A Nixie tube (English: // NIK-see), or cold cathode display, is an electronic device for displaying numerals or other information using glow discharge.
The glass tube contains a wire-mesh anode and multiple cathodes, shaped like numerals or other symbols. Applying power to one cathode surrounds it with an orange glow discharge. The tube is filled with a gas at low pressure, usually mostly neon and often a little mercury or argon, in a Penning mixture.
Although it resembles a vacuum tube in appearance, its operation does not depend on thermionic emission of electrons from a heated cathode. It is therefore called a cold-cathode tube (a form of gas-filled tube), and is a variant of the neon lamp. Such tubes rarely exceed 40 °C (104 °F) even under the most severe of operating conditions in a room at ambient temperature. Vacuum fluorescent displays from the same era use completely different technology—they have a heated cathode together with a control grid and shaped phosphor anodes; Nixies have no heater or control grid, typically a single anode (in the form of a wire mesh, not to be confused with a control grid), and shaped bare metal cathodes.
The early Nixie displays were made by a small vacuum tube manufacturer called Haydu Brothers Laboratories, and introduced in 1955by Burroughs Corporation, who purchased Haydu. The name Nixie was derived by Burroughs from "NIX I", an abbreviation of "Numeric Indicator eXperimental No. 1", although this may have been a backronym designed to justify the evocation of the mythical creature with this name. Hundreds of variations of this design were manufactured by many firms, from the 1950s until the 1990s. The Burroughs Corporation introduced "Nixie" and owned the name Nixie as a trademark. Nixie-like displays made by other firms had trademarked names including Digitron, Inditron and Numicator. A proper generic term is cold cathode neon readout tube, though the phrase Nixie tube quickly entered the vernacular as a generic name.
Burroughs even had another Haydu tube that could operate as a digital counter and directly drive a Nixie tube for display. This was called a "Trochotron", in later form known as the "Beam-X Switch" counter tube; another name was "magnetron beam-switching tube", referring to their derivation from a split-anode magnetron. Trochotrons were used in the UNIVAC 1101 computer, as well as in clocks and frequency counters.
The first trochotrons were surrounded by a hollow cylindrical magnet, with poles at the ends. The field inside the magnet had essentially-parallel lines of force, parallel to the axis of the tube. It was a thermionic vacuum tube; inside were a central cathode, ten anodes, and ten "spade" electrodes. The magnetic field and voltages applied to the electrodes made the electrons form a thick sheet (as in a cavity magnetron) that went to only one anode. Applying a pulse with specified width and voltages to the spades made the sheet advance to the next anode, where it stayed until the next advance pulse. Count direction was determined by the direction of the magnetic field, and as such was not reversible. A later form of trochotron called a Beam-X Switch replaced the large, heavy external cylindrical magnet with ten small internal metal-alloy rod magnets which also served as electrodes.
Glow-transfer counting tubes, similar in essential function to the trochotrons, had a glow discharge on one of a number of main cathodes, visible through the top of the glass envelope. Most used a neon-based gas mixture and counted in base-10, but faster types were based on argon, hydrogen, or other gases, and for timekeeping and similar applications a few base-12 types were available. Sets of "guide" cathodes (usually two sets, but some types had one or three) between the indicating cathodes moved the glow in steps to the next main cathode. Types with two or three sets of guide cathodes could count in either direction. A well-known trade name for glow-transfer counter tubes in the United Kingdom was Dekatron. Types with connections to each individual indicating cathode, which enabled presetting the tube's state to any value (in contrast to simpler types which could only be directly reset to zero or a small subset of their total number of states), were trade named Selectron tubes.
Devices that functioned in the same way as Nixie tubes were patented in the 1930s, and the first mass-produced display tubes were introduced in 1954 by National Union Co. under the brand name Inditron. However, their construction was cruder, their average lifetime was shorter, and they failed to find many applications due to their complex periphery.
