The Nixie Tube Clock
Orange numbers floating in glass: the Nixie tube was built for 1950s lab equipment and found a second life in the clocks of enthusiasts.
What a Nixie tube is
A Nixie tube is a small glass bulb filled with neon gas. Inside are ten thin metal cathodes, each shaped like one of the digits 0 to 9 and stacked one behind another.
When a high voltage is applied to one cathode, the gas around it glows, so that number lights up in a warm orange. IEEE Spectrum notes that ionizing the neon typically takes 200 volts or more, which is why Nixies are high-voltage devices.
Because the digits are stacked, each number sits at a slightly different depth inside the glass. That layered, almost three-dimensional glow is a big part of the appeal.
Glowing digits before the Nixie
Gas-discharge lighting goes back to the tubes Heinrich Geissler made in 1857, and IEEE Spectrum traces a string of patents for numeric display tubes long before anyone used the Nixie name.
Hans P. Boswau, working in Lorain, Ohio, filed two US patent applications on 9 May 1934 for a glow indicator with stacked cathodes that could be lit one at a time. Hermann Pressler and Hans Richter patented an electric discharge lamp in 1938, Northrop filed numeric tube patents in 1950, and Ericsson Telephones won a British patent in 1951.
There are also claims from outside the patent record. A donor's note in the Computer History Museum's catalogue credits a Chicago inventor named Henninger with originating the stacked-digit idea in 1929, with early tubes custom-made as advertising signs. The museum records this as the donor's account rather than its own finding.
Some tubes were actually made. Tube historian Udo Radtke says the first mass-produced display tubes came from National Union and Telefunken in the late 1930s, and the Computer History Museum likewise notes stacked-cathode tubes from those two firms before 1945. In May 1954 National Union unveiled a neon indicator called the Inditron, which Spectrum says was less successful than the Nixie.
Who invented it? It depends who you ask
The Computer History Museum says Nixies were invented at the Burroughs Corporation. Its own catalogue entry complicates that, though: it adds that the design used in mass-produced Nixies was developed around 1948 by the Haydu brothers, who sold the patent to Burroughs in 1952.
Other accounts give different dates. IEEE Spectrum says Burroughs bought Haydu Brothers of Plainfield, New Jersey, in 1954, unveiled the tube at the Wescon trade show in August 1955 and filed its patent that December. Udo Radtke credits Haydu with developing the Nixie in the early 1950s.
Radiomuseum.org, drawing on trade advertising, says Nixie displays were sold in 1955 under Haydu type numbers HB-105 and HB-106, and that the firm ran as Haydu Brothers, Subsidiary of Burroughs Corporation, from 1954 to 1956. By 1957 the plant belonged fully to Burroughs, and George and Zoltan Haydu had opened a new company of their own.
Even the firm's beginnings are told two ways. Spectrum says Haydu Brothers was founded in 1936 by George and Zoltan Haydu, Hungarian-American brothers, with their father John; Radtke also gives 1936, under an earlier company name, while Radiomuseum.org says the brothers started their activity in 1937. Radtke adds that the firm employed about 500 people around 1950 and also developed the Pixie, a round tube with numerals arranged like a clock face.
Burroughs also hired Saul Kuchinsky, a former National Union engineer, to run a display tube laboratory. Spectrum adds a marketing note: Kuchinsky believed good brand names often contained a k or an x.
What's in a name
The name has more than one origin story. Spectrum traces it to a prototype label, Numerical Indicator Experiment No. 1, shortened to NIX1.
The Computer History Museum says it grew from an internal Burroughs name, Numeric Indicator X, with the X standing for ten, shortened to NIX tube and then Nixie. A note in its catalogue also mentions a Burroughs draftsman labeling a drawing the NIX-1 device.
A small fix that made them last
Early prototypes had a serious flaw. Engineer Roger Wolfe recalled to IEEE Spectrum that after one overnight test, so much cathode material had sputtered onto the inside of the glass that the numerals could no longer be seen.
Adding a little mercury vapor to the gas solved it. With that change, Spectrum reports, tube life rose to more than 200,000 hours, which is over 22 years of continuous use.
The golden age and the fall
Through the 1960s the Nixie was the standard numeric display, and Spectrum says more than two dozen companies around the world made them. A note in the Computer History Museum's catalogue says they appeared in 90 percent of early frequency counters, digital voltmeters and similar instruments, as well as computer panels and many electronic desk calculators.
Then came the LED. Nick Holonyak Jr. developed the light-emitting diode at General Electric in 1962, and low-voltage LEDs suited digital integrated circuits far better than 200-volt tubes. The Computer History Museum says Nixies were replaced by vacuum fluorescent and LED displays by the mid-1970s.
Not everyone saw it coming. Spectrum quotes a 1971 editorial in Electronic Buyers' News that dismissed LEDs as also-rans and declared Nixies here to stay. Production lasted longest in the Soviet Union, where Spectrum says it continued into the early 1990s.
See also: how digital clock displays work on OnlineClock.app.
Why Nixie clocks are collected
Around 2000, hobbyists and collectors revived interest in the tubes, Spectrum reports, and prices climbed. The largest Nixie, the CD47, went from 100 dollars or less in 2000 to about 1,000 dollars.
A clock is a natural home for them, because its digits change all day and the glow is on constant display. Spectrum describes the warm light of the Nixie as evoking an era of great scientific and engineering ambition, and its 2024 update says the nostalgia for that mid-century look has not faded.
Supply is the worry. The same update says the last stock of genuine tubes, made in the Soviet Union and Eastern Europe in the 1980s, is reaching the end of its life, and that most people now get the look from lookalikes built with OLED displays, which run at much lower voltages.
A few makers have restarted production by hand. Spectrum names Czech engineer Dalibor Farny, who began reviving Nixie manufacture in 2012, along with Aleksander Zawada in Poland and Ron Soyland in the United States. If you are shopping for a Nixie clock, check whether it uses real neon tubes, and whether they are new or old stock.
See also: the retro flip-clock look on OnlineClock.app.
Questions people ask
What does Nixie stand for?
Accounts differ. IEEE Spectrum traces it to a prototype labeled Numerical Indicator Experiment No. 1 (NIX1), while the Computer History Museum says it came from Numeric Indicator X, an internal Burroughs name.
Are Nixie tubes still made?
Only in small numbers by a few specialist makers, such as Dalibor Farny, who began in 2012. Many tubes in hobby clocks are old stock made in the Soviet Union and Eastern Europe in the 1980s, and IEEE Spectrum says that stock is nearing the end of its life.
How long do Nixie tubes last?
With mercury vapor added, IEEE Spectrum reports a rated life of more than 200,000 hours. Old stock tubes may have less life left, depending on how they were used.
Are Nixie clocks safe?
Their tubes run at high voltage, typically 200 volts or more, so they need a properly designed power supply and enclosure. Unplug a Nixie clock before opening it.