Tubes plus a sub?

Hi, I was wondering if I can use a sub to augment the bass on my system which is currently using an old Dynaco ST-70 amplifier. I love the Dynaco and don't really want to part with it. Obviously, with this choice you can also see that I'm trying to work in a restricted budget (otherwise I'd just get a better amp and speakers) I was wondering if anyone has any experience with mating a sub and tube amps and what kind of subwoofer you'd use to achieve a good clean bass.
I may be wrong,but it might be too much to ask of your old Dyna.I have one and some good EL-34s will help give you a bit cleaner bass.(Svetlanas) I get good bass with my Paradigm Studio-80s. If you got speakers with powered subs in them that might be best if you are going to keepthe Dyna forever.
a powered sub is a good solution, finding one that is designed for music and not home theater special effects will be an excellent adventure. staying with a 10" driver, try to find something like a REL or Soliloquy. (I have listened to some small M&K subs that were really good, and are on the net used all the time. and this may get ridiculed but the small Polk Audio sub was not bad if your using it to augment bass)
Build your own. check out They even sell boxes. So does if you are on the west coast. has speakers and builds good boxes too if you are NYC area. There are many sites recommending tubes running top end down to 100 Hz and solid state bass the rest of the way. check out Marchand for cross-overs or pro-sound sites for other crossovers.