Okay I need help. I have an old early 70's Ampeg 8x10 cabinet. The jack on the back uses a very hard to find cable. the cable has a standard 1/4 plug on the one end and what looks like a female XLR plug on the other end but it has 4 pins in it. What is this? Where can I get one? Can this cabinet be retro fitted with a female phone jack?