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Mesa 400 with 6550 I did it!

Discussion in 'Amps and Cabs [BG]' started by sbakker, Aug 1, 2005.

  1. Well, after some discussions with my brother, we decided to give it a try. We pulled out the Ruby 6L6 and replaced it with SED 6550 :hyper:

    Wow! This thing is much louder and warmer with 6550 tubes than with 6L6! With 6L6 tubes the amp is very cold bias but with the SED 6550 the bias is perfect! Sounds almost as an SVT-II but than cleaner and more punch.

    here is some proof! :ninja:



  2. Looks good!

    (wish i could comp my SVT II to that ;) )

    So it was more than just doubling the output, good god :D
  3. Hurley


    Feb 12, 2004
    Cape Cod, MA
    Wow, nice job. I bet the Mesa/Ampeg combo sounds great. ;)
  4. Yes, that is the reason that i wanna sell my SVT-II ;)
  5. chaosMK


    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    Did you have to rebias it, or did you just switch the tubes and it worked? I am really new to tube amps and just got a 400 and your upgrade sounds awesome.
  6. This thing has a fixed bias. We just change the tubes and looked with a voltage-meter and a bias probe. The bias range was set well for the 6550. Even better than for 6L6... :bag:
  7. Like this? :D

  8. it just looks right, mine has the hollow writting on the "ampeg" bit and solid on the "SVT II" bit tho :p

    bet it sounded nice tho, im yet to try a 400 or 400+
  9. chaosMK


    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    What year was your 400 made btw?
  10. I haven't messed with Mesa amps, but I thought the 400 (not the 400+) came with 6550's originally...if that's so, and if the previously owner had put in 6L6's without changing the bias...then putting the 6550's back in would have been correct as far as the bias???
  11. IIRC the 400 (and the 400+ for that matter) have set bias's, you have to mod them so you can set the bias yourself

    The 400 was made so you could use either 6550's or 6L6's , and seeing that it was a set bias, i dont think there would be any problems that were bigger than changeing to power tubes of the same type, if im making sense, that im probably not!

  12. 1983

  13. With the 6l6 it was TOO COLD BIAS! Far below normal bias. With 6550 it's perfect bias and no corrections had to be made. :bassist:
  14. That's my point, if it was perfectly biased for 6550's, then I doubt it would also be biased correctly for 6L6's--they may be similar as far as pinouts but the operating characteristics of the tubes are different...I doubt you could just swap one for the other without changing the bias-which is indeed what someone else may have done, so the bias was cold for the 6L6's.

    Anyhow, the main thing is that you're set to go now. I wish I had an old 400 !!!
  15. One thing, im not sure if it'll affect you or not, but with the 6550's it will run a fair bit hotter, and i just saw you dont seem to have much breathing space in that rack, just a heads up, probably be ok tho :bassist:
  16. the mesa has a powerfull fan. Much more air movement than with a svt-II. The 6550 are hotter but no problems so far :smug: