6L6 or 6V6 in the same amp

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Brent Hutto, Apr 1, 2008.

  1. Brent Hutto

    Brent Hutto Member

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    So when you change between a 6L6 and a 6V6 power tube in a single-ended, cathode-biased Class A amp, what exactly are the change you would expect waveform-wise and tone-wise?

    Assume of course that you reconfigure the output stage to assure true within-spec Class A operation with each tube (i.e. change bias resistor, etc. as needed).
     
  2. Tallhorses

    Tallhorses Member

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    What you get is reduced headroom with the 6v6. I use to have a Headstrong (Prima 30) that would accept 6l6, 6v6 and el34 tubes. I lost little "volume" but the headroom was reduced significantly.
     
  3. EarlTX

    EarlTX Member

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    The pentode gain of a 6V6 is ~205, compared to a 6L6 which is ~135. Depending on the gain of your PI, you may not get the 6L6 into as much distortion as the 6V6.
     
  4. Brent Hutto

    Brent Hutto Member

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    So it sounds like you'd want the 6V6 for getting some grit at lowers volumes and conversely you'd prefer the 6L6 if you have a lot of gain early on but still want to play louder and cleaner.

    I don't know what "PI" stands for right off. I'm also curious how the amount of negative feedback interacts with those tube-gain amounts. Does a fixed negative feedback resistor tend to squeeze the ratio of those two gain ratings together a bit?
     
  5. mark norwine

    mark norwine Member

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    Single ended amps don't have a PI....
     
  6. Brent Hutto

    Brent Hutto Member

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    Good hint. Phase inverter. Got it.
     
  7. Brent Hutto

    Brent Hutto Member

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    It's a Richter RS 5.8 which was intended from the beginning to allow a choice of 6V6 or 6L6 power tubes. Switchable bias resistor (capacitor bypassed of course) in line with the cathode. Other than that it's an AA764 Blackface type circuit although with different NFB resistor and tone stack values. It uses a 5Y3GT so the plate voltage drops a fair bit with the 6L6 in there, as well. The builder says it sounds equally good but quite different with the two tubes.
     

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