It`s interesting that this joke is based on real EL503 reissue attempts from some "tube dreamers" a few yers ago, see the link:http://www.jogis-roehrenbude.de/Roehren-Geschichtliches/EL503/EL503.htm
For those without German language knowledge, there are some on-line translators, for example:
http://babelfish.altavista.com/