The most common form of Nixie tube has ten cathodes in the shapes of the numerals 0 to 9 (and occasionally a decimal point or two), but there are also types that show various letters, signs and symbols. Because the numbers and other characters are arranged one behind another, each character appears at a different depth, giving Nixie based displays a distinct appearance. A related device is the pixie tube, which uses a stencil mask with numeral-shaped holes instead of shaped cathodes. Some Russian Nixies, e.g. the ИH-14 (IN-14), used an upside-down digit 2 as the digit 5, presumably to save manufacturing costs as there is no obvious technical or aesthetic reason.
Each cathode can be made to glow in the characteristic neon red-orange color by applying about 170 volts DC at a few milliamperes between a cathode and the anode. The current limiting is normally implemented as an anode resistor of a few tens of thousands of ohms. Nixies exhibit negative resistance and will maintain their glow at typically 20 V to 30 V below the strike voltage. Some color variation can be observed between types, caused by differences in the gas mixtures used. Longer-life tubes that were manufactured later in the Nixie timeline have mercury added to reduce sputteringresulting in a blue or purple tinge to the emitted light. In some cases, these colors are filtered out by a red or orange filter coating on the glass.
One advantage of the Nixie tube is that its cathodes are typographically designed, shaped for legibility. In most types, they are not placed in numerical sequence from back to front, but arranged so that cathodes in front obscure the lit cathode minimally. One such arrangement is 6 7 5 8 4 3 9 2 0 1 from front (6) to back (1).Russian ИH-12A (IN-12A) & ИH-12B (IN-12B) tubes use the number arrangement 1 6 2 7 5 0 4 9 8 3 from back to front, with the 5 being an upside down 2. The 12B tubes feature a bottom far left decimal point between the numbers 8 and 3.
Nixies were used as numeric displays in early digital voltmeters, multimeters, frequency counters and many other types of technical equipment. They also appeared in costly digital time displays used in research and military establishments, and in many early electronic desktop calculators, including the first: the Sumlock-Comptometer ANITA Mk VII of 1961 and even the first electronic telephone switchboards. Later alphanumeric versions in fourteen segment display format found use in airport arrival/departure signs and stock ticker displays. Some elevators used Nixies to display floor numbers.
Average longevity of Nixie tubes varied from about 5,000 hours for the earliest types, to as high as 200,000 hours or more for some of the last types to be introduced. There is no formal definition as to what constitutes "end of life" for Nixies, mechanical failure excepted. Some sourcessuggest that incomplete glow coverage of a glyph ("cathode poisoning") or appearance of glow elsewhere in the tube would not be acceptable.
Nixie tubes are susceptible to multiple failure modes, including
Driving Nixies outside of their specified electrical parameters will accelerate their demise, especially excess current, which increases sputtering of the electrodes. A few extreme examples of sputtering have even resulted in complete disintegration of Nixie-tube cathodes.
Cathode poisoning can be abated by limiting current through the tubes to significantly below their maximum rating,through the use of Nixie tubes constructed from materials that avoid the effect (e.g. by being free of silicates and aluminum), or by programming devices to periodically cycle through all digits so that seldom-displayed ones get activated.
As testament to their longevity, and that of the equipment which incorporated them, as of 2006 [update] several suppliers still provide common Nixie tube types as replacement parts, new in original packaging.[ citation needed ] Equipment with Nixie-tube displays in excellent working condition is still plentiful, though much of it has been in frequent use for 30–40 years or more. Such items can easily be found as surplus and obtained at very little expense. In the former Soviet Union, Nixies were still being manufactured in volume in the 1980s, so Russian and Eastern European Nixies are still available.
