Vacuum tube

vacuum tubestubethermionic valvevalvevacuum-tubethermionic valvesvalvestubeselectron tuberadio tube
In electronics, a vacuum tube, an electron tube, or valve (British usage) or, colloquially, a tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.wikipedia
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Diode

diodessemiconductor diodegermanium diode
The simplest vacuum tube, the diode invented in 1904 by John Ambrose Fleming, contains only a heated electron-emitting cathode and an anode.
A diode vacuum tube or thermionic diode is a vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can flow in only one direction, from cathode to plate.

Electronics

electronicelectronic equipmentelectronic device
In electronics, a vacuum tube, an electron tube, or valve (British usage) or, colloquially, a tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. Although some applications had used earlier technologies such as the spark gap transmitter for radio or mechanical computers for computing, it was the invention of the thermionic vacuum tube that made these technologies widespread and practical, and created the discipline of electronics.
The identification of the electron in 1897, along with the invention of the vacuum tube, which could amplify and rectify small electrical signals, inaugurated the field of electronics and the electron age.

Vacuum

free spaceevacuatedhigh vacuum
In electronics, a vacuum tube, an electron tube, or valve (British usage) or, colloquially, a tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes, and a wide array of vacuum technologies has since become available.

John Ambrose Fleming

Ambrose FlemingSir Ambrose FlemingSir John Ambrose Fleming
The simplest vacuum tube, the diode invented in 1904 by John Ambrose Fleming, contains only a heated electron-emitting cathode and an anode.
Sir John Ambrose Fleming FRS (29 November 1849 – 18 April 1945) was an English electrical engineer and physicist who invented the first thermionic valve or vacuum tube, designed the radio transmitter with which the first transatlantic radio transmission was made, and also established the right-hand rule used in physics.

Thermionic emission

thermionicEdison effectthermionics
The type known as a thermionic tube or thermionic valve uses the phenomenon of thermionic emission of electrons from a heated cathode and is used for a number of fundamental electronic functions such as signal amplification and current rectification. Phototubes and photomultipliers rely on electron flow through a vacuum, though in those cases electron emission from the cathode depends on energy from photons rather than thermionic emission.
The classical example of thermionic emission is that of electrons from a hot cathode into a vacuum (also known as thermal electron emission or the Edison effect) in a vacuum tube.

Amplifier

amplifiersamplificationelectronic amplifier
The type known as a thermionic tube or thermionic valve uses the phenomenon of thermionic emission of electrons from a heated cathode and is used for a number of fundamental electronic functions such as signal amplification and current rectification.
The first practical electrical device which could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912.

Control grid

gridcontrolcontrol grids
Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by the voltage on the grid or grids.
The control grid is an electrode used in amplifying thermionic valves (vacuum tubes) such as the triode, tetrode and pentode, used to control the flow of electrons from the cathode to the anode (plate) electrode.

Semiconductor device

semiconductor devicessemiconductorsemiconductor electronics
In the 1940s the invention of semiconductor devices made it possible to produce solid-state devices, which are smaller, more efficient, reliable and durable, and cheaper than thermionic tubes.
Semiconductor devices have replaced vacuum tubes in most applications.

Phototube

photoelectric tubegas phototubesphotoelectric tubes
Non-thermionic types, such as a vacuum phototube however, achieve electron emission through the photoelectric effect, and are used for such as the detection of light levels. Phototubes and photomultipliers rely on electron flow through a vacuum, though in those cases electron emission from the cathode depends on energy from photons rather than thermionic emission.
A phototube or photoelectric cell is a type of gas-filled or vacuum tube that is sensitive to light.

Cathode-ray tube

cathode ray tubeCRTcathode ray tubes
However, the cathode-ray tube (CRT) remained the basis for television monitors and oscilloscopes until the early 21st century.
The cathode-ray tube (CRT) is a vacuum tube that contains one or more electron guns and a phosphorescent screen and is used to display images.

Tube sound

valve soundTubetube-like
Thermionic tubes still have some applications, such as the magnetron used in microwave ovens, certain high-frequency amplifiers, and amplifiers that audio enthusiasts prefer for their tube sound.
Tube sound (or valve sound) is the characteristic sound associated with a vacuum tube amplifier (valve amplifier in British English), a vacuum tube-based audio amplifier.

Triode

triode amplifiertriode tubeTriodes
Devices with three elements are triodes used for amplification and switching.
A triode is an electronic amplifying vacuum tube (or valve in British English) consisting of three electrodes inside an evacuated glass envelope: a heated filament or cathode, a grid, and a plate (anode).

