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6550's in a mesa 400+ !!!

Discussion in 'Amps and Cabs [BG]' started by Scutterflux, Mar 11, 2006.

  1. O.K. I havn't done this, but if you wanted to couldn't you just run 6 of them in the appropriate tube slots and still get your 300-500 Watts with a 6550 sound.

    It'd be like pulling tubes, only 6 tubes instead of 1 or 2, and then replacing the ones left with more powerful ones to make up for what you lost?

    Just curious!:)
  2. protoz


    Nov 30, 2000
    I don't think the transformer could handle the load of that many 6550s. The tubes it runs now don't put out as much power so you can have more in there for more power.
  3. Why not run 12 of them and get 600 watts? While you're at it, you should try connecting 4 4ohm cabinets to the 8 ohm jacks. Crank it up and let er rip. I think you should try it.
  4. ok ok ,
    12 6l6's @ 25W each = 300W
    6 6550's @ 50W each = 300W
    So you wouldn't be giving the transformer anymore juice would you now? Remember you'd be running it with 6 empty slots if you get what I mean. Would it still work?

    Hey NecroticImbecil Do you think if I conected the 2 speaker output jacks derectly up to your ears your mouth would produce a sound as loud as 4 4ohm cabs?
  5. BurningSkies

    BurningSkies CRAZY BALDHEAD Supporting Member

    Feb 20, 2005
    Syracuse NY
    Endorsing artist: Dingwall Guitars
    These tubes are not interchangeable in the 400+.

    Do a quick search here, and you'll see that a few other people have had the same brainstorm.
  6. Start jamming forks in electrical sockets too, i hear that works
  7. you'd probably hook them up wrong. one thing at a time, first try your experiment with the 400+ then we'll see about putting them in my ears. but after that, i get to plug a peavey classic 400 into one of your orifices.
  8. tadawson


    Aug 24, 2005
    Lewisville, TX
    It would probably require a redesign of the bias circuitry, and then perhaps a double check to make sure that the 6550 and 6L6/5881 had similar plate impedances (to determine which output tap to use with the 6550's - it might change . . . ) Mesa used both 6550s and 6L6/5881's in the 400, and the output circuit is very close to the same, so I really don't see any reason that you could not make it work, although it would be more involved than just changing the tubes . . . . and depending on the plate voltage that the 6550s want to see, you may not get full power out of them.

    - Tim
  9. To echo what tadawson said, you'd need a stronger bias supply. The output impedance of 6550's is lower than 6L6GC's and you'd have to compensate in the power supply to get them running at the same plate voltage in order to have the same amount of headroom.
  10. Skel


    Jun 19, 2005
    Boulder, Colorado
    Curious - do you like the tone your getting, and just trying to see if it can be improved upon?

  11. So maybe if you had bias trim pot put in, or had a tech look at it, then you probably could get it running about right, if you don't need to start upgrading transformers for it.

    By the way, I don't have a 400+ Just talking bull, but I'm looking for one. I just come across a trace vtype, so we'll see I might pick it up tommorow, or keep searching for a mesa. But I like kt88's so that's why I'm curious about mods on the 400+ because they are more common, and a very powerful clean tube amp. Just Talkin' bass
  12. A trim pot won't help. The bias supply is probably not strong enough to begin with. A pot can only decrease that voltage, not increase it. You'd need some sort of voltage increase, either a voltage doubler or replacing the the power transformer's bias line. You'd probably need to replace the power transformer anyway to get a high enough plate voltage for the amp to run clean with 6550's.
  13. (1.) Erase the "+" at the end of 400.

    (2.) Insert six 6550's in your amp.

    There, see? Now you own a Bass 400, and you can feel free to explore the world of 6550's!:rolleyes:
  14. Skel


    Jun 19, 2005
    Boulder, Colorado
    Now that you've said that - does the + have a sweeter, more "Fenderish" tone, and the 400 non + an "Ampegish" tone?

    Never tried either one.
  15. If you want a fenderish tone, get a fender, if you want an ampegish tone, get an ampeg, problem solved :rolleyes:
  16. or just get a sansamp

    ...somebody had to say it
  17. Skel


    Jun 19, 2005
    Boulder, Colorado
    Well sure - I was just curious if the 400 had a different tone that the plus. Now that I think about it, the Marshall guitar amps I've used with 6550s, had the same tone as the ones with EL34s, except the 6550's would *not* break up, which was a huge problem for a guitar player (me, anyway - I hated 6550s in Marshalls). But EL34s and 6L6s are two different animals as well.

    I'd just like to know why Mesa made this change from the 400 to the 400 +. Heat? Cost of 6550s?

  18. chaosMK


    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    I am not an expert on tube amps, but know a little.

    I think your idea might work. You would have problems if you put in 12 6550's, but 6 6550's placed in the right slots would draw the same voltage.

    However, I've never heard of anyone doing this.

    I use a Mesa Bass 400 with KT-88's. It is pretty sick. :bassist:
  19. chaos, they would not draw the same voltage
  20. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego

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