(!!!) (Recommended Pair) 6BQ7A RCA black plates NOS 1962-1972 same build (9.5/11.5ma and 9.2/11ma)
(!!!) 6BQ7A RCA black plates NOS 1970 era (14.0/15.2ma)
(!) 5BQ7A RCA black plates NOS 1964 (11.6/14.4ma)
5BQ7A GE Dumont gray plates "O" getter 1973 (12.8/8.2ma)
(!) (Best Single) 5BK7A GE branded GM Delco black plates "U" getter 1950's (12/13ma) (Highest Ma and Gm)
(!) (PAIR) 5BQ7A Dumont by GE gray plates NOS 1973 (12.6/10.2ma and 9.2/13.5ma)
(!) (PAIR) 5BQ7A GE gray plates NOS large "U" getter halo 1961 -1964
(!) (BEST PAIR) 5BQ7A RCA black plates NOS "D" getter 1957-1959
6BK7B Philco by Sylvania NOS 1960 (13.2ma/15.2ma)
6BQ7A RCA black plates branded Westinghouse NOS "D" getter halo 1950's (7.5/8.0ma)
(!!!!!) (INFORMATION) 6N1 or 6N1P (Best Sounding Substitutes = 6BK7B, 6BQ7A, 6BZ7)
(!!!) (Recommended Single) 6BK7A Tungsol black plates NOS "U" getter 1956 (8.6/9.6ma) (great sub for 6N1P)
(!!!!!) (Best Value Pair) 6BQ7A RCA black plates NOS "D" getter 1958-1959 (7.6/9ma and 7/9.6ma)
(!!!) (Recommended Pair) 6BK7B Tungsol black plates NOS "O" getter 1960's (7.5/8.6ma and 8.2/9.4ma)
(!!!) (Recommended Pair) 6BK7B Tungsol black plates NOS "O" getter 1960 era (9.5/12ma and 9.8/10.5ma)
(!!!) (Recommended Pair) 6BK7B Tungsol gray plates NOS "O" getter 1960's (10/11ma and 10.6/13.2ma)
(!!!) (Recommended Single) 6BK7B Tungsol gray plates NOS 1960's (8.0/9.8ma) (great sub for 6N1P)
(!!!!!) (Recommended Pair) 6BK7B RCA black plates NOS 1960's (9.5/10ma and 9.8/10.6ma)
(!!!!) (Recommended Pair) 6BK7B GE black plates NOS "U" getter halo 1960-1961 (7.2/7.2ma and 6/7ma) (Best 6N1P sub)
(!!!!) (Single) 6BK7B Tungsol branded RCA "U" getter 1957 (10/14ma)