I just got a one of the Dynaco ST70 upgrade driver boards from http://www.tubes4hifi.com/ the VTA70 and I was very happy with both the performance and customer services from the folks at Vacuum Tube Audio.
This driver board came with great quality components, as well as great instructions on how to assemble the kit. I had to order a replacement current regulator and they sent one out within one day of getting my payment. They also sent another layout diagram to make sure that I installed the transistor correctly. The service was top notch.
This board replaces the single bias control per channel with individual bias controls for each of the output tubes. (2 per channel) It also replaces the large can filter cap with 4 common electrolytic capacitors that are more cost effective to replace and easier to source.
So how does it sound? well after about 10 hours of listening all I can say is WOW it is a huge improvement over the old driver board, it sounds way more open and the sound stage is more focused. The amp also sounds much faster to me. I compared it to a Scott LK150 in the past before the upgrade the LK150 (stock) sounded much clearer and more transparent. and since the upgrade this ST70 is on par or exceeds the sound of the Scott. Overall I am in love with the new sound of my ST70.
- Dynaco ST70 with cloth leads on output transformers
- Winged C Svetlana EL34 Tubes
- RCA Blackplate NOS 12au7 Driver tubes in VTA70 driver board
- JJ gz34 Rectifier
the other mods are Gold Input Jacks, Updated binding posts (banana plug) and Dale 1% Resistors and 99.99 Silver wire