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    Tube converter adapter ?

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    scottlowe76

    Posts : 14
    Join date : 2017-06-15

    Tube converter adapter ?

    Post by scottlowe76 on Fri Nov 17, 2017 7:42 pm

    Hi I saw something called a 12au7 to 6sn7 tube converter adapter on ebay. Is that safe to try on an st 120 ? thanx ! scott
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    Kentley

    Posts : 460
    Join date : 2015-03-06
    Age : 65
    Location : Worcester, MA

    Re: Tube converter adapter ?

    Post by Kentley on Fri Nov 17, 2017 7:57 pm

    Yes, well-made adapters will work fine, with several caveats.
    First, buy a good solid unit. These should cost in the $10-12 range. I bought a cheap one and the pin sockets were too shallow.
    Second, buy one only, for the center driver tube. The splitters work fine with 12AU7s, and you will find that the extra current needed for three 6SN7s will tax a section of the PT, though this will only marginally affect the ST-120s PT. I wouldn't do this with any other Dynaco "clone" amp.
    Last, because the adapter will increase chances of bad connection issues, extreme care should be taken. Sockets on the amp and on the adapter itself (and pins, of course) should be carefully maintained and monitored. Every two months or so, I'll notice a 60 cycle hum coming from both channels. It's caused by bad contact in that center driver with the adapter.
    So yes, it will function. The ultimate solution, though, is to switch to the octal driver board, available from VTA. One of these days, Alice, I'll actually take my own advice (fer a change....)

    scottlowe76

    Posts : 14
    Join date : 2017-06-15

    Re: Tube converter adapter ?

    Post by scottlowe76 on Fri Nov 17, 2017 9:21 pm

    Thanx kently. Any 6sn7 types you think i should try ? i like the 12au7 cleartops .
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    sKiZo

    Posts : 1467
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Tube converter adapter ?

    Post by sKiZo on Fri Nov 17, 2017 9:28 pm

    If they're not safe, maybe I'm just lucky? ;-}



    (Yes - that IS an ST120. I took some "liberties" with the build.)

    Here's the one I used offa ebay ...



    Been using that with an RCA coin base for maybe a couple years now. Runs rings around any other tube I've tried in the center position.
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    Kentley

    Posts : 460
    Join date : 2015-03-06
    Age : 65
    Location : Worcester, MA

    Re: Tube converter adapter ?

    Post by Kentley on Fri Nov 17, 2017 11:44 pm

    6SN7s come in many flavors. Only way to find out what works for you is to experiment. Thankfully, many NOS brands, like sKiZo's beloved RCAs, are relatively cheap and in good supply. Sylvanias, especially the earlier ones, are prized by many. They tend to be a bit mellower on the top, most say.
    Of new brands, the TungSols are a solid contender, though few of us find them particularly remarkable. The EHs, I believe most would say, are not very good - dull and microphonic to an extreme. The real winners of new production are the Shuguang/Psvanes. They are, to my ears, and deepee's, absolutely stunning.

    scottlowe76

    Posts : 14
    Join date : 2017-06-15

    Re: Tube converter adapter ?

    Post by scottlowe76 on Sat Nov 18, 2017 3:18 pm

    Thanx ! My choices tend towards more top end . so the clear tops are what I have found to be my 12AU7 first pick . Thx Again . that looks like the exact one I saw.

    eickmewg

    Posts : 88
    Join date : 2014-08-29

    Re: Tube converter adapter ?

    Post by eickmewg on Sat Nov 18, 2017 4:50 pm

    I tried some adapters with my ST120 using nice Sylvania 6SN7's. I liked the result. I actually used three adapters for all three drivers. I then decided to build an octal driver board which was easy to populate and install. I now have the Sylvania's for the phase dividers and a very nice Shuguang CV181 Z for the center amplifier position. Certainly no loss in the top end with these.
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    erhard-audio

    Posts : 31
    Join date : 2017-04-07
    Age : 60
    Location : SW Coast OR

    Re: Tube converter adapter ?

    Post by erhard-audio on Sat Nov 18, 2017 5:48 pm

    keep in mind filament current!
    pretty much most 12XXX series are 300mA @ 6.3V. The 6SN7 is 600mA @ 6.3V, so, double that of the 12XXX!
    The ST120 power transformer will be able to handle the additional current, but an original ST70 probably not.
    Tube filament current is easily forgotten and a lot of times not taken into account when tube swapping.

    scottlowe76

    Posts : 14
    Join date : 2017-06-15

    Re: Tube converter adapter ?

    Post by scottlowe76 on Sat Nov 18, 2017 6:57 pm

    sKISo that is beautiful looking amp . Looks to have alot of thought behind it . I have an RCA and socket on the way . I think it will be fun to try a different type of tube . Thx to all .

    eickmewg

    Posts : 88
    Join date : 2014-08-29

    Re: Tube converter adapter ?

    Post by eickmewg on Sun Nov 19, 2017 7:35 am

    The new VTA ST70 can use 12BH7 drivers. They draw the same 600 mA current as the 6SN7's, so those shouldn't present a problem for either the VTA ST70 or VTA ST120. If you like the octals, you can then get an octal board, which is what I did for my ST120, with two 50's Baldwin-labelled Sylvania phase splitters and a very nice Shuguang CV181Z amplifier tube. A very nice combination.

    Dogstar

    Posts : 323
    Join date : 2014-06-23

    Re: Tube converter adapter ?

    Post by Dogstar on Sun Nov 19, 2017 11:20 am

    Kentley wrote:Yes, well-made adapters will work fine, with several caveats.
    First, buy a good solid unit. These should cost in the $10-12 range. I bought a cheap one and the pin sockets were too shallow.
    Second, buy one only, for the center driver tube. The splitters work fine with 12AU7s, and you will find that the extra current needed for three 6SN7s will tax a section of the PT, though this will only marginally affect the ST-120s PT. I wouldn't do this with any other Dynaco "clone" amp.
    Last, because the adapter will increase chances of bad connection issues, extreme care should be taken. Sockets on the amp and on the adapter itself (and pins, of course) should be carefully maintained and monitored. Every two months or so, I'll notice a 60 cycle hum coming from both channels. It's caused by bad contact in that center driver with the adapter.
    So yes, it will function. The ultimate solution, though, is to switch to the octal driver board, available from VTA. One of these days, Alice, I'll actually take my own advice (fer a change....)


    A while ago there was another thread that spoke about the adaptor for 6SN7 tubes. I tried the adapter and even purchased a few different tubes. The 6SN7 tube does alter the sound and in my opinion the sound is slightly better in some cases. In my opinion I don't think the sound is monumentally different even though at first I thought it did. I may spring for the octal board eventually but for the time being the 12AU7's sound good enough.

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