What is a Vacuum Tube?
The tube is basically an electronic valve that controls the flow of electrons. It consists of an envelope (bulb, usually glass) from which most air and other gasses have been removed. Inside this near vacuum are two systems. One is called the heater. This is in the center of the tube and is the portion you will normally see glowing orange (some tubes may have more than one heater). The other system consists of the cathode, grid(s), and plate (also called the anode). The plate is the largest metal structure you see inside the bulb. All of this is held to correct locations by thin disc spacers made of mica or ceramic. Be Careful – IT’S HOT Current tube technology requires high internal operating temperatures. As a result, the glass part of the tube can reach temperatures as high as 250 degrees. Always allow your amplifier to sit switched off for several minutes before you touch the tubes. Typically the hottest tubes are the large output tubes (such as KT88, EL34, 6L6, 6550, 6CA7, KT66, K
Before being replaced by transistors and integrated circuits, vacuum tubes (thermionic valves) were predominately used in electronic devices such as televisions, radios, and computers. They are still in use today in a few specialized devices. The invention of vacuum tubes dates back to the observation of the so-called Edison Effect, an observation made by Thomas Edison. Edison noted that current flows between an incandescent lamp’s filament and a plate within the vacuum, when the plate is connected to the positive end of the filament. Because the first computers ran on vacuum tubes instead of today’s small computer chips, a single computer had to contain thousands of vacuum tubes, and could fill an entire room. Early stereo amplifiers also used vacuum tubes, and even today, some audiophiles prefer them because they produce less distortion. Vacuum tubes are still used in some electric guitar amplifiers. Also, tubes are still used in some military applications, because tube electronics a
In electronics, a vacuum tube (U.S. and Canadian English) or (thermionic) valve (outside North America) is a device generally used to amplify, or otherwise modify, a signal by controlling the movement of electrons in an evacuated space. For most purposes, the vacuum tube has been replaced by the much smaller and less expensive transistor, either as a discrete device or in an integrated circuit. However, tubes are still used in several specialized applications such as guitar amplifiers (also called a valve amp outside the U.S.) and high power RF transmitters, as a display device in television sets and in microwave ovens.
