The N4 is a neon-filled decadic counting tube produced by the German company DGL Pressler (Deutsche Glimmlampen GmbH), mostly known for their special tubes. It functions in a unidirectional, single-pulse mode, with each of its ten stable cathodes accessible via separate pins. According to its datasheet, the tube is capable of up to 25,000 counts per second, making it exceptionally fast for a neon-filled Dekatron.

This unit’s glass envelope is covered with a silver coating likely intended to reduce light bleeding in from the sides affecting readability. Unlike the tiny pins typically used as cathodes in Dekatrons, the N4 features small plates, which give the discharge a noticeably wider appearance. Images of a transparent version, available here, reveal that the tube’s interior is almost empty, explaining its unusually light weight. A variant of the tube featuring a smaller phenolic base was also produced under the designation N3.

The GC12/4B is a neon-filled counting tube manufactured by ETL in Great Britain, capable of bi-directional operation and up to 4,000 counts per second. It features twelve stable cathodes, unlike the usual ten found in most Dekatrons, allowing it to count in base-12. Four of these cathodes are connected to output pins, enabling them to trigger actions such as advancing another Dekatron when active. Divide-by-12 Dekatrons like the GC12/4B were ideal for timekeeping applications since the division of hours, minutes, and seconds in a day aligns with multiples of twelve.

The IN-1 (“NH-1”) is the first generation of Nixie tube mass-produced in the Soviet Union by Anod. Like many other Soviet Nixie tubes, the IN-1 utilizes an inverted two to represent the number five, although at least some earlier models featured a proper five. This tube is notable for its large phenolic base, with each pin conveniently numbered. As is typical of early Nixie tube designs, the IN-1’s gas mixture lacks mercury vapor, which results in reduced longevity. It is, however, pin-compatible with and visually very similar to the Dolam LC-516, which could be considered as a longer-lasting alternative for those who appreciate the IN-1’s UFO-like design. Original U11 sockets are notoriously difficult to come by so building a device using either of them would likely require coming up with a custom made socket design.

The GN-2 is a large Nixie tube produced by STC as part of their ‘Nodistron’ line of display tubes. It is pin-compatible with and the direct successor to the GN-1 and already shows notable advancements in Nixie tube manufacturing. Unlike its predecessor, the GN-2 features digits stamped from sheet metal instead of ones made from bent wire. These digits are arranged in a more compact stack, separated by insulating rings. The thick wires previously used to connect the numerals to their corresponding pins have been replaced with the thinner leads seen in most later top-viewing Nixie tubes. Additionally, the GN-2 no longer employs evaporative getters and the pin connected to the anode meant for operation with rectified AC voltage on the GN-1 is now marked as NC in the tube’s datasheet. The tube’s numerals emit the same distinctive orange glow seen in the GN-1, indicative of a mercury-free production process suggesting a relatively short operational lifespan.

The 6E5 is one of the earliest examples of a magic eye tube, invented in 1932 by American electrical engineer Alan DuMont. Designed as a cost-effective alternative to expensive needle indicators, it was intended for use in devices like radios that required user tuning without high precision. The first commercially available 6E5 tubes, sold by RCA starting in 1935, featured a coke-bottle-shaped glass envelope common in early vacuum tubes.

Unlike more modern magic eye tubes, the 6E5 has a relatively simple display characteristic, consisting of a single shadow that expands or contracts based on the supplied input voltage.

The Tesla 11TU7 is an early neon-filled Nomotron counting tube allowing for up to 20,000 counts/second. It operates in a unidirectional, single-pulse mode, advancing the discharge by one position with each pulse and featuring ten stable positions. Unlike conventional decadic counting tubes (Dekatrons), its guiding electrodes are concealed behind a metal shell. Only the stable cathodes are visible through circular openings, each marked with its corresponding value on a transparent mica shield.

The DTF104B is a Numitron display tube produced by RCA. Internally, it is nearly identical to the more common DR2000 and similar to the DR2010, but it is designed to be read from the top rather than the side. A spot exists on the backplate where a left decimal point could have been included, but it lacks filaments and is therefore non-functional on this model. Its flat top gives the DTF104B a distinct look and helps reducing reflections from adjacent tubes.

When the Nixie tube was introduced in the 1950s, it faced a significant drawback: its driving circuitry required transistors with relatively high breakdown voltages capable of handling the elevated operating voltages. At the time, such transistors were not widely available. This limitation created a demand for an alternative display technology that could operate with low-voltage, low-current logic circuitry. The solution was the Pixie tube, initially designated as the Z550M and later renamed the ZM1050.

The LC-516, produced by Polish tube manufacturer Dolam (later known as Unitra Dolam), is pin-compatible with and visually similar to the Soviet IN-1 Nixie tube. However, unlike the IN-1—an early model with a relatively short lifespan—the LC-516 is mercury-doped, significantly enhancing its durability and giving its glow a subtle bluish tint. The LC-516 features a slightly smaller glass envelope and digits compared to the IN-1; a comparison between the two is shown below. Additionally, Dolam manufactured a version without the phenolic base, designated as the LC-513.

The National Union GI-10 is likely the first Nixie tube ever produced, belonging to National Union’s Inditron series of display tubes. Patented applied for in 1954 (and granted in 1956), it predates the original “NIXI” tube developed by Haydu Brothers and later Burroughs by at least a few months. Similar to other early Nixie tubes, such as the STC GN-1, its digits are not stamped from sheet metal but are crafted from wire. These digits are connected to the tube’s 10 pins via long rods covered in an insulating layer of ceramic that also serve to hold them in place. In contrast to more modern Nixie tubes, where the digits are arranged to minimize obstruction of each other, the digits in the GI-10 are organized in a straightforward, sequential manner. The zero digit is positioned at the very front, while the one is located at the farthest point in the stack. Unlike most later Nixie designs, the GI-10 lacks a dedicated anode; instead, activating a specific digit requires all other electrodes to be held at anode potential, which complicates the driving circuitry and makes it difficult to achieve uniform brightness across all digits. The tube uses a standard Noval 9-pin socket with an additional central pin.

The GR10H is an early Nixie tube produced by ETL, featuring digits visible through a small viewing window, with the majority of its envelope coated in black paint—likely intended to enhance contrast and minimize light bleed from adjacent tubes. Shown at the end of this page is a transparent GR10H revealing that, like in the STC GN-1, the digits are connected to the tube’s pins via thick wires and an evaporative getter was used.

The STC G10/241E is an early neon-filled Nomotron counting tube allowing for up to 20,000 counts/second. It operates in a unidirectional, single-pulse mode, advancing the discharge by one position with each pulse and featuring ten stable positions. Unlike conventional decadic counting tubes (Dekatrons), its guiding electrodes are concealed behind a metal shell. Only the stable cathodes are visible through circular openings, each marked with its corresponding value on a transparent mica shield.

The GN-1, manufactured by STC and sold under the name ‘Nodistron’, was among the earliest commercially available Nixie tubes. The oldest documentation I could locate dates back to December 1959 (referenced below). The tube’s design reflects its age, with the digits being formed from wire rather than stamped from sheet metal like in most later Nixies. The GN-1 emits a distinctly orange glow, indicative of a mercury-free design, which likely results in a shorter lifespan compared to later models. Unlike more modern Nixie tubes, the GN-1 includes two evaporative getters, clearly visible on the left and right sides of the glass envelope. Additionally, its numerals are not mounted on a metal pin insulated by spacers but are instead secured between two mica plates and connected to the tube’s pins via thick wires. Interestingly, according to the datasheet, the tube has two anodes for use with direct and alternating currrent respectively.