6V6s in a Twin Reverb/Dual Showman ????

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by TheAmpNerd, Oct 4, 2004.

  1. TheAmpNerd

    TheAmpNerd Member

    Sep 23, 2004
    I have a 70s Twin Reverb/Dual Showman amp that is just way too loud...

    ...so thinking that I'll plop some 6V6s in it.

    I'll know I'll need to change the bias
    resistor to enable a bias point of about
    9 watts per tube.

    RCA Receiving Tube Manual, RC-22
    has these tubes Max values as shown:

    Plate = 350 volts
    Screen = 314 volts
    PlDiss = 14 watts

    So, with this twin having 410 V on the B+
    any thoughts to using the following tubes?

    BlackPlate RCAs
    Mazda NOS
    JJ 6V6s

    Anyone have an Idea about cathode biasing these? I would use
    separate pairs or break them down

    1 cap/resistor 4 tubes
    2 caps/resistors 2 tubes
    4 caps/resistors 1 tube (4x)

    This might be an interesting project
    for the Guitar Amplifier Magizene.

  2. Roccaforte Amps

    Roccaforte Amps Member

    May 23, 2002

    Spike, the output transformer primary
    is way too low for 4 6V6 tubes in the twin circuit.
    You could try a 4K primary, but I wouldn't cathode
    bias it with the stock driver circuit, the OD will
    sound terrible when cranked. Doug
  3. TheAmpNerd

    TheAmpNerd Member

    Sep 23, 2004
    Thanks Doug,

    Yeah, that is what I wasn't sure about
    as well, how it would sound cranked.

    Typically the load resistance of a pair of 6V6s in push pull is about 8.5K and with
    two pair we would halve that getting to about 4.2K. So knowing that 6L6s
    load resistance is about 4.2K per pair,
    or 2.1K for two pair...that twin output tranny would need to go.

    It looks like a standard 6L6 pair Tranny would work for this project. I'm wondering now about the driver circuit.

    I supposed I could use a driver circuit from an EL84 amp; that would get me in the ball park for the 6V6 quad before I started tweaking it wouldn't it?


  4. theelectic

    theelectic Guest

    You know, with the amount of work & expense you're describing, you're pushing yourself into the "sell my loud amp and buy a smaller amp" territory :) :)

    That being said, I have put a pair of THD Yellowjackets in my SF Twin with good results (to my ears, anyway).
  5. TheAmpNerd

    TheAmpNerd Member

    Sep 23, 2004

    And there ya go upsetting the balance
    of the universe with common sense.

    Just one pair of EL84s at work there?


    The simpler, cheaper, more elegant solution may be at hand.

    That said, and I'm a preacher of the
    don't make an amp into something it is not, find the right amp to begin with.

    Then again, there is that evil tweaking side to me that says...I think I can.

  6. theelectic

    theelectic Guest

    Ha ha, you're right there. In my Twin I tried various combinations of the Yellowjackets: 2x6L6 with 2xYJ, 2xYJ alone, 2x6L6 alone. I liked the first combo at first (very nice low end and mids) but it was still a hair too loud, so I settled on the 2xYJ alone.

    I did not want to do alot of soldering mods since I KNEW eventually I would want that big bold hellacious 100W power, and it would be a PITA (compared to plugging/unplugging) to put it back. Yup, I've got 4x6L6 in there right now :)
  7. Jon Silberman

    Jon Silberman 10Q Jerry & Dickey Silver Supporting Member

    Jan 3, 2002
    Northern VA
    In the Dec. '04 (yes, it's already out :rolleyes: ) Vintage Guitar mag, on page 112, Gerald Weber provides 5 options for converting a 6L6 Fender amp to 6V6s.

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