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.
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Originally posted by pdf64 View PostWell 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.
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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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.My band:- http://www.youtube.com/user/RedwingBand
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Originally posted by pdf64 View PostConfused - 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.
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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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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How about if the awful standby isn’t 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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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, Laney, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk
If you can't fix it, I probably can.
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