Vacuum tube

In electronics, a vacuum tube (American English) or (thermionic) valve (British English) is a device generally used to amplify, or otherwise modify, a signal. Once used in most electronic devices, vacuum tubes are now used only in specialized applications. For most purposes, the vacuum tube has been replaced by the much smaller and less expensive transistor, either as a discrete device or in an integrated circuit. At the start of the 21st century there has been renewed interest in the vacuum tube, this time in the form of the Field-emitter microtube.

Vacuum tube solar heaters

The term vacuum tube has recently been used to refer to the tubular elements of solar panels used for heating water. Vacuum tube solar heaters are becoming increasingly popular.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~