Triode

Examples of low power triodes from 1918 (left) to miniature tubes of the 1960s (right)
De Forest Audion tube from 1908, the first triode. The flat plate is visible on the top, with the zigzag wire grid under it. The filament was originally present under the grid but was burnt out.
Lieben-Reisz tube, another primitive triode developed the same time as the Audion by Robert von Lieben
Structure of a modern low-power triode vacuum tube. The glass and outer electrodes are shown partly cut away to reveal the construction.
Schematic symbol used in circuit diagrams for a triode, showing symbols for electrodes.
Soviet lighthouse tube 6С5Д (6S5D)
ECC83 triode operating characteristic.

Electronic amplifying vacuum tube consisting of three electrodes inside an evacuated glass envelope: a heated filament or cathode, a grid, and a plate (anode).

- Triode
Examples of low power triodes from 1918 (left) to miniature tubes of the 1960s (right)

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Modern surface-mount electronic components on a printed circuit board, with a large integrated circuit at the top.

Electronics

Branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices.

Branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices.

Modern surface-mount electronic components on a printed circuit board, with a large integrated circuit at the top.
One of the earliest Audion radio receivers, constructed by De Forest in 1914.
Electronics technician performing a voltage check on a power circuit card in the air navigation equipment room aboard the aircraft carrier USS Abraham Lincoln (CVN-72).
Hitachi J100 adjustable frequency drive chassis

Practical applications started with the invention of the diode by Ambrose Fleming and the triode by Lee De Forest in the early 1900s, which made the detection of small electrical voltages such as radio signals from a radio antenna possible with a non-mechanical device.

Triode Audion from 1908. The filament (which was also the cathode) was at the lower left inside the tube, but the filament has burned out and is no longer present. The filament's connecting and supporting wires are visible. The plate is at the middle top, and the grid is the serpentine electrode below it. The plate and grid connections leave the tube at the right.

Audion

For other uses, see Audion (disambiguation).

For other uses, see Audion (disambiguation).

Triode Audion from 1908. The filament (which was also the cathode) was at the lower left inside the tube, but the filament has burned out and is no longer present. The filament's connecting and supporting wires are visible. The plate is at the middle top, and the grid is the serpentine electrode below it. The plate and grid connections leave the tube at the right.
An Audion radio receiver by de Forest. The Audion tubes were mounted upside down to prevent the delicate filaments from sagging and touching the grids. This receiver provided the ability to choose operation of either one of the two provided detector tubes. Image from Proceedings of the Institute of Radio Engineers, March 1914.
General Electric Company Pliotron
The first Audion AM radio transmitter, built by Lee de Forest and announced April, 1914
Some of the earliest Audion AM radio transmitters, built by de Forest around 1916. The invention of the Audion oscillator in 1912 made inexpensive sound radio transmission possible, and was responsible for the advent of radio broadcasting around 1920.
Audion advertisement, Electrical Experimenter magazine, 1916
1973 postage stamp honoring de Forest's audion

It was the first triode, consisting of an evacuated glass tube containing three electrodes: a heated filament, a grid, and a plate.

Schematic symbol used in circuit diagrams for a vacuum tube, showing control grid

Control grid

Schematic symbol used in circuit diagrams for a vacuum tube, showing control grid
Structure of a modern low-power triode vacuum tube. The glass and outer electrodes are shown partly cut away to reveal the construction.
Illustration representing various control grid configurations

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.

Later thermionic vacuum tubes, mostly miniature style, some with top cap connections for higher voltages

Vacuum tube

Device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.

Device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.

