Today built-in Nixie clocks tubes are found in old warehouses or removed from discarded equipment. Usually the built-in Nixie clocks tubes are approximately about 40 years old. Stocks of Nixie tubes are difficult to obtain and are expensive. These are rare.
Nixieclocks.ch installs right now unused tubes.
Nixie tubes are usually marked on the back with the name of the manufacturer, the type and year of manufacture.
The shown NH-8-2 tubes were produced in the years 1971, 1977, 1978 and 1979 in the Soviet Union (CCCP). The manufacturer was МЭЛЗ (MELZ, Moscow electrical equipment). MELZ is the oldest company in the Russian/Soviet electrical/electronics industry. Please refer www.ru.wikipedia.org.
Tubes produced by the same manufacturer are not always exactly identical.
In the left Nixie tubes, the anode is made of a finer structure. The tips of tubes ablated by glassblowers are of different lengths.
The manufacturer of the Nixie clock checks the function of tubes and is choosing identical tubes for installation in a clock.