What is "tetrode"

n. 1 A thermionic valve similar to a triode with the addition of a screen grid to protect the control grid 2 A dynatron

n. a thermionic tube having four electrodes

A tetrode is a vacuum tube (called valve in British English) having four active electrodes. The four electrodes in order from the centre are: a thermionic cathode, first and second grids and a plate. There are several varieties of tetrodes, the most common being the screen-grid tube and the beam tetrode. In screen-grid tubes and beam tetrodes, the first grid is the control grid and the second grid is the screen grid. In other tetrodes one of the grids is a control grid, while the other may have a variety of functions.

The tetrode was developed in the 1920s by adding an additional grid to the first amplifying vacuum tube, the triode, to correct deficiencies in the triode. During the period 1913 to 1927, three distinct types of tetrode valves appeared. All had a normal control grid whose function was to act as a primary control for current passing through the tube, but they differed according to the intended function of the other grid. In order of historical appearance these are: the space-charge grid tube, the bi-grid valve, and the screen-grid tube. The last of these appeared in two distinct variants with different areas of application: the screen-grid valve proper, which was used for medium-frequency, small signal amplification, and the beam tetrode which appeared later, and was used for audio or radio-frequency power amplification. The former was quickly superseded by the rf pentode, while the latter was initially developed as an alternative to the pentode as an audio power amplifying device. The beam tetrode was also developed as a high power radio transmitting tube.

Tetrodes were widely used in many consumer electronic devices such as radios, televisions, and audio systems until transistors replaced valves in the 1960s and 70s. Beam tetrodes have remained in use until quite recently in power applications such as audio amplifiers and radio transmitters.

A tetrode is a type of electrode used in neuroscience for electrophysiological recordings. They are generally used to record the extracellular field potentials from nervous tissue, e.g. the brain. Tetrodes are constructed by bundling together four very small electrodes; each wire is generally less than 30 μm in diameter. Tetrodes are used to classify extra-cellular action potentials into sets generated by the individual neurons, as each channel of the tetrode is usually close enough to a cell such that action potentials emitted by that cell are detected on each of the four channels, but because of the spatial distribution of the individual channels, the amplitude of the signal varies across the four channels.

Tetrode can refer to:

• Tetrode, an electronic device with four active electrodes, such as a vacuum tube
  • Beam tetrode
  • Field effect tetrode, a solid-state device
• Tetrode (biology), an electrode used in biology to sample neural signals
• Tetrode transistor, a transistor with four active terminals
• Sackur–Tetrode equation, an expression for the entropy of a monatomic classical ideal gas
• Hugo Tetrode, a Dutch physicist (1895 - 1931)
• Willem Danielsz van Tetrode, a Dutch sculptor (ca. 1530 - ca. 1587)

Tetrode, also given as van Tetrode and spelled variously as Tetterode, Tetteroo, Tettero, Thetrode and Tetroe, was a Dutch medieval noble family which later became a prominent patrician family in Holland. The most famous member of this family was the 16th-Century sculptor Willem Danielsz van Tetrode, who hailed from Delft. The coat of arms of the Tetrode family, showing three leaves of the yellow water-lily, is now used as the municipal coat of arms of Bloemendaal (which includes Overveen, formerly the estate of Tetterode).

The family name refers to the medieval clearing of forest in the area of dunes directly west of Haarlem, in what is now Overveen, to make the land suitable for cultivation. Rode means "clearing of land" while Tet may have been the first name of the original owner of the land. The eldest known member of the family is Gerard van Tetrode, who in 1310 donated land in the centre of Haarlem to build St. John's monastery; the monastery's church still exists today as the Janskerk (St. John's Church). The family had a fiefdom called Tetterode in what is now Overveen, west of Haarlem. There they built a fortified house or castle called Saxenburg. The house was sketched by Rembrandt in 1651. Salomon van Ruysdael painted Haarlem from the dunes of Tetterode in the early 17th Century. The place name Tetterode disappears from maps around 1648.

The Tetrodes were particularly prominent in Leiden, where members of this rich and influential family of brewers served as burgomasters and aldermen, sheriffs, militia officers and church officials. Aernt van Tetrode (circa 1430-1471), sheriff and priest in Wassenaar, is considered the founder of the South Holland branch of the family. His son Willem van Tetrode was a rich brewer who built a hofje for the elderly in Leiden, the Sint Stevenshofje (also called Convent van Tetterode). This 15th-Century hofje still exists today.

Elisabeth van Tetrode was the grandmother of the Leiden-born painter Rembrandt (1606-1669). However, she was actually not a member of the Tetrode family but assumed the noble name because she had a cousin who had married into the Tetrode family.