Tung-Sol.com:: FAQs What is a vacuum tube?

FAQs

Question:
What is a vacuum tube?
Answer:
A vacuum tube is an electronic device consisting of a minimum of four active elements: a heater (filament), a cathode, a grid and a plate, all sealed in a vacuum glass enclosure to prevent parts from burning. Once heated, the cathode begins to emit electrons, which flow from the cathode (which is negatively charged) toward the plate (which is positively charged). The grid's purpose is to control this flow, in effect, acting as a valve, which is why tubes are called "valves" in the U.K.