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Hiwatt 200 (DR201) bias pot + general questions

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  • #16
    Unfortunately I can't measure more than 375V anywhere on the tubes - might be diodes failed in power section?

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    • #17
      What do you measure at the CT of the OT? What is your heater voltage?
      What is your mains voltage? Where is "boro"?
      - Own Opinions Only -

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      • #18
        I think everything's OK:
        Click image for larger version

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        I may confused PIN2 and PIN3 with PIN3 and PIN4 because they are written between the pins, not "at the pin".
        But there's another case. I was told this amp is CLASS B amp. Could not find any information how I should bias Class B amp? Is the calculation the same as AB? At the moment tubes have got like 18-20mA each. Form the 70% safe plate dissipation rule, with 680v it would be 25mA... so 18 is a bit cold? But it may be Class B that is set differently?

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        • #19
          We still don't know your actual screen and plate voltages.

          The TFK EL34 datasheet recommends for what they call "Class B" 30mA@ Vp=500V/Vg2=400V and 25mA@ Vp=800V/Vg2=400V. If you measure cathode current, add 4mA for screen current.
          - Own Opinions Only -

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          • #20
            Thank you,

            Screen 375
            Plate 680 (720 when off standby)

            (I wrote those on the pic)

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            • #21
              (I wrote those on the pic)
              Oh, I see.


              Still wondering where Boro is. Indonesia?
              - Own Opinions Only -

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              • #22
                Originally posted by Helmholtz View Post
                Still wondering where Boro is. Indonesia?
                What does it have to do with the topic (that you ask 2 times)? Lithuania.

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                • #23
                  I think Helmholtz just wants to know what voltage AC is used in your country. Post #17

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                  • #24
                    I didn't get it, sorry. Felt a bit offended. Wall voltage 235-238V here.

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