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A beam tetrode, sometimes called a beam power tube, is a type of
vacuum tube
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied.
The type kn ...
or
thermionic valve
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
The type known as a ...
that has two grids and forms the electron stream from the cathode into multiple
partially collimated beams to produce a low potential
space charge
Space charge is an interpretation of a collection of electric charges in which excess electric charge is treated as a continuum of charge distributed over a region of space (either a volume or an area) rather than distinct point-like charges. This ...
region between the anode and screen grid to return anode
secondary emission
In particle physics, secondary emission 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 term often refers to the emi ...
electrons to the anode when the anode potential is less than that of the screen grid.
[Winfield G. Wagener, (May 1948]
"500-Mc. Transmitting Tetrode Design Considerations"
''Proceedings of the I.R.E.'', p. 612. Retrieved 10 June 2021 Beam tetrodes are usually used for power
amplification, from
audio frequency
An audio frequency or audible frequency (AF) is a periodic vibration whose frequency is audible to the average human. The SI unit of frequency is the hertz (Hz). It is the property of sound that most determines pitch.
The generally accepted ...
to
radio frequency
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upp ...
. The beam tetrode produces greater output power than a triode or pentode with the same anode supply voltage. The first beam tetrode marketed was the Marconi N40, introduced in 1935.
[Editors, (Feb. 1935]
"New Output Tetrode"
''Electronics'', vol. 8 no.2, p. 65. Retrieved 10 June 2021[K. R. Thrower, (2009) ''British Radio Valves The Classic Years: 1926-1946'', Reading, UK: Speedwell, pp. 125 - 126] Beam tetrodes manufactured and used in the 21st century include the 4CX250B, KT66 and variants of the 6L6.
History
In amplifier circuits, the useful anode voltage - anode current region of operation of the conventional tetrode tube was limited by the detrimental effect of secondary emission from the anode at anode potentials less than that of the screen grid. The detrimental effect of anode secondary emission was solved by
Philips
Koninklijke Philips N.V. (), commonly shortened to Philips, is a Dutch multinational conglomerate corporation that was founded in Eindhoven in 1891. Since 1997, it has been mostly headquartered in Amsterdam, though the Benelux headquarters i ...
/
Mullard
Mullard Limited was a British manufacturer of electronic components. The Mullard Radio Valve Co. Ltd. of Southfields, London, was founded in 1920 by Captain Stanley R. Mullard, who had previously designed thermionic valves for the Admiral ...
with the introduction of a
suppressor grid A suppressor grid is a wire screen (grid) used in a thermionic valve (vacuum tube) to suppress secondary emission. It is also called the ''antidynatron grid'', as it reduces or prevents dynatron oscillations. It is located between the screen grid ...
, which resulted in the
pentode
A pentode is an electronic device having five electrodes. The term most commonly applies to a three-grid amplifying vacuum tube or thermionic valve that was invented by Gilles Holst and Bernhard D.H. Tellegen in 1926. The pentode (called a ''tripl ...
design. Since Philips held a patent on this design, other manufacturers were keen to produce pentode type tubes without infringing the patent. In the UK, three
EMI
EMI Group Limited (originally an initialism for Electric and Musical Industries, also referred to as EMI Records Ltd. or simply EMI) was a British transnational conglomerate founded in March 1931 in London. At the time of its break-up in 201 ...
engineers (Isaac Shoenberg, Cabot Bull and Sidney Rodda) filed a patent on an alternative design in 1933. Their design had the following features (compared to the normal pentode):
* The apertures of the
control
Control may refer to:
Basic meanings Economics and business
* Control (management), an element of management
* Control, an element of management accounting
* Comptroller (or controller), a senior financial officer in an organization
* Controllin ...
and
screen grid
A tetrode is a vacuum tube (called ''valve'' in British English) having four active electrodes. The four electrodes in order from the centre are: a thermionic cathode, first and second grids and a plate (called ''anode'' in British English). Th ...
s were aligned,
[Schoenberg, Rodda, Bull, (1938]
''Electron discharge device''
US patent 2,107,519 by winding the grids with the same pitch (the grids of the pentode used different pitches).
* Greater distance between the screen grid and the anode than an ordinary tetrode or pentode.
* An auxiliary electrode structure at or near cathode potential and substantially outside of the electron stream, to establish a low electrostatic potential region between the screen grid and anode, limit the included angle of the beam and prevent anode secondary electrons outside of the beam region from reaching the screen
[ (the pentode has a suppressor grid in the electron stream).
