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„European Standard EN 50419”. European Committee for Electrotechnical Standardization. Arhivirano iz originala na datum 02. 05. 2014.. Pristupljeno 09. 04. 2012.
„European Standard EN 50419”. European Committee for Electrotechnical Standardization. Arhivirano iz originala na datum 23. 11. 2015. Pristupljeno 12. 11. 2018.
„European Standard EN 50419”. European Committee for Electrotechnical Standardization. Arhivirano iz originala na datum 02. 05. 2014.. Pristupljeno 09. 04. 2012.
„European Standard EN 50419”. European Committee for Electrotechnical Standardization. Arhivirano iz originala na datum 23. 11. 2015. Pristupljeno 12. 11. 2018.
Guarnieri, M. (2012). „The age of vacuum tubes: Early devices and the rise of radio communications”. IEEE Ind. Electron. M.6 (1): 41–43. DOI:10.1109/MIE.2012.2182822. ISSN1932-4529.