K&K Audio has a mod package for the ST-70. It converts the amp to 10 watts triode. Might be worth looking into.
ST-70 modifications
I tried a search, but had surprisingly little luck in finding info. I have a stock Dynaco ST-70. I am looking for opinions on what mods are recommended. I am thinking Curicio, Welborn/Kimmel, Van Alstine, Triode Electronics....etc. Looking to replace the driver board and the quad capacitor at a minimum. Thanks for your input