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Control Grid
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. The control grid usually consists of a cylindrical screen or helix of fine wire surrounding the cathode, and is surrounded in turn by the anode. The control grid was invented by Lee De Forest, who in 1906 added a grid to the Fleming valve ( thermionic diode) to create the first amplifying vacuum tube, the Audion (triode). Operation In a valve, the hot cathode emits negatively charged electrons, which are attracted to and captured by the anode, which is given a positive voltage by a power supply. The control grid between the cathode and anode functions as a "gate" to control the current of electrons reaching the anode. A more negative voltage on the grid will repel the electrons back toward the cathode so fewer get through to the anode. A less negative, or posi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triode Schematic Labeled
A triode is an electronic amplifying vacuum tube (or ''thermionic valve'' in British English) consisting of three electrodes inside an evacuated glass envelope: a heated filament or cathode, a grid, and a plate (anode). Developed from Lee De Forest's 1906 Audion, a partial vacuum tube that added a grid electrode to the thermionic diode (Fleming valve), the triode was the first practical electronic amplifier and the ancestor of other types of vacuum tubes such as the tetrode and pentode. Its invention helped make amplified radio technology and long-distance telephony possible. Triodes were widely used in consumer electronics devices such as radios and televisions until the 1970s, when transistors replaced them. Today, their main remaining use is in high-power RF amplifiers in radio transmitters and industrial RF heating devices. In recent years there has been a resurgence in demand for low power triodes due to renewed interest in tube-type audio systems by audiophiles who ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gold
Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal, a group 11 element, and one of the noble metals. It is one of the least reactivity (chemistry), reactive chemical elements, being the second-lowest in the reactivity series. It is solid under standard temperature and pressure, standard conditions. Gold often occurs in free elemental (native state (metallurgy), native state), as gold nugget, nuggets or grains, in rock (geology), rocks, vein (geology), veins, and alluvial deposits. It occurs in a solid solution series with the native element silver (as in electrum), naturally alloyed with other metals like copper and palladium, and mineral inclusions such as within pyrite. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides). Gold is resistant to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mullard
Mullard Limited was a British manufacturer of electronics, electronic components. The Mullard Radio Valve Co. Ltd. of Southfields, London, was founded in 1920 by Captain Stanley R. Mullard, who had previously designed thermionic valves (US term: vacuum tube) for the Admiralty before becoming managing director of the Z Electric Lamp Co. The company soon moved to Hammersmith, London and then in 1923 to Balham, London. The head office in later years was Mullard House at 1–19 Torrington Place, Bloomsbury, now part of University College London. Start-up In 1921, the directors were Sir Ralph Ashton (chairman), Basil Binyon of the Radio Communication Co, Cyril Frank Elwell, C.F. Elwell and S.R. Mullard (managing director). Partnership with Philips In 1923, to meet the technical demands of the newly formed BBC, Mullard formed a partnership with the Dutch manufacturer Philips. The vacuum tube, valves (vacuum tubes) produced in this period were named with the prefix PM, for Philip ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Screen Grid
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 (called ''anode'' in British English). 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 limitations of 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Miller Effect
In electronics, the Miller effect (named after its discoverer John Milton Miller) accounts for the increase in the equivalent input capacitance of an inverting voltage amplifier due to amplification of the effect of capacitance between the amplifier's input and output terminals, and is given by :C_=C (1+A_v)\, where -A_v is the voltage gain of the inverting amplifier (A_v positive) and C is the feedback capacitance. Although the term ''Miller effect'' normally refers to capacitance, any impedance connected between the input and another node exhibiting gain can modify the amplifier input impedance via this effect. These properties of the Miller effect are generalized in the Miller theorem. The Miller capacitance due to undesired parasitic capacitance between the output and input of active devices like transistors and vacuum tubes is a major factor limiting their gain at high frequencies. History When Miller published his work in 1919, he was working on vacuum tube triodes. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Grid Bias
