I have the opportunity to buy a late 70's/early 80's Fender Studio Bass combo. It is an all-tube (6-6L6 power section), 200 watt combo with an EV 15" speaker. These are pretty uncommon amps from what I can see. They are, more or less, the bass version of the SuperTwin (a/k/a the "evil twin")Does anybody have any experience with this amp? How much should I expect to pay for one in very good - excellent condition?