An electron tube is a sealed glass container that controls the flow of electricity using electrons moving through empty space (a vacuum). Before transistors were invented in the 1940s, electron tubes were the essential components that made radios, televisions, computers, and radar systems work.

Inside an electron tube, a heated metal element releases electrons, which are tiny particles that carry electrical charge. These electrons travel through the vacuum inside the tube to another metal element, creating an electrical current that can be controlled and amplified. By changing the voltage on a metal grid inside the tube, engineers could make the electron flow stronger or weaker, turning the tube into an amplifier or a switch.

The earliest computers, like ENIAC, built in 1946, used thousands of electron tubes and filled entire rooms. These tubes generated tremendous heat and frequently burned out, requiring constant replacement. When transistors arrived, they did the same job as electron tubes but were much smaller, cooler, more reliable, and used less power. This made modern computers possible.

You might also hear electron tubes called vacuum tubes or simply tubes. Some guitar amplifiers still use them today because musicians prefer the warm, rich sound they produce compared to modern transistors.