6L6
Encyclopedia
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 triode
s due to their greater efficiency. The beam tetrode
design of the 6L6 allowed RCA to circumvent Philips' pentode patent.
, 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 redirect some secondary electrons back to the anode. The beam tetrode design was also undertaken to avoid the patents which the giant Philips
firm held on power pentode
s 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 amplifier
s to become unstable, MOV (Marconi-Osram Valve, a subsidiary of EMI
jointly owned with General Electric Company plc) marketed this tube family under the sobriquet "KT", meaning "kinkless tetrode".
Because MOV's engineers did not feel the kinkless tetrode could be successfully mass-produced, they licensed the design to RCA. This proved to be a poor business decision on MOV's part. RCA subsequently had enormous success with the 6L6. It replaced the use of power triodes in public-address amplifiers almost overnight. So many applications were found for the 6L6 that a complete list would be impossible to assemble. MOV introduced their version, the KT66
, a year later.
RCA's first version had a metal-canister shell rather than glass — being one of the early octal base
tubes, most of which had metal shells. Later versions, including the 6L6G, 6L6GA, 6L6GB, 5881, 5932, 7027, and the final version 6L6GC had glass envelopes, which made radiation
cooling of the anode easier. The voltage and power rating of the 6L6 series were gradually pushed upwards by adding features such as a micanol base, thicker plates, thicker grid wires, grid cooling fins, and special ultra-black plate coatings. The original metal version was rated for 19 watts dissipation while the later 6L6GC is usually rated for 30 watts.
(1937) with 6.3V heater and equivalent 12.6V 1625, the smaller 6V6
(1937), the many KT versions marketed in Europe, and a subsequent vast array of audio and RF power tubes. One of the largest post-WWII applications was in the basic design of television sweep power tubes, starting with the 6BG6G (1946), a modified 807
. TV sweep tubes were not replaced by transistor
s in earnest until the 1970s.
Further testimony for this device's success would be even simpler: the 6L6GC version is still being manufactured and is used, primarily in guitar amplifier
s. Manufacture continues in Russia
(two factories), China
(two factories), and Slovakia
. (In 2006, Ei Electronics in Serbia
discontinued making tubes.) Thus, the 6L6 has enjoyed one of the longest active lifetimes of any electronic component at more than 70 years.
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 Radio Corporation of America in July 1936. At the time Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....
had already developed and patented 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...
designs, which were fast replacing power triode
Triode
A triode is an electronic amplification device having three active electrodes. The term most commonly applies to a vacuum tube with three elements: the filament or cathode, the grid, and the plate or anode. The triode vacuum tube was the first electronic amplification device...
s due to their greater efficiency. The beam tetrode
Beam tetrode
A beam tetrode is a type of vacuum tube specially designed to produce greater output power than a similar pentode...
design of the 6L6 allowed RCA to circumvent Philips' pentode patent.
History
The 6L6 is a 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 tetrodeTetrode
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 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 redirect some secondary electrons back to the anode. The beam tetrode design was also undertaken to avoid the patents 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 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 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 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 to become unstable, MOV (Marconi-Osram Valve, a subsidiary of 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...
jointly owned with General Electric Company plc) marketed this tube family under the sobriquet "KT", meaning "kinkless tetrode".
Because MOV's engineers did not feel the kinkless tetrode could be successfully mass-produced, they licensed the design to RCA. This proved to be a poor business decision on MOV's part. RCA subsequently had enormous success with the 6L6. It replaced the use of power triodes in public-address amplifiers almost overnight. So many applications were found for the 6L6 that a complete list would be impossible to assemble. MOV introduced their version, the KT66
KT66
The KT66 is a beam tetrode/kinkless tetrode vacuum tube for audio amplification.KT66 is the designator for a vacuum tube introduced by Marconi-Osram Valve Co. Ltd. of Britain in 1937....
, a year later.
RCA's first version had a metal-canister shell rather than glass — being one of the early octal base
Octal
The octal numeral system, or oct for short, is the base-8 number system, and uses the digits 0 to 7. Numerals can be made from binary numerals by grouping consecutive binary digits into groups of three...
tubes, most of which had metal shells. Later versions, including the 6L6G, 6L6GA, 6L6GB, 5881, 5932, 7027, and the final version 6L6GC had glass envelopes, which made radiation
Thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....
cooling of the anode easier. The voltage and power rating of the 6L6 series were gradually pushed upwards by adding features such as a micanol base, thicker plates, thicker grid wires, grid cooling fins, and special ultra-black plate coatings. The original metal version was rated for 19 watts dissipation while the later 6L6GC is usually rated for 30 watts.
Variations
Early variations included transmitting tubes such as the 807807/ATS25
The 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:...
(1937) with 6.3V heater and equivalent 12.6V 1625, the smaller 6V6
6V6
The 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...
(1937), the many KT versions marketed in Europe, and a subsequent vast array of audio and RF power tubes. One of the largest post-WWII applications was in the basic design of television sweep power tubes, starting with the 6BG6G (1946), a modified 807
807/ATS25
The 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:...
. TV sweep tubes were not replaced by transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
s in earnest until the 1970s.
Further testimony for this device's success would be even simpler: the 6L6GC version is still being manufactured and is used, primarily in guitar amplifier
Guitar amplifier
A guitar amplifier is an electronic amplifier designed to make the signal of an electric or acoustic guitar louder so that it will produce sound through a loudspeaker...
s. Manufacture continues in Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
(two factories), China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
(two factories), and Slovakia
Slovakia
The Slovak Republic is a landlocked state in Central Europe. It has a population of over five million and an area of about . Slovakia is bordered by the Czech Republic and Austria to the west, Poland to the north, Ukraine to the east and Hungary to the south...
. (In 2006, Ei Electronics in Serbia
Serbia
Serbia , officially the Republic of Serbia , is a landlocked country located at the crossroads of Central and Southeast Europe, covering the southern part of the Carpathian basin and the central part of the Balkans...
discontinued making tubes.) Thus, the 6L6 has enjoyed one of the longest active lifetimes of any electronic component at more than 70 years.
See also
- 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...
- KT63
- KT66KT66The KT66 is a beam tetrode/kinkless tetrode vacuum tube for audio amplification.KT66 is the designator for a vacuum tube introduced by Marconi-Osram Valve Co. Ltd. of Britain in 1937....
- 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...
- :6550
- 6CA7
- EL34EL34The EL34 is a thermionic valve or vacuum tube of the power pentode type. It has an international octal base and is found mainly in the final output stages of audio amplification circuits and was designed to be suitable as a series regulator by virtue of its high permissible voltage between heater...
- 6CM5
- 6DQ5
- 6DQ6
- 807/ATS25807/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...
- Tube data archive
- List of vacuum tubes