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    6550s vs KT-88s plate dissipation

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    deepee99

    Posts : 1337
    Join date : 2012-05-23
    Location : Wallace, Idaho

    6550s vs KT-88s plate dissipation

    Post by deepee99 on Sat Nov 16, 2013 4:06 pm

    I've recently come across some NOS 6550s quads. One is a late-1990s-vintage Svetlana SED that look like the old GEs, the other are genuine 3-holer coke-bottle Tung-Sols. Haven't installed them in the M-125s yet as I'm evaluating some other system tweaks and don't want to add more variables into the equation, but will probably commence tube-rolling soon. The plate dissipation on 6550s is, according to some other threads, is a tad lower (35 watts) than that for KT-88 and 6550C SED type tubes at 42 watts. Some folks say a Citation II will chew up a 6550 and spit it out. Question being, then, is this a problem with the M-125s as well? Should the bias volatge be backed off a bit, say to .55 or .50, for the 6550s to avoid cooking them? I'm especially concerned about the Tung-Sols as the four of them cost about a month's rent . . . Thoughts?

    skriefal

    Posts : 118
    Join date : 2011-09-20
    Location : Utah, USA

    Re: 6550s vs KT-88s plate dissipation

    Post by skriefal on Sat Nov 16, 2013 4:23 pm

    6550s were rated under the design center system; KT88s under the design maximum system. So the numbers cannot be directly compared. I've seen multiple posts from those in the know, describing how the two tubes have the same equivalent ratings (for dissipation, anyway).

    http://www.audiokarma.org/forums/showpost.php?p=6483365&postcount=6


    Last edited by skriefal on Sat Nov 16, 2013 4:35 pm; edited 1 time in total

    deepee99

    Posts : 1337
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: 6550s vs KT-88s plate dissipation

    Post by deepee99 on Sat Nov 16, 2013 4:34 pm

    Interesting. Many thanks. Just didn't want to send those coke-bottles into low-earth orbit or turn them in to 90-day wonders.

    skriefal

    Posts : 118
    Join date : 2011-09-20
    Location : Utah, USA

    Re: 6550s vs KT-88s plate dissipation

    Post by skriefal on Sat Nov 16, 2013 4:38 pm

    Well, anything is possible with new-production tubes which may or may not meet the original specs. But for NOS tubes it shouldn't be an issue. Probably not an issue for SED (Winged-C) 6550Cs either... they're some of the best of "new" production. I'm using SED 6550Cs in a pair of M-125s.

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