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    tube options st 120

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    rfbro

    Posts : 26
    Join date : 2014-12-28
    Age : 61
    Location : Vancouver WA

    tube options st 120

    Post by rfbro on Thu Jul 02, 2015 12:03 am

    woundering other then kt 88 can you use any other tubes be dropped in the st 120 without making any changes

    skriefal

    Posts : 116
    Join date : 2011-09-20
    Location : Utah, USA

    Re: tube options st 120

    Post by skriefal on Thu Jul 02, 2015 12:22 am

    You can also use 6550, KT-90, or KT-120 power tubes. You'll need to re-bias, of course, but no other changes are needed.

    sKiZo

    Posts : 1287
    Join date : 2013-04-01
    Location : Michigan USA

    Re: tube options st 120

    Post by sKiZo on Thu Jul 02, 2015 11:57 am

    Just be aware that you will NOT see the full rated power of a KT120. That would take some serious tweaks in the circuitry. You should see a good 10% increase over a KT88 though.

    I find them to be an exceptional tube in these amps, with full bass and excellent response throughout the range. Also a great value. I paid more for a set of TAD KT88's. I've heard nothing but rave reviews from those who've tried them. Seems to me Mr Bob is still running a set in his amp?

    I expect mine to last forever as they're not being pushed all that hard. I do bias mine at 60mV - the iron is strong enough to handle that, and they do develop more punch at that level.

    One caution - the pins run slightly larger than most KT88's, so you'll want to retention the sockets any time you swap tubes. Common sense and easy enough to do with ANY tube swap, so not a bad habit to pick up if you're a roller like me.

    PS ... I wouldn't try the higher bias settings using a 5AR4 rectifier. Those are working hard enough as is in an ST120. A Weber WZ68 is highly recommended - I myself use a Mullard GZ37, but those are getting pricey and can be a bit hard to find.

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