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  • #31
    Well done spotting that! I guess your amp was half wave rectified all these years. The HT should have been more saggy under load. The weird HT winding Vac in standby are probably due to the bias supply rectifier being half wave and connected to the pin 6 winding leg, as standby lift the CT 0V connection.
    Last edited by pdf64; 04-15-2020, 10:42 AM.
    My band:- http://www.youtube.com/user/RedwingBand

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    • #32
      Originally posted by pdf64 View Post
      Well done spotting that! I guess your amp was half wave rectified all these years. The HT should have been more saggy under load. The weird HT winding Vac in standby are probably due to the bias supply rectifier being half wave and connected to the pin 6 winding leg, as standby lift the CT 0V connection.
      I get that, but what's up with 200V on the plates/ps_caps when not in playing mode (4+6pin) ---> and when I resolder 6pin to 7pin I have no voltages on plates/ps_caps and amp have correct (quick) bias ramp buildup then. So with that type of connection I have more sag but proper voltages everyhwere?

      Let me tell you what I see it. Should there be 720V on pin6? I think it could kill a rectifier tube quick? If the amp would have 0V on pins 4 and 6, and then after standby - 360V on each one, then it's a perfect connection? Do I think right?

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      • #33
        Confused - is the amp now working right? The HT should have been saggy before, when it was half wave rectified, stiffer now that itís full wave.
        It would be best not to use this hot switching type standby with a tube rectifier http://www.valvewizard.co.uk/standby.html
        The 720Vac is immaterial; as thereís no current flow via the tube itís equivalent to a spurious voltage, similar to static electricity.
        My band:- http://www.youtube.com/user/RedwingBand

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        • #34
          Originally posted by pdf64 View Post
          Confused - is the amp now working right? The HT should have been saggy before, when it was half wave rectified, stiffer now that it’s full wave.
          It would be best not to use this hot switching type standby with a tube rectifier http://www.valvewizard.co.uk/standby.html
          The 720Vac is immaterial; as there’s no current flow via the tube it’s equivalent to a spurious voltage, similar to static electricity.
          Maybe I got it wrong, sorry, once again... I understood that connecting of of those wires to "dummy" PIN7 makes the amp more saggy? Or the other way? (when it's connected to PIN6 to one of the half of the recitfier)?

          The case is, I've got four B15Ns here.
          1st - c. 1962 with factory pins connected to 4+6. No voltages on PS caps/anodes when powered on. Full voltages when in playing mode, bias ramp up very quickly. -> ALL OK
          2nd - c. 1969 with factory pins connected to 4+7(dummy). No voltages on PS caps/anodes when powered on. Full voltages when in playing mode, bias ramp up very quickly. -> ALL OK
          3rd - c. 1969 with pins connected to 4+6. around 200V on caps and anodes when powered on. Full voltages when in playing mode, bias ramp up very slowly (gets like above when pin 6 is unsoldered or soldered to pin7)
          4th - 1972 with pins connected to 4+6. No voltages on PS caps/anodes when powered on. Full voltages when in playing mode, bias ramp up very quickly. -> ALL OK

          So, no circuit changes, no schematic changes in this section.

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          • #35
            No doubt that connecting to pins 4+6 is correct. Using pin 7 makes no sense. It results in utilizing only one half of the HT winding and only one of the rectifier diodes, resulting in increased sag and low frequency (60Hz) ripple. It's a wiring error.
            - Own Opinions Only -

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            • #36
              How about if the awful standby isnít used?
              To me, it looks to be doubly crap, as it may be preventing the bias supply from charging up probably and hot switching the rectifier.
              My band:- http://www.youtube.com/user/RedwingBand

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              • #37
                When powered on it's 0vac on one red HV (pin2) and 720vac on another red wire (pin6 or 7). After standby is hit it divides to 360+360vac. I wonder - isn't 720vac a bit too high on the cold rectifier tube side?

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                • #38
                  Standby switching has been used to no ill effect for many years. If there was an issue, it wouldn't be used.
                  Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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