Structure of a vacuum tube diode

Structure of a vacuum tube triode

An old NEC vacuum tube

In electronics, a vacuum tube, electron tube (in North America), thermionic valve, or just valve (elsewhere, especially in Britain) is a (usually tubular) device used to amplify, switch, otherwise modify, or create an electrical signal by controlling the movement of electrons in a low-pressure space. is a Japanese multinational IT company headquartered in Minato Tokyo, Japan. Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical Generally an amplifier or simply amp, is any device that changes usually increases the amplitude of a signal. A switch is a mechanical device used to connect and disconnect an electric Circuit at will In the fields of communications, Signal processing, and in Electrical engineering more generally a signal is any time-varying or spatial-varying quantity The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J Some special function vacuum tubes are filled with low-pressure gas: these are so-called soft valves (or tubes), as distinct from the hard vacuum type which have the internal gas pressure reduced as far as possible. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. Almost all depend on the thermal emission of electrons, hence thermionic. Thermionic emission is the flow of Charge carriers from a surface or over some other kind of Electrical potential barrier caused by thermal vibrational energy

Vacuum tubes were critical to the development of electronics technology, which drove the expansion and commercialization of radio broadcasting, television, radar, sound reproduction, large telephone networks, analog and digital computers, and industrial process control. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships High-end audio is a term used to describe higher priced and/or higher quality audio equipment Basic principle A traditional landline telephone system also known as "plain old telephone service" (POTS, commonly handles both signaling and audio information A computer is a Machine that manipulates data according to a list of instructions. Process control is a Statistics and Engineering discipline that deals with Architectures mechanisms and Algorithms for controlling Some of these applications pre-dated electronics, but it was the vacuum tube that made them widespread and practical.

For most purposes, the vacuum tube has been replaced by solid-state semiconductor devices such as transistors and solid-state diodes. Solid-state Electronic components devices and systems are based entirely on the Semiconductor, such as Transistors Microprocessor chips and Semiconductor devices are Electronic components that exploit the electronic properties of Semiconductor materials principally Silicon, Germanium In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes Solid-state devices are smaller, more efficient, more reliable, and cheaper than equivalent vacuum tube devices. However, tubes are still used in specialized applications: for engineering reasons, as in high-power radio frequency transmitters; or for their aesthetic appeal, as in audio amplification. Tube sound (or valve sound) is the characteristic sound associated with a Vacuum tube -based Audio amplifiers Some Audiophiles Cathode ray tubes are still used as display devices in television sets, video monitors, and oscilloscopes, although they are being replaced by LCDs and other flat-panel displays. The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic A visual display unit, often called simply a monitor or display, is a piece of Electrical equipment which displays images generated from the Video An oscilloscope (commonly abbreviated to scope or O-scope) is a type of Electronic test equipment that allows signal Voltages to be viewed Flat panel displays encompass a growing number of technologies enabling video displays that are lighter and much thinner than traditional television and video displays that use Cathode A specialized form of the electron tube, the magnetron, is the source of microwave energy in microwave ovens and some radar systems. A cavity magnetron is a high-powered Vacuum tube that generates coherent Microwaves They are commonly found in Microwave ovens as well as various A microwave oven, or a microwave, is a Kitchen appliance that cooks or heats Food by Dielectric heating.

Explanation

A vacuum tube consists of electrodes in a vacuum in an insulating heat-resistant envelope. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. Many tubes have glass envelopes, though some types such as power tubes may have ceramic or metal envelopes. The electrodes are attached to leads which pass through the envelope via an airtight seal. On most tubes, the leads are designed to plug into a tube socket for easy replacement. Tube sockets were ubiquitous in early electronic equipment to allow Vacuum tubes (also known as valves) to be easily removed for testing and replacement

The simplest vacuum tubes resemble incandescent light bulbs in that they have a filament sealed in a glass envelope which has been evacuated of all air. Incandescence is the emission of Light (visible Electromagnetic radiation) from a hot body due to its temperature The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric Light that works by Incandescence, (a general An electrical filament is a thread of Metal, usually Tungsten, which is used to convert Electricity into light in Incandescent light bulbs (as developed Glass-to-metal seals are a very important element of the construction of vacuum tubes, electric discharge tubes incandescent light bulbs, glass encapsulated When hot, the filament releases electrons into the vacuum: a process called thermionic emission. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J Thermionic emission is the flow of Charge carriers from a surface or over some other kind of Electrical potential barrier caused by thermal vibrational energy The resulting negatively-charged cloud of electrons is called a space charge. Space charge is a concept in which excess Electric charge is treated as being a Continuum of charge distributed over a region of space (either a volume or an area These electrons will be drawn to a metal plate inside the envelope, if the plate (also called the anode) is positively charged relative to the filament (or cathode). An anode is an Electrode through which Electric current flows into a polarized electrical device Hot cathode is also a name for a Hot filament ionization gauge, a vacuum measuring device The result is a flow of electrons from filament to plate. This cannot work in the reverse direction because the plate is not heated and does not emit electrons. This very simple example described can thus be seen to operate as a diode: a device that conducts current only in one direction. Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes The vacuum tube diode conducts conventional current from plate (anode) to the filament (cathode); this is the opposite direction to the flow of electrons (called electron current). Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere.

Vacuum tubes operate primarily on the function of the heat gradient difference between the hot cathode and the cold anode. Because of this operating requirement, vacuum tubes are inherently power-inefficient; enclosing the tube within a heat-retaining envelope of insulation would allow the entire tube to reach the same temperature, resulting in electron emission from the anode that would counter the normal one-way current flow. Because the tube requires a vacuum to operate, convection cooling of the anode is typically not possible. Instead anode cooling occurs primarily through black-body radiation and conduction of heat to the outer glass envelope via the anode mounting frame. In Physics, a black body is an object that absorbs all light that falls on it Cold cathode tubes do exist but are used primarily in lighting systems, where unidirectional power regulation is not the functional purpose of the tube. A cold cathode is an element used within some Nixie tubes Gas discharge lamps Gas filled tubes and Vacuum tubes Cold cathodes do not

The vacuum tube is a voltage-controlled device, with the relationship between the input and output circuits determined by a transconductance function. Transconductance, also known as mutual conductance, is a property of certain electronic components The solid-state device most closely analogous to the vacuum tube is the JFET, although the vacuum tube typically operates at far higher voltage (and power) levels than the JFET. The junction gate field-effect transistor ( JFET or JUGFET) is the simplest type of Field effect transistor.

History of development

Inside of a vacuum tube with plate cut open.