The design is today known as the beam tetrode but historically was also known as a kinkless tetrode, since it had the same number of grids as the conventional tetrode but without the ]negative resistance
In electronics, negative resistance (NR) is a property of some electrical circuits and devices in which an increase in voltage across the device's terminals results in a decrease in electric current through it.
This is in contrast to an ordi ...
kink in the anode current vs anode voltage characteristic curves of a true tetrode. Some authors, notably outside the United Kingdom, argue that the beam plates constitute a fifth electrode.
The EMI design had the following advantages over the pentode:
* The design produced more output power than a similar power pentode.
* The transconductance was higher than a similar power pentode.[Geppert (1951) p. 169]
* The plate resistance was lower than a similar power pentode.
* The screen grid
A tetrode is a vacuum tube (called ''valve'' in British English) having four active electrodes. The four electrodes in order from the centre are: a thermionic cathode, first and second grids and a plate (called ''anode'' in British English). Th ...
current was about 5–10% of the anode current compared with about 20% for the pentode, thus the beam tetrode was more power-efficient.
* The design produced less third-harmonic distortion
In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...
in class A operation than a comparable power pentode.
The new tube was introduced at the Physical and Optical Societies' Exhibition in January 1935 as the Marconi N40. Around one thousand of the N40 output tetrodes were produced, but MOV (Marconi-Osram Valve
M-OV (Marconi-Osram Valve Company) was a British manufacturer of thermionic valves (vacuum tubes). It was a subsidiary of the (British) General Electric Company Ltd.
The company was founded in 1919, when the valve making interests of GEC (Osram ...
) company, under the joint ownership of EMI
EMI Group Limited (originally an initialism for Electric and Musical Industries, also referred to as EMI Records Ltd. or simply EMI) was a British transnational conglomerate founded in March 1931 in London. At the time of its break-up in 201 ...
and GEC, considered the design too difficult to manufacture due to the need for good alignment of the grid wires. As MOV had a design-share agreement with RCA
The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Comp ...
of America, the design was passed to that company. RCA had the resources to produce a workable design, which resulted in the 6L6
6L6 is the designator for a beam power tube introduced by Radio Corporation of America in April 1936 and marketed for application as a power amplifier for audio frequencies.J. F. Dreyer Jr."The Beam Power Output Tube" New York: McGraw-Hill, ''Ele ...
. Not long after, the beam tetrode appeared in a variety of offerings, including the 6V6
The 6V6 is a beam-power tetrode vacuum tube. The first of this family of tubes to be introduced was the 6V6G by Kentucky Electrical Lamp Company, Ken-Rad Tube & Lamp Corporation in late 1936, with the availability by December of both Kentucky Elec ...
in December 1936, the MOV KT66
KT66 is the designator for a beam power tube introduced by Marconi-Osram Valve Co. Ltd. (M-OV) of Britain in 1937 and marketed for application as a power amplifier for audio frequencies and driver for radio frequencies.Editors "The New Valves" ''W ...
in 1937 and the KT88 The KT88 is a beam tetrode/kinkless tetrode (hence "KT") 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 ...
in 1956, designed specifically for audio and highly prized by collectors today.
After the Phillips patent on the suppressor grid had expired, many beam tetrodes were referred to as "beam power pentodes". In addition, there were some examples of beam tetrodes designed to work in place of pentodes. The ubiquitous EL34
The EL34 is a thermionic vacuum tube of the power pentode type. The EL34 was introduced in 1955 by Mullard, who were owned by Philips. The EL34 has an octal base (indicated by the '3' in the part number) and is found mainly in the final output st ...
, although manufactured by Mullard/Phillips and other European manufacturers as a true pentode, was also produced by other manufacturers (namely GE, Sylvania, and MOV) as a beam tetrode instead. The 6CA7 as manufactured by Sylvania and GE is a beam tetrode drop-in replacement for an EL34, and the KT77 is a similar design to the 6CA7 made by MOV.
A beam tetrode family widely used in the US comprised the 25L6, 35L6, and 50L6, and their miniature versions the 50B5 and 50C5. This family is not to be confused with the 6L6 despite similar designations. They were used in millions of All American Five
The term All American Five (abbreviated AA5) is a colloquial name for mass-produced, superheterodyne radio receivers that used five vacuum tubes in their design. These radio sets were designed to receive amplitude modulation (AM) broadcasts in the ...
