Gas Discharge Displays

Gas discharge displays are low pressure neon lamps with multiple, shaped or shape-shaded cathodes. Tubes in this family include Nixie, Pixie and Panaplex displays, designs primarily of Burroughs origin. Nixie tubes were driven by a range of decade counter technologies, including hard valve and thyratron decades, dekatrons, beam switching tubes, discrete transistor counters and specialized TTL devices.

The earliest gas discharge displays were patented in 1934 by inventor Hans Paul Boswau, who envisioned all sorts of useful applications for such numeric display tubes. Boswau's primitive design consisted of shaped wire cathodes sandwiched between glass or mica discs in a large end-view envelope; this device never entered commercial production.

In 1954, National Union began to market their own numeric gas discharge tube, which dispensed with the glass plates of Boswau's device and replaced them with stiff wire supports. Sold under the 'Inditron' trade name, National Union's display was a cumbersome, experimental device, and was only produced in limited quantities.

Less than a year later, Burroughs introduced a new design which incorporated an anode mesh and a new gas mixture, transforming the numeric gas discharge display into a practical device. Electronics lore states that the name 'Nixie' originated when a Burroughs draftsman labeled drawings of the tube NIX1, shorthand for Numerical Indicator Experimental 1. Though Burroughs filed the Nixie term for trademark status in 1956, 'Nixie' has since become a generic descriptor used to refer to any gas discharge numerical display which contains an anode grid.

Burroughs 4021L
 
Burroughs 4021L


This Nixie tube ranks as one of the smallest circular envelope displays ever made; the digits are a mere 8 mm high. This model of tube was made in both standard pin and flying lead variants; the flying lead model is shown. The 4021L has digits 0-9, with no decimal point.

One of our samples is still mounted in its Lucite store display. It is hard to imagine a time when you could walk into a store and see an array of Nixie tubes on display like a row of blenders at Wal-Mart.

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Burroughs B4998
 
Burroughs B4998


The Burroughs B4998 is the smallest Nixie tube ever mass produced, it's tiny elliptical envelope is only 15mm high and 10mm wide. The B4998 contains the same 8mm digits as the 4021L tube shown above, but the elliptical envelope reduces the overall size of the tube and allows for tighter side-by-side installation of multiple digit displays. B4998 nixie tubes are highly coveted among modern hobbyists for use in construction of 'Nixie watches' and other tiny Nixie displays.

Ironically, the integrated driver modules provided by Burroughs for use with the B4998 are much bulkier than those manufactured for it's larger tubes.

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Burroughs B5971
 
Burroughs B5971


Devices included in this entry:

National NL-5971 (13 segment display)
Burroughs 5971 (13 segment display, pictured in thumbnail)


The Burroughs B5971 is a small segmented Nixie tube capable of displaying both numbers and alphanumeric characters. Though the tube appears to have the same 17-segment configuration made popular by later LED displays, the 5971 is actually only a 13-segment device. The top and bottom horizontal segments as well as the middle vertical segment are each single elements, which prevents the tube from displaying a traditional capital 'Y' as well as various specialty characters. The 5971 uses the same style of oval envelope as Burroughs common numeric 8422 nixie display tube, though it is far more rare, and commands a significant price premium over the 8422 and similar numeric Nixies.

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Burroughs B-5560
 


The B-5560 is an oddity, an upside-down mount tube. Unlike most side view nixie tubes, which have leads exiting the bottom of the envelope, the B-5560's leads exit at the top of the envelope. Digit height is 13mm and the height of the envelope is 30mm. The B-5560 is primarily used in Hewlett Packard test equipment.

Note: Despite the color in the photo, the discharge from this tube is orange like other nixie tubes. The bright pink glow in the photo is an artifact of the high amount of UV generated from the glow dischage.

Burroughs B7971
 
Burroughs B7971


The large and unwieldy Burroughs 7971 is the iconic example of an alphanumeric Nixie tube. The display contains a series of wire cathodes arranged into an array of 15 segments and an underscore character, unlike modern 17-segment LED displays, the top and bottom vanes have been ganged together on a single control line. Despite their staggeringly high price on the resale market, 7971's are a relatively common tube, the tube's large size and high functionality have made it the display choice for nixie projects and demand has increased accordingly. In the time before the Nixie clock craze, 7971's could regularly be bought from electronics suppliers for less than a dollar per tube.

Despite electronics lore to the contrary, 7971 nixie tubes were never used in the marquee at the New York Stock Exchange. The primary (possibly only) commercial use for the 7971 is in Ultronic Letrascan stock tickers, which collectively generated sales for hundreds of thousands of tubes. The Lectrascan display contained a staggering 48 7971 display tubes, along with a veritable hardware store of transistors and other discrete driver circuitry.

