^ Verhoeven CJM, van Staveren A, Monna GLE, Kouwenhoven MHL and Yildiz E (2003). Structured electronic design: negative feedback penguats. Boston/Dordrecht: Kluwer Academic. pp. 10. ISBN 1-4020-7590-1. http://worldcat.org/isbn/1-4020-7590-1.
^ Robert S. Symons (1998). "Tubes: Still vital after all these years". IEEE Spectrum 35 (4): 52–63. doi:10.1109/6.666962.
^ OTB - Below 535, A Historical Review of Continuous Wave Radio Frequency Power Generators
