These guys www.charleshyde.co.uk sell the plug needed to use that none standard (or should I just say 'uncommon' ) socket on the back of our amp. It was nearly £4 for that and P&P was an extra £3, but it was the only place I could see it at. Oh! Looking at their site brings back painfull memories! I know they sell it, but I couldn't find it. I'll make it easier for any of you that are interested - the part code is 42007 .