Vacuum tubes: What makes them tick?

As part of the Sierra Foothills ARC's on-going series on Components, Greg KO6TH discusses the venerable Vacuum Tube. In his talk, he covers a bit of its early history, how it evolved, how it works, and how it is used.
Greg has been a ham since 1992, currently holding an Amateur Extra license. But his dabbling with electronics and computers dates back to his teenage years, when he was given (and promptly tore apart) any number of old TVs and radios for their parts, which were re-assembled into a variety of other bits of audio and radio equipment, sometimes successfully.