User manual – Glass Clock Design #3
rev 1.2
2 Introduction to Nixie Tubes
Nixie tubes (gas indicator tubes) were invented during the Cold War in the early
50's by a small vacuum tube manufacturer called Haydu Brothers Laboratories.
These tubes were sold by the Burroughs Corporation, who came up with the trade
name “Nixie”. This name refers to "NIX I", an abbreviation that stood for,
"Numeric Indicator eXperimental No. 1”, which was a label for one of the
drawings for the tube. This was shortened to “NIXIE” and the name stuck.
Early computers and test instruments didn't have any means to display digits
easily until the Nixie tube appeared. Nixies found their way into numerical
computer displays, volt/ohm meters, frequency counters, radiation counters and
even calculators. By the mid 1970's, they were obsolete (replaced by LED's and
LCD displays) and were discontinued.
A Nixie tube display, which should really be called a gas indicator tube, works
like a neon bulb. A neon bulb works by a high voltage ionizing neon gas, causing
the gas to glow with an orange color. The Nixie tube takes this a step further, by
shaping the cathodes like a numeral (0 – 9). When the cathode is energized, the
numeral glows orange. There are individual cathodes for each digit, 0 – 9. Some
tubes have decimal points, and others may contain special characters, such as “F”
or “Hz”.
Nixie tubes require high voltage with special drivers for each digit, provided by a
special high voltage converter on the circuit board. There are many failure modes
for Nixie tubes. Breakage of the glass tube, loss of seal between the metal pins
and the glass, and cathode poisoning. Cathode poisoning is when unused or
seldom used digits acquire a coating of material “sputtered” off of the active
digits. This coating insulates the metal, making it difficult for the digit to glow.
Page 4 of 27
Illustration 1: Exploded view of a
Nixie tube