Kt66

KT66 - Wikipedia, the free encyclopedia
KT66 is the designator for a vacuum tube introduced by Marconi-Osram Valve Co. ... The KT66 was very popular in European radios and audio amplifiers. ...
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KT66 is the designator for a vacuum tube introduced by Marconi-Osram Valve Co. Ltd. (M-OV) of United Kingdom in 1937.

The KT66 is the direct descendant of the "Harries Valve" developed by British engineer J. Owen Harries and marketed by the Hivac Co. Ltd. in 1935. Harries is believed to be the first engineer to discover the "critical distance" effect, which maximized the efficiency of a power tetrode by positioning its anode at a distance which is a specific multiple of the screen grid-cathode distance. This design also minimized interference of secondary emission electrons dislodged from the anode.

EMI engineers Cabot Bull and Sidney Rodda improved the Harries design with a pair of beam plates, connected to the cathode, which directed the electron streams into two narrow areas and also acted like a suppressor grid to absorb some secondary electrons. The beam design was also undertaken to avoid the patents which the giant Philips firm held on power pentodes in Europe. Because this overall design eliminated the "tetrode kink" in the lower parts of the tetrode's voltage-current characteristic curves (which sometimes caused tetrode amplifiers to become unstable), M-OV marketed this tube family under the sobriquet "KT", meaning "kinkless tetrode".

A number of different KT tubes were marketed by M-OV thereafter. Some were versions of existing American beam tubes or European power pentodes, such as the KT66 (6L6), KT77 (EL34) and KT63 (6V6); while others were unique to the KT series.

Although the RCA 6L6 of 1936 (the result of a license agreement between RCA and M-OV) was the first true "beam power tube" on the market, the later KT66 became almost equally famous, at least in Europe. The two tubes were nearly interchangeable, except that the KT66 was somewhat more rugged than the early metal 6L6.

The KT66 was very popular in European radios and audio amplifiers. It was the standard output tube in the classic Quad Electroacoustics II (1952, a version of which is still being manufactured today) and in the LEAK Type 15 (1945) and TL/12 (1948), both among the earliest British hi-fi amplifiers. Because of their excellent electrical characteristics and overload tolerance, KT66s are preferred by some guitar players for use in guitar amps in place of 6L6GC. It should be noted, however, that the 6L6GC has ratings that in practice substantially exceed the ratings of the KT66. (Readjustment of the amplifier's Grid_bias is necessary.)

M-OV ceased glass vacuum tube manufacture in 1988, yet their old audio tube types have become valuable collectibles. As of 2004, an old M-OV KT66 (bearing the official "Genalex" marketing brand that M-OV used outside the UK), unused in its original carton, can easily bring US$250. KT66 tubes are still being manufactured at Reflektor Saratov in Russia, and at Liuzhou in China.

References

Barbour, Eric. "History of the 6L6" in Vacuum Tube Valley, issue 4 (1996), p. 3.
Schade, O. H. "Beam Power Tubes" in Proc. of IRE, Feb. 1938.
Stokes, John. 70 Years of Radio Tubes and Valves. Vestal Press, NY, 1982.
Thrower, Keith. History of the British Radio Valve to 1940. MMA International, 1982, p. 59.

KT66 - Wikipedia, the free encyclopedia
KT66 is the designator for a vacuum tube introduced by Marconi-Osram Valve Co. Ltd. (M-OV) of Britain in 1937. The KT66 is the direct descendant of the "Harries Valve" developed by ...

KT66 Tube Types
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el84 el34, 6l6, ecc83, ef86, gz34, valve, kt66, kt88, auvalves.htm
MOST POPULAR VALVES USED IN OLD GUITAR AMPS INCLUDE:-Output Valves EL84, EL34, 6L6, KT66, KT88, 6550.An amp with equally matched output valves correctly biased ...

6L6 / 5881 / KT66 / 7027 Tube Types
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Cathedral Stone - GEC KT66 - MO Valve Company - Marconi Osram ...
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KT66 @ The National Valve Museum
The KT66 is a very well known audio output beam tetrode valve. Our exhibit is a post-WW2 device, probably dating from the 1960s. The production from the 1970s lacked the internal ...

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The KT66 Tube
These specifications are provided 'as-is', with no warranty of any kind. Use of these parameters shall be entirely at the user's own risk.

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