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Magnatone weirdness

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  • #16
    Originally posted by Helmholtz View Post

    Is that plate or cathode current? What is the 6V6 cathode voltage?
    You could lower the cathode resistor to 220R, aiming for a cathode current of 50mA.



    Does that include the cathode bypass cap?

    Best measure output power.
    Should be around 4W.
    6v6 cath is 10.6v
    257 ohm cath resistor
    10.6 257 = .041ma
    cath bypass cap new
    i swapped the 3 tubes and got some slightly higher volts

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    • #17
      Put a 220k plate resistor for the 6sj7.

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      • #18
        About what acv should i see at the output of this 5y3 ? Pin 8 is 41vac . 317vdc is there

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        • #19
          Generally your voltages look ok.
          What is the remaining problem?

          What is the HT winding AC voltage?
          What is the heater voltage?

          Can you measure output power?
          - Own Opinions Only -

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          • #20
            41VAC on 317VDC B+ seems high. I wonder if the 317 is not really all there but fooling your meter. Do you have a scope?
            "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
              As there's is a 1k resistor before the reservoir/first filter cap, I'd expect high ripple voltage at the 5Y3 cathode/heater.
              But as that node is not used to supply the circuit, it's not relevant.

              A (say 10) cap there would decrease ripple and increase B+.
              Last edited by Helmholtz; 08-06-2022, 07:09 PM.
              - Own Opinions Only -

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              • #22
                Sorry been busy...i tried adding the 10uf filter as Helmholtz mentioned and the amp is hum free ! Sounds ok through my 4x12 , but more raspy with stock 70 year old speaker when cranked up.

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