Contents 1 Classifications 2 Description 3 History and development 3.1 Diodes 3.2 Triodes 3.3 Tetrodes and pentodes 3.4 Multifunction and multisection tubes 3.5 Beam power tubes 3.6 Gas-filled tubes 3.7 Miniature tubes 3.8 Improvements in construction and performance 3.9 Indirectly heated cathodes 3.10 Use in electronic computers 3.10.1 Colossus 3.10.2 Whirlwind and "special-quality" tubes 4 Heat generation and cooling 5 Tube packages 6 Names 7 Special-purpose tubes 8 Powering the tube 8.1 Batteries 8.2 AC power 9 Reliability 9.1 Vacuum 9.2 Transmitting tubes 9.3 Receiving tubes 9.4 Failure modes 9.4.1 Catastrophic failures 9.4.2 Degenerative failures 9.4.3 Other failures 10 Testing 11 Other vacuum tube devices 11.1 Cathode ray tubes 11.2 Electron multipliers 12 Vacuum tubes in the 21st century 12.1 Niche applications 12.1.1 Audiophiles 12.2 Vacuum fluorescent display 12.3 Vacuum tubes using field electron emitters 13 See also 14 Patents 15 References 16 Further reading 17 External links

Classifications One classification of vacuum tubes is by the number of active electrodes, (neglecting the filament or heater). A device with two active elements is a diode, usually used for rectification. Devices with three elements are triodes used for amplification and switching. Additional electrodes create tetrodes, pentodes, and so forth, which have multiple additional functions made possible by the additional controllable electrodes. Other classifications are: by frequency range (audio, radio, VHF, UHF, microwave) by power rating (small-signal, audio power, high-power radio transmitting) by cathode/filament type (indirectly heated, directly heated) and Warm-up time (including "bright-emitter" or "dull-emitter") by characteristic curves design (e.g., sharp- versus remote-cutoff in some pentodes) by application (receiving tubes, transmitting tubes, amplifying or switching, rectification, mixing) specialized parameters (long life, very low microphonic sensitivity and low-noise audio amplification, rugged/military versions specialized functions (light or radiation detectors, video imaging tubes) tubes used to display information (Nixie tubes, "magic eye" tubes, Vacuum fluorescent displays, CRTs) Multiple classifications may apply to a device; for example similar dual triodes can be used for audio preamplification and as flip-flops in computers, although linearity is important in the former case and long life in the latter. Tubes have different functions, such as cathode ray tubes which create a beam of electrons for display purposes (such as the television picture tube) in addition to more specialized functions such as electron microscopy and electron beam lithography. X-ray tubes are also vacuum tubes. Phototubes and photomultipliers rely on electron flow through a vacuum, though in those cases electron emission from the cathode depends on energy from photons rather than thermionic emission. Since these sorts of "vacuum tubes" have functions other than electronic amplification and rectification they are described in their own articles.

Heat generation and cooling The anode (plate) of this transmitting triode has been designed to dissipate up to 500 W of heat A considerable amount of heat is produced when tubes operate, both from the filament (heater) but also from the stream of electrons bombarding the plate. In power amplifiers this source of heat will exceed the power due to cathode heating. A few types of tube permit operation with the anodes at a dull red heat; in other types, red heat indicates severe overload. The requirements for heat removal can significantly change the appearance of high-power vacuum tubes. High power audio amplifiers and rectifiers required larger envelopes to dissipate heat. Transmitting tubes could be much larger still. Heat escapes the device by black body radiation from the anode (plate) as infrared radiation, and by convection of air over the tube envelope.[30] Convection is not possible in most tubes since the anode is surrounded by vacuum. Tubes which generate relatively little heat, such as the 1.4-volt filament directly heated tubes designed for use in battery-powered equipment, often have shiny metal anodes. 1T4, 1R5 and 1A7 are examples. Gas-filled tubes such as thyratrons may also use a shiny metal anode, since the gas present inside the tube allows for heat convection from the anode to the glass enclosure. The anode is often treated to make its surface emit more infrared energy. High-power amplifier tubes are designed with external anodes which can be cooled by convection, forced air or circulating water. The water-cooled 80 kg, 1.25 MW 8974 is among the largest commercial tubes available today. In a water-cooled tube, the anode voltage appears directly on the cooling water surface, thus requiring the water to be an electrical insulator to prevent high voltage leakage through the cooling water to the radiator system. Water as usually supplied has ions which conduct electricity; deionized water, a good insulator, is required. Such systems usually have a built-in water-conductance monitor which will shut down the high-tension supply if the conductance becomes too high. The screen grid may also generate considerable heat. Limits to screen grid dissipation, in addition to plate dissipation, are listed for power devices. If these are exceeded then tube failure is likely.

