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  • KT150 push pull

    An ad on kt150 tung sol tubes says :
    With a massive plate dissipation of 70 watts, the Tung-Sol KT150 is the most powerful octal beam tetrode ever produced. A pair of KT150s can allow an amplifier with a power output approaching 300 watts to be built.
    Tung sol says that a pair of 6550 can go to 100w, it's acceptable, but how can 2x70 = 300 ?

  • #2
    Plate dissipation is the power that heats up the plate and thus is lost and does not contribute to output power. Max output power with a PP pair can be 2..4 times higher than the single tube's plate dissipation. There is no simple relation between dissipation and output power.
    Last edited by Helmholtz; 09-04-2019, 12:36 AM.
    - Own Opinions Only -

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    • #3
      Up to 200W
      http://www.tungsol.com/tungsol/specs/kt150-tung-sol.pdf

      OR
      For 6550 - how can 2 x 42 W = 100W
      Answer is Class B Operation (or Class AB with very low idle currents , that is close to Class B)

      http://www.tungsol.com/html/faqs11.html

      Cheers
      Ian

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      • #4
        A pair of EL34s (Pa,max= 25W) can put out up to 100W (Ip = 25mA, biased at 80%, datasheet calls it class B). The trick is 800V plate voltage and very high Raa (11k).
        I am speaking of a serious data sheet example.

        Not much sense trying to calculate output from dissipation only.
        Last edited by Helmholtz; 09-04-2019, 01:26 PM.
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        • #5
          If you draw up the load line for most push pull guitar amps you'll notice that some part of the load line exceeds the maximum plate disippation. Given that for approximately half the time a given tube is 'off' that's ok. Cross 2x max plate dissipation and it'd red plating time. Quite how far this can be pushed before bad things happen is tricky. Give this analysis of a JMP poweramp a read, if it weren't for significant power supply sag it'd be bad news!

          http://ax84.com/bbs/dm.php?thread=409091

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          • #6
            Originally posted by Helmholtz View Post
            A pair of EL34s (Pa,max= 25W) can put out up to 100W (Ip = 25mA, biased at 80%, datasheet calls it class B). The trick is 800V plate voltage and very high Raa (11k).
            It works in simulation but I wouldn't want to try it for real.
            Max plate dissipation is at 25W output.

            Click image for larger version

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            • #7
              It works in simulation but I wouldn't want to try it for real.
              Why not? I have an old Siemens lab amp that operates at these conditions. Puts out around 90W before clipping.

              What is the x-coordinate in your picture?
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              • #8
                Originally posted by Helmholtz View Post
                Why not? I have an old Siemens lab amp that operates at these conditions. Puts out around 90W before clipping.

                What is the x-coordinate in your picture?
                Fear, the voltage is too high with too much current behind it for me

                The x axis is input voltage steps adjusted to take the output from zero full power.
                It makes a pretty pattern.

                Click image for larger version

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