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    Tubes for VTA ST-120

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    Dogstar

    Posts : 274
    Join date : 2014-06-23

    Tubes for VTA ST-120

    Post by Dogstar on Fri Jun 02, 2017 2:29 pm

    I could have sworn I read at some point it time which tubes can be used in the VTA-ST-120 but cannot seem to locate that list anywhere.

    I am searching because only a short time ago I thought the only tubes I could use in the preamp section were 12AU7's and 12BH7' and their European equivalents as well as 6SN7's (but only in the Octal PCB). And in the Driver section I thought it was limited to 6550's, KT-88's, KT-66's, KT-120's and KT-150's.

    Now we find out 6SN7's can be used in the standard PCB with an adapter. That was an interesting experiment.

    Can 6L6's be used in the VTA ST-120? I'm asking because I thought I read that someone is using them in the VTA ST-70.

    I'm really not sure why I should be so curious since I don't consider myself to be a tube roller.

    Thanks,

    Blake
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    Bob Latino
    Admin

    Posts : 2567
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Tubes for VTA ST-120

    Post by Bob Latino on Fri Jun 02, 2017 5:25 pm

    In the VTA ST-120 for output tubes you can use > 6550, KT88 and KT120. You can also use KT90 and KT100 tubes but these two tubes are not that common. A few have also used the newer Tung-Sol KT150 output tube. The Tung-Sol KT150's are very expensive @ $100 USD per tube and don't really give any advantage in the ST-120 over the Tung-Sol KT120 which is $45 - $50 a tube. For driver tubes you can use a 12AU7 and any of its military/industrial versions > 5963, 5814 and 6189 and the Mullard CV4003. You can also use a 12BH7 driver tube which is a slightly taller tube than a 12AU7 and has very slightly less gain that a 12AU7. Take note also that the earlier VTA ST-120's (June of 2008 to April of 2012) used an earlier version of the VTA driver board which took higher gain 12AT7 driver tubes.

    Bob
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    Tubes4ever

    Posts : 103
    Join date : 2015-07-14
    Location : Star, Idaho

    Re: Tubes for VTA ST-120

    Post by Tubes4ever on Fri Jun 02, 2017 6:02 pm

    Dogstar wrote:Can 6L6's be used in the VTA ST-120? I'm asking because I thought I read that someone is using them in the VTA ST-70.
    Dogstar,

    I'm one here who uses the 6L6GC in my ST70. I believe the voltage level on the ST120 is too high for the 6L6, or you would be pushing it really close to its limit. The voltage on the ST70 is about 425V. It is definitely higher on the 120.

    Tim L.
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    Bob Latino
    Admin

    Posts : 2567
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Tubes for VTA ST-120

    Post by Bob Latino on Fri Jun 02, 2017 6:10 pm

    Yes .. Tubes4ever is on the mark... 6L6, EL34, KT66 or KT77 type tubes are fine in an ST-70 type amp. The VTA ST-120 has a B+ 50 to 60 volts higher than an ST-70 type amp. I would not use these 4 tubes previously mentioned in an ST-120. If you do, my guess is that the life of the tube would be noticeably shorter than normal. These 4 tubes also may not bias properly in an ST-120.

    Bob

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