Tube packages Metal-cased tubes with octal bases High power GS-9B triode transmitting tube with heat sink at bottom. Most modern tubes have glass envelopes, but metal, fused quartz (silica) and ceramic have also been used. A 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 was a modern receiving tube using a very small metal and ceramic package. The internal elements of tubes have always been connected to external circuitry via pins at their base which plug into a socket. Subminiature tubes were produced using wire leads rather than sockets, however these were restricted to rather specialized applications. In addition to the connections at the base of the tube, many early triodes connected the grid using a metal cap at the top of the tube; this reduces stray capacitance between the grid and the plate leads. Tube caps were also used for the plate (anode) connection, particularly in transmitting tubes and tubes using a very high plate voltage. High-power tubes such as transmitting tubes have packages designed more to enhance heat transfer. In some tubes, the metal envelope is also the anode. The 4CX1000A 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 4CM2500KG, a forced water-cooled power tetrode capable of dissipating 2.5 megawatts.[31] By comparison, the largest power transistor can only dissipate about 1 kilowatt.

Names The generic name "[thermionic] valve" used in the UK derives from the unidirectional current flow allowed by the earliest device, the thermionic diode emitting electrons from a heated filament, by analogy with a non-return valve in a water pipe.[32] The US names "vacuum tube", "electron tube", and "thermionic tube" all simply describe a tubular envelope which has been evacuated ("vacuum"), has a heater, and controls electron flow. In many cases manufacturers and the military gave tubes designations which said nothing about their purpose (e.g., 1614). In the early days some manufacturers used proprietary names which might convey some information, but only about their products; the KT66 and KT88 were "Kinkless Tetrodes". Later, consumer tubes were given names which conveyed some information, with the same name often used generically by several manufacturers. In the US, Radio Electronics Television Manufacturers' Association (RETMA) designations comprise a number, followed by one or two letters, and a number. The first number is the (rounded) heater voltage; the letters designate a particular tube but say nothing about its structure; and the final number is the total number of electrodes (without distinguishing between, say, a tube with many electrodes, or two sets of electrodes in a single envelope—a double triode, for example). For example, the 12AX7 is a double triode (two sets of three electrodes plus heater) with a 12.6V heater (which, as it happens, can also be connected to run from 6.3V). The "AX" has no meaning other than to designate this particular tube according to its characteristics. Similar, but not identical, tubes are the 12AD7, 12AE7...12AT7, 12AU7, 12AV7, 12AW7 (rare!), 12AY7, and the 12AZ7. A system widely used in Europe known as the Mullard–Philips tube designation, also extended to transistors, uses a letter, followed by one or more further letters, and a number. The type designator specifies the heater voltage or current (one letter), the functions of all sections of the tube (one letter per section), the socket type (first digit), and the particular tube (remaining digits). For example, the ECC83 (equivalent to the 12AX7) is a 6.3V (E) double triode (CC) with a miniature base (8). In this system special-quality tubes (e.g., for long-life computer use) are indicated by moving the number immediately after the first letter: the E83CC is a special-quality equivalent of the ECC83, the E55L a power pentode with no consumer equivalent.

