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  • #31
    Originally posted by Helmholtz View Post

    What made you choose an unrealistic grid bias of -9V?

    That would result in an idle current of 75mA per tube or a plate dissipation of 24W (!) or 200% at idle acc.to Nick's tool.
    The example illustrates why it’s unrealistic.
    I wanted to show a 30% difference for so choose -14V vs -10V, or whatever.
    If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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    • #32
      Originally posted by SoulFetish View Post
      I wanted to show a 30% difference for so choose -14V vs -10V, or whatever.
      Actually I'm not sure how to interpret the "Max Dissipation watts (sine wave, per tube) =16.13" value in Nick's tool.

      If it actually means max dissipation it can't be lower than the idle dissipation (24W in the example).

      Maybe it should read Max Power Dissipation instead? Dissipation at full power can be lower than idle dissipation in very hot biased amps.

      Fixed bias Class AB amps often have a dissipation maximum at some medium output.
      Last edited by Helmholtz; 05-17-2021, 03:30 PM.
      - Own Opinions Only -

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      • #33
        Originally posted by Helmholtz View Post

        the idle dissipation (24W in the example).
        How are you getting these idle figures from the tool? I set grid signal to 0, but still don't see any numbers like the 24W you mention, or the 200% ?

        "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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        • #34
          Originally posted by g1 View Post
          How are you getting these idle figures from the tool? I set grid signal to 0, but still don't see any numbers like the 24W you mention, or the 200% ?
          You need to point to the operating point in the Ip/Vp graph. A little black window pops up showing plate current at different conditions.
          Use the value labelled "Load Line" for Ip and multiply by plate voltage.

          Or just read the idle current from the loadline graph.
          Last edited by Helmholtz; 05-16-2021, 04:46 PM.
          - Own Opinions Only -

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          • #35
            Originally posted by Helmholtz View Post

            Maybe it should read Max Power Dissipation instead? Dissipation at full power can be lower than idle dissipation in very hot biased amps
            absolutely. Good point
            If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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