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Spark Your Future with a nixie tube clock

So What Is A Nixie tube?

The Nixie tube

A Nixie tube or cold cathode display, is an electronic device used 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 a small amount of argon, in a Penning mixture. In later nixies, in order to extend the usable life of the device, a tiny amount of mercury was added to reduce cathode poisoning and sputtering.

Although it resembles a vacuum tube in appearance, its operation does not depend on thermionic emission of electrons from a heated cathode. It is hence 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.

Pic By Georg-Johann Lay with a slight edit by Richard Bartz - Own work, CC BY-SA 3.0,

History

Nixie tubes were invented by David Hagelbarger. The early Nixie displays were made by a small vacuum tube manufacturer called Haydu Brothers Laboratories, and introduced in 1955 by Burroughs Corporation, who purchased Haydu. The name Nixie was derived by Burroughs from "NIX I", an abbreviation of "Numeric Indicator eXperimental No. 1".

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.

Design

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.

Each cathode can be made to glow in the characteristic neon red-orange colour 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 colour 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 sputtering resulting in a blue or purple tinge to the emitted light. In some cases, these colours 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 to back Russian ИH-12A (IN-12A) and ИH-12B (IN-12B) tubes use the number arrangement 3 8 9 4 0 5 7 2 6 1 from front to back with the 5 being an upside down 2. The ИH-12B tubes feature a bottom far left decimal point between the numbers 8 and 3.

Applications And Lifetime

Nixies were used as numeric displays in early digital voltmeters, multimeters and 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 lifts 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. telephone switchboards. There is no formal definition as to what constitutes "end of life" for Nixies, mechanical failure excepted. Some sources suggest 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:

Simple breakage
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
Internal open or short circuits which may be due to physical abuse or sputtering

As testament to their longevity, and that of the equipment which incorporated them, as of 2006 several suppliers still provided common Nixie tube types as replacement parts, new in original packaging.