RCA's first 6L6
had a metal-canister shell rather than glass; most of the early
octal-based tubes of the era were being manufactured with metal
shells and many radio users were nervous about being injured by
glass from a broken tube. Later versions, including the 6L6G,
6L6GA, 6L6GB, 5881, 5932, and the final version 6L6GC had glass
envelopes, which facilitated radiation cooling of the anode. The
original metal version was rated for 19 watts dissipation, while
the 6L6GC was capable of 30 watts.
The list of variations of the 6L6 design is quite
extensive. Early variations included transmitting tubes such as
the 807 (1937) and the giant 813 (1938), the smaller 6V6 (1937)
not to mention the many KT versions marketed in Europe. One of
the largest post-WWII applications was in the basic design of
television sweep power tubes, starting with the 6BG6 (1946), a
modified 807. Interestingly, transistors did not fully replace
TV sweep tubes until the 1970s.
Classic amps using the 6L6 / 6L6GC
Fisher 80-AZ & 100-AZ
Grommes Little Jewel LJ-6
Scott 210-C/D, 220-A & 223
Harman Kardon A-250 'Epic'
The success of the 6L6GC is clearly illustrated
by the fact that after 70 years it is still being used (primarily
in guitar amplifiers) and manufactured by numerous factories in
Russia, China, Slovakia and Serbia.