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    ST70 driver circuit and transformers

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    dmfraser66

    Posts : 1
    Join date : 2015-03-16

    ST70 driver circuit and transformers

    Post by dmfraser66 on Mon Mar 16, 2015 5:07 pm

    If you were to recreate the ST70 today not using any NOS tubes, what driver configuration would you feel is the very best sounding.

    Perhaps using a 12AU7 and a pair of pair of EF86.

    Or perhaps three 12AU7 tubes.

    Or something else from the tubes available from the EHX web site.

    What would be your favorite output and power transformers? Not necessarily the same maker.



    Any thoughts would be appreciated. Or links.

    peterh

    Posts : 642
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: ST70 driver circuit and transformers

    Post by peterh on Mon Mar 16, 2015 5:18 pm

    dmfraser66 wrote:If you were to recreate the ST70 today not using any NOS tubes, what driver configuration would you feel is the very best sounding.

    Perhaps using a 12AU7 and a pair of pair of EF86.

    Or perhaps three 12AU7 tubes.

    Or something else from the tubes available from the EHX web site.

    What would be your favorite output and power transformers? Not necessarily the same maker.



    Any thoughts would be appreciated. Or links.
    Tubes as linear as possible , such as ecc88, should be easier to get good undistorted sound. But the tube choosen is of less importence as the complete design. Even 12au7 can be used, as examples shows. Using triodes as powertubes is beneficial if one can compensate for the increased drive
    power needed. Careful use of feedback, and matching speakers ( yes they interact)
    And, finally, well matched tubes that works within spec.


    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: ST70 driver circuit and transformers

    Post by MontanaWay on Tue Mar 17, 2015 9:10 pm

    I'd use transistors! Evil or Very Mad
    But seriously, I would use KT88's, say Gold Lion, 12BH7's and a good solid state power supply...yes...SS, with a nice B+ time delay circuit as well as speaker protection.
    For transformers, I'd use Lundahl's.
    The VTA driver circuit is about as good as its gonna get. But will use component values to REALLY match the characteristics of the 12BH7.

    eickmewg

    Posts : 38
    Join date : 2014-08-29

    Re: ST70 driver circuit and transformers

    Post by eickmewg on Wed Mar 18, 2015 6:35 am

    So, what exactly would need to be changed to optimize the driver circuit for 12BH7 vs. 12AU7 tubes? Or put another way, what compromises are being made by using 12BH7 tubes with the stock driver board?

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: ST70 driver circuit and transformers

    Post by tubes4hifi on Wed Mar 18, 2015 11:28 am

    12BH7s are a heavy duty version of the 12AU7, they use twice as much filament current, and they can handle twice as much power (either in voltage or current or both),
    but even that doesn't make it as good as a 6SN7 tube, which sounds incredible. The VTA octal driver circuit is already set up to work perfectly with the 6SN7
    to drive any push-pull power amplifier.

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: ST70 driver circuit and transformers

    Post by MontanaWay on Wed Mar 18, 2015 11:35 am

    tubes4hifi wrote:12BH7s are a heavy duty version of the 12AU7, they use twice as much filament current, and they can handle twice as much power (either in voltage or current or both),
    but even that doesn't make it as good as a 6SN7 tube, which sounds incredible.   The VTA octal driver circuit is already set up to work perfectly with the 6SN7
    to drive any push-pull power amplifier.

    that is a very good point. I myself swear by the 6XX7's. I have not tried the 6XX7's with the ST70, only the ST120, and I have no doubt that the 6XX7's will work just as great with the ST70.

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