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An octal-base dekatron. Dekatron.jpg
An octal-base dekatron.

In electronics, a Dekatron (or Decatron, or generically three-phase gas counting tube or glow-transfer counting tube or cold cathode tube) 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 (ETL), of Beeston, Nottingham (not to be confused with the Swedish TelefonAB Ericsson of Stockholm).

Electronics physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter

Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter.

Generic trademark trademark or brand name that has become the generic name for a class of product or service, sometimes resulting in loss of legal protection

A generic trademark, also known as a genericized trademark or proprietary eponym, is a trademark or brand name that, due to its popularity or significance, has become the generic name for, or synonymous with, a general class of product or service, usually against the intentions of the trademark's holder. The process of a product's name becoming genericized is known as genericide.

Ericsson Telephones Limited (ETL) was a British telephone equipment manufacturer based in Beeston.


A dekatron in operation. Dekatron.gif
A dekatron in operation.

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(s), 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 (kHz) 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 longer life, but their counting frequency is limited to 10 kHz (1–2 kHz is more common).

Hydrogen Chemical element with atomic number 1

Hydrogen is the chemical element with the symbol H and atomic number 1. With a standard atomic weight of 1.008, hydrogen is the lightest element in the periodic table. Hydrogen is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass. Non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton and no neutrons.

An inert gas is a gas which does not undergo chemical reactions under a set of given conditions. The noble gases often do not react with many substances, and were historically referred to as the inert gases. Inert gases are used generally to avoid unwanted chemical reactions degrading a sample. These undesirable chemical reactions are often oxidation and hydrolysis reactions with the oxygen and moisture in air. The term inert gas is context-dependent because several of the noble gases can be made to react under certain conditions.

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 (or two) between each cathode. When the guide electrode(s) is pulsed properly, the neon gas will activate near the guide pins then "jump" to the next cathode. Pulsing the guide electrodes (negative going pulses) repeatedly will cause the neon dot to move from cathode to cathode.

A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic CCD for Cathode Current Departs. A conventional current describes the direction in which positive charges move. Electrons have a negative electrical charge, so the movement of electrons is opposite to that of the conventional current flow. Consequently, the mnemonic cathode current departs also means that electrons flow into the device's cathode from the external circuit.

Anode electrode through which conventional current flows into a polarized electrical device

An anode is an electrode through which the conventional current enters into a polarized electrical device. This contrasts with a cathode, an electrode through which conventional current leaves an electrical device. A common mnemonic is ACID for "anode current into device". The direction of conventional current in a circuit is opposite to the direction of electron flow, so electrons flow out the anode into the outside circuit. In a galvanic cell, the anode is the electrode at which the oxidation reaction occurs.

Detail of the top of a dekatron -- central anode disk surrounded by 30 internal cathode pins. Dekatron top.jpg
Detail of the top of a dekatron — central anode disk surrounded by 30 internal cathode pins.
Sending sequenced pulses to guide electrodes will determine the direction of movement. Dekatron operation neg.png
Sending sequenced pulses to guide electrodes will determine the direction of movement.

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 (and are much dimmer than neon).

Counter (common-cathode) 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.

In elementary arithmetic, a carry is a digit that is transferred from one column of digits to another column of more significant digits. It is part of the standard algorithm to add numbers together by starting with the rightmost digits and working to the left. For example, when 6 and 7 are added to make 13, the "3" is written to the same column and the "1" is carried to the left. When used in subtraction the operation is called a borrow.

Counter/Selector (separate-cathode) 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.

A frequency divider, also called a clock divider or scaler or prescaler, is a circuit that takes an input signal of a frequency, , and generates an output signal of a frequency:

Dekatrons come in various physical sizes, ranging from smaller than a 7-pin miniature vacuum 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.

Vacuum tube Device that controls electric current between electrodes in an evacuated container

In electronics, a vacuum tube, an electron tube, or valve or, colloquially, a tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.

Quinary Positional number system with base 5

Quinary is a numeral system with five as the base. A possible origination of a quinary system is that there are five fingers on either hand.

Duodecimal base-12 number system

The duodecimal system is a positional notation numeral system using twelve as its base. The number twelve is instead written as "10" in duodecimal, whereas the digit string "12" means "1 dozen and 2 units". Similarly, in duodecimal "100" means "1 gross", "1000" means "1 great gross", and "0.1" means "1 twelfth".

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 (50 Hz or 60 Hz) or as a numeric indicator for homemade clocks.

See also

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In Europe, the principal method of numbering vacuum tubes was the nomenclature used by the Philips company and its subsidiaries Mullard in the UK, Valvo(de, it) in Germany, Radiotechnique (Miniwatt-Dario brand) in France, and Amperex in the United States, from 1934 on. Adhering manufacturers include AEG (de), CdL (1921, French Mazda brand), CIFTE (fr, Mazda-Belvu brand), EdiSwan (British Mazda brand), Lorenz (de), MBLE(fr, nl), RCA (us), RFT(de, sv) (de), Siemens (de), Telefunken (de), Tesla (cz), Toshiba (ja), Tungsram (hu), and Unitra. This system allocated meaningful codes to tubes based on their function and became the starting point for the Pro Electron naming scheme for active devices.

Noise generator

A noise generator is a circuit that produces electrical noise. Noise generators are used to test signals for measuring noise figure, frequency response, and other parameters. Noise generators are also used for generating random numbers.