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8422 / CK8422 Series
 
8422 / CK8422 Series


Devices included in this entry:

Burroughs 8422 (0-9 display)
Raytheon CK8422 (0-9 display, pictured in thumbnail)
Raytheon CK1903 (symbol tube)


Also known as the B-5991, the 8422 is a common Burroughs top-viewing Nixie, which features a moderate digit height in a compact envelope. The 8422 displays digits 0-9, with no decimal point. Raytheon manufactured a variant of this part under their 'Datavue' trademark, the CK8422. The example shown in the thumbnail is a rare engineering sample variant of the CK8422, which is marked with a paper label instead of a traditional printed part number.

Raytheon also made a symbol tube companion to the CK8422, the CK1903. This tube displays plus and minus symbols and has a special reduced size anode mesh to match the size of the digit stack.

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Burroughs HB-105
 
Burroughs HB-105


The problem with Nixie tubes, both in the 1960s and now, is that they are simply far too expensive. Pixie tubes are a curious technological dead-end, an attempt by Burroughs to make a cheaper, more affordable gas discharge display. Instead of having a series of shaped cathodes for each digit, a Pixie tube has a single shaped anode with number shaped holes over each of the pins in the stamped glass base. Stub cathodes are attached to the top of each pin, which glow through the holes in the anode during operation to indicate a numeric value. Pixie tubes cost only about a quarter as much to manufacture as a Nixie tube of similar size. The low cost did not win over users however, a Pixie tube produces a remarkably tiny and unreadable display, and most early Nixie tubes were used in equipment costing many multiples of thousands of dollars where the expense of the display could be justified. Nobody knows what the first Pixie tube part number is, but given the HB105's Haydu part number and ridiculous oversized envelope, it is definitely an early example.

Ironically, Pixie tubes are now quite a bit more expensive than the Nixie tubes they were originally designed to undercut; they are quite popular among electronics hobbyists for making clocks and other novelty items. Burroughs originally marketed the tube's ability to be controlled by a five volt differential in an attempt to make the tubes seem more 'transistor friendly', but modern hobbyists typically drive them with standard Nixie circuits instead.

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Burroughs B9012
 
Burroughs B9012


The B9012 pixie tube, made by Burroughs, is the replacement for the short-lived HB-105 shown above. The B9012 has the same display face as the HB-105 and uses the same obscure double-ring 13 pin base, but has a long life mercury doped fill gas and more refined internal construction. The tube dispenses with the high domed envelope of the HB105 and replaces it with a more conventional envelope that only has a height of 20mm. While still rare, the B9012 is not pure unobtainium like the HB-105, and its long life makes it the obvious choice for any sort of electronics project.

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Phillips Z550
 
Phillips Z550


The Z550 is a pixie tube with a twist, it is a display that includes its own switching thyratrons for easy control from a 5 volt TTL signal. Each digit contains a small starter electrode that pierces a ring anode and cathode plates to poke into the cavity behind the digit stamp. By controlling the voltages present on the anode and cathode, it is possible to put the tube in a state where a mere five volt pulse on the starter electrode will trigger the glow discharge for the selected digit. The entire display assembly is constructed on a thick glass billet which is then sealed in the tube's 13 pin envelope; unlike the Burroughs HB-105 and 9012, the Z550 envelope is relatively devoid of empty space. As with the Burroughs pixie tubes discussed above, the 5 volt control scheme is almost never used by modern experimenters, who typically use a traditional Nixie control system connected to the tube's starter electrodes instead.

It should be noted that all Z550 tubes were made by Phillips in their Eindhoven plant, regardless of the manufacturer's stamp. Z550 tubes were restamped near the time of sale to match the nameplate for the target country.

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Burroughs HB-106
 
Burroughs HB-106


The HB-106, as indicated by its Haydu part number, is an early model of Burroughs top view nixie tube. Burroughs parts which were manufactured at the Haydu plant begin with the "HB" prefix; Burroughs eventually stopped using the Haydu brand name and later part numbers were prefixed with a "B". This tube has a silicone surround that is integral to the part, which was included to increase readability in high brightness conditions. The part number is printed on a plastic wrapper affixed to the surround. Unfortunately, as this example shows, the plastic wrapper is just as prone to disintegration as the water soluble paint used on most other models of tubes.

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National Union GI-10 'Inditron'
 
National Union GI-10 'Inditron'


The GI-10 'Inditron' is an historical curiosity, a Nixie-style numerical indicator tube which was developed in parallel to the more successful Burroughs Nixie, and may actually predate the Burroughs Nixie by as much as a year. Beginning in 1954, National Union produced a small number of neon-filled indicator tubes which used bent wire cathodes to indicate a numeric value. The tubes had very short operational lifespans and were difficult to drive with the contemporaneous technology, which prevented widespread use and ultimately doomed the tube to failure in the market.

