(!!!) 31 RCA Radiotron Balloon NOS 1920's (13.2ma)
(!!) (#1 31 Pair) 31 National Union engraved base NOS 1930's (13.8ma and 14.2ma)
(!!) (#2 31 PAIR) 31 Tungsol and RCA Victor NOS same build 1940-1947 (12.8ma and 13.0ma)
(!!) (#3 31 Pair) 31 Philco and RCA engraved base different top mica NOS 1930's (13.4ma and 14.2ma)
(!!) (#4 31 PAIR) 31 Westinghouse and Sylvania NOS same build 1940's (12.0ma and 12.8ma)
(!!) (Recommended Pair) 31 GE and Coronado same build different shape top mica 1940's (15.0ma and 15.6ma) (Highest Ma)
31 Coronado by Sylvania engraved base used/good 1930's (11.5ma Gm=700)