Later thermionic vacuum tubes, mostly miniature style, some with top cap connections for higher voltages
Audio power amplifier using tubes, in operation. Red-orange glow is from heated filaments.
Illustration representing a primitive triode vacuum tube and the polarities of the typical dc operating potentials. Not shown are the impedances (resistors or inductors) that would be included in series with the C and B voltage sources.
Radio station signal generator with vacuum tubes
One of Edison's experimental bulbs
Fleming's first diodes
The first triode, the de Forest Audion, invented in 1906
Triodes as they evolved over 40 years of tube manufacture, from the RE16 in 1918 to a 1960s era miniature tube
Triode symbol. From top to bottom: plate (anode), control grid, cathode, heater (filament)
General Electric Company Pliotron, Science History Institute
Tetrode symbol. From top to bottom: plate (anode), screen grid, control grid, cathode, heater (filament).
The useful region of operation of the screen grid tube (tetrode) as an amplifier is limited to anode potentials in the straight portions of the characteristic curves greater than the screen grid potential.
The pentagrid converter contains five grids between the cathode and the plate (anode)
Beam power tube designed for radio frequency use
Miniature tube (right) compared to the older octal style. Not including pins, the larger tube, a 5U4GB, is 93 mm high with a 35 mm diameter base, while the smaller, a 9-pin 12AX7, is 45 mm high, and 20.4 mm in diameter.
Subminiature CV4501 tube (SQ version of EF72), 35 mm long x 10 mm diameter (excluding leads)
RCA 6DS4 "Nuvistor" triode, c. 20 mm high by 11 mm diameter
Commercial packaging for vacuum tubes used in the latter half of the 20th century including boxes for individual tubes (bottom right), sleeves for rows of the boxes (left), and bags that smaller tubes would be put in by a store upon purchase (top right)
The 1946 ENIAC computer used 17,468 vacuum tubes and consumed 150 kW of power
Vacuum tubes seen on end in a recreation of the World War II-era Colossus computer at Bletchley Park, England
Circuitry from core memory unit of Whirlwind
The anode (plate) of this transmitting triode has been designed to dissipate up to 500 W of heat
Metal-cased tubes with octal bases
Triode tube type GS-9B; designed for use at radio frequencies up to 2000 MHz and rated for 300 watts anode power dissipation. The finned heat sink provides conduction of heat from anode to air stream.
Voltage-regulator tube in operation. Low-pressure gas within tube glows due to current flow.
Batteries for a vacuum-tube circuit. The C battery is highlighted.
Tube tester manufactured in 1930.
Getter in opened tube; silvery deposit from getter
Dead vacuum fluorescent display (air has leaked in and the getter spot has become white)
Universal vacuum tube tester
70-watt tube-hybrid audio amplifier
Typical Triode Plate Characteristics

Devices with three elements are triodes used for amplification and switching.

Size comparison of BJT transistor packages, from left to right: SOT-23, TO-92, TO-126, TO-3

Transistor

Semiconductor device used to amplify or switch electrical signals and power.

Semiconductor device used to amplify or switch electrical signals and power.

Size comparison of BJT transistor packages, from left to right: SOT-23, TO-92, TO-126, TO-3
Metal-oxide-semiconductor field-effect transistor (MOSFET), showing gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink).
Julius Edgar Lilienfeld proposed the concept of a field-effect transistor in 1925.
John Bardeen, William Shockley and Walter Brattain at Bell Labs in 1948. Bardeen and Brattain invented the point-contact transistor in 1947 and Shockley the bipolar junction transistor in 1948.
A replica of the first working transistor, a point-contact transistor invented in 1947
Herbert Mataré in 1950. He independently invented a point-contact transistor in June 1948.
Philco surface-barrier transistor developed and produced in 1953
A Darlington transistor opened up so the actual transistor chip (the small square) can be seen inside. A Darlington transistor is effectively two transistors on the same chip. One transistor is much larger than the other, but both are large in comparison to transistors in large-scale integration because this particular example is intended for power applications.
A simple circuit diagram to show the labels of an n–p–n bipolar transistor
BJT used as an electronic switch, in grounded-emitter configuration
Amplifier circuit, common-emitter configuration with a voltage-divider bias circuit
Operation of a FET and its Id-Vg curve. At first, when no gate voltage is applied, there are no inversion electrons in the channel, so the device is turned off. As gate voltage increases, the inversion electron density in the channel increases, current increases, and thus the device turns on.
Transistor symbol created on Portuguese pavement in the University of Aveiro
Assorted discrete transistors
Soviet KT315b transistors

The thermionic triode, a vacuum tube invented in 1907, enabled amplified radio technology and long-distance telephony.

