Though I think a good ss amp would be better for the Advents, if you insist on a tube one, and you're patient, you can get yourself a much better amp than a Dynaco Stereo 70, for around the same price. I've had a stock ST70, a modified one (ala Frank Van Alstine), and now have what I recommend you look for instead:
a Music Reference RM-10 Mk.2. Same power as the ST70 (35w/ch into 8 ohms, from a pair of EL84's per channel), but better designed, better built (hard-wired point-to-point, state-of-the-art transformers), and better sounding. Occasionally available second hand for $1200-$1500.