The 19th century saw increasing research with evacuated tubes, such as the Geissler and Crookes tubes. The Geissler tube is a glass tube for demonstrating the principles of electrical Glow discharge. A Crookes tube is an early experimental Discharge tube, invented by British physicist William Crookes and others around 1875 in which Cathode rays Scientists who experimented with such tubes included Eugen Goldstein, Nikola Tesla, Johann Wilhelm Hittorf, Thomas Edison, and many others. Eugen Goldstein ( September 5, 1850 &ndash December 25, 1930) was a German Physicist. There have already been discussions about Tesla's ethnicity on the talk page Johann Wilhelm Hittorf ( March 27, 1824 &ndash November 28, 1914) was a German Physicist who was born in Bonn, and died These tubes were mostly for specialized scientific applications, or were novelties, with the exception of the light bulb. The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric Light that works by Incandescence, (a general The groundwork laid by these scientists and inventors, however, was critical to the development of vacuum tube technology.

Though the thermionic emission effect was originally reported in 1873 by Frederick Guthrie, it is Thomas Edison's 1884 investigation of the "Edison Effect" that is more often mentioned. Thermionic emission is the flow of Charge carriers from a surface or over some other kind of Electrical potential barrier caused by thermal vibrational energy Frederick Guthrie (1833 - 1886 was a British scientific writer and professor Thermionic emission is the flow of Charge carriers from a surface or over some other kind of Electrical potential barrier caused by thermal vibrational energy Edison patented what he found,^[1] but he did not understand the underlying physics, or the potential value of the discovery.

Diodes and triodes

The English physicist John Ambrose Fleming worked as an engineering consultant for technology firms, including Edison Telephone; in 1904, as a result of experiments conducted on Edison Effect bulbs imported from the USA and while working as scientific adviser to the Marconi company, he developed a device he called an "oscillation valve" (because it passes current in only one direction) or kenotron, which can also be used as part of a radio wave detector. Sir John Ambrose Fleming ( November 29, 1849 - April 18, 1945) was an English Electrical engineer and Physicist The Marconi Company Ltd was founded by Guglielmo Marconi in 1897 as The Wireless Telegraph & Signal Company (sometimes presented as Wireless Later known as the Fleming valve and then the diode, it allowed electrical current to flow in only one direction, enabling the rectification of alternating current. The Fleming valve, also called the Fleming oscillation valve, was a Vacuum tube Diode invented by John Ambrose Fleming and used in the earliest Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. A rectifier is an electrical device that converts Alternating current (AC to Direct current (DC a process known as rectification.

In 1906 Robert von Lieben filed^[2] for a three electrode amplifying vacuum tube. Robert von Lieben ( September 5, 1878 in Vienna &ndash February 20, 1913 in Vienna) was a notable Austrian His invention included also a beam focusing electromagnet.

In 1907 Lee De Forest placed a bent wire serving as a screen, later known as the "grid" electrode, between the filament and plate electrode. Lee De Forest, ( August 26, 1873 – June 30, 1961) was an American Inventor with over 300 patents to his credit The control grid is an Electrode used in thermionic valves (vacuum tubes used to modulate the flow of electrons in the Cathode to Anode or See Anode.A plate is a type of Electrode that formed part of a Vacuum tube. As the voltage applied to the grid was varied from negative to positive, the number of electrons flowing from the filament to the plate would vary accordingly. Thus the grid was said to electrostatically "control" the plate current. The resulting three-electrode device was therefore an excellent and very sensitive amplifier of voltages. Generally an amplifier or simply amp, is any device that changes usually increases the amplitude of a signal. DeForest called his invention the "Audion". The Audion is an electronic Amplifier device invented by Lee De Forest in 1906 In 1907, DeForest filed^[3] for a three-electrode version of the Audion for use in radio communications. The device is now known as the triode. A triode is an electronic amplification device having three active electrodes De Forest's device was not strictly a vacuum tube, but clearly depended for its action on ionisation of the relatively high levels of gas remaining after evacuation. The De Forest company, in its Audion leaflets, warned against operation which might cause the vacuum to become too hard. The Finnish inventor Eric Tigerstedt significantly improved on the original triode design in 1914, while working on his sound-on-film process in Berlin, Germany. Eric Magnus Campbell Tigerstedt ( August 4, 1887 &ndash April 20, 1925) was one of the most significant inventors in Finland at the beginning A sound film is a motion picture with synchronized sound, or sound technologically coupled to image as opposed to a Silent film. The first true vacuum triodes were the Pliotrons developed by Irving Langmuir at the General Electric research laboratory (Schenectady, New York) in 1915. Irving Langmuir ( January 31, 1881 in Brooklyn New York – August 16, 1957 in Woods Hole Massachusetts) was an Schenectady (skəˈnɛktədi Θkahnéhtati in Tuscarora) is a City in Schenectady County, New York, United States Langmuir was one of the first scientists to realize that a harder vacuum would improve the amplifying behaviour of the triode. Pliotrons were closely followed by the French 'R' Type which was in widespread use by the allied military by 1916. These two types were the first true vacuum tubes. Historically, vacuum levels in production vacuum tubes typically ranged between 10 µPa to 10 nPa.

The non-linear operating characteristic of the triode caused early tube audio amplifiers to exhibit harmonic distortions at low volumes. This is not to be confused with the overdrive that tube amplifiers exhibit at high volume levels (known as the tube sound). Tube sound (or valve sound) is the characteristic sound associated with a Vacuum tube -based Audio amplifiers Some Audiophiles To remedy the low-volume distortion problem, engineers plotted curves of the applied grid voltage and resulting plate currents, and discovered that there was a range of relatively linear operation. In order to use this range, a negative voltage had to be applied to the grid to place the tube in the "middle" of the linear area with no signal applied. This was called the idle condition, and the plate current at this point the "idle current". Today this current would be called the quiescent or standing current. The controlling voltage was superimposed onto this fixed voltage, resulting in linear swings of plate current for both positive and negative swings of the input voltage. This concept was called grid bias. Grid bias is a DC voltage applied to electron tubes (or valves in British English with three electrodes or more such as triodes

Batteries provided the voltages required by tubes in early radio sets. In electronics a battery is a combination of two or more Electrochemical cells which store chemical Energy which can be converted into electrical energy In North American terminology, the "A" batteries provided the filament voltage. Although North American terminology calls this the A battery, most of the English-speaking world knows it by a descriptive label: the LT (low-tension) supply or battery. These were often rechargeable—usually of the lead-acid type ranging from 2 to 12 volts (1-6 cells) with single, double and triple cells being most common. Lead-acid batteries, invented in 1859 by French Physicist Gaston Planté, are the oldest type of Rechargeable battery. Because these batteries produced 2 V, 4 V or 6 V, tube heaters were designed to operate at those voltages—a scheme which continues to be followed today. In portable radios, flashlight (torch) batteries were sometimes used.

