Need help with my early 70's 810 SVT cab. Jack issues. I have never been happy with my jack on the back of my 810 cab. It's a Switchcraft 3-Conductor Female XLR. It looks original, but I don't know if it is. Aren't these cabs supposed to have a 4-conductor jack? The jack is missing the clip to unlock the matching cable, so I want to replace it with the appropriate correct receptical, which I believe should be a 4 pin. I can't find any info on wiring, or jack hook up for this cab. It has original speakers, and there are only two wires going to the jack that's there. It does work as it is though. I read that there is a reason for the four pin cable, and that it protects the amp. Can anyone give me some good information on restoring my cab? BTW, I just got my 73 head back from service. A few microphonic preamp tubes and 2 questionable power tubes replaced, as well as a couple resistors, power cord, and new feet. Jim Walton is the amp tech. He's in Philadelphia. Great guy. Really knows vintage tube amps, and came highly recommended for working on my SVT. Taught me a bit about my head before I left too. Interesting. I didn't know it was only 200watt at 4ohm with one cab, and 300 at 2ohm with two. He said these amps were made to be all purpose amps, not just bass amps, and showed me that the midrange is active. Really colors the sound when you dial it. He said the switch above the midrange will blow speakers if not careful, and he demonstrated the amp when I picked it up. I also hooked up with a speaker repair guy this week. Miller Sound. World famous. His family's been in the business since the 30's. Lives right down the road. Says he's got cones to recone my vintage speakers if I ever need to. I told him I thought one was buzzing. He fixed a torn cone on a Celestion guitar speaker for me when I dropped off a couple shot vintage Sunn 15's for a friend of mine.