Other numeric-display technologies concurrently in use included backlit columnar transparencies ("thermometer displays"), light pipes, rear-projection and edge-lit lightguide displays (all using individual incandescent or neon light bulbs for illumination), Numitron incandescent filament readouts,Panaplex seven-segment displays, and vacuum fluorescent display tubes. Before Nixie tubes became prominent, most numeric displays were electromechanical, using stepping mechanisms to display digits either directly by use of cylinders bearing printed numerals attached to their rotors, or indirectly by wiring the outputs of stepping switches to indicator bulbs. Later, a few vintage clocks even used a form of stepping switch to drive Nixie tubes.
Nixie tubes were superseded in the 1970s by light-emitting diodes (LEDs) and vacuum fluorescent displays (VFDs), often in the form of seven-segment displays. The VFD uses a hot filament to emit electrons, a control grid and phosphor-coated anodes (similar to a cathode ray tube) shaped to represent segments of a digit, pixels of a graphical display, or complete letters, symbols, or words. Whereas Nixies typically require 180 volts to illuminate, VFDs only require relatively low voltages to operate, making them easier and cheaper to use. VFDs have a simple internal structure, resulting in a bright, sharp, and unobstructed image. Unlike Nixies, the glass envelope of a VFD is evacuated rather than being filled with a specific mixture of gases at low pressure.
Specialized high-voltage driver chips such as the 7441/74141 were available to drive Nixies. LEDs are better suited to the low voltages that integrated circuits used, which was an advantage for devices such as pocket calculators, digital watches, and handheld digital measurement instruments. Also, LEDs are much smaller and sturdier, without a fragile glass envelope. LEDs use less power than VFDs or Nixie tubes with the same function.
Citing dissatisfaction with the aesthetics of modern digital displays and a nostalgic fondness for the styling of obsolete technology, significant numbers of electronics enthusiasts have shown interest in reviving Nixies. [ citation needed ]Unsold tubes that have been sitting in warehouses for decades are being brought out and used, the most common application being in homemade digital clocks. During their heyday, Nixies were generally considered too expensive for use in mass-market consumer goods such as clocks. This recent surge in demand has caused prices to rise significantly, particularly for large tubes, making small-scale production of new devices again viable. Amongst others, Dalibor Farny has established himself as a manufacturer of new tubes since the mid 2010s.
In addition to the tube itself, another important consideration is the relatively high-voltage circuitry necessary to drive the tube. The original 7400 series drivers integrated circuits such as the 74141 BCD decoder driver have long since been out of production and are rarer than NOS tubes. Only "Integral" in Belarus lists the 74141and its Soviet equivalent, the K155ID1 as still in production. However modern bipolar transistors with high voltage ratings are now available cheaply, such as MPSA92 or MPSA42 – an unusual example where an original IC design has been replaced by discrete transistors.
An anode is an electrode through which the conventional current enters into a polarized electrical device. This contrasts with a cathode, an electrode through which conventional current leaves an electrical device. A common mnemonic is ACID, for "anode current into device". The direction of conventional current in a circuit is opposite to the direction of electron flow, so electrons flow out the anode into the outside circuit. In a galvanic cell, the anode is the electrode at which the oxidation reaction occurs.
Cathode rays are streams of electrons observed in vacuum tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to electrons emitted from the cathode. They were first observed in 1869 by German physicist Julius Plücker and Johann Wilhelm Hittorf, and were named in 1876 by Eugen Goldstein Kathodenstrahlen, or cathode rays. In 1897, British physicist J. J. Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, which was later named the electron. Cathode ray tubes (CRTs) use a focused beam of electrons deflected by electric or magnetic fields to render an image on a screen.
A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic CCD for Cathode Current Departs. A conventional current describes the direction in which positive charges move. Electrons have a negative electrical charge, so the movement of electrons is opposite to that of the conventional current flow. Consequently, the mnemonic cathode current departs also means that electrons flow into the device's cathode from the external circuit.