Spark-gap transmitter

spark gap transmitterspark transmitterspark transmitters
Although some applications had used earlier technologies such as the spark gap transmitter for radio or mechanical computers for computing, it was the invention of the thermionic vacuum tube that made these technologies widespread and practical, and created the discipline of electronics.
After World War 1, transmitters based on vacuum tubes were developed, which were cheaper and produced continuous waves which had a greater range, produced less interference, and could also carry audio, making spark transmitters obsolete by 1920.

Photomultiplier tube

photomultiplier tubesPMTPhoto-multiplier tube
Phototubes and photomultipliers rely on electron flow through a vacuum, though in those cases electron emission from the cathode depends on energy from photons rather than thermionic emission.
Photomultiplier tubes (photomultipliers or PMTs for short), members of the class of vacuum tubes, and more specifically vacuum phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum.

X-ray tube

X-ray tubestube voltageCoolidge tube
X-ray tubes are also vacuum tubes.
An X-ray tube is a vacuum tube that converts electrical input power into X-rays.

Pentode

penthode
Additional electrodes create tetrodes, pentodes, and so forth, which have multiple additional functions made possible by the additional controllable electrodes.
The term most commonly applies to a three-grid amplifying vacuum tube (thermionic valve), which was invented by Gilles Holst and Bernhard D.H. Tellegen in 1926.

Transistor

transistorstransistorizedsilicon transistor
From the mid-1960s, thermionic tubes were then being replaced with the transistor.
Compared with the vacuum tube, transistors are generally smaller, and require less power to operate.

Glass-to-metal seal

glass-metal sealglass-to-metal-sealjoined with metals
Most tubes have glass envelopes with a glass-to-metal seal based on kovar sealable borosilicate glasses, though ceramic and metal envelopes (atop insulating bases) have been used.
Glass-to-metal seals are a very important element of the construction of vacuum tubes, electric discharge tubes, incandescent light bulbs, glass encapsulated semiconductor diodes, reed switches, pressure tight glass windows in metal cases, and metal or ceramic packages of electronic components.

Magic eye tube

tuning indicatorCat eye tubeMagic Eye
At one time many radios used "magic eye tubes", a specialized sort of CRT used in place of a meter movement to indicate signal strength, or input level in a tape recorder.
A magic eye tube or tuning indicator, in technical literature called an electron-ray indicator tube, is a vacuum tube which gives a visual indication of the amplitude of an electronic signal, such as an audio output, radio-frequency signal strength, or other functions.

Computer

computerscomputer systemdigital computer
They were crucial to the development of radio, television, radar, sound recording and reproduction, long-distance telephone networks, and analogue and early digital computers.
These devices had a low operating speed and were eventually superseded by much faster all-electric computers, originally using vacuum tubes.

Tube socket

octal baseoctalLoctal
Most vacuum tubes have a limited lifetime, due to the filament or heater burning out or other failure modes, so they are made as replaceable units; the electrode leads connect to pins on the tube's base which plug into a tube socket.
Tube sockets are electrical sockets into which vacuum tubes (electronic valves) can be plugged, holding them in place and providing terminals, which can be soldered into the circuit, for each of the pins.

Anode

anodicanodes(anode)
In both types, the electrons are accelerated from the cathode to the anode by the electric field in the tube.
The definition of anode and cathode is slightly different for electrical devices such as diodes and vacuum tubes where the electrode naming is fixed and does not depend on the actual charge flow (current).

Rectifier

rectificationrectifiedrectifiers
The type known as a thermionic tube or thermionic valve uses the phenomenon of thermionic emission of electrons from a heated cathode and is used for a number of fundamental electronic functions such as signal amplification and current rectification.
Very common double-diode rectifier vacuum tubes contained a single common cathode and two anodes inside a single envelope, achieving full-wave rectification with positive output.

Klystron

reflex klystronKlystron tubeklystrons
Klystrons and magnetrons often operate their anodes (called collectors in klystrons) at ground potential to facilitate cooling, particularly with water, without high-voltage insulation.
A klystron is a specialized linear-beam vacuum tube, invented in 1937 by American electrical engineers Russell and Sigurd Varian, which is used as an amplifier for high radio frequencies, from UHF up into the microwave range.

Cavity magnetron

magnetronmagnetronssplit-anode magnetron
Thermionic tubes still have some applications, such as the magnetron used in microwave ovens, certain high-frequency amplifiers, and amplifiers that audio enthusiasts prefer for their tube sound. Klystrons and magnetrons often operate their anodes (called collectors in klystrons) at ground potential to facilitate cooling, particularly with water, without high-voltage insulation.
The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series of open metal cavities (cavity resonators).