Special-purpose tubes Voltage-regulator tube in operation. Low pressure gas within tube glows due to current flow. 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, which will ionize at predictable voltages. The thyratron is a special-purpose tube filled with low-pressure gas or mercury vapor. Like vacuum 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, after which the control electrode can no longer stop the current; the tube "latches" into conduction. Removing anode (plate) voltage lets the gas de-ionize, restoring its non-conductive state. Some thyratrons can carry large currents for their physical size. One example is the miniature type 2D21, often seen in 1950s jukeboxes as control switches for relays. A cold-cathode version of the thyratron, which uses a pool of mercury for its cathode, is called an ignitron; some can switch thousands of amperes. Thyratrons containing hydrogen have a very consistent time delay between their turn-on pulse and full conduction; they behave much like modern silicon-controlled rectifiers, also called thyristors due to their functional similarity to thyratrons. Hydrogen thyratrons have long been used in radar transmitters. A specialized tube is the krytron, which is used for rapid high-voltage switching. Krytrons are used to initiate the detonations used to set off a nuclear weapon; krytrons are heavily controlled at an international level. X-ray tubes are used in medical imaging among other uses. X-ray tubes used for continuous-duty operation in fluoroscopy and CT imaging equipment may use a focused cathode and a rotating anode to dissipate the large amounts of heat thereby generated. These are housed in an oil-filled aluminium housing to provide cooling. The photomultiplier tube is an extremely sensitive detector of light, which uses the photoelectric effect and secondary emission, rather than thermionic emission, to generate and amplify electrical signals. Nuclear medicine imaging equipment and liquid scintillation counters use photomultiplier tube arrays to detect low-intensity scintillation due to ionizing radiation.

Testing Universal vacuum tube tester Main article: Tube tester Vacuum tubes can be tested outside of their circuitry using a vacuum tube tester.

Vacuum tubes in the 21st century Niche applications Although vacuum tubes have been largely replaced by solid-state devices in most amplifying, switching, and rectifying applications, there are certain exceptions. In addition to the special functions noted above, tubes still[update] have some niche applications. In general, vacuum tubes are much less susceptible than corresponding solid-state components to transient overvoltages, such as mains voltage surges or lightning, the electromagnetic pulse effect of nuclear explosions[42] or geomagnetic storms produced by giant solar flares.[43] This property kept them in use for certain military applications long after more practical and less expensive solid-state technology was available for the same applications, as for example with the MiG-25.[42] In that plane, output power of the radar is about one kilowatt and it can burn through a channel under interference.[citation needed] Vacuum tubes are still practical alternatives to solid-state devices in generating high power at radio frequencies in applications such as industrial radio frequency heating, particle accelerators, and broadcast transmitters. This is particularly true at microwave frequencies where such devices as the klystron and traveling-wave tube provide amplification at power levels unattainable using current[update] semiconductor devices. The household microwave oven uses a magnetron tube to efficiently generate hundreds of watts of microwave power. In military applications, a high-power vacuum tube can generate a 10–100 megawatt signal that can burn out an unprotected receiver's frontend. Such devices are considered non-nuclear electromagnetic weapons; they were introduced in the late 1990s by US and Russia.