Old TVs, early supercomputers, and modern fancy sound equipment all use vacuum tubes. But why? What does a vacuum tube do?
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A vacuum tube is a switch with no mechanical parts. It allows you to turn one current on or off with another current.
A vacuum tube has 3 terminals, a place where current goes in, goes out, and a controller.
Current goes into the one side, and a beam of electrons is created from there. The controller can steer that beam of electrons by cresting a magnetic field. If it steers the beam right, it can hit the other side and allow current to come out the other side. If you change the controller current, the beam no longer makes contact and current stops.
This process creates a lot of waste heat and light, and vacuum tubes need to warm up before use to function properly. Due to that heating and cooling, they are prone to breaking.
They fell out of use when the transistor was invented. The transistor does the same job, but without needing to warm up, a fraction of the energy, and with 1000x the reliability.
Fun fact: CRTs (cathod ray televisions, the old big ones) use a similar method to work. The TV signal comes in and turns an electron beam on and off while another current steers that beam into the screen. The electron beam then hits phosphors (chemicals that light up when hit with high energy) that glow with the corresponding color of that pixel, resulting in an image scanned one line at a time on the screen.
Fun fact: the term “debugging” comes from the fact that vacuum tubes would sometimes burn moths onto them, and impede their function, so you would occasionally have to “debug” the system by removing the dead moths.
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