The "B" batteries (in North American English) provided the plate voltage. These were generally of dry cell construction, containing many small 1. A dry cell is a galvanic Electrochemical cell with a pasty low-moisture Electrolyte. 5 volt cells in series. If two or more circuit components are connected end to end like a daisy chain it is said they are connected in series. They typically came in ratings of 22. 5, 45, 67. 5, 90 or 135 volts. To this day, plate voltage is referred to as B⁺, but only in North America. The rest of the English-speaking world calls this the HT (high-tension) supply or battery.

Some sets used "C" batteries (North American English) to provide grid bias, although many circuits used grid leak resistors, voltage dividers or cathode bias to provide proper tube bias. Grid leak is the small current through the grid of a thermionic valve into the circuit which feeds the grid |- align = "center"| |width = "25"| | |- align = "center"| || Potentiometer |- align = "center"| | | |- align = "center"| Resistor| | In Electronics, a voltage divider (also known as a potential divider) is a simple Linear circuit that produces an output Voltage ( In order for a Vacuum tube (or valve to operate in a fairly linear region of its characteristic curve the grid element must be maintained at a bias voltage more negative than the Most of the English-speaking world calls this simply the 'grid bias battery'.

Direct and indirect heating

Many innovations followed. It became common to use the filament to heat a separate electrode called the cathode, and to use this cathode as the source of electron flow in the tube rather than the filament itself. This minimized the introduction of hum when the filament was energized with alternating current. An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant In such tubes, the filament is called a heater to distinguish it as an inactive element. A heater is any object that emits Heat or causes another body to achieve a higher Temperature.

Tetrodes and pentodes

A two-tube homemade radio from 1958. The tubes are the two columns with the dark tops. The flying leads connect to the low-voltage filament and high-voltage anode supplies.

When triodes were first used in radio transmitters and receivers, it was found that they had a tendency to oscillate due to parasitic anode-to-grid capacitance. Many circuits were developed to reduce this problem (e. g. the Neutrodyne amplifier), but proved unsatisfactory over wide ranges of frequencies. The Neutrodyne was a particular type of Tuned Radio Frequency (TRF Radio receiver, in which the instability-causing inter-electrode Capacitance of the It was discovered that the addition of a second grid, located between the control grid and the plate and called a screen grid could solve these problems. The screen grid is a Grid introduced into a Vacuum tube (thermionic valve to greatly reduce the capacitance between two other parts of the electrode structure A positive voltage slightly lower than the plate voltage was applied to it, and the screen grid was bypassed (for high frequencies) to ground with a capacitor. This arrangement decoupled the anode and the first grid, completely eliminating the oscillation problem. An additional side effect of this second grid is that the Miller capacitance is also reduced, which improves gain at high frequency. In Electronics, the Miller effect accounts for an increase in the equivalent input Capacitance of an inverting voltage Amplifier due to amplification of This two-grid tube is called a tetrode, meaning four active electrodes. A tetrode is an electronic device having four active Electrodes The term most commonly applies to a two-grid Vacuum tube.

Radio transmitter high-power vacuum tube. The braided copper leads provide heater current for the cathode. The tube also has a heat sink. Dubendorf Museum of Military Aviation. Dübendorf is a municipality in the district of Uster in the canton of Zürich in Switzerland.

However, the tetrode has some new problems. In any tube, electrons strike the anode hard enough to knock out secondary electrons. Secondary emission is a phenomenon where additional electrons called Secondary electrons, are emitted from the surface of a material when an incident particle (often charged In a triode these (less energetic) electrons cannot reach the grid or cathode, and are re-captured by the anode. But in a tetrode, they can be captured by the second grid, reducing the plate current and the amplification of the circuit. Since secondary electrons can outnumber the primary electrons, in the worst case, particularly when the plate voltage dips below the screen voltage, the plate current can actually go down with increasing plate voltage. ^[4] This is the "tetrode kink" (see the reference for a plot of this effect in the RCA-235 tetrode). Another consequence of this effect is that under severe overload, the current collected by the screen grid can cause it to overheat and melt, destroying the tube.

Again the solution was to add another grid, called a suppressor grid. A suppressor grid is a Grid used in a Thermionic valve (also called Vacuum tube) to suppress Secondary emission. This third grid was biased at either ground or cathode voltage and its negative voltage (relative to the anode) electrostatically suppressed the secondary electrons by repelling them back toward the anode. This three-grid tube is called a pentode, meaning five electrodes. 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

Other variations

12SA7 Pentagrid converter tube.

Frequency conversion can be accomplished by various methods in superheterodyne receivers. In Electronics, the superheterodyne receiver (also known by its full name the supersonic heterodyne receiver, or by the abbreviated form superhet) is a Tubes with 5 grids, called pentagrid converters, were generally used, although alternatives such as using a combination of a triode with a hexode were also used. The pentagrid converter was a radio receiving valve ( Vacuum tube) with five grids used as the Frequency mixer stage of a Superheterodyne radio receiver A triode is an electronic amplification device having three active electrodes The pentagrid converter was a radio receiving valve ( Vacuum tube) with five grids used as the Frequency mixer stage of a Superheterodyne radio receiver Even octodes have been used for frequency conversion. The pentagrid converter was a radio receiving valve ( Vacuum tube) with five grids used as the Frequency mixer stage of a Superheterodyne radio receiver The additional grids are either control grids, with different signals applied to each one, or screen grids. The control grid is an Electrode used in thermionic valves (vacuum tubes used to modulate the flow of electrons in the Cathode to Anode or The screen grid is a Grid introduced into a Vacuum tube (thermionic valve to greatly reduce the capacitance between two other parts of the electrode structure In many designs a special grid acted as a second 'leaky' plate to provide a built-in oscillator, which then coupled this signal with the incoming radio signal. These signals create a single, combined effect on the plate current (and thus the signal output) of the tube circuit. The heptode, or pentagrid converter, was the most common of these. The pentagrid converter was a radio receiving valve ( Vacuum tube) with five grids used as the Frequency mixer stage of a Superheterodyne radio receiver 6BE6 is an example of a heptode (note that the first number in the tube ID indicates the filament voltage).

