This document provides information on STC’s GN-1 Nixie tube. It includes a datasheet outlining the electrical specifications for both DC and rectified AC operation, as well as mechanical details such as tube dimensions and digit height. Additionally, it features circuit diagrams illustrating how the tube can be used in conjunction with the G10/241E counting tube. This document describes a very early version of the GN-1 without an anode grid. Later units included one, likely to achieve more even illumination.

The G10/241E is a neon-filled Nomotron made by the British manufacturer STC and capable of speeds of 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 ten stable cathodes are visible through circular openings, each marked with its corresponding value on a transparent mica shield.

The GN-1 (also known as G10/201E) was among the earliest commercially available Nixie tubes. It was manufactured by the British company STC and sold under their brand name “Nodistron.” The oldest piece of documentation on the tube I could find is the original STC datasheet linked below, which is dated 1959. This places the tube towards the very beginning of Nixie tube manufacturing.

The tube’s age is reflected in its design and construction. Unlike virtually all Nixie tubes manufactured later, the digits on the GN-1, which are also quite large for a top viewing tube, are not stamped from sheet metal but are formed from pieces of wire that have been bent into the shape of digits. Furthermore, they are not arranged on a rod and separated from one another by insulators, but are mounted directly between two mica shields enclosing the anode cage at the top and bottom. The discharge surrounding them when active exhibits the characteristic orange glow typically associated with mercury-free neon fillings, which greatly limited the effective lifespan of early Nixie tubes. Other interesting features include the use of braided cables, which connects two of the tube’s cathodes to their respective pins, and the two evaporative getters clearly visible on the left and right sides of the glass envelope. Finally, the tube’s rugged base is partly made of sheet metal, which, while not unusual for early vacuum tubes, is very rare in Nixie tubes.

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 GN-5A (military code CV5351) is a large top-viewing Nixie tube produced by the British manufacturer STC and marketed under the “Nodistron” brand. It succeeds the GN-1 and GN-2 models, maintaining the same pinout and compatible electrical specifications. A distinguishing feature of the GN-5A is the faint bluish glow emitted by its illuminated digits, indicating the presence of mercury in the gas mixture which was absent from its predecessors. This mercury addition likely contributes to a significantly extended lifespan. Visually, the GN-5A closely resembles the GN-2, with the main external difference being the addition of a non-evaporative getter, a feature commonly found in later-generation Nixie tubes.

This document details the design, functionality, and application of the STC G10-241E Nomotron, a unidirectional single pulse counting and display tube. It describes its operation and highlights its applications in areas such as tachometry, counting and batching, and frequency and time measurement. Besides a general overview over its mechanism of operation, it also contains detailed diagrams of the tube and example circuits for many of its aforementioned use cases.

Detail pictures of the G10/241E can be found here.