Below is one of those old educational films from Westinghouse on vacuum tubes. A lot of vacuum tubes are still available and they are costly. Radio Shack used to have them. Pay now and have them shipped to your address. Some of those old vacuum tubes reach an art form of construction. The old radio broadcasting tubes were huge, expensive [like $20,000 or more], and generated enough heat to cook a side of beef. They even looked like something that would be at home in a mad scientist's lab. Solid state electronics was the killer.
Electronics at Works
Vacuum Tube [Wikipedia]