The early Nixie tubes were made by a small vacuum tube manufacturer called Haydu Brothers Laboratories, and introduced in 1955 by Burroughs Corporation, who purchased Haydu. The name Nixie was derived by Burroughs from “NIX I”, an abbreviation of “Numeric Indicator eXperimental No. 1”, although this may have been a backronym designed to justify the evocation of the mythical creature with this name. Hundreds of variations of this design were manufactured by many firms, from the 1950s until the 1990s. The Burroughs Corporation introduced “Nixie” and owned the name Nixie as a trademark. Nixie-like displays made by other firms had trademarked names including Digitron, Inditron and Numicator. A proper generic term is cold cathode neon readout tube, though the phrase Nixie tube quickly entered the vernacular as a generic name.
The most common form of Nixie tube has ten cathodes in the shapes of the numerals 0 to 9 (and occasionally a decimal point or two), but there are also types that show various letters, signs and symbols. Because the numbers and other characters are arranged one behind another, each character appears at a different depth, giving Nixie based displays a distinct appearance. A related device is the pixie tube, which uses a stencil mask with numeral-shaped holes instead of shaped cathodes. Some Russian Nixies, e.g. the IN-14, used an upside-down digit 2 as the digit 5, presumably to save manufacturing costs as there is no obvious technical or aesthetic reason.
Each cathode can be made to glow in the characteristic neon red-orange color by applying about 170 volts DC at a few milliamperes between a cathode and the anode. The current limiting is normally implemented as an anode resistor of a few tens of thousands of ohms. Nixies exhibit negative resistance and will maintain their glow at typically 20 V to 30 V below the strike voltage. Some color variation can be observed between types, caused by differences in the gas mixtures used. Longer-life tubes that were manufactured later in the Nixie timeline have mercury added to reduce sputtering resulting in a blue or purple tinge to the emitted light. In some cases, these colors are filtered out by a red or orange filter coating on the glass.
One advantage of the Nixie tube is that its cathodes are typographically designed, shaped for legibility. In most types, they are not placed in numerical sequence from back to front, but arranged so that cathodes in front obscure the lit cathode minimally. One such arrangement is 6 7 5 8 4 3 9 2 0 1 from front (6) to back (1).Russian NH-12A & NH-12B tubes use the number arrangement 1 6 2 7 5 0 4 9 8 3 from back to front, with the 5 being an upside down 2.
A vacuum fluorescent display (VFD) is a display device used commonly on consumer-electronics equipment such as video cassette recorders, car radios, and microwave ovens, specially in the late 1980s
A VFD operates on the principle of cathodoluminescence, roughly similar to a cathode ray tube, but operating at much lower voltages. Each tube in a VFD has an anode coated phosphor that is bombarded by electrons emitted from the cathode filament. In fact, each tube in VFD is a triode vacuum tube because it also has a mesh control grid.
Unlike liquid crystal displays, a VFD emits a very bright light with high contrast and can support display elements of various colours. Standard illumination figures for VFDs are around 640 cd/m2 with high-brightness VFDs operating at 4,000 cd/m2, and experimental units as high as 35,000 cd/m2 depending on the drive voltage and its timing. The choice of color (which determines the nature of the phosphor) and display brightness significantly affect the lifetime of the tubes, which can range from as low as 1,500 hours for a vivid red VFD to 30,000 hours for the more common green ones.
VFDs can display seven-segment numerals, multi-segment alpha-numeric characters or can be made in a dot-matrix to display different alphanumeric characters and symbols. In practice, there is little limit to the shape of the image that can be displayed: it depends solely on the shape of phosphor on the anode(s).
The first VFD was the single indication DM160 by Philips in 1959. The first multi-segment VFD was the 1962 Japanese single-digit, seven-segment device. The displays became common on calculators and other consumer electronics devices. In the late 1980s hundreds of millions of units were made yearly.
A Numitron utilizes eight filaments for the display, seven for the segments, and one for the decimal point, all of which are enclosed in a typical tube glass body. In effect it can be seen as an eight-way incandescent globe.
The big advantage of using a Numitron as compared to the more popular Nixie tube is that it only requires a very low control voltages of 5VDC as opposed to about 170VDC for the typical Nixie tube or around 5 VAC and more than 20 VDC for the well known green / bluish VFD displays.
Because of these lower voltages a Numitron, such as the smaller IV-9, can be directly driven from the control counter circuits. For this reason there are already a number of Numitron clocks using this smaller IV-9.
However using the much larger IV-13 requires a more complex and powerful driver circuit as each of the eight segments of the IV-13 draws about 32mA of current!
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