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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all products

    ST-70 VTA Driver and Triode Cap Board upgrade results.


    Posts : 18
    Join date : 2018-10-31

    ST-70 VTA Driver and Triode Cap Board upgrade results. Empty ST-70 VTA Driver and Triode Cap Board upgrade results.

    Post by Sfguitarworks Mon Dec 27, 2021 6:15 pm


    I was given the VTA driver board, 12au7 version, and the Triode Cap Board for a gift last week. Just wanted to post some thoughts.

    I installed the Triode board first, as I wasn't exactly sure how the two would go together, and wanted to verify functionality on each separately. The population of the board was easy, with good instructions. I had to clip a transformer screw shorter to get it into the chassis with no flex. The hookups were straightforward, except for the wires from the bias pots. They are designated as "left and right." Trouble is you can look at it from two directions. I powered it up and smoked a cathode resistor and popped the fuse. I assumed the bias was off, reversed my wires and all was good.

    Hooked it back up to my system - NAD 1155 pre, recapped and modified as per Lee Stereo, B&W P4 speakers, Technics SL-1200 with AT VM540ML cart - and checked it for noise. Very quiet. I could turn up to 10 and have just a tiny hum if I got right next to the speaker. Listening to it revealed a stronger bass response. It was really obvious. Definitely worth doing.

    Next day I installed the driver board. It took a bit of looking but I got the info for how to hook the two together here on the forum. I can't recall the post, but I googled vta driver with triode cap board. At any rate, hooked it up, went through the tests and brought it back in. It's hard to explain, but everything I liked about my amp is better with the driver board. Imaging, separation, high end clarity, mid range presence are all improved. It was a significant difference. The bias is rock solid, and it is very stable so far. I have JJ EL34s and JJ long plate 12au7s in the driver section. I use a SS rectifier.

    I have not heard a mega-buck amp in my system, but I can't imagine it would sound any better. I think I'm at the point of seriously diminishing returns here. Thanks to everyone for posting such useful info here, and to the designers and producers of these fine parts.

    Take care,


      Current date/time is Thu Jan 20, 2022 9:14 am