Vacuum tube

From HvWiki

A vacuum tube is device that can switch and amplify signals. Vacuum tubes are arrangements of electrodes in vacuum. They work by thermionic emission. A filament (anode) similar to that of the light bulb emits electrons to the plate (cathode). Depending on the arrangment of the filament and plate makes the vacuum tube perform diffrent aoperations such as amplification, rectifier, and some high power microwaves. They are similar to transistors