To reduce the cost and complexity of radio equipment, by 1940 it was common practice to combine more than one function, or more than one set of elements in the bulb of a single tube. The only constraint was where patents, and other licencing considerations required the use of multiple tubes. See British Valve Association

For example, the RCA Type 55 was a double diode triode used as a detector, automatic gain control rectifier and audio preamp in early AC powered radios. The British Valve Association ( BVA) was a Cartel of valve manufacturers in the United Kingdom of Great Britain and Northern Ireland (UK A double diode triode is a type of electronic Vacuum tube widely used in Radio receivers Automatic gain control (AGC is an adaptive System found in many electronic devices A preamplifier (preamp or control amp in some parts of the world is an Electronic amplifier which precedes another amplifier to prepare an electronic The same set of tubes often included the 53 Dual Triode Audio Output.

Another early type of multi-section tube, the 6SN7, is a "dual triode" which, for most purposes, can perform the functions of two triode tubes, while taking up half as much space and costing less. 6SN7 is a dual Triode Vacuum tube, on an 8 pin octal base. Although the 6S-- series tubes are often metal cased the 6SN7 is generally found only in a

An RCA 12AX7 dual-triode tube (1947)

The 12AX7 is a dual high-gain triode widely used in guitar amplifiers, audio preamps, and instruments. A guitar amplifier is an Electronic amplifier designed for use with an electric or electronic Musical instrument, such as an Electric guitar.

The invention of the 9-pin miniature tube base, besides allowing the 12AX7 family, also allowed many other multi section tubes, such as the 6GH8 triode pentode. Along with a host of similar tubes, the 6GH8 was quite popular in television receivers. Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic Some color TV sets used exotic types like the 6JH8 which had two plates and beam deflection electrodes (known as 'sheet beam' tube). Vacuum tubes used like this were designed for demodulation of synchronous signals, an example of which is color demodulation for television receivers. Demodulation is the act of removing the Modulation from an analog signal to get the original Baseband signal back

1960s era miniature tubes from Australia.

The desire to include many functions in one envelope resulted in the General Electric Compactron. The Compactron is a 12-pin Vacuum tube family introduced in 1961 by General Electric in Owensboro Kentucky with the express purpose of keeping tubes in A typical unit, the 6AG11 Compactron tube contained two triodes and two diodes, but many in the series had triple triodes.

An early example of multiple devices in one envelope was the Loewe 3NF. The Loewe 3NF was an early attempt to combine several functions in one electronic device This 1920s device had 3 triodes in a single glass envelope together with all the fixed capacitors and resistors required to make a complete radio receiver. As the Loewe set had only one tubeholder, it was able to substantially undercut the competition since, in Germany, state tax was levied by the number of tubeholders. However, reliability was compromised, and production costs for the tube were much greater.

Loewe were to also offer the 2NF (two tetrodes plus passive components) and the WG38 (two pentodes, a triode and the passive components).

Vacuum tubes in an Australian radio of the late 1930s

The beam power tube is usually a tetrode with the addition of beam-forming electrodes, which take the place of the suppressor grid. These angled plates focus the electron stream onto certain spots on the anode which can withstand the heat generated by the impact of massive numbers of electrons, while also providing pentode behavior. The positioning of the elements in a beam power tube uses a design called "critical-distance geometry", which minimizes the "tetrode kink", plate-grid capacitance, screen-grid current, and secondary emission effects from the anode, thus increasing power conversion efficiency. The control grid and screen grid are also wound with the same pitch, or number of wires per inch. Aligning the grid wires also helps to reduce screen current, which represents wasted energy. This design helps to overcome some of the practical barriers to designing high-power, high-efficiency power tubes. 6L6 was the first popular beam power tube, introduced by RCA in 1936. 6L6 is the designator for a Vacuum tube introduced by Radio Corporation of America in July 1936. RCA Corporation, founded as Radio Corporation of America, was an electronics company in existence from 1919 to 1986 Corresponding tubes in Europe were the KT66, KT77 and KT88 by GEC (the KT standing for "Kinkless Tetrode"). KT66 is the designator for a Vacuum tube introduced by Marconi-Osram Valve Co KT88 Vacuum tubes or valves are used in the power sections of Tube amplifiers The KT88 is a beam (kinkless tetrode tube fitting a standard eight-pin

Variations of the 6L6 design are still widely used in guitar amplifiers, making it one of the longest lived electronic device families in history. Similar design strategies are used in the construction of large ceramic power tetrodes used in radio transmitters.

Special-purpose tubes

Some special-purpose tubes are constructed with particular gases in the envelope. For instance, voltage regulator tubes contain various inert gases such as argon, helium or neon, and take advantage of the fact that these gases will ionize at predictable voltages. A voltage regulator is an electrical regulator designed to automatically maintain a constant Voltage level A gas-filled tube, also known as a discharge tube, is an arrangement of Electrodes in a Gas within an insulating, temperature-resistant Envelope "Inert gases" is also used in a narrower sense for Noble gases An inert gas is any Gas that is not reactive with elements This article pertains to the chemical element For other uses see Argon (disambiguation. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Neon (ˈniːɒn is the Chemical element that has the symbol Ne and Atomic number 10 An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge The thyratron is a special-purpose tube filled with low-pressure gas or mercury, some of which vaporizes. A thyratron is a type of Gas filled tube used as a high Energy electrical Switch and controlled Rectifier. Like other tubes, it contains a hot cathode and an anode, but also a control electrode, which behaves somewhat like the grid of a triode. When the control electrode starts conduction, the gas ionizes, and the control electrode no longer can stop current flow; the tube "latches" into conduction. Removing plate (anode) voltage lets the gas de-ionize, restoring its non-conductive state. Some thyratrons can carry relatively large currents for their physical size. One example is the miniature type 2D21, often seen in 1950s jukeboxes as control switches for relays. jukebox is a partially automated music-playing device usually a Coin -operated machine that can play specially selected songs from self-contained media A relay is an electrical Switch that opens and closes under the control of another Electrical circuit. A cold-cathode version of the thyratron, which uses a pool of mercury for its cathode, is called an Ignitron (tm). It can switch thousands of amperes in its largest versions. Thyratrons containing hydrogen have a very consistent time delay between their turn-on pulse and full conduction, and have long been used in radar transmitters. Thyratrons behave much like silicon-controlled rectifiers. A silicon-controlled rectifier (or semiconductor-controlled rectifier) is a four-layer solid state device that controls current.

