I have an early 70's B15 that recently came into my shop. Blown fuse, bad rectifier tube, burnt traces on OT secondary, bad xlr connector, etc. I'm not understanding how to convert the xlr connector to standard 1/4" connector. The amp has been recapped, power tubes bias is good. Does the speaker cable connection on the circuit board look ok? I haven't found a schematic that matches this amp. I have a feeling something is not correct because when it's plugged in there is a loud AC hum like something isn't grounded properly and it sounds awful. https://www.flickr.com/photos/34258368@N03/albums/72157667697597042 Here are some detailed photos. Any other techs out there willing to help me out? I'd gladly send you some old preamp tubes as trade for your time.