Dawkman

Can someone help me identify my Variax? I got it used several years ago. and never used it since I bought it. I downloaded a manual but they don't quite match so I need to find a manual by model number. There is some sort of what looks like a covered jack next to the quarter inch plug and not sure how to access it and am afraid to break it.Isthere som sort of special plug for that other jack and if so is there other hardware involved? SN is 05020520