|vacuum tube or vacuum valve|
|another name for valve|
|vacuum valve or vacuum valve|
|the offspring of a zebra and a donkey.|
|an extraordinary or unusual thing, person, or event; an exceptional example or instance.|
An electron tube from which all air has been removed. The vacuum ensures transparency inside the tube for electric fields and moving electrons. Most electron tubes are vacuum tubes; cathode-ray tubes, which include television picture tubes and other video display tubes, are the most widely used vacuum tubes. In other electronic applications, vacuum tubes have largely been replaced by transistors.