Tubes usually have glass envelopes, but metal, fused quartz (silica), and ceramic are possible choices. The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide The word ceramic is derived from the Greek word κεραμικός ( keramikos) The first version of the 6L6 used a metal envelope sealed with glass beads, while a glass disk fused to the metal was used in later versions. Metal and ceramic are used almost exclusively for power tubes above 2 kW dissipation. The nuvistor is a tiny tube made only of metal and ceramic. The nuvistor is a type of Vacuum tube announced by RCA in 1959 In some power tubes, the metal envelope is also the anode. 4CX800A is an external anode tube of this sort. Air is blown through an array of fins attached to the anode, thus cooling it. Power tubes using this cooling scheme are available up to 150 kW dissipation. Above that level, water or water-vapor cooling are used. The highest-power tube currently available is the Eimac 8974, a forced water-cooled power tetrode capable of dissipating 1. Eimac is a registered trademark used by the Microwave Power Products Eimac operation of CPI Communications & Power Industries. 5 megawatts. (By comparison, the largest power transistor can only dissipate about 1 kilowatt. ) A pair of 8974s is capable of producing 2 megawatts of audio power. The 8974 is used only in military and commercial radio-frequency installations.

Reliability

Tube tester manufactured in 1930

The chief reliability problem of a tube is that the filament or cathode is slowly "poisoned" by atoms from other elements in the tube, which damage its ability to emit electrons. Hot cathode is also a name for a Hot filament ionization gauge, a vacuum measuring device Trapped gases or slow gas leaks can also damage the cathode or cause plate-current runaway due to ionization of free gas molecules. Ionization is the physical process of converting an Atom or Molecule into an Ion by adding or removing charged particles such as Electrons Vacuum hardness and proper selection of construction materials are the major influences on tube lifetime. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. Depending on the material, temperature and construction, the surface material of the cathode may also diffuse onto other elements. The resistive heaters that heat the cathodes may break in a manner similar to incandescent lamp filaments, but rarely do, since they operate at much lower temperatures than lamps. The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric Light that works by Incandescence, (a general The heater's failure mode, due to its positive temperature coefficient, is generally associated with the power-up period as a result of the switch-on current surge. A negative temperature coefficient device, such as a thermistor, was sometimes incorporated in the equipment heater supply to compensate. A thermistor is a type of Resistor with resistance varying according to its Temperature.

Another important reliability problem is caused by air leakage into the tube. Usually oxygen in the air reacts chemically with the hot filament or cathode, quickly ruining it. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Designers developed tube designs that sealed reliably. This was why most tubes were constructed of glass. Metal alloys (such as Cunife and Fernico) and glasses had been developed for light bulbs that expanded and contracted in similar amounts, as temperature changed. Cunife is an Alloy of Copper (Cu Nickel (Ni Iron (Fe and in some cases Cobalt (Co Fernico is an alloy of Iron (Fer Nickel (Ni and Cobalt (Co The abbreviation forms the name which is (or was a Trademark. These made it easy to construct an insulating envelope of glass, while passing connection wires through the glass to the electrodes.

When a vacuum tube is overloaded or operated past its design dissipation, its anode (plate) may glow red. In consumer equipment, a glowing plate is universally a sign of an overloaded tube. When a Vacuum tube circuit malfunctions and draws excessive current the Anode ("plate" may overheat sometimes causing a visible Red or orange glow However, some large transmitting tubes are designed to operate with their anodes at red, orange, or in rare cases, white heat.

Vacuum

The vacuum inside the envelope must be as perfect, or "hard", as possible. Any gas atoms remaining might be ionized at operating voltages, and will conduct electricity between the elements in an uncontrolled manner. Ionization is the physical process of converting an Atom or Molecule into an Ion by adding or removing charged particles such as Electrons This can lead to erratic operation or even catastrophic destruction of the tube and associated circuitry. Unabsorbed free air sometimes ionizes and becomes visible as a pink-purple glow discharge between the tube elements. Electric glow discharge is a type of plasma formed by passing a current at 100 V to several kV through a gas usually Argon or another Noble

To prevent any remaining gases from remaining in a free state in the tube, modern tubes are constructed with "getters", which are usually small, circular troughs filled with metals that oxidize quickly, with barium being the most common. This page is about the physical properties of gas as a state of matter Getters are reactive materials used for removing traces of gas from vacuum systems Barium (ˈbɛəriəm is a Chemical element. It has the symbol Ba, and Atomic number 56 While the tube envelope is being evacuated, the internal parts except the getter are heated by RF induction heating to extract any remaining gases from the metal. Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz Induction heating is the process of Heating an electrically conducting object (usually a Metal) by Electromagnetic induction, where Eddy currents The tube is then sealed and the getter is heated to a high temperature, again by radio frequency induction heating. This causes the material to evaporate, absorbing/reacting with any residual gases and usually leaving a silver-colored metallic deposit on the inside of the envelope of the tube. The getter continues to absorb any gas molecules that leak into the tube during its working life. If a tube develops a crack in the envelope, this deposit turns a white color when it reacts with atmospheric oxygen. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Large transmitting and specialized tubes often use more exotic getter materials, such as zirconium. Zirconium (zɚˈkoʊniəm /ˌzɝˈkoʊniəm/ is a Chemical element with the symbol Zr and Atomic number 40 Early gettered tubes used phosphorus based getters and these tubes are easily identifiable, as the phosphorus leaves a characteristic orange or rainbow deposit on the glass. The use of phosphorus was short-lived and was quickly replaced by the superior barium getters. Unlike the barium getters, the phosphorus did not absorb any further gases once it had fired.

Schematic diagram of a 1948 vacuum tube radio from Poland.

Transmitting tubes

Large transmitting tubes have tungsten filaments containing a small trace of thorium. Tungsten (ˈtʌŋstən also known as wolfram (/ˈwʊlfrəm/ is a Chemical element that has the symbol W and Atomic number 74 Thorium (ˈθɔːriəm is a Chemical element with the symbol Th and Atomic number 90 A thin layer of thorium atoms forms on the outside of the wire when heated, serving as an efficient source of electrons. The thorium slowly evaporates from the wire surface, while new thorium atoms diffuse to the surface to replace them. Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement Such thoriated tungsten cathodes deliver lifetimes in the tens of thousands of hours. The claimed record is held by an Eimac power tetrode used in a Los Angeles radio station's transmitter, which was removed from service after 80,000 hours (~9 years) of operation. Transmitting tubes are also claimed to survive lightning strikes more often than transistor transmitters do. For RF power levels above 20 kilowatts, vacuum tubes are commonly more efficient and reliable than similar solid-state circuits.

