They were used in front of broadcast transmitters. Depending on the maintenance they've seen (or not seen) they can go from OK, to real bucket of shit.

I've used them on things like 'bass' in a mixing situation, but after they'd seen more money in maintenance than they cost to buy.

Other than that, all the controls are beneath a drop down cover, and will require a screwdriver to adjust. If you plan on owning the thing for a while, remove the cover and put knob caps on the adjustment pots (try not to lose the cover). It'll make life a bit easier. Chances are you won't be selling them anytime soon, as you will rarely ever get out of them what you have into them after maintenance.

Hope this helps.