I have a copy of an article that is about 5-6 pages long that discusses the history of the tube, the current uses of tubes / tube industry, the stopage of the development of the tube and why there is a resurgence in the development of the tube. The article basically states that tube development is becoming mainstream and that it is a micro varient similar to the solid state device that replaced it; but with tube design topology. If anyone is interested, I will see if I still have the article or can get my hands on a copy.
Chuck
Chuck