[citation needed] Audiophiles Main article: tube sound 70-watt tube-hybrid audio amplifier selling for US$2,680[44] in 2011, about 10 times the price of a comparable model using transistors.[45] Enough people prefer tube sound to make tube amplifiers commercially viable in three areas: musical instrument (guitar) amplifiers, devices used in recording studios, and audiophile equipment.[46] Many guitarists prefer using valve amplifiers to solid-state models, often due to the way they tend to distort when overdriven. (Any amplifier can only accurately amplify a signal to a certain volume; past this limit, the amplifier will begin to distort the signal. Different circuits will distort the signal in different ways; some guitarists prefer the distortion characteristics of vacuum tubes.) Most popular vintage models use vacuum tubes. Vacuum fluorescent display Main article: Vacuum fluorescent display Typical VFD used in a videocassette recorder A modern display technology using a variation of cathode ray tube is often used in videocassette recorders, DVD players and recorders, microwave oven control panels, and automotive dashboards. Rather than raster scanning, these vacuum fluorescent displays (VFD) switch control grids and anode voltages on and off, for instance, to display discrete characters. The VFD uses phosphor-coated anodes as in other display cathode ray tubes. Because the filaments are in view, they must be operated at temperatures where the filament does not glow visibly. This is possible using more recent cathode technology, and these tubes also operate with quite low anode voltages (often less than 50 volts) unlike cathode ray tubes. Their high brightness allows reading the display in bright daylight. VFD tubes are flat and rectangular, as well as relatively thin. Typical VFD phosphors emit a broad spectrum of greenish-white light, permitting use of color filters, though different phosphors can give other colors even within the same display. The design of these tubes provides a bright glow despite the low energy of the incident electrons. This is because the distance between the cathode and anode is relatively small. (This technology is distinct from fluorescent lighting, which uses a discharge tube.) Vacuum tubes using field electron emitters Main article: Nanoscale vacuum-channel transistor In the early years of the 21st century there has been renewed interest in vacuum tubes, this time with the electron emitter formed on a flat silicon substrate, as in integrated circuit technology. This subject is now called vacuum nanoelectronics.[47] The most common design uses a cold cathode in the form of a large-area field electron source (for example a field emitter array). With these devices, electrons are field-emitted from a large number of closely spaced individual emission sites. Such integrated microtubes may find application in microwave devices including mobile phones, for Bluetooth and Wi-Fi transmission, in radar and for satellite communication[citation needed]. As of 2012[update] they were being studied for possible applications in field emission display technology, but there were significant production problems. As of 2014, NASA's Ames Research Center was reported on working on vacuum-channel transistors produced using CMOS techniques.[48] See also Bogey value, close to manufacturer's stated parameter values List of vacuum tubes, a list of type numbers. List of vacuum tube computers Mullard–Philips tube designation Nixie tube, a gas-filled display device sometimes misidentified as a vacuum tube Fetron, a solid-state plug-compatible replace for vacuum tubes Electronics portal RETMA tube designation RMA tube designation Russian tube designations Tube caddy Tube tester Valve amplifier Zetatron Patents 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 References ^ Reich, Herbert J. (13 April 2013). Principles of Electron Tubes (PDF). Literary Licensing, LLC. ISBN 