Receiving tubes

Cathodes in small "receiving" tubes are coated with a mixture of barium oxide and strontium oxide, sometimes with addition of calcium oxide or aluminium oxide. Barium oxide, BaO is a white Hygroscopic compound formed by the burning of Barium in Oxygen, although it is often formed through the decomposition Strontium oxide or strontia, SrO is formed when Strontium reacts with Oxygen. Calcium oxide ( CaO) commonly known as burnt lime, lime or quicklime, is a widely used Chemical compound. An electric heater is inserted into the cathode sleeve, and insulated from it electrically by a coating of aluminium oxide. This complex construction causes barium and strontium atoms to diffuse to the surface of the cathode when heated to about 780 degrees Celsius, thus emitting electrons.

Computer vacuum tubes

See also: List of vacuum tube computers

Colossus

The Colossus computer's designer, Dr Tommy Flowers, had a theory that most of the unreliability was caused during power down and (mainly) power up. This is a list of Vacuum tube computers, arranged by date put into service Atanasoff–Berry Computer (1942 - not Turing complete The Colossus machines were electronic Computing devices used by British codebreakers to read Encrypted German messages during Thomas (Tommy Harold Flowers MBE ( 22 December 1905 &ndash 28 October 1998) was an English engineer Once Colossus was built and installed, it was switched on and left switched on running from dual redundant diesel generators (the wartime mains supply being considered too unreliable). The only time it was switched off was for conversion to the Colossus Mk2 and the addition of another 500 or so tubes. Another 9 Colossus Mk2s were built, and all 10 machines ran with a surprising degree of reliability. The 10 Colossi consumed 15 kilowatts of power each, 24 hours a day, 365 days a year—nearly all of it for the tube heaters.

Whirlwind

To meet the reliability requirements of the early digital computer Whirlwind, it was necessary to build special "computer vacuum tubes" with extended cathode life. The Whirlwind Computer was developed at the Massachusetts Institute of Technology. The problem of short lifetime was traced to evaporation of silicon, used in the tungsten alloy to make the heater wire easier to draw. Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Tungsten (ˈtʌŋstən also known as wolfram (/ˈwʊlfrəm/ is a Chemical element that has the symbol W and Atomic number 74 Elimination of the silicon from the heater wire alloy (and paying extra for more frequent replacement of the wire drawing dies) allowed production of tubes that were reliable enough for the Whirlwind project. A wire is a single usually cylindrical, elongated string of drawn Metal. A die is a specialized Tool used in Manufacturing industries to cut shape and form a wide variety of products and components The tubes developed for Whirlwind later found their way into the giant SAGE air-defense computer system. The Semi-Automatic Ground Environment ( SAGE) was an automated control system for tracking and intercepting enemy Bomber aircraft used by NORAD from High-purity nickel tubing and cathode coatings free of materials that can poison emission (such as silicates and aluminium) also contribute to long cathode life. Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 For the Artificial intelligence Androids of the 1990s Science fiction series Space Above and Beyond, see Silicate (AI WikipediaNaming The first such "computer tube" was Sylvania's 7AK7 of 1948. By the late 1950s it was routine for special-quality small-signal tubes to last for hundreds of thousands of hours, if operated conservatively. This reliability made mid-cable amplifiers in submarine cables possible. A submarine communications cable is a cable laid beneath the sea to carry Telecommunications between countries

World War II

A CV4501 subminiature tube for use in a military radio set. The tube is a special quality type based on the EF72, 35 mm long and 10 mm in diameter (excluding leads).

Near the end of World War II, to make radios more rugged, some aircraft and army radios began to integrate the tube envelopes into the radio's cast aluminium or zinc chassis. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including WikipediaNaming Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 The radio became just a printed circuit with non-tube components, soldered to the chassis that contained all the tubes. Another WWII idea was to make very small and rugged glass tubes, originally for use in radio-frequency metal detectors built into artillery shells. Artillery (from French artillerie) is a military Combat Arm which employs any apparātus machine These proximity fuzes made artillery more effective. A proximity fuze (also called a VT fuze for "variable time" is a fuze that is designed to detonate an explosive device automatically when the distance Tiny tubes were later known as "subminiature" types. They were widely used in 1950s military and aviation electronics.

Applications

Tubes were heavily used in the early generations of electronic devices, such as radios, televisions, and early computers such as the Colossus which used 2000 tubes, the ENIAC which used nearly 18,000 tubes, and the IBM 700 series. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic A computer is a Machine that manipulates data according to a list of instructions. The Colossus machines were electronic Computing devices used by British codebreakers to read Encrypted German messages during ENIAC, short for Electronic Numerical Integrator And Computer, was the first general-purpose electronic Computer. The IBM 700/7000 series was a series of large scale ( mainframe) Computer systems made by IBM through

Vacuum tubes are less susceptible than corresponding solid-state components to the electromagnetic pulse effect of nuclear explosions. The term electromagnetic pulse ( EMP) has the following meanings Electromagnetic radiation from an Explosion (especially a Nuclear A nuclear explosion occurs as a result of the rapid release of energy from an intentionally high-speed Nuclear reaction. This property kept them in use for certain military applications long after transistors had replaced them elsewhere. A military is an Organization authorized by its Nation to use force usually including use of Weapons in defending its Country (or by attacking Vacuum tubes are still used for very high-powered applications such as microwave ovens, industrial radio-frequency heating, generating large amounts of RF energy for particle accelerators, and power amplification for broadcasting. A microwave oven, or a microwave, is a Kitchen appliance that cooks or heats Food by Dielectric heating. Many audiophiles, professional audio engineers, and musicians prefer the tube sound of audio equipment based on vacuum tubes over electronics based on transistors. An audiophile, from Latin audio "I hear" and Greek philos "loving" is an audio reproduction enthusiast who typically listens Tube sound (or valve sound) is the characteristic sound associated with a Vacuum tube -based Audio amplifiers Some Audiophiles In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals There are companies which still make specialized audio hardware featuring tube technology. Tubes are still being manufactured today in China (Shuguang), Russia (Reflector Corp. and Svetlana Electron Devices), USA (Westrex Inc. ), Slovakia (JJ-Electronic) and Serbia (Ei RC).

Russian 12AX7 tubes inside a modern guitar amplifier.

The sound produced by a tube based amplifier with the tubes overloaded (overdriven) is widely used in electric guitar amplification, and has defined the texture of some genres of music such as classic rock and blues. An electric guitar is a type of Guitar that uses pickups to convert the vibration of its steel-cored strings into an electrical current which is made louder An instrument amplifier is an Electronic amplifier that converts the inaudible electric or electronic signal from musical instruments such as an Electric guitar Guitarists often prefer tube amplifiers for the perceived warmth of their tone and the natural compression effect they can apply to an input signal.

