(!!!!!) (2nd Best Tungsol Single) 6550 Tungsol black plate NOS 1957 (125ma) (Recommended for Audio Research power supply)
(!!!!!) (BEST GE PAIR) 6550A GE NOS "stapled plates" late 1970's same build (135.5ma and 136.5ma)
(!!!!!) (BEST SYLVANIA PAIR) 6550 Sylvania welded plates NOS same date codes 1970's (140ma and 142ma) (BEST PAIR)
(!!!!!) (Best Tungsol Single) 6550 Tungsol branded Raytheon black plate NOS original box 1950's (144ma) (Recommended for Audio Research power supply)
(!!!!!) (Best Tungsol Single) 6550 Tungsol USA NOS gray smooth plate 1960 era (142.5ma) (Recommended for Audio Research power supply)
(!!!!) (Best Overall 6550 Pair) 6550 Tungsol USA gray plate NOS smooth gray plates 1963 same date codes in white boxes (136.5ma and 139.5ma) (Closely matched Ma and Gm)
(!!!) (2nd Best 6550 Pair) 6550 Tungsol USA gray plate NOS smooth gray plates 1962-1963 in white boxes (127ma and 129ma)
(!!!) (3rd Best Single) 6550 Tungsol USA NOS branded Sylvania gray smooth plate 1960 era (128.5ma) (Recommended for Audio Research power supply)
(!!!) (Best KT88 Gold Lion Single) KT88 Genalex Gold Lion England NOS circa 1960 in original box (155ma) (1 TUBE ONLY - NO PAIRS OR QUADS)
(!!!) (Best Single) 6550 Tungsol USA NOS gray smooth plate 1961 (126.5ma) (Recommended for Audio Research power supply)
(!!!) (Best Value) 6550 Tungsol black plate used/tests like new 1956 (143ma) (1st series made with single top getter)
(!!!) (BEST VALUE) 6550 Tungsol USA NOS gray smooth plate rebranded RCA 1962 (123ma) (Recommended for Audio Research Ref power supply)
(!!!) 6550 Sylvania branded International NOS 1979 (146ma)
(!!) (BEST VALUE) 6550A GE stapled plates NOS around 1980 (119ma) (nice single)
(!!) (Recommended Single) 6550A GE stapled plates NOS 1979 (136.5ma)
(!) 6550 Sylvania branded RCA used/tests like new 1984 (134ma)
6550 Sylvania branded RCA used/good 1979 (112ma)
6550 Sylvania used/very good 1970's rattle inside base (126ma)
