How does a vacuum triode work and why was it invented? This is the story of a smudge in a light bulb, an assistant with a good memory and a con artist working around a patent and one of the most important wires in history! Check it out.
The movie where they extoled the virtues of the vacuum tube is from:
https://youtu.be/_-JzxX75oYc
And, as usual, the music is from the amazing Kim Nalley.