5R4GYB RCA brown base NOS 1970's part of glass melted into bottom mica (50/40 and 53/40)
5U4GB Sylvania Canada NOS 1960's (61/40 and 64/40) (similar build to RCA)
6550A GE stapled plates used/good 1980's (115ma)
6688 GE 5 Star used/good (7.2ma)
6688 GE NOS 1966 (9ma)
6973 Sylvania gray plate NOS 1970's (61ma)
6AS7GA Sylvania metal base NOS 1960's (77/87ma)
6BQ5 GE NOS 1960's (40ma)
6BQ5 GE NOS 1960's (47ma)
6BQ5 GE NOS 1960's (70ma) (recommended for FIXED-BIAS amp only due to high current)
6BQ5 GE NOS 1971 (43.5ma)
6BQ5 GE NOS 1977 (58.5ma)
6BQ5 GE NOS/80-85% 1959 (36ma)
6BQ5 Lindal Japan like new 1970's (50ma)
6BQ5 Lindal Japan NOS 1970's (42ma)
6BQ5 Lindal Japan NOS 1978 (59.5ma)
6BQ5 RCA gray plate used/good 1967 (32.6ma)
6BQ5 RCA Magnavox gray plate used/good 1961 (44ma)
6CA7=EL34 Siemens Germany skinny bottle branded CEI NOS 1975 (79ma)
6CA7=EL34 Siemens Germany skinny bottle branded CEI NOS 1975 (85ma)