A triode is an electronic amplifying vacuum tube consisting of three electrodes inside an evacuated glass envelope: a heated filament or cathode, a grid, and a plate (anode). Developed from Lee De Forest's 1906 Audion, a partial vacuum tube that added a grid electrode to the thermionic diode, the triode was the first practical electronic amplifier and the ancestor of other types of vacuum tubes such as the tetrode and pentode. Its invention founded the electronics age, making possible amplified radio technology and long-distance telephony. Triodes were widely used in consumer electronics devices such as radios and televisions until the 1970s, when transistors replaced them. Today, their main remaining use is in high-power RF amplifiers in radio transmitters and industrial RF heating devices. In recent years there has been a resurgence in demand for low power triodes due to renewed interest in tube-type audio systems by audiophiles who prefer the sound of tube-based electronics.
A vacuum tube, an electron tube, or valve or, colloquially, a tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
A cold cathode is a cathode that is not electrically heated by a filament. A cathode may be considered "cold" if it emits more electrons than can be supplied by thermionic emission alone. It is used in gas-discharge lamps, such as neon lamps, discharge tubes, and some types of vacuum tube. The other type of cathode is a hot cathode, which is heated by electric current passing through a filament. A cold cathode does not necessarily operate at a low temperature: it is often heated to its operating temperature by other methods, such as the current passing from the cathode into the gas.
The ANITA Mark VII and ANITA Mark VIII calculators were launched simultaneously in late 1961 as the world's first all-electronic desktop calculators. Designed and built by the Bell Punch Co. in Britain, and marketed through its Sumlock Comptometer division, they used vacuum tubes and cold-cathode switching tubes in their logic circuits and nixie tubes for their numerical displays.
A neon lamp is a miniature gas discharge lamp. The lamp typically consists of a small glass capsule that contains a mixture of neon and other gases at a low pressure and two electrodes. When sufficient voltage is applied and sufficient current is supplied between the electrodes, the lamp produces an orange glow discharge. The glowing portion in the lamp is a thin region near the cathode; the larger and much longer neon signs are also glow discharges, but they use the positive column which is not present in the ordinary neon lamp. Neon glow lamps were widely used as indicator lamps in the displays of electronic instruments and appliances.
A thyratron is a type of gas-filled tube used as a high-power electrical switch and controlled rectifier. Thyratrons can handle much greater currents than similar hard-vacuum tubes. Electron multiplication occurs when the gas becomes ionized, producing a phenomenon known as Townsend discharge. Gases used include mercury vapor, xenon, neon, and hydrogen. Unlike a vacuum tube (valve), a thyratron cannot be used to amplify signals linearly.
A vacuum fluorescent display (VFD) is a display device once commonly used on consumer electronics equipment such as video cassette recorders, car radios, and microwave ovens.
An electron gun is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy. The largest use is in cathode ray tubes (CRTs), used in nearly all television sets, computer displays and oscilloscopes that are not flat-panel displays. They are also used in field emission displays (FEDs), which are essentially flat-panel displays made out of rows of extremely small cathode ray tubes. They are also used in microwave linear beam vacuum tubes such as klystrons, inductive output tubes, travelling wave tubes, and gyrotrons, as well as in scientific instruments such as electron microscopes and particle accelerators. Electron guns may be classified by the type of electric field generation, by emission mechanism, by focusing, or by the number of electrodes.
A gas-filled tube, also known as a discharge tube, is an arrangement of electrodes in a gas within an insulating, temperature-resistant envelope. Gas-filled tubes exploit phenomena related to electric discharge in gases, and operate by ionizing the gas with an applied voltage sufficient to cause electrical conduction by the underlying phenomena of the Townsend discharge. A gas-discharge lamp is an electric light using a gas-filled tube; these include fluorescent lamps, metal-halide lamps, sodium-vapor lamps, and neon lights. Specialized gas-filled tubes such as krytrons, thyratrons, and ignitrons are used as switching devices in electric devices.