978-1258664060. Archived (PDF) from the original on 2 April 2017. ^ Fundamental Amplifier Techniques with Electron Tubes: Theory and Practice with Design Methods for Self Construction. Elektor Electronics. January 1, 2011. ISBN 978-0905705934. ^ "RCA Electron Tube 6BN6/6KS6". Retrieved 2015-04-13. ^ Hoddeson, L. "The Vacuum Tube". PBS. Archived from the original on 15 April 2012. Retrieved 6 May 2012. ^ Jones, Morgan (2012). Valve Amplifiers. Elsevier. p. 580. ISBN 0080966403. ^ Olsen, George Henry (2013). Electronics: A General Introduction for the Non-Specialist. Springer. p. 391. ISBN 1489965351. ^ Rogers, D. C. "Triode amplifiers in the frequency range 100 Mc/s to 420 Mc/s". Journal of the British Institution of Radio Engineers. 11 (12): 569–575. Archived from the original on 15 June 2015. , p.571 Archived 5 January 2018 at the Wayback Machine. ^ Bray, John (2002). Innovation and the Communications Revolution: From the Victorian Pioneers to Broadband Internet. IET. ISBN 9780852962183. Archived from the original on 3 December 2016. ^ Guthrie, Frederick (1876). Magnetism and Electricity. London and Glasgow: William Collins, Sons, & Company. Archived from the original on 17 May 2015. [page needed] ^ Thomas A. Edison U.S. Patent 307,031 "Electrical Indicator", Issue date: 1884 ^ Guarnieri, M. (2012). "The age of vacuum tubes: Early devices and the rise of radio communications". IEEE Ind. Electron. M. 6 (1): 41–43. doi:10.1109/MIE.2012.2182822. ^ White, Thomas, United States Early Radio History, archived from the original on 18 August 2012 ^ "Mazda Valves". Archived from the original on 2013-06-28. Retrieved 2017-01-12. ^ "Robert von Lieben — Patent Nr 179807 Dated November 19, 1906" (PDF). Kaiserliches Patentamt. 19 November 1906. Archived (PDF) from the original on 28 May 2008. Retrieved 30 March 2008. ^ "Archived copy". Archived from the original on 5 October 2013. Retrieved 21 August 2013. ^ Räisänen, Antti V.; Lehto, Arto (2003). Radio Engineering for Wireless Communication and Sensor Applications. Artech House. p. 7. ISBN 1580536697. ^ J.Jenkins and W.H.Jarvis, "Basic Principles of Electronics, Volume 1 Thermionics", Pergamon Press (1966), Ch.1.10 p.9 ^ Guarnieri, M. (2012). "The age of vacuum tubes: the conquest of analog communications". IEEE Ind. Electron. M. 6 (2): 52–54. doi:10.1109/MIE.2012.2193274. ^ Introduction to Thermionic Valves (Vacuum Tubes) Archived 28 May 2007 at the Wayback Machine., Colin J. Seymour ^ "Philips Historical Products: Philips Vacuum Tubes". Archived from the original on 6 November 2013. Retrieved 3 November 2013. ^ Baker, Bonnie (2008). Analog circuits. Newnes. p. 391. ISBN 0-7506-8627-8. ^ Modjeski, Roger A. "Mu, Gm and Rp and how Tubes are matched". Välljud AB. Archived from the original on 21 March 2012. Retrieved 22 April 2011. ^ Ballou, Glen (1987). Handbook for Sound Engineers: The New Audio Cyclopedia (1st ed.). Howard W. Sams Co. p. 250. ISBN 0-672-21983-2. Amplification factor or voltage gain is the amount the signal at the control grid is increased in amplitude after passing through the tube, which is also referred to as the Greek letter μ (mu) or voltage gain (Vg) of the tube. ^ C H Gardner (1965) The Story of the Valve Archived 23 December 2015 at the Wayback Machine., Radio Constructor (See particularly the section "Glass Base Construction") ^ L.W. Turner (ed.) Electronics Engineer's Reference Book, 4th ed. Newnes-Butterworth, London 1976 ISBN 0-408-00168-2 pages 7–2 through 7-6 ^ Guarnieri, M. (2012). "The age of Vacuum Tubes: Merging with Digital Computing". IEEE Ind. Electron. M. 6 (3): 52–55. doi:10.1109/MIE.2012.2207830. ^ a b c d From part of Copeland's "Colossus" available online Archived 23 March 2012 at the Wayback Machine. ^ Randall, Alexander 5th (14 February 2006). "A lost interview with ENIAC co-inventor J. Presper Eckert". Computer World. Archived from the original on 2 April 2009. Retrieved 25 April 2011. ^ The National