The primary difference between a GI-10 and a Burroughs-style Nixie tube is the lack of an anode grid. With no anode grid, the GI-10 is rather difficult to drive; an adjacent cathode must be pulled high to start the glow discharge. The GI-10's wire numerals look quite different from the stamped metal numerals used in the Burroughs design, and are much more prone to failure. The unusual 10-pin base is designed to fit into a modified 9-pin socket with a metal bushing around the hole in the center. The long pin in the center of the tube protrudes down the hole, and a spring on the side of the pin engages the bushing, allowing a common 9-pin socket to function with a 10-pin tube.

Special thanks to Randall Logan for providing an excellent scan of the GI-10 datasheet.

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Sperry SP-15x & SP-35x Series
 
Sperry SP-15x & SP-35x Series


Devices included in this entry:

Sperry SP-152 panaplex (1.5-digit bathtub; pictured in thumbnail)
Beckman SP-353 panaplex (3-digit bathtub)
Beckman SP-356 panaplex (4-digit bathtub)


Panaplex displays are a late development in neon display technology. Instead of encasing the display elements in a tube style envelope, panaplex displays use a long flat bathtub-shaped envelope, to which a piece of glass is bonded after the internals of the tube have been assembled. This example is an earlier style of panaplex display, with rear mounted leads and a thick black envelope. Newer displays have thinner envelopes and leads that exit the bottom edge of the display.

The SP-152 pictured in the thumbnail is a 1.5 digit variant without sign. This display has a set of colon separators to the right of the least significant digit, for use as a clock display.

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Sperry SP-33x Series
 
Sperry SP-33x Series


Devices included in this entry:

Beckman SP-332 panaplex (2-digit bathtub, pictured in thumbnail)
Sperry SP-333 panaplex (3-digit bathtub)


The SP-332 is one of the smallest panaplex displays ever made, with a digit height of only 7 mm. The SP-332 has an identical internal layout to the larger and more common SP-352. Sperry also manufactured a three digit display in this form factor, the SP-333.

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Beckman SP-450 Panaplex Display
 
Beckman SP-450 Panaplex Display


This late model panaplex display shows many of the manufacturing changes that Beckman and others made to their designs as panaplex manufacturing techniques matured. Instead of using the black glass "bathtub" style envelope seen on earlier displays, the SP-450 uses a glass sandwich which is almost identical to the package seen on early LCD displays. All of the leads exit along the edge of the envelope instead of out of the back, and no provision is provided to socket the display for easy replacement. The display itself is 6 digit 7 segment with decimal points. There are also twelve triangular indicators on the sides of the display, normally the small triangle shaped cathodes inside of such a display are intended to be used as "keepalive" electrodes for faster striking, but the location of these cathodes in the package suggests that they may be intended for actual information display.

The board shown contains two SP-450 displays and no other driver hardware.

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Melz ITS1A
 
Melz ITS1A


Another very unusual Soviet tube, the ITS1A is an indirect gas discharge display configured for seven-segment number generation. Despite appearances the ITS1A is not a VFD; the device contains seven gas thyratrons, one for each segment, which are painted with green phosphor. When the tube is energized with a high voltage source and a given thyratron is triggered, the neon fill gas will ionize and excite the phosphor in the triggered segment, producing a piercing green glow. As with the ITM2M display shown above, these tubes have complex power supply requirements and must be supplied with separate -300VDC, 100VDC, and 50VDC signals to function properly. Once these needs are met the tube can be controlled with a 5VDC signal, resulting in a neon display that can be directly attached to a microcontroller with no intermediate hardware. The ITS1A is also self-latching, which eliminates the need to multiplex large displays.

Related: An ITS1A 'Thyratron' Clock Project

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Pantek NCR08501
 
Pantek NCR08501


It is hard to think of a time when VFDs would have commanded such a premium over neon-filled Panaplex displays that a manufacturer would actually try to paint a Panaplex display to make it look more like a VFD, yet the NCR08501 is just such a boondoggle device. Every one of the NCR08501's eight digits has been painted with a white stencil, to trick the user into thinking they are looking at a VFD. Make no mistake though, the NCR08501 is a Panaplex device, it is filled with neon, it lacks filaments and control grids, and the digits light up with an orange gas discharge. The display has 84 pins and is quite large; much of the display's surface area is taken up by the illuminated arrows that ring the numeric portion of the display. Though the display panels are welded together with a fritted glass barrier that should be nearly indestructible, the evacuation nipple appears to soft-sealed with nothing more than a blob of epoxy. This example still has it's original fill gas, but soft-seal epoxy is notoriously failure prone; it is unknown how much extended use such a display could endure.

