Nixie tube

From Academic Kids

A nixie tube is an electronic device for displaying numbers or other information, in the form of a glass tube containing multiple cathodes and a wire mesh anode, filled with neon and often a little mercury and/or argon at a small fraction of atmospheric pressure. Although it resembles a vacuum tube in appearance, its operation does not depend on heating of a cathode to cause it to emit electrons (the thermionic effect). It is therefore called a cold-cathode tube, a form of gas filled tube.

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NL5441NixieTubes.JPG
Pair of NL-5441 Nixie display tubes

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. Each cathode can be made to glow in the characteristic neon red-orange color by applying about 170 volts DC between it and the anode. Some color variation can be observed between types, caused by differences in the materials and gas mixtures used.

Contents

Applications & Lifetime

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 vacuum tube-based Sumlock-Comptometer Anita Mk VII of 1961. Later alphanumeric versions in fourteen segment display format found use in airport arrival/departure signs and stock ticker displays. Some elevators also used nixies to display the floor numbers.

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NixieFrequencyCounter.jpg
Systron-Donner frequency counter from 1973 with Nixie-tube display

Average longevity of nixie tubes varied depending on the manufacturing technique, materials, etc., and increased tremendously over the span of their prominence 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. Nixie tubes are susceptible to multiple failure modes including: simple breakage or cracks and hermetic seal leaks allowing the atmosphere to enter, cathode poisoning preventing part or all of one or more characters from illuminating, increased striking voltage causing flicker or failure to light, sputtering of electrode metal onto the glass envelope blocking the cathodes from view, and internal open or short circuits which may be due to physical abuse or sputtering. Driving nixies outside of their specified electrical parameters will accelerate their demise, especially excess current, which increases sputtering of the electrodes.

History

The Nixie display was developed by a small vacuum tube manufacturer called Haydu Brothers Laboratories, and introduced in 1954 by Burroughs Corporation, who purchased Haydu and owned the name Nixie as a trademark. Similar devices that functioned in the same way were patented in the 1920s, and the first mass-produced display tubes were introduced in the late 1930s by National Union Co. and Telefunken. However, their construction was cruder, and they failed to find many applications until digital electronics reached a suitable level of development in the 1950s.

According to an article in the June 1973 issue of Scientific American magazine (p.66), the name Nixie was derived by Burroughs from "NIX I", an abbreviation of "Numeric Indicator eXperimental No. 1".

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. Trochotrons were used in the UNIVAC 1101 computer, as well as in clocks and frequency counters.

Some Nixie-like displays made by other firms were called by various trademarked names including Numicator and Digitron. A proper generic term is "cold cathode neon readout tube", though the phrase "nixie tube" quickly entered the vernacular as a generic name. Hundreds of variations of this design were manufactured by many firms, from the 1950s until the 1990s.

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B7971NixieTubes.JPG
Giant alphanumeric Nixie tubes, Burroughs B-7971

Other numeric display technologies concurrently in use included backlit columnar transparencies (a.k.a. "thermometer displays"), light pipe, rear-projection and edge-lit lightguide displays (all using individual incandescent or neon light bulbs for illumination); Numitron incandescent filament readouts; and vacuum fluorescent display tubes.

Nixie tubes were superseded in the 1970s by light-emitting diodes (LEDs), often in the form of seven-segment displays. LEDs were better suited to the low voltages that integrated circuits used, which was a definite (sometimes essential) advantage for portable devices such as the emerging pocket calculators and handheld digital measurement instruments.

Citing dissatisfaction with the aesthetics of modern digital displays and a nostalgic fondness for the styling of obsolete technology, significant numbers of electronics enthusiasts in recent years have shown interest in reviving nixies. 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 using modern semiconductors. This is somewhat ironic, since 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 increase significantly, particularly for large tubes. The largest type, the Rodan CD-47/GR-414 (220mm [8.7 in.] tall), have been sold for hundreds of dollars apiece, but these are extremely rare and only found in a few areas of the world by persistent and fortunate seekers. Prices for other large types displaying digits over 25mm (1 inch) tall have increased by double, triple or more between 1998 and 2005.

Some people have begun to offer nixie clocks for sale in various forms from bare circuit boards alone, to kits complete with all electronic parts (with or without cases), to fully assembled and ready-to-run; however, high prices ($100 - $200 and up) and lack of electronics knowledge and assembly skills discourage many potential buyers.

See also

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