JJ 6V6 (sorry)

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Avatar Tech, Apr 22, 2015.

  1. Avatar Tech

    Avatar Tech Member

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    So I have a little project amp running JJ 6V6's in fixed bias. SS rectified. Plate voltage is 445 ad I have it biased at about 75%. It sounds great but the plate voltage concerns me somewhat. My intention is to build and sell more of these, ad I'm convinced the JJ tubes will be fine. But would you worry about a different tube brand? I'm considering just using some sag resistors to drop the HT, but I personally like the tone better without them.
    What do you think?

    Colin
     
  2. RiftAmps

    RiftAmps Member

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    The JJ 6V6S datasheet shows a maximum plate voltage of 500v and a maximum screen voltage of 455v. These will be fine.

    However......

    Most other brands of 6V6 are 450v plate, 400v screen so I'd make sure the amp is running well within these specs....customers like to roll tubes and don't like it when the amp keeps eating them.
     
  3. swiveltung

    swiveltung Member

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    JJ's will be fine. But others .. maybe not. Definitely not EH's.
     
  4. Steppin' Wolfe

    Steppin' Wolfe Member

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    RiftAmps, are those specs for modern production 6V6's like the Russian and Chinese? The specs for vintage 6V6's are nowhere near 450V....closer to 350, IIRC.
     
  5. RiftAmps

    RiftAmps Member

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    Yes, modern production. I did use the term 'most' ;)

    Deluxe Reverbs have been putting 415V on the plates of 6V6s for 50 years now, nothing to worry about.
     
    Last edited: Apr 22, 2015
  6. pdf64

    pdf64 Member

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    Doesn't the DR power supply sags rather under load though?
    I seem to recall they're down to ~370V B+ at full squarewave.
     
  7. RiftAmps

    RiftAmps Member

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    Yes it does sag, anywhere between 30-50v is not uncommon.

    I've got an original '66 here in for service, it's got 455v on the plate at idle and it drops to 412v at full crank with 1khz sine wave @ 150mA. The valves are original RCA - the datasheet says max plate voltage for those is 315v yet they've lasted 49 years and still test v.strong on my tester.

    Maybe the OP's amp will be fine, guess I was being too cautious with my original replies.
     
  8. swiveltung

    swiveltung Member

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    My 65 runs 455-460v, some tubes def don't hold up to that. My other 3 DR's I had were pretty much 450+.
    One blew up a NOS RCA BP and the OT. After that with a new OT I used EH's for a while. Two sets shorted, both at about 3 months use.
    My other current BFeDluxe (non verb) runs 445.I only use JJ's now.
     
  9. Avatar Tech

    Avatar Tech Member

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    That's interesting. My amp is using DR iron and power supply, but I suspect it's sagging less than a true DR would because of the ss recto and lack of trem/verb circuitry.
    Whatever brand of tubes are installed, I know I can bias them to avoid over dissipation. I just wonder if that high a plate voltage will cause internal arcing in certain tubes.

    Colin
     
  10. dbeeman

    dbeeman Gold Supporting Member

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    maybe use a different PT with lower volts? No fun eating tubes
     
  11. xtian

    xtian Member

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  12. Avatar Tech

    Avatar Tech Member

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    Thanks! I had kind of dismissed this type of circuit. Might be perfect!
     

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