A fourteen-segment display (FSD) is a type of display based on 14 segments that can be turned on or off to produce letters and numerals. It is an expansion of the more common seven-segment display, having an additional four diagonal and two vertical segments with the middle horizontal segment broken in half. A seven-segment display suffices for numerals and certain letters, but unambiguously rendering the ISO basic Latin alphabet requires more detail. A slight variation is the sixteen-segment display which allows additional legibility in displaying letters or other symbols.
A glow discharge is a plasma formed by the passage of electric current through a gas. It is often created by applying a voltage between two electrodes in a glass tube containing a low-pressure gas. When the voltage exceeds a value called the striking voltage, the gas ionization becomes self-sustaining, and the tube glows with a colored light. The color depends on the gas used.
A Geissler tube is an early gas discharge tube used to demonstrate the principles of electrical glow discharge, similar to modern neon lighting. The tube was invented by the German physicist and glassblower Heinrich Geissler in 1857. It consists of a sealed, partially evacuated glass cylinder of various shapes with a metal electrode at each end, containing rarefied gasses such as neon, argon, or air; mercury vapor or other conductive fluids; or ionizable minerals or metals, such as sodium. When a high voltage is applied between the electrodes, an electrical current flows through the tube. The current dissociates electrons from the gas molecules, creating ions, and when the electrons recombine with the ions, the gas emits light by fluorescence. The color of light emitted is characteristic of the material within the tube, and many different colors and lighting effects can be achieved. The first gas-discharge lamps, Geissler tubes were novelty items, made in many artistic shapes and colors to demonstrate the new science of electricity. In the early 20th century, the technology was commercialized and evolved into neon lighting.
Gas-discharge lamps are a family of artificial light sources that generate light by sending an electric discharge through an ionized gas, a plasma. Typically, such lamps use a noble gas or a mixture of these gases. Some include additional substances, like mercury, sodium, and metal halides, which are vaporized during startup to become part of the gas mixture. In operation, some of the electrons are forced to leave the atoms of the gas near the anode by the electric field applied between the two electrodes, leaving these atoms positively ionized. The free electrons thus released flow onto the anode, while the cations thus formed are accelerated by the electric field and flow towards the cathode. Typically, after traveling a very short distance, the ions collide with neutral gas atoms, which transfer their electrons to the ions. The atoms, having lost an electron during the collisions, ionize and speed toward the cathode while the ions, having gained an electron during the collisions, return to a lower energy state while releasing energy in the form of photons. Light of a characteristic frequency is thus emitted. In this way, electrons are relayed through the gas from the cathode to the anode. The color of the light produced depends on the emission spectra of the atoms making up the gas, as well as the pressure of the gas, current density, and other variables. Gas discharge lamps can produce a wide range of colors. Some lamps produce ultraviolet radiation which is converted to visible light by a fluorescent coating on the inside of the lamp's glass surface. The fluorescent lamp is perhaps the best known gas-discharge lamp.
A Penning mixture, named after Frans Michel Penning, is a mixture of gases used in electric lighting or displaying fixtures. Although the popular phrase for the most common of these is a neon lamp, it is more efficient to have the glass tube filled not with pure neon, but with a Penning mixture, which is defined as a mixture of one inert gas with a minute amount of another gas, one that has lower ionization voltage than the main constituent.
In electronics, a Dekatron is a gas-filled decade counting tube. Dekatrons were used in computers, calculators and other counting-related products during the 1950s and 1960s. "Dekatron," now a generic trademark, was the brand name used by Ericsson Telephones Limited (ETL), of Beeston, Nottingham.
A magic eye tube or tuning indicator, in technical literature called an electron-ray indicator tube, is a vacuum tube which gives a visual indication of the amplitude of an electronic signal, such as an audio output, radio-frequency signal strength, or other functions. The magic eye is a specific type of such a tube with a circular display similar to the EM34 illustrated. Its first broad application was as a tuning indicator in radio receivers, to give an indication of the relative strength of the received radio signal, to show when a radio station was properly tuned in.
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