A/DA made some very good gear back in the 80's, but they've been out of business for a long time. Their rack preamps still have an avid cult following, and command decent prices on Ebay. Their other products--cabs, combos, power amps, and effects--have all been surpassed by technological improvements over the years. I mean they were all good stuff, but not as good as more recent gear. As to the worth of that cab, what size is it? What speakers are in it? What does "good shape" mean exactly? It could be worth $25, or $225, or anywhere in between.