A tetrode is a vacuum tube having four active electrodes. There are several varieties of tetrode with screen-grid tube, and the beam tetrode being the most common. The four electrodes in order from the centre are: a thermionic cathode, first and second grids and a plate. 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.
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 The former was quickly superseded by the rf pentode, while the latter was initially developed as an alternative to the pentode as an audio power amplifying device.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, and has remained in use until quite recently in both applications.
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.
Tetrode can refer to:
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