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  1. Replies
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    Is yours the ‘d’ version under discussion here?...

    Is yours the ‘d’ version under discussion here? Earlier jets implement trem with a more common ‘power tube bias variation’ method, later ones use an optocoupler. ...
  2. Replies
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    It’s worth noting that catalin gramada’s circuit...

    It’s worth noting that catalin gramada’s circuit looks to be using a 12AT7.
  3. Replies
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    The second triode inverting amplifier will have...

    The second triode inverting amplifier will have much lower output impedance than the first, so the bias ripple present at its ac node will be (much?) more attenuated. So the bias ripple will no...
  4. I think a 1M trimmer could replace both resistors.

    I think a 1M trimmer could replace both resistors.
  5. A 1M trimmer could be tweaked to find the optimum...

    A 1M trimmer could be tweaked to find the optimum compromise https://www.newark.com/bourns/3386p-1-105lf/trimmer-potentiometer-1mohm-1turn/dp/62J2252?st=bourns%201m%20trimmer
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    Perhaps the paraphase’s greater output signal...

    Perhaps the paraphase’s greater output signal swing is more of a drawback than benefit for most applications? As it may worsen bias shift / blocking distortion when overdriven.
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    When I've tinkered with both simple and floating...

    When I've tinkered with both simple and floating paraphase circuits with a type 1 master vol after it, I found that if the cathode resistor was shared and unbypassed, horrid blips of parasitic...
  8. Sticky: Also OTs, especially vintages ones that are being...

    Also OTs, especially vintages ones that are being tortured in a guitar amp, have the potential to short primary to secondary. A solid chassis ground reference for the OT secondary will protect the...
  9. Unfortunately the intended mains voltage isn't...

    Unfortunately the intended mains voltage isn't always noted on every vintage Fender schematic or layout (might be on either, both or neither); however, by checking others contemporary to that of...
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    Yes, that thought struck me too.

    Yes, that thought struck me too.
  11. Whenever you put an amp on the bench to check its...

    Whenever you put an amp on the bench to check its operation, the first measurements to be made should be the mains and heater Vac; the ratio between the actual mains voltage and the nominal voltage...
  12. Replies
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    I think you will need to provide info regarding...

    I think you will need to provide info regarding the intended application (eg schematic with voltages) before anyone can have a chance of helping.
  13. No need to take my word, see...

    No need to take my word, see https://tubedata.altanatubes.com.br/sheets/163/6/6V6S.pdf
    But the logic of idling a design max 14 watt 6V6 hotter than a design centre 12 watt 6V6 seems flawed. Until...
  14. Just to note that the JJ6V6S has a 14 watt plate...

    Just to note that the JJ6V6S has a 14 watt plate limit. I assume that’s under the design max rating system commonly used for 6V6GTA info, rather than the design centre system used for 6V6GT info. The...
  15. I think it’s fine to fuse the 0V return of the HT...

    I think it’s fine to fuse the 0V return of the HT winding CT, as long as a tube rectifier has adequate back up silicon diodes, and there isn’t a tap, eg for the bias supply.
    If fusing each winding...
  16. Maybe a bad batch of tubes? Try one from a...

    Maybe a bad batch of tubes?
    Try one from a completely different manufacturer.
  17. Exactly:-) Merlin has a page on it...

    Exactly:-)
    Merlin has a page on it http://www.valvewizard.co.uk/paraphase.html see the last 2 ‘anode follower’ paragraphs.

    The old JMI Vox AC50 has a variant...
  18. You may be getting mixed up between HT and heater...

    You may be getting mixed up between HT and heater fusing?
    I seem to remember RG Keen recommending the use of automotive blade type fusing for protecting heater windings as, unlike regular cartridge...
  19. Yes, I was looking into adding fusing for the HT...

    Yes, I was looking into adding fusing for the HT winding of a Fender 75 a while back, and decided it was too complicated. The CT feeds the half voltage output used for the low 1/4 power mode. ...
  20. Have a read of...

    Have a read of http://www.valvewizard.co.uk/bridge.html
    The way I see it, on the negative going swing of its HT winding leg, the diode's anode will get pulled down to -Vp whilst its cathode is up at...
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    Is the standby hot switching the reservoir cap on...

    Is the standby hot switching the reservoir cap on to the rectifier?

    If you've traced the schematic, I'd be grateful for a copy (with one repair after another I can see you're a busy guy so...
  22. With HT windings much over 600Vac (unless used as...

    With HT windings much over 600Vac (unless used as series pairs), 1N4007 are underrated for use as backup diodes for the rectifier tube. It would be a dreadful shame for failure of the rectifier tube...
  23. The voltage across the cathode bias resistor will...

    The voltage across the cathode bias resistor will increase at high signal levels, perhaps double at full overdrive. But that would still be under 6 watts, so your resistor should stay well within...
  24. Yes, it's not critical, just need a reasonable...

    Yes, it's not critical, just need a reasonable degree of voltage and current 'headroom', so 1250V 1.5A should be fine.

    With a directly heated cathode like a 5U4, the cathodes and heater are all...
  25. The schematic is correct but if they are called...

    The schematic is correct but if they are called into use by tube failure, 1kV diodes are underrated for HT windings much over 600V.
    Need to factor in highest mains voltage (eg x 1.08) and unloaded...
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    Try JPF Amps https://jpfamps.com/ at Regent...

    Try JPF Amps https://jpfamps.com/ at Regent Sounds in Denmark St. They’re members here, probably been too busy to visit for a while.
    Fixed fee of £22 plus parts for pedals, though not sure how...
  27. As the MV is being used set high, thereby making...

    As the MV is being used set high, thereby making power tube gk diodes (rather than the 3rd gain stage) the most significant clipping point, it may be feasible to move the ‘warmth’ circuit back so...
  28. I wonder if different eras of Fenders had a...

    I wonder if different eras of Fenders had a different rake angle on their control panel? As some seem to have more room for such pots etc than others.
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