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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Vacuum tubes were replaced by modern transistors.
Transistors act like valves where an input voltage A can control how much voltage flows through input B, to output C. This is really useful for, say, a radio where you can have a *really tiny* voltage on A that opens the “valve” and lets a much larger voltage through B, which makes it an amplifier.
It also lets you use one voltage A as a switch to turn on or off voltage B, which lets you do all sorts of things with logic gates.
So how do vacuum tubes do this? Put two plates of metal and put a positive charge on one and negative on the other, and put them in a vacuum. Electrons will “jump” off of the negative plate and onto the positive plate, creating a voltage that flows across the plates. Then, put another plate between them with lots of holes, or a grid of wires. If you put a positive charge on the grid, it’ll help the electrons jump across and increase the voltage. If you put a negative charge on it, it’ll block the electrons and reduce or completely stop the voltage.
So, just like the transistors that came afterwards, the vacuum tube acts as a “switch” where the input on A (the grid) controls the voltage passing through the plates (B and C).
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