Ei tube refers to those valve (plate) tubes, most known being Ei Ecc83 / 12AX7 tubes produced in the former Yugoslavia by Electronic Industry Nis (El Nis / Holding Korporacija Elektronska Industrija a.d. Nis).
Just a little history on Ei tube
Ei tube factory was founded in 1948 in Nis, Serbia (former Yugoslavia) as a production facility for Institute for the Production of Radio Sets and Roentgen Machines – RR NIS.
In the Golden Age of this holding company. more than 10000 people worked here so it become one of the most important Yugoslavian companies.
Because of the bad management and due to lack of investing in research part of things, and most of all because of the economic embargo and other international commercial restrictions most of the company business and manufacturing facilities collapsed including the one of the few remaining line of production of electronic vacuum tubes.
Just for the record here are some numbers. In 2006, Elektronska Industrija had 73 subsidiaries and 360 production facilities including the line of production of the vacuum tubes Ei Ecc83 / 12AX7 which was the single breakeven one. Over all it generated revenues of EUR 6.2 millions but a net loss of EUR 13.4 millions. Value of operating assets was EUR 41.1 millions.
In 2016, after a decade of agony RR NIS was shut down and the Business Court declared bankruptcy and this is the moment we’ve lost the link with the ORIGINAL EI TUBES, those produced on Telefunken machinery.
Where you can buy EI TUBES now ???
Original EI TUBES are hard to find today. Ebay can be a good point to start your searches. If you need them for different applications, preamp or amps or something else you can take in consideration the clones for Ei Ecc83 / 12AX7 tubes because some of them will do the job just fine.