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, of Beeston, Nottingham. The dekatron was useful for computing, calculating and frequency-dividing purposes because one complete revolution of the neon dot in a dekatron means 10 pulses on the guide electrode, and a signal can be derived from one of the ten cathodes in a dekatron to send a pulse, possibly for another counting stage. Dekatrons usually have a maximum input frequency in the high kilohertz range – 100 kHz is fast, 1 MHz is around the maximum possible. These frequencies are obtained in hydrogen-filled fast dekatrons. Dekatrons filled with inert gas are inherently more stable and have a longerlife, but their counting frequency is limited to 10 kHz. Internal designs vary by the model and manufacturer, but generally a dekatron has ten cathodes and one or two guide electrodes plus a common anode. The cathodes are arranged in a circle with a guide electrode between each cathode. When the guide electrode is pulsed properly, the neon gas will activate near the guide pins then "jump" to the next cathode. Pulsing the guide electrodes repeatedly will cause the neon dot to move from cathode to cathode. Hydrogen dekatrons require high voltages ranging from 400 to 600 volts on the anode for proper operation; dekatrons with inert gas usually require ~350 volts. When a dekatron is first powered up, a glowing dot appears at a random cathode; the tube must then be reset to zero state, by driving a negative pulse into the designated starting cathode. The color of the dot depends on the type of gas that is in the tube. Neon-filled tubes display a red-orange dot; argon-filled tubes display a purple dot. Counter dekatrons have only one carry/borrow cathode wired to its own socket pin for multistage cascading and the remaining nine cathodes tied together to another pin; therefore they don't need bases with more than 9 pins. Counter/Selector dekatrons have each cathode wired to its own pin; therefore their bases have at least 13 pins. Selectors allow for monitoring the status of each cathode or to divide-by-n with the proper reset circuitry. This kind of versatility made such dekatrons useful for numerical division in early calculators. Dekatrons come in various physical sizes, ranging from smaller than a 7-pin miniaturevacuum tube to as large as an octal base tube. While most dekatrons are decimal counters, models were also made to count in base-5 and base-12 for specific applications. The dekatron fell out of practical use when transistor-based counters became reliable and affordable. Today, dekatrons are used by electronic hobbyists in simple "spinners" that run off the mains frequency or as a numeric indicator for homemade clocks.
