Yep, it's an old one and I cannot even remember what the matching preamp was called.My guess would be a bit of both!
A normal XLR, with a hole apparently specific to Rega.
If I were you Grant, I'd be looking at the connections inside the amp. I reckon you'll find there are only 3 terminals. While you're there you can confirm it's conventionally wired.
Screen (or green sleeve) to pin 1, red or white to pin 2 and blue or black to pin 3?Thank you both, will take a look inside to see what is wired up. If all 4 terminal are connected a call to Rega will be my only option 👍