KT66
Encyclopedia
The KT66 is a beam tetrode
/kinkless tetrode (hence "KT") vacuum tube
for audio
amplification
.
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 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 deflect some secondary electrons back to the anode. The beam tetrode design was also undertaken to avoid the patent
s 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 as the "KT" series, standing for "kinkless tetrode".
A number of different KT tubes were later marketed by M-OV. Some, but not all, were versions of existing American beam tetrode
tubes or European power pentode
s, such as the KT66 (6L6), KT77 (EL34) and KT63 (6V6).
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 radio
s and audio amplifier
s. It was the standard output tube in the classic Quad
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. However, the 6L6GC has ratings that in practice substantially exceed the ratings of the KT66. (Readjustment of the amplifier's 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 original M-OV KT66 tubes (bearing the official "Genalex" marketing brand that M-OV used outside the UK), unused in original carton, can sell for US$250. KT66 tubes are still being manufactured at Reflektor Saratov in Russia, and at Liuzhou in China.
Beam tetrode
A beam tetrode is a type of vacuum tube specially designed to produce greater output power than a similar pentode...
/kinkless tetrode (hence "KT") vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
for audio
Audio frequency
An audio frequency or audible frequency is characterized as a periodic vibration whose frequency is audible to the average human...
amplification
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
.
KT66 is the designator for a vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
introduced by Marconi-Osram Valve Co. Ltd. (M-OV) of Britain
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
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
Tetrode
A tetrode is an electronic device having four active electrodes. The term most commonly applies to a two-grid vacuum tube. It has the three electrodes of a triode and an additional screen grid which significantly changes its behaviour.-Control grid:...
by positioning its anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
at a distance which is a specific multiple of the screen grid-cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
distance. This design also minimized interference of secondary emission
Secondary emission
Secondary emission in physics is a phenomenon where primary incident particles of sufficient energy, when hitting a surface or passing through some material, induce the emission of secondary particles. The primary particles are often charged particles like electrons or ions. If the secondary...
electrons dislodged from the anode.
EMI
EMI
The EMI Group, also known as EMI Music or simply EMI, is a multinational music company headquartered in London, United Kingdom. It is the fourth-largest business group and family of record labels in the recording industry and one of the "big four" record companies. EMI Group also has a major...
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
Suppressor grid
A suppressor grid is a grid used in a thermionic valve to suppress secondary emission. A suppressor grid is also called the antidynatron grid, as it helps to reduce the dynatron effect.- Placement :...
to deflect some secondary electrons back to the anode. The beam tetrode design was also undertaken to avoid the patent
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....
s which the giant Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....
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 as the "KT" series, standing for "kinkless tetrode".
A number of different KT tubes were later marketed by M-OV. Some, but not all, were versions of existing American beam tetrode
Beam tetrode
A beam tetrode is a type of vacuum tube specially designed to produce greater output power than a similar pentode...
tubes or European power pentode
Pentode
A pentode is an electronic device having five active electrodes. The term most commonly applies to a three-grid vacuum tube , which was invented by the Dutchman Bernhard D.H. Tellegen in 1926...
s, such as the KT66 (6L6), KT77 (EL34) and KT63 (6V6).
Although the RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
6L6
6L6
6L6 is the designator for a vacuum tube introduced by Radio Corporation of America in July 1936. At the time Philips had already developed and patented power pentode designs, which were fast replacing power triodes due to their greater efficiency...
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 radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
s and audio amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
s. It was the standard output tube in the classic Quad
Quad Electroacoustics
Quad Electroacoustics is a British manufacturer of hi-fi equipment, based in Huntingdon, England.- Corporate history :The company was founded by Peter J. Walker in 1936 in London, and was initially called S.P. Fidelity Sound Systems. In 1936 the name was changed to the Acoustical Manufacturing Co....
II (1952, a version of which is still being manufactured today) and in the LEAK
LEAK
LEAK is the brand name for high-fidelity audio equipment made by H. J. Leak & Co. Ltd, of London, England. The company was founded in 1934 by Harold Joseph Leak and was sold to the Rank Organisation in January 1969. During the 1950s and 60s, the company produced high-quality amplifiers, radio...
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. However, the 6L6GC has ratings that in practice substantially exceed the ratings of the KT66. (Readjustment of the amplifier's bias
Grid bias
Grid bias is a DC voltage applied to electron tubes with three electrodes or more, such as triodes. The control grid of these devices is used to control the electron flow from the heated cathode to the positively charged anode...
is necessary.)
M-OV ceased glass vacuum tube manufacture in 1988, yet their old audio tube types have become valuable collectibles. As of 2004 original M-OV KT66 tubes (bearing the official "Genalex" marketing brand that M-OV used outside the UK), unused in original carton, can sell for US$250. KT66 tubes are still being manufactured at Reflektor Saratov in Russia, and at Liuzhou in China.
See also
- KT63
- KT77
- KT88KT88The KT88 is a beam tetrode/kinkless tetrode vacuum tube for audio amplification.- Features :The KT88 fits a standard eight-pin octal socket and has similar pinout and applications as the 6L6 and EL34. Specifically designed for audio amplification, the KT88 has similar ratings to the American 6550...
- 6L66L66L6 is the designator for a vacuum tube introduced by Radio Corporation of America in July 1936. At the time Philips had already developed and patented power pentode designs, which were fast replacing power triodes due to their greater efficiency...
- 6CA7/EL34
- 6CM5
- 6DQ5
- 6DQ6
- 6V66V6The 6V6 is a beam-power tetrode, introduced by Radio Corporation of America RCA United States in late 1937, and still in use in niche applications.Similar to its predecessor the 6L6, the 6V6 was far more widely used...
- 807807/ATS25The 807 is a beam tetrode vacuum tube, widely used in AF and RF power amplifier applications. The 807 is one of the most ubiquitous and recognizable of thermionic valves/vacuum tubes.-Audio uses:...
- Beam tetrodeBeam tetrodeA beam tetrode is a type of vacuum tube specially designed to produce greater output power than a similar pentode...