This is something to think about. The research that went into things like this was so intense and demanded very rare individuals to become deeply engaged in th

This is something to think about. The research that went into things like this was so intense and demanded very rare individuals to become deeply engaged in the applicable aspects of natural science, that key progress was made in scattered areas after leaving the rest of the world's equally-qualified technologists in the dust. The companies were built as manufacturers of consumables, based on cheap materials, labor, and mass production. All this had occurred with wartime stakes and urgency. With the arrival of transistors, a new generation of researchers was deployed and the vacuum tube people continued their momentum not that much longer. Different kinds of fabrication facilities were needed for transistors, and mainly for supplying OEMs, these were also not consumable like bulbs in sockets. The strong urgency could not be re-established and I think a lot of the manufacturers had difficulty navigating technology migrations like this. A number of pivots did not include continued component manufacturing. Interestingly, a big vacuum chamber is where they make the semiconductors, carefully vaporizing solid-state materials in the process. And when the silicon comes out, you can make a radio without needing the little bulbs containing your own personal vacuums. Take a look at the comments here for some 21st century readings of an EF50: https://www.radiomuseum.org/tubes/tube_ef50.html https://www.radiomuseum.org/tubes/tube_ef50.html Another decade of advances gave us things like the EF96 (6AG5/6186) for much higher frequency use: https://tube-data.com/sheets/093/6/6AG5.pdf https://tube-data.com/sheets/093/6/6AG5.pdf Well I'm not a radio man but these are great for audio, even though they're a preamp their internal structure is a bit like a beam power tube: https://www.radiomuseum.org/tubes/tube_6186.html https://www.radiomuseum.org/tubes/tube_6186.html So pentode, triode, tetrode they are tasty and the sockets are not too unobtainable.