In 2002, computer motherboard maker AOpen brought back the vacuum tube for modern computer use by releasing the AX4GE Tube-G motherboard. This motherboard uses a Sovtek 6922 vacuum tube (a version of the 6DJ8) as part of AOpen’s TubeSound Technology. The 6DJ8 is a miniature 9-pin medium gain dual Triode Vacuum tube. AOpen claims that the vacuum tube brings superior sound.

Cooling

Like any electronic device, vacuum tubes produce heat while operating. Compared to semiconductor devices, larger tubes operate at higher power levels and hence dissipate more heat. The majority of the heat is dissipated at the anode, though some of the grids can also dissipate power. The tube's heater also contributes to the total (and is a heat source that is absent in semiconductors).

Various methods of cooling are used to remove generated heat. For low-power dissipation devices the heat is radiated from the anode, which often is blackened on the external surface to assist infrared radiation. Natural air circulation or convection is usually required to keep power tubes from overheating. Convection in the most general terms refers to the movement of molecules within Fluids (i For larger power dissipation, forced-air cooling (fans) may be required.

From the inception of this technology until the 1950s, the dominant approach to cooling low-power tubes remained aimed at avoiding immediate or very short term failures. For noncritical consumer applications, and in absence of technological alternatives, tube failures did not create major problems for equipment manufacturers, as the cost of tube replacements was borne by end users long accustomed to the experience. Some tubes for the US defense market featured a metal casing, as opposed to glass, and an opaque, black finish that facilitated both heat conduction and radiative cooling. In some highly specialized professional applications where replacement was out of the question, such as undersea cable repeaters, no failures were acceptable. A submarine communications cable is a cable laid beneath the sea to carry Telecommunications between countries Moreover, as vacuum tube based defence systems became increasingly complex and deployed in ever increasing numbers, it became clear that point failures which were individually easy to diagnose and rectify had a devastating effect on the uptime of systems that contained hundreds of tubes. Uptime is a measure of the time a Computer system has been "up" and running This resulted in both the creation of special long lasting tubes for projects such as Whirlwind and SAGE, and also in special tube shields that aided heat dispersal and could be retrofitted on existing equipment. The Whirlwind Computer was developed at the Massachusetts Institute of Technology. The Semi-Automatic Ground Environment ( SAGE) was an automated control system for tracking and intercepting enemy Bomber aircraft used by NORAD from These shields act by improving heat conduction from the surface of the tube to the shield itself by means of tens of copper tongues in contact with the glass tube, and have an opaque, black outside finish for improved heat radiation.

High-power tubes in older, large transmitters or power amplifiers are liquid cooled, usually with deionised water for heat transfer to an external radiator, similar to the cooling system of an internal combustion engine. Since the anode is usually the cooled element, the anode voltage appears directly on the cooling water surface, thus requiring the water to be an electrical insulator. Otherwise the high voltage can be conducted through the cooling water to the radiator system; hence the need for deionised water. Such systems usually have a built-in water-conductance monitor which will shut down the high-tension supply (often tens of kilovolts) if the conductance becomes too high. Some very high-power transmitters, such as those used in shortwave broadcasting and VLF communications, use pressurized steam for cooling. Modern transmitters using tubes mainly in the PA section are now largely cooled by forced air through a radiator or other heat-sinking device.

Other vacuum tube devices

Many devices were built during the 1920–1960 period using vacuum-tube techniques. Most such tubes were rendered obsolete by semiconductors; some techniques for integrating multiple devices in a single module, sharing the same glass envelope have been discussed above, such as the Loewe 3NF. The Loewe 3NF was an early attempt to combine several functions in one electronic device Vacuum-tube electronic devices still in common use include the magnetron, klystron, photomultiplier, x-ray tube and cathode ray tube. A cavity magnetron is a high-powered Vacuum tube that generates coherent Microwaves They are commonly found in Microwave ovens as well as various A klystron is a specialized linear-beam Vacuum tube (evacuated electron tube Photomultiplier tubes ( photomultipliers or PMT s for short members of the class of Vacuum tubes and more specifically Phototubes are extremely An X-ray tube is a Vacuum tube that produces X-rays They are part of X-ray machines X-rays are part of the Electromagnetic spectrum, an The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or The magnetron is the type of tube used in all microwave ovens. A microwave oven, or a microwave, is a Kitchen appliance that cooks or heats Food by Dielectric heating. In spite of the advancing state of the art in power semiconductor technology, the vacuum tube still has reliability and cost advantages for high-frequency RF power generation. Photomultipliers are still the most sensitive detectors of light. Many televisions, oscilloscopes and computer monitors still use cathode ray tubes, though flat panel displays are becoming more popular as prices drop. Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic An oscilloscope (commonly abbreviated to scope or O-scope) is a type of Electronic test equipment that allows signal Voltages to be viewed Flat panel displays encompass a growing number of technologies enabling video displays that are lighter and much thinner than traditional television and video displays that use Cathode

The fluorescent displays commonly used on VCRs and automotive dashboards are actually vacuum tubes, using phosphor-coated anodes to form the display characters, and a heated filamentary cathode as an electron source. A phosphor is a substance that exhibits the phenomenon of Phosphorescence (sustained glowing after exposure to energized particles such as Electrons These devices are properly called "VFDs", or Vacuum Fluorescent Displays. A vacuum fluorescent display (VFD is a Display device used commonly on consumer-electronics equipment such as Video cassette recorders Car radios Because the filaments are in view, they must be operated at temperatures where the filament does not glow visibly. These devices are often found in automotive applications, where their high brightness allows reading the display in daylight.

Some tubes, like magnetrons, traveling wave tubes, carcinotrons, and klystrons, combine magnetic and electrostatic effects. A cavity magnetron is a high-powered Vacuum tube that generates coherent Microwaves They are commonly found in Microwave ovens as well as various A traveling-wave tube (TWT is an electronic device used to amplify Radio frequency signals to high power usually in an electronic assembly known as a traveling-wave A backward wave oscillator ( BWO) also called carcinotron (a trade name for tubes manufactured by CSF, now Thales) or backward wave tube A klystron is a specialized linear-beam Vacuum tube (evacuated electron tube These are efficient (usually narrow-band) RF producers and still find use in radar, microwave ovens and industrial heating. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships A microwave oven, or a microwave, is a Kitchen appliance that cooks or heats Food by Dielectric heating.

