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).
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
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.
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.
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.
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.
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.
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
Sumlock ANITA calculator
Sumlock ANITA calculator — The world's first desktop electronic
calculators, which used Dekatrons.
WITCH — Early British relay-based computer that used Dekatrons.
Ericsson Telephones computing tubes designation system
Special Quality gas-filled tubes designation system
Jennings, Thomas ‘Tom’, Nixie Indicators and Decimal Counting
Tubes (project), WPS .
"Vacuum Tubes (Thermionic Valves), Cold-
Cathode Switching Tubes &
Dekatron Counter Tubes", Calculator Electronics, Vintage Calculators
Web Museum .
"Spinner for European mains", Electric stuff, UK .
"Spinner for American mains", Electronix & more (project),
archived from the original on 2007-06-07 .
"Dekatrons", Tube tester (information and photos) (in English and
"Comprehensive dekatron table", Decade counter, Vintage Technology
Wikimedia Commons has media related to Dekatrons.
Sandor, Nagy, "A
Dekatron tube display", Asimov Teka (interactive
stochastic simulation), EU .
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