4-1000A 1 KW radial beam power tetrode in an amateur radio transmitter

Tetrode

Vacuum tube having four active electrodes.

Vacuum tube having four active electrodes.

4-1000A 1 KW radial beam power tetrode in an amateur radio transmitter
Tetrode of the Bi-Grid Valve type
Circuit using bi-grid tetrode oscillator as AM transmitter
View of the interior of an Osram S23 screen grid valve. In this valve the anode is in the form of two flat plates. The wires of the screen grid can also be seen. The anode connection is at the top of the envelope to minimise anode-grid capacitance
At anode voltages less than that of the screen grid, the tetrode characteristic curves are kinked due to secondary emission from the anode. In the normal range of anode voltages, the anode current is substantially constant with respect to anode voltage. Both features are quite unlike the corresponding curves for a triode, for which anode current increases continuously with increasing slope throughout.
The Marconi-Osram S625, the first commercially produced screen grid tube. The screen is a cylinder with a metal gauze face that completely surrounds the anode, and the tube is double-ended, with the anode terminal at one end and the grid at the other, to improve isolation between the electrodes.
Two S23 screen grid valves in a 1929 Osram Music Magnet receiver
Typical triode anode characteristics
Typical pentode anode characteristic. There are a wide range of anode voltages over which the characteristic has a small positive slope. In a screen-grid tube this region is restricted to anode voltages greater than that of the screen grid.
EIMAC 4-250A radial beam power tetrode
Top view cross-section showing typical 6L6 type electrode structures and beam formation
Typical beam tetrode anode characteristics. The anode characteristics of beam tetrodes are very similar to those of pentodes.

The tetrode was developed in the 1920s by adding an additional grid to the first amplifying vacuum tube, the triode, to correct limitations of the triode.

A high power vacuum diode used in radio equipment as a rectifier.

Diode

Two-terminal electronic component that conducts current primarily in one direction ; it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other.

Two-terminal electronic component that conducts current primarily in one direction ; it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other.

A high power vacuum diode used in radio equipment as a rectifier.
Various semiconductor diodes. Bottom: A bridge rectifier. In most diodes, a white or black painted band identifies the cathode into which electrons will flow when the diode is conducting. Electron flow is the reverse of conventional current flow.
Close-up view of a silicon diode. The anode is on the right side; the cathode is on the left side (where it is marked with a black band). The square silicon crystal can be seen between the two leads.
Structure of a vacuum tube diode. The filament itself may be the cathode, or more commonly (as shown here) used to heat a separate metal tube which serves as the cathode.
A vacuum tube containing two power diodes
Close-up of an EFD108 germanium point-contact diode in DO7 glass package, showing the sharp metal wire (cat whisker) that forms the semiconductor junction.
I–V (current vs. voltage) characteristics of a p–n junction diode
A PN junction diode in forward bias mode, the depletion width decreases. Both p and n junctions are doped at a 1e15/cm3 doping level, leading to built-in potential of ~0.59V. Observe the different quasi Fermi levels for conduction band and valence band in n and p regions (red curves).
A simple envelope demodulator circuit.
Schematic of basic ac-to-dc power supply
This simple diode clamp will clamp the negative peaks of the incoming waveform to the common rail voltage
Diode
Light-emitting diode (LED)
Photodiode
Schottky diode
Transient-voltage-suppression diode (TVS)
Tunnel diode
Varicap
Zener diode
Typical diode packages in same alignment as diode symbol. Thin bar depicts the cathode.

The word diode, however, as well as triode, tetrode, pentode, hexode, were already in use as terms of multiplex telegraphy.

Long wave radio broadcasting station, Motala, Sweden

Radio broadcasting

Transmission of audio , sometimes with related metadata, by radio waves to radio receivers belonging to a public audience.

