Basics: Vacuum Tubes

(Editors Note: this blog post was first published on a, which has now been merged into

When I was a kid, I knew that televisions, radios and all sorts of electronics used vacuum tubes prior to the invention and widespread use of transistors. In fact, the black and white television on which I watched Gilligan’s Island used a special type of vacuum tube called a CRT (cathode ray tube). What I didn’t understand was how a vacuum (the household appliance used to suck dirt out of the carpet) made all these electronic devices possible. It was mind boggling. I didn’t think much of our vacuum, but it somehow held a secret I could not understand.

Well, it turns out that it was just a misunderstanding. My vacuum wasn’t responsible for the electronics revolution. The term vacuum tube was used to describe the glass tube that most of the ‘air’ removed under low pressure and filled with inert gases. A vacuum is a place that is empty of matter. If the tube was filled with air…that would not be a vacuum, since oxygen and other gasses in the air are matter.

But a vacuum tube is not truly a vacuum. They are manufactured under low pressure conditions (not no pressure conditions) and the gases inside are replaced with gases that won’t react. Then they are sealed while still in this condition making a near vacuum. It’s just that ‘near vacuum tubes’ never caught on.

Well, even with this misunderstanding cleared up, I still didn’t understand how vacuum tubes made the miracle of Gilligan’s Island possible. Turns out that if you understand how vacuum tubes work, it makes a lot of other electronics easier to understand too.

I found this video on YouTube. It’s a 21 min movie made by Westinghouse in 1943. And it’s fascinating, not to mention historically interesting when you note how many references it makes to the war effort. If I would have only seen this movie back when I was watching Gilligan’s Island, maybe I would have seen Gilligan and my vacuum in a different light.






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