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Mesa 400+, 5751+KT66

Discussion in 'Amps and Cabs [BG]' started by Ruptured, May 14, 2003.

  1. Ruptured


    May 14, 2003
    Anyone use these tubes in their Mesa?

    How do they sound?

  2. stevekim


    Feb 11, 2000
    los angeles, ca
    i don't know...can mesas even take kt66's? i'd wait for what psycho has to say.
  3. KT66's should work just fine, although the Mesa doesn't operate at voltages where they would really be beneficial. A KT66 is basically a beefed up 6L6, just like a KT88 is a beefed up 6550. They're what originally came in old Marshall amps. They typically give 3-5 more watts per tube than a 6L6GC but they like to be run MUCH hotter. Their sound is also more midrangey. If you got a deal deal on twelve of 'em matched, they'd be good, but you're not going to get any more power out of them.

    The 5751 is just a lower gain preamp tube and the Mesa can do a nice clean tone already. They're mechanically more stable so if you've got problems with microphony in your preamp, they'll help. Won't hurt anything to try 'em.
  4. Ruptured


    May 14, 2003
    Thanks Psycho.

    I was told this combination would give the Mesa a cleaner sound at high volumes,when a 12ax7-6L6 combo would normally break up.


    When you say "more midrangey",does this mean low mids,high mids or just depends on other factors?

    This is the sound I'm after-

    Big lows,strong pushing low mids and cutting high mids/treble,at a high volume without buzzy distortion.

    Am I asking too much from a tube amp?
    Would these tubes suffice for this sound?

    Thanks very much
  5. stevekim


    Feb 11, 2000
    los angeles, ca
    i don't know...the ideal sound you described sounds a lot like my mesa bass 400. if you want to go super hifi then i would suggest some sort of solid state setup.
  6. Not without other modifications to the power supply. A KT66 IS a "cleaner" tube than a 6L6GC but it also requires more voltage than the 6L6GC to run that way.

    I'm curious; are you having problems getting a "clean" sound out of your 400+ as is? They do a clean tone pretty well, and unless it's got Mesa's ultra-cheapie old Chinese 6L6's in it, there shouldn't be any reason you couldn't get a LOUD clean tone out of it. If that's the case, something's outta whack and it needs to go to the shop to a good tech, which does NOT necessarily mean a Mesa tech. (Doesn't necessarily rule one out either, but Mesa is a company built more on advertising reputation than actual quailty, IME, and some of their "certified" techs that I know are complete morons. )

    A KT66 has a higher upper midrange content. It's more nasal sounding. The preamp is the biggest factor in your overall tone, but you will notice a difference in tone with different power tubes.

    Your amp SHOULD be doing that already. If it's not, there is something wrong with either it or your speakers. How are you running it with what cabs?
  7. Rockbobmel

    Rockbobmel Supporting Member

    I just bought some G.E. JAN 5751 (NOS 1967) and put them in the Mesa preamp. I like them so far, but they will have to pass the stage test, not just the living room test. I thought the JJ ECC83s were too hot and darker sounding. I wanted to use more of the 6L6's power. Man! this amp is loud! I am running into both channels. One on 4, two on 2, and I can hardly crank the master past 3. With a little tweaking, I can get some snarl.
    Bob Pletka preamp tubes are the two middle ones. The outside ones are PIs.
    I also heard the 12Ax7EH were the bomb.
  8. Ruptured


    May 14, 2003

    I play a Rickenabacker thru the Mesa,from there into 2x 600 watt Warwick 4x10s.

    I play with a pick and strum alot of chords which 'cause a certain amount of buzzy distortion.

    I love a bit of tube overdrive but there's a bit too much going on there for my tastes.

  9. stevekim


    Feb 11, 2000
    los angeles, ca
    a 400+ into eight 10's should give you all the clean power you need. maybe your tubes are old and need replacing? what kind of tubes are in there now and how old are they?


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