Moorehead Laboratories Vacuum Tube, circa 1917

Vacuum tubes appear in older radios, televisions, amplifiers, computers, and other electronic devices. Their function: to amplify and strengthen weak electronic signals. Typical tubes are sealed glass bulbs evacuated of gas, allowing electron flow to be influenced by an interior cathode, plate and grid. Perfected in 1906 by Lee De Forest, the vacuum tube was the genesis of a communications revolution.