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ETL GR10A
 


Though it resembles a dekatron, the GR10A is actually a register tube - basically a Nixie or Pixie tube shaped like a dekatron. Register tubes were designed to provide a consistent display when dekatrons were used in conjuntion with beam switching tubes or hard valve decades in the same counter. The visible glow extinguishes above ~50 kHz, and reappears at lower speeds.

Soviet Anod IN-1
 
Soviet Anod IN-1


The IN-1 is a large Soviet nixie tube with an end-view envelope and phenolic base. The IN-1, unlike most other gas discharge displays, does not contain any mercury in it's fill gas, which substantially shortens the tube's lifespan. Under normal conditions, the number cathodes in an IN-1 will completely dissolve after only a few thousand hours of operation. The IN-1 is a larger nixie; digit height is 12mm and the tube has a diameter of 30mm and a height of 60mm. The tube's unusual 11 pin phenolic base is practically impossible to find a socket for, though the truly desperate can repurpose Molex pins from an ATX power supply to act as a socket stand-in. The combination of the IN-1's short operational lifespan, obscure base, and abysmally poor, "prop from The Dark Crystal"-style construction make this tube almost universally loathed by electronics hobbyists.

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Soviet Anod IN-2
 


The IN-2 is the Soviet equivalent of tiny American tubes like the Burroughs 4021. The digit height on the IN-2 is 10mm and the envelope diameter is 17mm, which makes it slightly larger than a 4021. The IN-2 has a high domed front and a side nipple that exits the tube at a 45 degree angle to the digit, for multiple tube displays. The print on the side of the tube is covered with a resinous coating, which protects the print from being wiped off by the person installing the tube. The main drawback of the tube is its tiny base, the socket for the tube is rather hard to find, and the pin spacing is very narrow, making attachment of leads difficult. It should be noted that while it is common to blindly refer to all Soviet tubes as being manufactured by 'Sovtek', the example shown here was actually manufactured by Anod.

Soviet Gazotron IN-12
 
Soviet Gazotron IN-12


The IN12 is the Soviet analog to Western oval Nixie tubes such as the Burroughs B5991 and 8422. To save on costs, the tube does not have a cathode to represent the number '5', instead an additional '2' stencil is used, mounted upside down. Digit height is 19mm and the diameter of the tube is 30mm at it's widest point. This tube is actually mechanically compatible with the 14 pin sockets used by the B5991, though the underside nipple requires that said sockets have a centrally located perforation for clearance.

This tube comes in two slightly different versions, the IN12B, which has a decimal point, and the IN12A, which does not. The IN-12 is widely used by hobbyists in projects, due to it's low cost and general ruggedness.

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Soviet Gazotron IN-17
 


The IN-17 is believed to be the smallest nixie tube that was manufactured in Russia. Digit height is 9mm and the envelope is only 10mm wide at its narrowest point. The IN-17 has a flying lead base with a colorful plastic spacer to hold the tube away from the board it is being attached to. The spacers on the IN-17 come in a wide array of different colors.

Soviet Gazotron IN-28
 
Soviet Gazotron IN-28


The IN-28 is a top view Soviet neon display tube designed to be used as a single dot indicator in large tiled displays. Large numbers of IN-28 tubes would be chained together to form segmented and dot matrix patterns with each tube acting as a single pixel. The IN-28 uses the same size envelope as the popular Soviet-made IN-4 nixie tube but is equipped with a different base, a 7 pin flying lead type that required the tube to be directly soldered into the target device. The IN-28 is very bright, and displays built using this tube have excellent visibility.

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Soviet Gazotron MTX-90
 
Soviet Gazotron MTX-90


The MTX90 is a small neon filled thyratron designed specifically for use as a latching single dot indicator, and has a curved glass magnifier incorporated into the top of the tube envelope for this function. The MTX90 was used in a myriad devices in the former Soviet Union, and a causal Google search will turn up examples of the tube lurking in everything from wall switches to quackery-medical skin care lamps. Interestingly, the tube's leads come pre-clipped to length from the factory and each lead has a ball of solder installed on it's base for easy soldering, much like a modern ball grid array integrated circuit.

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RFT Z560M
 
RFT Z560M


The Z560M is a top-view Nixie display in a compactron style envelope with a 13 pin base. Made by RFT, the Z560M is a shorter, stubbier analog to the Burroughs B5092, which is shown below. The upper surface of the Z560M is coated with a layer of translucent red paint, which increases the contrast of the displayed numbers. Digit height on this Z560M is 15mm, the tube has a diameter of 30mm and a height of 24mm.

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Rodan MG-17F
 
Rodan MG-17F


An unusual tiny 7-segment nixie display. This tube has upper and lower decimal points, allowing it to be mounted normally or with the leads exiting the top of the envelope.

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Burroughs B-5092
 
Burroughs B-5092


A medium sized round top view Nixie with standard numerals and a 13-pin base. Digit height is 16mm and the envelope is 20mm in diameter.

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