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Bogen CH8 to 3-knob champ with 6L6 conversion filter capacitor questions

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  • #31
    "17.1W is correct but there's a typo. It should read (440v - 39.8v)"

    Yes, thank you. I fixed it.

    I found a bad supply node resistor. It was a 10 ohm where a 1000 ohm should have been, and was distressed to the point it read 968 ohms in circuit, tricking me into thinking it was the 1K it was supposed to be. During unsoldering, one leg fell away. So now that it is corrected, and I have realized I forgot two things, A: this is class A operation so that whole 70% thing is not in play, and B: 6L6GC is 30 watts, not 25 watts. So now I am back to the original 470 ohm cathode resistor.

    Here's where I'm at now.

    Cathode resistor = 464 ohms
    Plate voltage = 402.5 v
    Cathode voltage = 31.6 v
    6L6GC = 30 watts

    This has this tube idling at 25.2.watts, and that is where I am going to leave it. Once again, trying to fix a problem in my own head only.
    Last edited by Randall; 02-05-2019, 07:29 PM.
    It's weird, because it WAS working fine.....

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    • #32
      Originally posted by g1 View Post
      Hot for a 6L6 single ended?
      Randall said it was running at over 100mA and burning out 6L6s.

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      • #33
        Originally posted by Dave H View Post
        Randall said it was running at over 100mA and burning out 6L6s.
        Oh, ok. We are talking about different points in time.
        I was talking about with the cathode R changed to 931R and idling at 17W.
        I thought you were also speaking of the 17W iteration but you were talking about when he received the amp. Thanks for the clarification.
        "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
          I was talking about with the cathode R changed to 931R and idling at 17W.
          I should have guessed that I agree 17W and 42mA cathode current is low for 6L6 but it looks like Randell has fixed it. If the OT impedance is 7k like the marked taps on the chart below then I think he has it about right.

          Click image for larger version

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          • #35
            I think the bad node resistor was skewing things under load. It seems to be settled in now. I'll leave it to the owner/builder, a smart guy, to decide where to take it from here if he wants to adjust the cathode resistor/current.
            It's weird, because it WAS working fine.....

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