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  • #16
    Originally posted by Randall View Post
    He didn't think matching tubes was a thing, or even from side to side on a Twin as far as I know.
    The later SF Twins etc. did have the 'output tubes matching' trim pot, but it was all about nulling audible hum, not balancing power output (or symmetrical clipping).
    Modern Fender's no longer have this, but they come equipped with matched power tubes, so excess hum due to mis-match is not an issue.

    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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    • #17
      Originally posted by g1 View Post
      The later SF Twins etc. did have the 'output tubes matching' trim pot, but it was all about nulling audible hum, not balancing power output (or symmetrical clipping).
      Not so sure about the last part, as minimum power stage hum is a consequence of equal gain on both sides of the primary, which typically means balancing.

      - Own Opinions Only -

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      • #18
        Equal gain? Or equal idle current?
        Education is what you're left with after you have forgotten what you have learned.

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        • #19
          Originally posted by Enzo View Post
          Equal gain? Or equal idle current?
          Equal gain (at idle) I think, but might be wrong.
          Hum cancelling requires AC currents through both primary halves to be identical (and in-phase).
          I'm not sure if equal DC currents can ensure that with somewhat different tubes.

          With similar tubes, equal gain at idle typically (though not always exactly) goes along with equal idle currents.

          Neither equal gain nor equal idle currents ensures symmetrical clipping, but chances are good, if tube characteristics
          - especially saturation voltages - don't differ much.
          Helmholtz
          Old Timer
          Last edited by Helmholtz; 10-16-2021, 04:31 PM.
          - Own Opinions Only -

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          • #20
            Well a bit of 'chicken or egg first' scenario then. The instructions were to adjust for minimum hum. Maybe that was actually the goal, or maybe they thought it was the simplest way to get to symmetrical clipping.
            "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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            • #21
              Originally posted by g1 View Post
              Well a bit of 'chicken or egg first' scenario then. The instructions were to adjust for minimum hum. Maybe that was actually the goal, or maybe they thought it was the simplest way to get to symmetrical clipping.
              What I meant say is, that I think it's both "chicken and egg"".

              Adjusting for least hum allows any untrained user to get decent balancing without using a meter.

              - Own Opinions Only -

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