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    ST-70 Driver Board Decision

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    awise1961

    Posts : 7
    Join date : 2011-12-15
    Age : 55
    Location : New Hampshire

    ST-70 Driver Board Decision

    Post by awise1961 on Wed Feb 15, 2012 3:31 pm

    I'm ready to upgrade the driver board on my ST-70 and need to decide between the VTA low gain 12AU7 version or the new octal 6SN7 version. Either way I will probably go with the Russion Oil caps.
    Last September I completely rebuilt the amp with parts from Dynakitparts.com. Now I want to take it to the next level, but I am having a tough time deciding between the two options.
    I'm running a rebuilt/modded PAS-2/3 with boards and parts from Roy here at Tubes4Hifi and really like what I was provided.
    Also, I just added a new matched quad of Genelex Gold Lion KT-77's this morning.

    Thanks, Al. Wise

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: ST-70 Driver Board Decision

    Post by mantha3 on Wed Feb 15, 2012 5:02 pm

    Do you have good 12AU7s on hand? Like some Mullard etc level tubes? If you do I'd go with the 12AU7 version.

    awise1961

    Posts : 7
    Join date : 2011-12-15
    Age : 55
    Location : New Hampshire

    Re: ST-70 Driver Board Decision

    Post by awise1961 on Wed Feb 15, 2012 6:35 pm

    No, I do not have any 12AU7s in my collection. Only 12AX7s.

    Al. Wise

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: ST-70 Driver Board Decision

    Post by mantha3 on Wed Feb 15, 2012 6:44 pm

    Ah... Octal tubes like these 6SN7 are kinda trendy now.. I think these historically were replaced by the smaller 12AX7, 12AU7, 12AT7 etc tubes... I prefer the sound from these small preamp tubes personally. Look into NOS tube prices if you want any NOS. These Octal tubes are older then the small tubes I think and a little more sparse. I think I'm about to be savaged/beaten for down-talking Octals.

    Given you don't have tubes just do some tube research.. what is available and price... etc. I think you can't really go wrong.

    Oh, bigger tubes look cooler.






    burnedfingers

    Posts : 31
    Join date : 2009-05-06

    Re: ST-70 Driver Board Decision

    Post by burnedfingers on Thu Feb 16, 2012 7:10 am

    Make a decision based on what you want not what others like. The 6SN7 is not a trendy tube it is very linear unlike the 12aU7. It is not out of date by any means. The 12Au7 deserves to be thrown at a brick wall. Like I said its not linear and anything it can do the 12Bh7 can do better. If you like a syrupy sound then go for it. Just because a tube was replaced by a smaller 9 pin the 9 pin is not necessarily better. The 6FQ7/6CG7 is the same as a 6SN7 only in a 9 pin. The 12at7 is avery decent tube as is the 6SL7 basically pretty close in gain.

    burnedfingers

    Posts : 31
    Join date : 2009-05-06

    Re: ST-70 Driver Board Decision

    Post by burnedfingers on Thu Feb 16, 2012 7:10 am

    If you are looking to go 12AU7 then see what modifications are needed to throw in a 12BH7 in place of the 12AU7. It a much better tube.


    Last edited by burnedfingers on Thu Feb 16, 2012 7:12 am; edited 1 time in total (Reason for editing : double post)

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: ST-70 Driver Board Decision

    Post by mantha3 on Thu Feb 16, 2012 9:46 am

    I run in place of a 12AT7 a 7062 tube. This is between a 12AU7 and 12AT7 gain wise. Same with a 5965. Lots of options and they sound excellent. My ears love the Mullard CV4003 12AU7. Unreal how good it sounds. That is what matters and I would go by that instead of going with the advice of thowing tubes against a wall. Roy has been selling his low gain VTA for many years and has many happy customers with happy ears... I'm one of em. I'm sure the new VTA sounds excellent and 6SN7 I'm sure is excellent as well. Read up on tubes.. Shop around options and go with one or the other knowing ya can't really screw it up.

    Have fun and report back. Whatever you do don't throw any tubes against a wall


    awise1961

    Posts : 7
    Join date : 2011-12-15
    Age : 55
    Location : New Hampshire

    Re: ST-70 Driver Board Decision

    Post by awise1961 on Thu Feb 16, 2012 9:58 am

    Thanks guys.
    I spent last night researching availability and pricing of the 12AU7, 12BH7, and 6SN7 tubes.
    It appears that there are plenty of the 12AU7s and 6SN7s, but not so for the 12BH7. I'll keep loooking.
    With either choice would you run the same tube in all three locations, or would you use them in the outter most locations and something else in the center?
    If so, what would be your reccomendation?

    Thanks, Al. Wise

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: ST-70 Driver Board Decision

    Post by mantha3 on Thu Feb 16, 2012 12:48 pm

    Mullard CV4003 12AU7 in the middle would sound excellent. I like the RCA 12au7 clear tops... Those on the side would be excellent. Amprex, Siemens, Phillips... so many good ones

    The middle tube is the key for sound. The center of the VTA is the voltage amp tube (impacts both R and L channel)and the tubes on each side are the phase splitter spots (One side R and one side L). The center tube you should get the best "balanced sections" tubes... The center tube has the most impact on the sound overall. The sides a nice matched pair of tubes. I think this goes for both the 12 volt small 12AU7 VTA or the 6 volt 6SN7... Center volt amp and sides phase splitters

    6SN7 tubes have a strong following. No mistake to go this direction. I would not throw a 6sn7 tube against a wall for any reason. I would pamper it and love it. ;-)

    This stuff is all preference and it boils down to what your ears like. Go VTA!


    awise1961

    Posts : 7
    Join date : 2011-12-15
    Age : 55
    Location : New Hampshire

    Re: ST-70 Driver Board Decision

    Post by awise1961 on Thu Feb 16, 2012 5:25 pm

    Decision made; I'm going with the low gain 12AU7/12BH7 board kit with Russian PIO .22uf caps.
    Helping that decision along was my finding of one of my lost tube stashes.
    In it was a 12AU7 EICO labled Made By Mullard Great Britain. It tests as new on my Hickock 6000a.
    I will use this tube in the center position and order a matched pair of 12BH7As for the outter two.
    Thank you for all of your help.

    Al. Wise

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