Gyrotrons or vacuum masers, used to generate high-power millimetre band waves, are magnetic vacuum tubes in which a small relativistic effect, due to the high voltage, is used for bunching the electrons. Gyrotrons are high powered Vacuum tubes which emit Millimeter Wavelength beams by bunching Electrons with Cyclotron motion This page is about the scientific concept of relativity for philosophical or sociological theories about relativity see Relativism. Free electron lasers, used to generate high-power coherent light and perhaps even X rays, are highly relativistic vacuum tubes driven by high-energy particle accelerators. A free-electron laser, or FEL is a Laser that shares the same optical properties as conventional lasers such as emitting a Beam consisting of coherent X-radiation (composed of X-rays) is a form of Electromagnetic radiation.

Particle accelerators can be considered vacuum tubes that work backward, the electric fields driving the electrons, or other charged particles. In this respect, a cathode ray tube is a particle accelerator.

A tube in which electrons move through a vacuum (or gaseous medium) within a gas-tight envelope is generically called an electron tube.

Some condenser microphone designs use built-in vacuum tube preamplifiers. A preamplifier (preamp or control amp in some parts of the world is an Electronic amplifier which precedes another amplifier to prepare an electronic

Jolida JD502B, a modern tube integrated amplifier, with preamp tubes in front, power tubes in back. An integrated amplifier is an electronic device containing an audio Preamplifier and Amplifier in one unit as opposed to separating the two

As of 2008, scores of small companies are manufacturing audiophile amplifiers and preamps that use vacuum tubes. An audiophile, from Latin audio "I hear" and Greek philos "loving" is an audio reproduction enthusiast who typically listens ^[5]

Vacuum tube can also mean a tube with a vacuum. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. It is e. g. used for demonstration of, and experiments with, free-fall. Free fall is motion with no Acceleration other than that provided by Gravity.

Field emitter vacuum tubes

In the early years of the 21st century there has been renewed interest in vacuum tubes, this time in the form of integrated circuits. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside The most common design uses a cold cathode field emitter, with electrons emitted from a number of sharp nano-scale tips formed on the surface of a metal cathode. A cold cathode is an element used within some Nixie tubes Gas discharge lamps Gas filled tubes and Vacuum tubes Cold cathodes do not Field emission (FE is the emission of electrons from the surface of a condensed phase into another phase due to the presence of high electric fields A Spindt tip is a tiny conical tip microfabricated on a substrate which emits electrons by Field emission.

Their advantages include greatly enhanced robustness combined with the ability to provide high power outputs at low power consumptions. Operating on the same principles as traditional tubes, prototype device cathodes have been constructed with emitter tips formed using nanotubes, and by etching electrodes as hinged flaps (similar to the technology used to create the microscopic mirrors used in Digital Light Processing) that are stood upright by a electrostatic charge. An inorganic nanotube is a Cylindrical Molecule often composed of Metal Oxides and morphologically similar to a Carbon nanotube Digital Light Processing (DLP is a Trademark owned by Texas Instruments, representing a technology used in projectors and Video projectors It was Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction.

Such integrated microtubes may find application in microwave devices including mobile phones, for Bluetooth and Wi-Fi transmission, in radar and for satellite communication. Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 Bluetooth is a wireless protocol utilizing short-range communications technology facilitating data transmission over short distances from fixed and/or mobile devices creating wireless Wi-Fi (ˈwaɪfaɪ is the trade name for the popular wireless technology used Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships This article is about artificial satellites For natural satellites also known as moons see Natural satellite. Presently they are being studied for possible application to flat-panel display construction.

See also

Patents

• U.S. Patent 307,031  - Electrical indicator
• U.S. Patent 514,170  - Incandescent electric light
• U.S. Patent 803,684  - Instrument for converting alternating electric currents into continuous currents (Fleming valve patent)
• U.S. Patent 841,387  - Device for amplifying feeble electrical currents
• U.S. Patent 879,532  - De Forest's Audion
• U.S. Patent 2,141,059  - Television system

Notes

References

• Spangenberg, Karl R. (1948). Vacuum Tubes. McGraw-Hill. LCC TK7872.V3 OCLC 567981. The Library of Congress Classification ( LCC) is a system of Library classification developed by the Library of Congress. The OCLC Online Computer Library Center is according to its website a "nonprofit membership computer library service and research organization dedicated to the public purpose  
• Millman, J. & Seely, S. Electronics, 2nd ed. McGraw-Hill, 1951.
• Shiers, George, "The First Electron Tube", Scientific American, March 1969, p. 104.
• Tyne, Gerald, Saga of The Vacuum Tube, Ziff Publishing, 1943, (reprint 1994 Prompt Publications), pp. 30-83.
• Stokes, John, 70 Years of Radio Tubes and Valves, Vestal Press, NY, 1982, pp. 3-9.
• Thrower, Keith, History of The British Radio Valve to 1940, MMA International, 1982, pp 9-13.
• Eastman, Austin V. , Fundamentals of Vacuum Tubes, McGraw-Hill, 1949
• Philips Technical Library. A range of books published in the UK in the 1940s and 50s by Cleaver Hume Press on all aspects of the design and application of vacuum tubes. They were originally published in Dutch in Holland. French and German editions were probably also published.
• RCA "Radiotron Designer's Handbook" 1953(4th Edition) Contains very useful chapters on the design and application of receiving tubes.
• RCA "Receiving Tube Manual" RC15, RC26 (1947, 1968) Issued every two years, contains details of the technical specs of the tubes that RCA sold at the time.
• Wireless World. "Radio Designer's Handbook". UK reprint of the above.

External links

• How vacuum tubes really work - John Harper's webpage about thermionic emission and vacuum tube theory, using introductory college-level mathematics.
• The Vacuum Tube FAQ - Henry Pasternack's FAQ from rec. audio
• The invention of the thermionic valve. Fleming discovers the thermionic (or oscillation) valve, or 'diode'.
• Tubes Vs. Transistors : Is There An Audible Difference? - 1972 AES paper on audible differences in sound quality between vacuum tubes and transistors.
• The Virtual Valve Museum
• The cathode ray tube site
• O'Neill's Electronic Museum - Vacuum tube museum
• Vacuum Tubes for Beginners -- Japanese Version
• NJ7P Tube Database - Searchable online electronic data manual for tubes used in North America.
• Vacuum tube data sheet locator
• Large tube chart listing some characteristics and giving access to datasheets for most of them
• A video of a French amateur radio operator making his own vacuum tube triodes