Mullard–Philips tube designation
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In Europe, the principal method of numbering vacuum tubes ("thermionic valves") was the nomenclature used by the Philips company and its subsidiaries Mullard in the UK, Valvo(de, it) in Germany, Radiotechnique (Miniwatt-Dario brand) in France, and Amperex in the United States, from 1934 on. Adhering manufacturers include AEG (de), CdL (1921, French Mazda brand), CIFTE (fr, Mazda-Belvu brand), EdiSwan (British Mazda brand), Lorenz (de), MBLE(fr, nl) (be, Adzam brand), RCA (us), RFT(de, sv) (de), Siemens (de), Telefunken (de), Tesla (cz), Toshiba (ja), Tungsram (hu), and Unitra (pl; Dolam, Polam, Telam brands). This system allocated meaningful codes to tubes based on their function and became the starting point for the Pro Electron naming scheme for active devices (including tubes and transistors).