Before being replaced by transistors and integrated circuits, vacuum tubes (thermionic valves) were predominantly used in electronic devices such as televisions, radios, and computers. They are still in use today in some specialized devices.
Thomas Edison helped invent vacuum tubes.
The invention of vacuum tubes dates back to the observation of the so-called Edison Effect, an observation made by Thomas Edison. Edison observed that current flows between the filament of an incandescent light bulb and a plate in a vacuum when the plate is connected to the positive end of the filament.
Vacuum tubes are used in some electric guitar amplifiers.
Because early computers were powered by vacuum tubes rather than today’s tiny 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, the tubes are still used in some military applications because the electronics in the tubes are not affected by the radio waves produced by atomic explosions.
The tube amp was responsible for the easily recognizable guitar licks of some of modern rock ‘n’ roll’s most famous guitarists.
Vacuum tubes are normally encased in a glass shell, although some tubes use ceramic or metal. In its most basic diode design, the tube, or envelope, is hermetically sealed to create a vacuum. The electrodes inside the casing are attached to leads, which protrude outside the casing and plug into an outlet. A basic vacuum tube contains filaments inside the casing, similar to those in a light bulb. The filaments heat up and then release electrons, creating a cloud of negatively charged electrons. The electrons are attracted to an anode, or a small metal plate, inside the tube, which is positively charged, and a unidirectional flow is established between the filament and the plate.
With traditional music cables, electric guitars can be connected to amplifiers and other music equipment equipped with quarter-inch connectors.
Sometimes the tube contains an additional electrode in the form of a small screen-like grid, later called a triode, which is more efficient and capable of amplifying the voltage. As voltage is applied to the grid, the flux between the filament and the plate can vary. In addition to diodes and triodes, other innovations followed, including tetrodes, hexodes, heptodes, and octodes, designed for a variety of specialty applications and to minimize distortion. Some vacuum tubes combine the function of two or more diodes or triodes in a single unit.
One of the main disadvantages of vacuum tubes is that the filament becomes unstable over time. Also, if air leaks into the tube, the oxygen will react with the hot filament and damage it. The properties of a tube change over time, so early vacuum tube televisions had to be adjusted frequently to produce a good picture.
Tube amps, which tend to produce louder sounds than solid-state amps, were commonly used by musicians before the 1970s.
