Guild amps don't get any respect; there's probably an argument that says they don't deserve any. Regardless of condition, this one is about maxed out at $400. They weren't considered 'hot' back in the day and unless one of our Boardistas hits it big with his Guild amp, chances are they're going to remain a 1960s footnote.
They handicapped themselves with self-destructing particleboard cabinets, stick-em-on wood-grain shelf paper on the sides, and kooky 6GW8 output tubes in the combo amps. At least (what's left of) John K's Thunderbird has 7591s; many of the T1 RVTs (including mine) have Euro radio tubes for outputs. As an aside, there are 1960s Univoxs out there that run on the 6GW8.
Based on some pics that matsickma posted, his late 50s/early 60s J Models look considerably better made than the mid-60s Thunder 1s and RVTs. Can't say about the bass amps but one of the reasons it's hard to get pumped about G combo amps is that, due to their crappy cabinets, not many functional copies have survived for people to refurbish, show off, and thereby regenerate interest.
BTW: the mid-60s T1 RVTs have the fuse in a clip inside the chassis. If you blow one, you have to take the chassis out. Fair enough - what the hell, something's wrong that another fuse probably won't fix anyway.
However, to remove the chassis, you have to remove one of the 'faux' handle fasteners that isn't a screw, it's a bolt. For the sake of design symmetry, there's another bolt there but it's a dummy that doesn't do anything.
The real bolt passes through the handle base and down into the chassis space, threads into a hole in a metal cross-member, and provides dead-weight support because the chassis isn't stiff enough to support it own weight; an after-the-fact manufacturing band-aid if there ever was one.
Now that I'm done venting, the fact is a T1 RVT puts out a very pleasing clean signal; smooth, deep, articulated, and sweet highs. Because it doesn't break up, it does acoustic and jazz tones very well. The reverb, as Jay Pilzer said, is lush, deep and nicely variable - as much or little as you want and the trem is as nice as any. Putting a Celestion Greenback in it won't hurt it either.
At the end of the day, the T1 RVT was well-designed but poorly made. I don't know if any of that stink got on the bass amps or not; even if they didn't deserve it, it wouldn't be the first time that one part of a product line got smoked by another.
cj