Museum of Computing – Rebuilding Colossus The National Museum of Computing – The Colossus Gallery ^ RCA "Transmitting Tubes Manual" TT-5 1962, p. 10 ^ "MULTI-PHASE COOLED POWER TETRODE 4CM2500KG" (PDF). Archived (PDF) from the original on 11 October 2016. The maximum anode dissipation rating is 2500 kilowatts. ^ The Oxford Companion to the History of Modern Science, J. L. Heilbron , Oxford University Press 2003, 9780195112290, "valve, thermionic" ^ Okamura, Sōgo (1994). History of electron tubes. IOS Press. pp. 133–. ISBN 978-90-5199-145-1. Archived from the original on 22 June 2013. Retrieved 9 May 2011. ^ National Valve Museum: audio double triodes ECC81, 2, and 3 Archived 7 January 2011 at the Wayback Machine. ^ Certified by BBC central valve stores, Motspur Park ^ Mazda Data Booklet 1968 Page 112. ^ C. Robert Meissner (ed.), Vacuum Technology Transactions: Proceedings of the Sixth National Symposium, Elsevier, 2016,ISBN 1483223558 page 96 ^ 31 Alumni. "The Klystron & Cactus". Archived from the original on 20 August 2013. Retrieved 29 December 2013. ^ Tomer, Robert B. (1960), Getting the most out of vacuum tubes, Indianapolis, IN, USA: Howard W. Sams, LCCN 60-13843 . available on the Internet Archive. Chapter 1 ^ Tomer 1960, 60, chapter 2 ^ Tomer 1960, 60, chapter 3 ^ a b Broad, William J. "Nuclear Pulse (I): Awakening to the Chaos Factor", Science. 29 May 1981 212: 1009–1012 ^ Y Butt, The Space Review, 2011 Archived 22 April 2012 at the Wayback Machine. "... geomagnetic storms, on occasion, can induce more powerful pulses than the E3 pulse from even megaton type nuclear weapons." ^ Price of$4,680 for the "super enhanced version." Includes 90-day warranty on tubes "under normal operation conditions." See Model no: SE-300B-70W Archived 12 January 2012 at the Wayback Machine. ^ Rolls RA200 100 W RMS/Channel @ 4 Ohms Power Amplifier Archived 12 January 2012 at the Wayback Machine.. Full Compass. Retrieved on 2011-05-09. ^ Barbour, E. (1998). "The cool sound of tubes – vacuum tube musical applications". Spectrum, IEEE. 35 (8). IEEE. pp. 24–35. Archived from the original on 4 January 2012.  ^ Ackerman, Evan. "Vacuum tubes could be the future of computing". Dvice. Dvice. Archived from the original on 25 March 2013. Retrieved 8 February 2013.  ^ Anthony, Sebastian. "The vacuum tube strikes back: NASA's tiny 460GHz vacuum transistor that could one day replace silicon FETs". ExtremeTech. Archived from the original on 17 November 2015.

Further reading Basic Electronics : Volumes 1–5; Van Valkenburgh, Nooger, Neville; John F. Rider Publisher; 1955. Spangenberg, Karl R. (1948). Vacuum Tubes. McGraw-Hill. OCLC 567981. LCC TK7872.V3.  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. Books published in the UK in the 1940s and 1950s by Cleaver Hume Press on design and application of vacuum tubes. RCA Radiotron Designer's Handbook, 1953 (4th Edition). Contains chapters on the design and application of receiving tubes. Wireless World. "Radio Designer's Handbook". UK reprint of the above. RCA "Receiving Tube Manual" RC15, RC26 (1947, 1968) Issued every two years, contains details of the technical specs of the tubes that RCA sold.

External links Wikimedia Commons has media related to Vacuum tubes. http://www.pentalabs.com/Limited-Warranty/Tube-Maintenance-Education/How-a-Vacuum-Tube-Works – The history of vacuum tubes http://www.cfp-radio.com/realisations/rea03/rea03.html – (FR) How to build a vacuum tube tester. The Thermionic Detector – HJ van der Bijl (October 1919) How vacuum tubes really work – Thermionic emission and vacuum tube theory, using introductory college-level mathematics. The Vacuum Tube FAQ – 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 – Data manual for tubes used in North America. Vacuum tube data sheet locator Characteristics and datasheets Video of amateur radio operator making his own vacuum tube triodes Tuning eye tubes. 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