6SN7 - History

History

Originally released in 1939 it was officially registered in 1941 as the glass-cased 6SN7GT. During World War II a slightly improved 6SN7A was developed, then a more rugged 6SN7W for military use. Numerous variations on the 6SN7 type have been offered over the years, including 7N7 (Sylvania 1940, loktal-base version), 5692 (RCA 1948, a super-premium version with guaranteed 10,000 hour lifetime), 12SX7 (RCA 1946, intended for use in 26-volt aircraft electronics), 1633 (RCA 1941, also for 26-V radios), 6042 (1951, another 1633 type), and 6180 (1952). American military designator for the 6SN7GA was VT-231, and the British called it CV1988. European designations include ECC32, 13D2 and B65.

The 6SN7 has a 6.3 V 600 mA heater/filament. The 12-volt 300 mA filament equivalent is the 12SN7GT or 12SN7GTA. There was also a comparatively rare 8V 8SN7 for 450 mA series-string TV sets). The 6J5 (British version L63) was an octal single triode with identical characteristics to one half of a 6SN7. The later 6CG7 is electrically equivalent to the 6SN7, with 9-pin miniature base (RCA, 1951), also made as an 8.4V 450mA series string type as the 8CG7. The miniature 12AU7, with similar, but not identical, electrical characteristics to the 6SN7, and a filament usable on either 6.3 or 12.6V supplies, was more widely used than the 6CG7.

The 6SN7 was often used as an audio amplifier in the 1940-1955 period, usually in the driver stages of power amps. The designer of the famous Williamson amplifier, one of the first true high-fidelity designs, suggested use of the 6SN7 since it was similar to the British triodes that he used in his circuit.

The 6SN7 was one of the most important components of the first programmable digital computer, the ENIAC, which contained several thousand. The SAGE computer systems used hundreds of 5692s as flip-flops.

With the advent of television the 6SN7 was well suited for use as a vertical-deflection amplifier. As screen sizes became larger, voltage and power headroom became insufficient. To address this, uprated versions with higher peak voltage and power ratings were introduced. The GE 6SN7GTA (GE, 1950) had anode dissipation uprated to 5.0 watts. The 1954 GE 6SN7GTB also had controlled heater warmup time, better for series heater strings.

The 6SN7 was considered to be obsolete by the 1960s, replaced by the 12AU7, and was almost unobtainable. With the introduction of semiconductor electronics, vacuum tubes of all types ceased to be manufactured by the major producers.

A small demand for vacuum tubes in guitar amplifiers and very expensive high-fidelity equipment remained; as existing stocks ran out, factories in eastern Europe and China started to manufacture the 6SN7, and higher-gain 6SL7. As of 2012, 6SN7s were manufactured in Russia and China under the old Soviet designator 6N8S.