Ive recently acquired a large cabinet, but its been giving me a few problems. Its got two 15" in it and the cabinet and the head probably date back to the 70's. I get a lot of fuzz and mild amounts of feedback, is this because of the cab or the head? The cab looks like good working order, it just has this slight feedback that drives me up the wall. The head on the other hand is old and only has tone knobs for bass and treble, no mids. It has two little switches that are labeled gnd and bright; what the hell is that? I cant afford a new head at the moment (poor college student), so I wanna make what I have work the best it can. What should I do? Should I replace the speakers or is the old outdated head my problem?