I had owned quite a few modded Dyna. One which I was fond with is the (defunct) GSI mod. It had 6DJ8/6922 in the driver board. I had modded an ST70 with the Triode driver and power supply cap boards. It sounds quite nice, balanced and detailed. I initially used Kimber coupling caps but have switched to Audiocap Theta bypassed with the Russian FT1 teflon, which is a few steps up. However, when compared with the Fisher SA-16 and Pilot SA-232 (both EL84 amps) modded with the same Theta/FT1, the EL84 amps easily trump the ST70 in my system, even with reissue Genalex KT77 or JJ KT77 in the Dyna. My ST70 does not have stock Dyna OPTs though, it has Magnequest/Kimber OPT. That said I can recommend the triode boards as they do have excellent documentations.
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