The Super Twin Reverb isn't one of the "sought after" older Fender amps, so its value isn't too high. I played through one for a few months, but didn't care for it. I bought it from a friend because I needed a louder amp, and when I quit the band I just left it behind...it wasn't worth the hassle of lugging that monster back home again. I think it had a total of 12 or 13 tubes: 6 power tubes, tube rectifier, tube-driven reverb, and a couple of other oddball tubes that you'd probably never find at your local music stores. Re-tubing this beast could cost a bit of cash. IMO, this amp isn't worth buying; if you want a real loud Fender amp get a Twin (100 watts) or Twin Reverb (85 watts).
(Edited to add: When I owned it, I asked a lot of questions about it on the Fender Forum, and got the impression that no one really liked this amp.)