Need two 4-pin PL-50 connectors. Four-pin tube bases will not work. Here are two views: http://home.netcom.com/~arc5/PL50A.JPG http://home.netcom.com/~arc5/PL50B.JPG I have many types of connectors to trade or will buy. (Don't have ART-13 or 12-pin MD-7; sorry). TNX ES 73 DE Dave AB5S