This era of Vox amplifiers has a notoriously bad input jack design. The plastic jack is mounted on its own little PCB with a tether that connects it to the rest of the amp. When the jack becomes loose (it will) any attempt to tighten it will spin the PCB around and reel up the tether like a fishing pole. Eventually the multi pin connector at either end will unplug or just snap off. Not only was this jack wrapped up like a ball of knitting yarn, it had also been cracked. The pound and a half of super glue that was holding it all together was also keeping the Input PCB from grounding to the chassis like it's supposed to. The resulting BUZZZZZZZZ was not the classic British tone Jamie was looking for. Replacing the broken jack and adding a metal lock washer solved the issue.