AM radio receivers. Most of these used a transformerless power supply circuit. In American radio receivers with transformer power supplies, built from about 1940–1950, the 6V6, 6V6G, 6V6GT and miniature 6AQ5 beam tetrodes were very commonly used.
In military equipment, the 807
__NOTOC__
Year 807 ( DCCCVII) was a common year starting on Friday (link will display the full calendar) of the Julian calendar.
Events
By place
Abbasid Empire and Byzantine Empire
* Emperor Nikephoros I is forced to sue for peace, on ...
and 1625, with rated anode dissipations of 25 watts and operating from a supply of up to 750 volts, were in widespread use as the final amplifier in radio-frequency
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upp ...
transmitters of up to 50 watts output power and in push-pull applications for audio. These tubes were very similar to a 6L6 but had a somewhat higher anode dissipation rating and the anode was connected to the top cap
A spinning top, or simply a top, is a toy with a squat body and a sharp point at the bottom, designed to be spun on its vertical axis, balancing on the tip due to the gyroscopic effect.
Once set in motion, a top will usually wobble for a few ...
instead of a pin at the base. Large numbers entered the market after World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
and were used widely by radio amateurs in the USA and Europe through the 1950s and 1960s.
In the 1950s, the ultra-linear audio amplifier circuit was developed for beam tetrodes.[Alt URL]
This amplifier circuit links the screen grids to taps on the output transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
, and provides reduced intermodulation distortion
Intermodulation (IM) or intermodulation distortion (IMD) is the amplitude modulation of signals containing two or more different frequencies, caused by nonlinearities or time variance in a system. The intermodulation between frequency com ...
.
Operation
The beam tetrode eliminates the dynatron region or tetrode kink of the screen grid tube by developing a low potential space charge region between the screen grid and anode that returns anode secondary emission electrons to the anode. The anode characteristic of the beam tetrode is less rounded at lower anode voltages than that of the power pentode, resulting in greater power output and less third harmonic distortion with the same anode supply voltage.[J. F. Dreyer Jr., (April 1936]
"The Beam Power Output Tube"
New York: McGraw-Hill, ''Electronics'' p. 21
In beam tetrodes, the apertures of the control grid and the screen grid are aligned. The wires of the screen grid are aligned with those of the control grid so that the screen grid lies in the shadow of the control grid. This reduces the screen grid current, contributing to the tube's greater power conversion efficiency. Alignment of the grid apertures concentrates the electrons into dense beams in the space between the screen grid and the anode, permitting the anode to be placed closer to the screen grid than would be possible without the beam density. The intense negative space charge
Space charge is an interpretation of a collection of electric charges in which excess electric charge is treated as a continuum of charge distributed over a region of space (either a volume or an area) rather than distinct point-like charges. This ...
of these beams developed when the anode potential is less than that of the screen grid prevents secondary electrons
Secondary electrons are electrons generated as ionization products. They are called 'secondary' because they are generated by other radiation (the ''primary'' radiation). This radiation can be in the form of ions, electrons, or photons with suffici ...
from the anode from reaching the screen grid.
In receiving type beam tetrodes, beam confining plates are introduced outside of the beam region to constrain the electron beams to certain sectors of the anode which are sections of a cylinder. These beam confining plates also set up a low electrostatic potential region between the screen grid and anode and return anode secondary electrons from outside of the beam region to the anode.
In beam tetrodes that have complete cylindrical symmetry, a kinkless characteristic can be achieved without the need for beam confining plates.[ This form of construction is usually adopted in larger tubes with an anode power rating of 100W or more. The Eimac 4CX250B (rated at 250W anode dissipation) is an example of this class of beam tetrode. Note that a radically different approach is taken to the design of the support system for the electrodes in these types. The 4CX250B is described by its manufacturer as a 'radial beam power tetrode, drawing attention to the symmetry of its electrode system.
Beam tetrode application circuits often include components to prevent spurious oscillation, suppress transient voltages and smooth out frequency response. In radio frequency applications, shielding is required between the plate circuit components and grid circuit components.][D. Mix (Aug. 1946]
pp. 25, 26
/ref>
Dissection of a beam tetrode
References
External links
Tube Data Archive, thousands of tube data sheets
Beam tetrode - additional data information and graphs
{{Electronic components
Vacuum tubes
ru:Тетрод#Лучевой тетрод