Nixie Tube (Vacuum Fluorescent Display Tube)

Nixie Tubes (Glow Discharge Tubes)
A Nixie tube, or cold-cathode glow discharge indicator tube, is an electronic tube that was invented in the 1950s. It was initially created by the Haydon Brothers Lab, and in 1955, the company was acquired by Burroughs Corporation of the United States, which renamed the device "Nixie" and registered the trademark. From the 1950s to the 1990s, Burroughs Corporation and many other companies around the world manufactured and used these devices in various applications.

With the development of modern display technologies, such devices are no longer mass-produced. The closest modern equivalent is the Soviet-era IN-14 Nixie tube, which was produced before 1991. This means that Nixie tubes have been out of production for nearly 30 years globally. If some lucky individuals still have these old devices or vintage measuring instruments, they may still see Nixie tubes in use. The reason for their discontinuation is primarily the emergence of other display technologies, such as VFD (Vacuum Fluorescent Display) and LED, which surpassed Nixie tubes in terms of functionality. However, due to the unique and artistic appearance of the glowing tubes, many electronic enthusiasts still build or assemble these vintage items, and some have even repurposed them into modern devices such as watches or clocks, allowing these tubes to continue shining in everyday life.

In their era, Nixie tubes were used to display digits and certain special characters. They were the only electronic device capable of displaying numbers and symbols from the 1950s to the 1990s. As a result, Nixie tubes were commonly found in early calculators, audio equipment, car displays, and other early electronic instruments. They also made appearances in films, representing a technological era.

Nixie tubes can be classified into two main types: side-view and top-view.

  • Side-view: The tube is oriented vertically, with the digits displayed from the front side of the tube.
  • Top-view: The tube’s top is used to display and read the digits.

Main Models of Nixie Tubes by Region
Nixie tubes were manufactured in several regions worldwide, and we can categorize the key models as follows:

  • United States
    Brands: Burroughs Corporation, National Electronics, Richardson Electronics
    Models: B-6844, B-7153, B-7011, B-8091
  • Soviet Union
    Brands: VNIIT, M3, Elpida
    Models: IN-1, IN-4, IN-12, IN-14, IN-16, IN-19, IN-18
  • China
    Brands: Ningbo, Hengyang, Xinguang, Nanchang
    Models: QS30-1, QS27-1, SZ-4, SZ-2, SZ-J2, QS18-12
  • Japan
    Brands: Hitachi, Matsushita, Rodan, NEC, JRC
    Models: CD27, CD47, CD66, CD71, CD78, CD79, CD88
  • Germany
    Brands: Telefunken, Valvo, Siemens
    Models: Z560M, Z566M, Z568M, Z570M, ZM1000, ZM1020, ZM1040
  • United Kingdom
    Brands: Mullard, ITT, Plessey, GEC, Marconi
    Models: PL-2, PL-6, GEC ZM-1, ZM-4, MK1, MK2

Other countries also produced Nixie tubes.

Internal Structure
Nixie tubes are filled with neon and argon gas, and some models even contain mercury vapor. The most common Nixie tubes display digits 0-9, but some are designed to display characters as well. Most Nixie tubes have several cathodes, with each cathode forming a unique shape. A tube displaying digits 0-9, for example, has 10 cathodes, each made of a separate metal piece, but only one anode inside the tube. This design allows the display to be visible through a mesh anode in side-view tubes or a mesh top in top-view tubes, which allows light from the cathodes to be seen.

Working Principle
Nixie tubes work based on a phenomenon known as "glow discharge." In simple terms, two electrodes are placed inside a sealed container, and when a current flows through them, the cathode releases electrons that excite the atoms of the gas inside the tube, causing them to emit light. Depending on the type of gas used (such as helium, neon, argon, krypton, xenon, etc.), different gases emit different colors of light. For example, helium produces a reddish-purple glow, neon emits an orange-red glow, and argon emits a blue-purple glow.

The glow discharge principle is crucial because the light emitted by the discharge always surrounds the cathode electrode. This is how Nixie tubes can display digits. To accommodate the 10 digits (0-9), a Nixie tube needs to have 10 cathodes arranged in a specific sequence.

Lifespan
The lifespan of Nixie tubes depends on factors like materials, manufacturing processes, and actual usage. Early Nixie tubes lasted only a few thousand hours, but over time, improved manufacturing led to tubes with lifespans of up to 200,000 hours or more, such as the Burroughs B-5440/5441 series.

Various factors can affect the lifespan, including:

  • Damage: If the glass tube is cracked, the gas inside can leak out, disrupting the glow discharge effect.
  • Gas Leaks: Cracks or breaks can lead to slow gas leaks, impacting the tube's performance.
  • Cathode Poisoning: This occurs when metal ions from the cathodes are transferred to neighboring cathodes, reducing their ability to discharge properly.
  • Metal Deposits: The process of electron transfer can cause metal ions to accumulate on the inner surface of the tube, darkening the glass and affecting visibility.

To extend the lifespan of a Nixie tube, it’s important to avoid impacts, control the operating current, and regularly cycle the display content to prevent uneven wear on the cathodes.

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