Hmm, craptacular. I missed this thread, hope you're still looking.
I actually have a few ST-70s and PAS-2s along with a bunch of other tube gear. Personally I really dig the Dynaco sound. I HIGHLY recommend it. The ST-70 particularly is very easy to work on if thats your schtick, if not it should not be costly to have a tech check it out. Watch out for items on ebay that say they have been gone through and the tubes replaced. Fact is most old tubes are MUCH better than the russian/chinese/eastern block tubes that are in current production. Dynaco originally stocked their amps with mullard tubes for the EL-34s and 5AR4, the ST-70 doesn't drive the outputs that hard so most original EL-34s should still be OK and the mullard 5AR4 is possibley the best ever made and should have a ton of life left. If you must go new production, look for a sovtek 5ar4, SED EL34s or EH Big bottles. The 7199s are another thing, Dynaco used RCA black plate tubes in most of the ones I have seen, these are great tubes, but are a little pricey, the Sylvania grey plates are decent, but stay away from the newer sovtek production if you can i'm not hot on them.
Rebuilding a ST-70 should be pretty easy, there are many sights that will walk you through it, i've done 3 so far. You will just need to replace a few things to get it back in tip top shape:
The filter Cap
Coupling Capacitors
Sellenium Rectifier stack
Other goodies would be:
Tube sockets
RCA Jacks
Output Terminals with some 5 way binding posts
Sheldon Stokes put out a replacement driver that sounds really nice, you can buy one through Ned Carlson at Triode Electronics; the circuit uses a 12AU7 splitter into 2 EF86s, its a nice design and maintains the essensce of the original circuit so it doesn't change the sound too much. I would also consider this a nice upgrade.
The PAS is a bit more of a pain in the ass to work with... With a few mods it can sound really nice, it just needs a few things updated and put back in spec.
At any rate, I would REALLY recommend dynaco gear, it sounds night and day nicer than a lot of current produciton SS gear, and even much of the new tube gear i've heard (perhaps thats becasue you get used to that nice deep soundstage dynaco has??)
if you need any advice on dyna gear, just let me know! Let us know what you decide.