Clean power testing a 6G2 Princeton on an oscilloscope

Discussion in 'Amp Tech Center' started by peteb, Nov 30, 2019.

  1. peteb

    peteb Friend of Leo's

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    Small wave


    13659EEB-5D66-4834-A011-6DF4E3E66FF1.jpeg

    Cross over distortion




    C916C48E-5ABC-40E1-905D-62E363755A7A.jpeg

    Saturation on the top and the bottom

    See how uneven the two halves are? Is this the uneven nature of the cathodyne phase inverter. Is the clipping in the PI?

    Taking it one step farther, is it saturation on top and cut off on the bottom, since the PI is not pushpull?

    2E5FCD9F-B71F-4F83-A5C2-B0145FE0F124.jpeg



    It’s easy to see the size of the maximum clean wave as six grid lines, 5V per.

    The maximum wave is balanced.







    The maximum clean signal at the speaker, ignoring cross over distortion looks like 15 peak volts (calculated to be 10.6 RMs), measured 8.75 volts AC RMS on a DMM for 15 W or 10 W into a 7.5 ohm dummy load.
     
    Last edited: Nov 30, 2019
  2. D'tar

    D'tar Friend of Leo's

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    Maybe PI or perhaps your tubes are not a matched pair, no big deal. Scope the power tube grids to see if you have pi clipping.
    Swap tube to see if the harder clip moves with the tubes.
     
  3. peteb

    peteb Friend of Leo's

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    Thanks Dtar. Those would be good tests.



    I think the small signal to bias ratio shows that the clipping is not in the power tubes.

    I don’t thing a 9-10 volt RMS signal is enough to make the tube saturate when the bias is -40 VDC.




    I wouldn’t be surprised if the power tubes had some mismatch. They are newer tungsols, and I have seen newer tungsols match and then not match after some use.


    Also, the wave looks very equal on both sides prior to clip. I don’t think they would so equal if there was a significant mismatch between the two power tubes.
     
  4. peteb

    peteb Friend of Leo's

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    I take this back. Any PI only sees peaks and no valleys. Waves in Phase inverters are only subjected to saturation and not cut off.
     
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