(!!!) (Best Mullard Single) 6688=E180F Mullard branded Philips SQ gold pins NOS 1971 (11.5ma)
(!!!) (Best Single #2) 6688=E180F Amperex PQ USA NOS 1965 (15.2ma)
(!!!) (Single) 6688=E180F Amperex PQ USA NOS "O" getter 1968 (9ma)
6688 GE 5 Star used/good (7.2ma)
6688 GE NOS 1966 (9ma)
6688=E180F National UK black plate NOS probably made by Amperex (9ma)
6688=E180F National UK gray plate NOS probably made by Amperex (16ma)
