6V6
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6V6 is the designator for a vacuum tube introduced by Radio Corporation of America RCA United States in late 1937.
6V6 is a beam-power tetrode, similar to its predecessor the 6L6. While the 6L6 was an excellent tube, it was not really suitable for use in home consumer electronic devices because its output, especially in a push-pull pair, was so high. With the introduction of the lower-powered 6V6, which required only half the heater power of the 6L6, the beam-power tetrode became a usable technology for the home, and began to see common use as the audio output stage of radios and other electronic home entertainment devices where standard power pentodes such as the 6F6 had previously held sway. The 6V6 required less heater power and provided less distortion than the 6F6, while still offering higher output in both single-ended and push-pull configurations.
The 6V6 was introduced in both metal and shouldered glass tubes. RCA was promoting the superiority of its metal tube designs in the second half of the 1930s, and this tube, having been introduced during that period, was produced in large quantities in this format. Other tube manufacturers also produced the 6V6 in glass tubes, which were commonly found in radios not made by RCA. By 1940 the 6V6 was mostly being produced in a smaller "GT" glass envelope, and later the 6V6GTA was introduced which had a controlled warm-up period. Also similar is 6AQ5, which has similar specifications to the 6V6GT, but in a miniature glass shell, and the 7408 as well as the Soviet-produced 6P1P, which is essentially the same as 6AQ5, but has a 9-pin base.
In the Soviet Union a version of the 6V6GT was produced since the late 1940's which appears to be a close copy of the 1940's Sylvania-issue 6V6GT - initially under its American designation (in both Latin and Cyrillic lettering), but later, after USSR had adopted its own sytem of designations, the tube was being marked 6P6S (6П6С in Cyrillic.)
Generally 6V6 tubes are sturdy and can be run beyond their published specifications, except for the 6P6S, which has poor tolerance for out-of-spec operation versus most American and West European-made 6V6 variants. Because of this, the 6V6 became very popular for use in instrument_amplifiers. This market allows China, Slovak and Russian tube factories to keep the 6V6 in production to this day. It is very often used in guitar amplifiers.
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