Transmission of audio , sometimes with related metadata, by radio waves to radio receivers belonging to a public audience.

Long wave radio broadcasting station, Motala, Sweden
Slovak Radio Building, Bratislava, Slovakia (architects: Štefan Svetko, Štefan Ďurkovič and Barnabáš Kissling, 1967–1983)
Broadcasting tower in Trondheim, Norway
Advertisement placed in the November 5, 1919 Nieuwe Rotterdamsche Courant announcing PCGG's debut broadcast scheduled for the next evening.
Use of a sound broadcasting station
Transmission diagram of sound broadcasting (AM and FM)
AM broadcasting stations in 2006
FM radio broadcast stations in 2006
Worldwide presence of Radio Maria broadcasters.

The triode (mercury-vapor filled with a control grid) was created on March 4, 1906, by the Austrian Robert von Lieben independent from that, on October 25, 1906, Lee De Forest patented his three-element Audion.

Headphones on a stand

Headphones

Headphones are a pair of small loudspeaker drivers worn on or around the head over a user's ears.

Headphones are a pair of small loudspeaker drivers worn on or around the head over a user's ears.

Headphones on a stand
Wireless headphones
Bone conduction headphones.
Brandes radio headphones, circa 1920
Sennheiser HD 555 headphones, used in audio production environments (2007)
Headphone cord with integrated potentiometer for volume regulation
Circumaural headphones have large pads that surround the outer ear.
A pair of supra-aural (on-ear) headphones
In-ear monitors extend into the ear canal, providing isolation from outside noise.
A typical example of a headset used for voice chats
Sony Ericsson Cordless bluetooth headset
Lightspeed Aviation 30 3G ANR Aviation headset used by aviators
In-ears are among those good for noise isolation.
A typical moving-coil headphone transducer
Electrostatic loudspeaker diagram
Balanced armature transducer with armature balanced and exerting no force on diaphragm
A custom in-ear monitor which uses 8 balanced armatures in a triple crossover configuration (4 low/2 mid/2 high). Headphone designs often use multiple balanced armatures to provide a higher fidelity sound.
Sony MDR-7506 headphones in stowed configuration
Product testing - headphones in an anechoic chamber

Impedance of 1,000 to 2,000 ohms was common, which suited both crystal sets and triode receivers.

Lee de Forest c. 1904

Lee de Forest

American inventor and early pioneer in radio and in the development of sound-on-film recording used for motion pictures.

American inventor and early pioneer in radio and in the development of sound-on-film recording used for motion pictures.

Lee de Forest c. 1904
De Forest, some time between 1914 and 1922, with two of his Audions, a small 1 watt receiving tube (left), and a later 250-watt transmitting power tube (right), which he called an "oscillion".
American DeForest Wireless Telegraph Company's observation tower, 1904 Louisiana Purchase Exposition at Saint Louis, Missouri
Ohio Historical Marker. On July 18, 1907 Lee de Forest transmitted the first ship-to-shore messages that were sent by radiotelephone
February 24, 1910 radio broadcast by Mme. Mariette Mazarin of the Manhattan Opera Company.
De Forest grid Audion from 1906.
California Historical Landmark No. 836, located at the eastern corner of Channing Street and Emerson Avenue in Palo Alto, California, stands at the former location of the Federal Telegraph laboratory, and references Lee de Forest's development there, in 1911–1913, of "the first vacuum-tube amplifier and oscillator".
Audion advertisement, Electrical Experimenter magazine, August 1916
De Forest broadcasting Columbia phonograph records (October 1916)
Poster promoting a Phonofilm demonstration (December 1925)
Lee De Forest visiting Beckman Industries in Germany, 1955
The DeForest Lofts at Santana Row, San Jose, California, are in this building named for Lee de Forest.
Mary Mayo, his third wife

His most famous invention, in 1906, was the three-element "Audion" (triode) vacuum tube, the first practical amplification device.