In electronics, biasing is the setting of DC (direct current) operating conditions (current and voltage) of an electronic component that processes time-varying signals. Many electronic devices, such as diodes, transistors and vacuum tubes, whose function is processing time-varying ( AC) signals, also require a steady (DC) current or voltage at their terminals to operate correctly. This current or voltage is called ''bias''. The AC signal applied to them is superposed on this DC bias current or voltage. The operating point of a device, also known as bias point, quiescent point, or Q-point, is the DC voltage or current at a specified terminal of an active device (a transistor or vacuum tube) with no input signal applied. A bias circuit is a portion of the device's circuit that supplies this steady current or voltage. Overview In electronics, 'biasing' usually refers to a fixed DC voltage or current applied to a terminal of an electronic component such as a diode, transistor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
GRIDS TM11 662 FIG 39
Grid, The Grid, or GRID may refer to: Space partitioning * Regular grid A regular grid is a tessellation of ''n''-dimensional Euclidean space by Congruence_(geometry), congruent parallelepiped#Parallelotope, parallelotopes (e.g. bricks). Its opposite is Unstructured grid, irregular grid. Grids of this type appear on ..., a tessellation of space with translational symmetry, typically formed from parallelograms or higher-dimensional analogs ** Grid graph, a graph structure with nodes connected in a regular grid ** Square grid, a grid of squares ** Triangular grid, a grid of triangles ** Hexagonal grid, a grid of hexagons ** Unstructured grid, a tessellation of a space by simple shapes such as triangles or tetrahedra in an irregular pattern * Grid reference system, a coordinate system relative to a particular map projection * Grid (spatial index), a discretization of a geometric domain into a set of contiguous cells, used to organize information ** Discrete global grid (DGG), a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superheterodyne
A superheterodyne receiver, often shortened to superhet, is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency. It was invented by French radio engineer and radio manufacturer Lucien Lévy. Virtually all modern radio receivers use the superheterodyne principle. Precursors Early radio Early Morse code radio broadcasts were produced using an alternator connected to a spark gap. The output signal was at a carrier frequency defined by the physical construction of the gap, modulated by the alternating current signal from the alternator. Since the output frequency of the alternator was generally in the audible range, this produces an audible amplitude modulated (AM) signal. Simple radio detectors filtered out the high-frequency carrier, leaving the modulation, which was passed on to the user's headphones as an audible signal of d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hexode
The pentagrid converter is a type of radio receiving valve (vacuum tube) with five grids used as the frequency mixer stage of a superheterodyne radio receiver. The pentagrid was part of a line of development of valves that were able to take an incoming RF signal and change its frequency to a fixed intermediate frequency, which was then amplified and detected in the remainder of the receiver circuitry. The device was generically referred to as a ''frequency changer'' or just ''mixer''. Origins The first devices designed to change frequency in the manner described above seem to have been developed by the French, who simply put two grids into what would otherwise have been an ordinary triode valve (the bi-grille or bi-grid). Although technically a four electrode device, neither the term tetrode nor the tetrode valve as it is known today had yet appeared. The bi-grid differed from the later tetrode because the second (outer) grid was coarsely wound compared with the tetrode's scr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Noise Figure
Noise figure (NF) and noise factor (''F'') are figures of merit that indicate degradation of the signal-to-noise ratio (SNR) that is caused by components in a signal chain. These figures of merit are used to evaluate the performance of an amplifier or a radio receiver, with lower values indicating better performance. The noise factor is defined as the ratio of the output noise power of a device to the portion thereof attributable to thermal noise in the input termination at standard noise temperature ''T''0 (usually 290 K). The noise factor is thus the ratio of actual output noise to that which would remain if the device itself did not introduce noise, which is equivalent to the ratio of input SNR to output SNR. The noise ''factor'' and noise ''figure'' are related, with the former being a unitless ratio and the latter being the logarithm of the noise factor, expressed in units of decibels (dB). General The noise figure is the difference in decibel (dB) between the noise ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
