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(!!!) (Best Pair #1) 6GM5 Sylvania rebranded Tungsol and Sylvania NOS 1960 era (59ma and 60ma)
(!!) (Best Pair #2) 6GM5 Sylvania branded RCA NOS (52ma and 52ma)
6GM5 Sylvania rebranded GE NOS 1960's (56.5ma)
6GM5 Sylvania rebranded GE NOS 1966 (64.5ma)