The 1954 6CG7[REF] and 6FQ7 are electrically equivalent to the 6SN7, with 9-pin miniature ("Noval") base (RCA, 1951), also made as an 8.4V 450mA series string heater type as the 8CG7.
The 1948 ECC40 with Rimlock base can also considered a successor to the 6SN7[REF] (but closer in characteristics to the ECC32).