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single ended 6v6 preamp question

Discussion in 'Shock Brother's DIY Amps' started by subgenius_one, Feb 20, 2021.

  1. subgenius_one

    subgenius_one TDPRI Member

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    Nickfl, That's really close to what I was thinking about, although I wasn't thinking of mixing them. I had thought that I would send the 6SJ7 straight to the 6V6 instead of to the second triode of the 12ax7.

    Can you tell me of the 2 channels sound different to you? How would you describe them?

    When I have some time I will check the values of the components against the magnatone circuit to see how close they are.
     
  2. Wally

    Wally Telefied Ad Free Member

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    Nickel, What does the 6SJ7 channel do with that triode added as a driver? Is it hotter than the 12AX7 channel?
     
  3. gigante

    gigante Tele-Meister

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    Nickfl, while answering Wally's question, do you happen to know what the gains of the 6SJ7 and 6SL7 triode are? I'm working on something similar and I'm trying to decide on gain levels.

    @subgenius_one - looking forward to what you come up with.
     
  4. Wally

    Wally Telefied Ad Free Member

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    gigante, the spec sheet specifies a gain factor of 19 for the 6SJ7 in triode mode. It does not give a gain factor for the pentode mode...or at least I could not find it when I looked yesterday.
    The 6SL7 has a gain factor of 70. The 6SN7 has a gain factor of 20. The 6SC7 has a gain of 70 with a different pinout compared to the 6SL7.
    http://tdsl.duncanamps.com/tubesearch.php
     
    Last edited: Feb 22, 2021
  5. gigante

    gigante Tele-Meister

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    Wally, I'll be using the 6SJ7 in pentode mode, just haven't decided how much gain I want to get out of it, with a triode feeding into it.
     
  6. Wally

    Wally Telefied Ad Free Member

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    I have looked through the 6SJ7 and 12SJ7 spec sheets. None of them give an amplification factor for the pentode operation????
     
  7. Nickfl

    Nickfl Friend of Leo's

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    Yeah, its definitely hotter. More high end, more crunch and easier to push into overdrive. That 6SJ7 is a pentode and grid leak biased so it has both of those factors working to make it hotter. The triode channel is warmer and less overdriven, it needs a P-90s or a humbucker (or a pedal) to get crunchy.
     
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  8. Wally

    Wally Telefied Ad Free Member

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    Thanks for the feedback, Nick. Have you ever considered a switch to go to triode operation with that 6SJ7? It would interesting to see how much more gain there is in the pentode since none of the sheets give us a clue on that aspect of pentode operation.
     
  9. Nickfl

    Nickfl Friend of Leo's

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    Pentodes don't have a set amplification factor because of the effect of the screen. The screen voltage sets the grid curve, which determines gain and headroom. Lower screen voltage equals more gain and less headroom.

    I don't have those numbers right now but I'll see if I can calculate them when I get a chance.
     
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  10. 2L man

    2L man Tele-Meister

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