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    Identify the Driver Board on a Modded ST-70

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    Mandopicker

    Posts : 5
    Join date : 2016-07-29
    Age : 46
    Location : Danville, CA

    Identify the Driver Board on a Modded ST-70

    Post by Mandopicker on Mon Aug 15, 2016 7:48 pm

    I've already sent images of the board to Bob, but thought you all might like to see the inside of one of my ST-70.  I acquired it along with four others and a Pilot - this one was modded by a real great guy and a tube amp genius/mentor and friend.  Bob hasn't confirmed this, but he believes, from my description, that the board is an earlier version from the 1990's.

    It did not have the tubes so I wanted to be sure which version it could be.  The 12AU7 version, or the 12AT7 version.  I had a suspicion from the part values...but good to know for sure.

    Thanks for looking into it Bob. Enjoy.





    Bob Latino
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    Re: Identify the Driver Board on a Modded ST-70

    Post by Bob Latino on Mon Aug 15, 2016 8:01 pm

    I Emailed Roy Mottram who designed this board. His reply was that the board on your amp is "an early version of the VTA driver board that dates back 20 - 25 years." I believe the board did use 12AT7 driver tubes.

    Bob

    Mandopicker

    Posts : 5
    Join date : 2016-07-29
    Age : 46
    Location : Danville, CA

    Re: Identify the Driver Board on a Modded ST-70

    Post by Mandopicker on Tue Aug 16, 2016 2:46 am

    That's amazing Bob. Thanks a bunch. There is a lot going on inside this thing, and I will enjoy/go mad working it all out. Any chance of a schematic being available? Lots of things I haven't seen...not saying a whole lot...and certainly unique to my original ST-70's.

    Again, many thanks to yourself and Mr. Mottram for sharing your valuable time.

    Best, David


    tubes4hifi
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    Re: Identify the Driver Board on a Modded ST-70

    Post by tubes4hifi on Tue Aug 16, 2016 12:10 pm

    yes, that's a board from 1989 or early 90s, using 12AT7 tubes, my original design

    Mandopicker

    Posts : 5
    Join date : 2016-07-29
    Age : 46
    Location : Danville, CA

    Re: Identify the Driver Board on a Modded ST-70

    Post by Mandopicker on Tue Aug 16, 2016 12:33 pm

    Honored that you took the time to confirm it and doubly cool to meet the designer.  Kudos to this fantastic site!

    Ever since I cobbled up a my first guitar amp as a kid, I have been fascinated with all of this stuff. Especially tubes of all kinds. Since, have built many guitar amplifiers, etc.

    Only recently, due to the fantastic gifts from a dear friend and mentor, have I started to dive deep into hifi designs.  I love the cross training!

    If I might ask while I have this unique opportunity, is it pretty much the same circuit or have there been improvements to it as the years have gone on?  It sounds great and I will enjoy its uniqueness.

    Again, your time and attention is greatly appreciated.

    Best,
    David

    tubes4hifi
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    Re: Identify the Driver Board on a Modded ST-70

    Post by tubes4hifi on Tue Aug 16, 2016 1:23 pm

    welcome David,
    the circuit you have is schematically identical to what was offered up until about 3-4 years ago (no improvements really necessary!!)
    The only real change the past couple years was to change a few components to use lower gain 12AU7 tubes and to add a CCS circuit for each phase splitter.
    From what I could see in the photos, there is a pretty good chance that I actually stuffed the parts on your board,
    and punched the holes in the chassis for the 3 large capacitors.
    Roy Mottram - Vacuum Tube Audio - tubes4hifi

    Mandopicker

    Posts : 5
    Join date : 2016-07-29
    Age : 46
    Location : Danville, CA

    Re: Identify the Driver Board on a Modded ST-70

    Post by Mandopicker on Tue Aug 16, 2016 4:02 pm

    Even more cool to know you might have stuffed it. Not sure how my friend acquired all of these Dynaco units I now have, but I do know he would appreciate; and likely knows full well, your expertise. I do appreciate this very much.

    Now I got to dig into several PAS preamps (3,4's), FM-3's etc. to put together a kick-butt system.

    Have a fantastic day.

    Sincere regards,

    David

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