Posted on October 22, 2007
Every now and then I discover something on the internet that captivates my imagination and fires up my creativity. Most of the time I can’t help myself from wanting to know more about the discovery and sometimes I end up with a whole new hobby :0P Well “Nixie tubes” have proven to be another one of those discoveries and so far I am hooked.
A “Nixie tube” is a generalized term for a cold-cathode neon indicator tube which was popularized by the Burroughs Corporation in 1956. It is a common belief that the term “NIXIE” was derived from Burroughs term “Numeric Indicator eXperimental No.1” or “NIX1”. Later other companies would call the indicator tubes “Numicators” or “Digitrons” but for the most part would always be known as the Nixie Tube.
Nixie tube displays were used on equipment that needed a digital readout like calculators, frequency counters and early computers. This was long before LCD (Liquid Crystal Display) and LED (Light Emitting Diode) displays were available for use. Several variations of the Nixie were developed all having the display elements encased in a glass envelope. Incandescent filament readouts or “Numitrons” as well as Vacuum Florescent Displays or VFDs were other popular display tubes but only the Nixie used a neon gas to illuminate a cold-cathode element.
A Nixie tube is comprised of glass tube envelope containing several alphanumerical display cathodes stacked on each other (usually numerals 0-9) but electrically insulated from one another. A screen mesh anode surrounds the cathodes but allows the viewing of the front of the cathode indicators. A low pressure neon gas is used inside the glass envelope and is illuminated when DC current flows through any one of the cathode indicators. The voltage used to excite the neon gas is around 140-180 volts DC at anywhere from .5 to 25 ma (depending on the size of the tube). This current produces a very warm glow of neon gas that surrounds the cathode and creates that very desirable “Nixie” tube look.
Several factors predict the life of a Nixie tube including burn time, cathode current, the tubes hermetic seal integrity and something called “cathode poisoning”. Cathode poisoning is where unused cathodes accumulate “sputtering” from other working cathodes preventing them from illuminating. This sputter is material emitted from the working cathodes and can deposit on other cathodes or just deposit on the glass itself making the display unreadable. Typically healthy Nixie tubes can have a working life anywhere from 5,000 to 200,000 hours, depending on what technology was used to manufacture them.
Below are a couple of examples of Nixie tubes. On the left is a Telefunken ZM 1210 tube which is about 1.9” tall and on the right are the highly prized and rare Okaya Rodan CD 47/GR 414 Nixie tubes which stand 8.7” tall !!!