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KT-120s in an SVT?

Discussion in 'Amps and Cabs [BG]' started by Charlie_brxwn, Jan 18, 2017.

  1. Charlie_brxwn


    Dec 12, 2016
    Richmond VA
    There's an SVT I'm talking to a dude about buying.

    He said it's got KT-120s in it and insists that it's cool. Says it's just an issue of correctly biasing. Although I can find no information to support this claim anywhere.

    Seems sketchy to me, but I don't honestly know so I don't wanna grill him about it. I don't want a fixer upper to deal with.

    Technical expertise appreciated
  2. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    I've heard mixed things. Some people are using them in SVTs, if you search KT-120 you'll pull up a bunch of threads. This comment is interesting.

    I think if I were buying that amp I'd get a set of 6550s and set it up properly.
    Charlie_brxwn likes this.
  3. Charlie_brxwn


    Dec 12, 2016
    Richmond VA
    Yeah that was my plan. I guess it depends on what I can talk him down to. Thanks for the info
  4. cerrem


    Apr 4, 2006
    San Diego
    KT120 runs perfect in the SVT heads... I have installed them in many SVT heads with no issues..
    The Heater current is about 12.5% higher... which is not a big deal with the small temperature rise of the Filament Transformer...can easily handle it..
    The KT120 transconductance is on par with a good strong 6550A @ 12.5 ma/v ...
    KT120 has better capabilities, so the SVT wont beat it up as much...so it will last quite some time and will have good headroom..
    As for biasing, if the tubes are healthy, should be fairly close to 6550A biasing...
    All tubes even of same designation can have normal variance..
    The comment about plate load mismatch is nonsense and doesn't add up.. Not how pentodes operate in this situation... KT120 is no harder to drive than a 6550...
    Last edited: Jan 19, 2017
    Charlie_brxwn likes this.
  5. Charlie_brxwn


    Dec 12, 2016
    Richmond VA
    Well I remain at the mercy of yalls technical knowledge - knowing very little about the subject beyond the rudimentary. Based on yalls experiences/professional opinions it seems like the best case scenario is a great sounding amp, and the worst case is a retube. Not the end of the world.

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