fender tube rectifier and voltage question

Discussion in 'The Workbench' started by tone seaker, Mar 1, 2021.

  1. tone seaker

    tone seaker Well-Known Member

    Jan 20, 2011
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    Where the Rock Rolls Hard and the Blues Rains Down
    im running 488V on the plates on my 67 Black face pro reverb with 123V ac on the wall and some one told me i could put a 5R4GB rectifier in instead of my 5AR4/GZ34 and it would lower the plates down to around 435V. i looked at my bias chart and would have to rebias from 36ma up to around 45ma. Would this make the tubes run just as hot or hard and would my heater voltages go to low? Also what would it do to the sound? My attenutator has a 105V ac tap i could plug my amp into. what would this do sound wise and would the heaters go low (the heaters go low out of tolerence on my Marshall when i use the tap) and i would need to rebias for that? i coould just leave it as i have looked in my records and i have been running 480V on the plates for decades with no issues but it does get hot when i play for long periods. i do crank it to 7 and push a tube screamer into it thks
  2. thetragichero

    thetragichero Well-Known Member

    Jun 6, 2010
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    flo rida
    as long as it's biased properly and you're getting less than 450v on the screens why mess with it? it's below the 500v max plate voltage for 6l6gc. many fenders seem to have higher voltages than the schematics anyway
    5r4gyb has a max first capacitance of 20uf so you'd need to change out that first supply node. you'd also likely end up with lower plate voltage than the 440v on the schematic. higher plate voltage will give you more volume before output stage clipping. only thing I'd be concerned with are the screens

    change in ht voltage has no effect on the heaters as they're a separate winding
    Last edited: Mar 1, 2021
    South Park and tone seaker like this.
  3. South Park

    South Park Well-Known Member

    Sep 14, 2019
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    You would be lowering your preamp tubes plates to . So it is not going to sound the same .
  4. Matthews Guitars

    Matthews Guitars Well-Known Member

    Aug 17, 2019
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    You can also run the 5U4. (5U4GB) In a Pro that'll make the power supply very stiff and make the amp very dynamic. It won't sag. A single 5U4 can provide 100 watts to the amp. Since the Pro is, at most, 60 watts on a good day, the 5U4 will not even break a sweat and will last a VERY long time.

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