanced triode in the PI spot ;)
     
  9. scottosan

    scottosan Supporting Member

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    And you anticipate that there will be no drift?
     
  10. Matt H

    Matt H Guest

    regardless of drift- the design (assuming the "standard" LTPI) isn't balanced totally to begin with... it's entirely possible that you'll end up with BETTER balance using a "normal, not balanced" tube in that spot.

    it's such a crapshoot i honestly don't even think about it.

    besides- asymmetrical waveforms are what really make life worth living... mmhmm.
     
  11. Blue Strat

    Blue Strat Member

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    ...and it's possible that if the circuit is unbalanced, that using a balanced tube will maintain the asymmetry...or vice versa.
     
  12. fullerplast

    fullerplast Senior Member

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    Very true....in fact one could argue that the biggest advantage of knowing how your halves are matched is consistency when you replace the PI tube. You may find a big difference between a 30% mismatch one way vs a 30% mismatch the other way.
     
  13. Matt H

    Matt H Guest

    splatt, believe you've referred to this as "zhoozh" heheh (or someone has)

    funny thing about it- running a "boring little stock SD-1" can do the same thing... hahaha

    ah how i love asymmetrical waveforms!!!!
     
  14. johnny q

    johnny q Member

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    I knew there was a reason I liked doing business with you! :)
     

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