The siemens (symbol: S ) is the unit of electric conductance , electric susceptance , and electric admittance in the International System of Units (SI). Conductance, susceptance, and admittance are the reciprocals of resistance , reactance , and impedance respectively; hence one siemens is equal to the reciprocal of one ohm ( Ω ) and is also referred to as the mho . The siemens was adopted by the IEC in 1935, and the 14th General Conference on Weights and Measures approved the addition of the siemens as a derived unit in 1971.
19-405: MHO or mho may refer to: Mho , a former name for the siemens (unit) Metabolically healthy obesity (MHO) Mashi language (ISO 639-3 language code mho) Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title MHO . If an internal link led you here, you may wish to change
38-428: A triple-grid amplifier in some literature ) was developed from the screen-grid tube or shield-grid tube (a type of tetrode tube) by the addition of a grid between the screen grid and the plate. The screen-grid tube was limited in performance as an amplifier due to secondary emission of electrons from the plate. The additional grid is called the suppressor grid . The suppressor grid is usually operated at or near
57-635: Is an inverted capital Greek letter omega : U+2127 ℧ INVERTED OHM SIGN . NIST 's Guide for the Use of the International System of Units (SI) refers to the mho as an "unaccepted special name for an SI unit", and indicates that it should be strictly avoided. The SI term siemens is used universally in science and often in electrical applications, while mho is still used in some electronic contexts. The inverted capital omega symbol (℧), while not an official SI abbreviation,
76-499: Is less likely to be confused with a variable than the letter "S" when writing the symbol by hand. The usual typographical distinctions (such as italic for variables and roman for units) are difficult to maintain. Likewise, it is difficult to distinguish the symbol "S" ( siemens ) from the lower-case "s" ( seconds ), potentially causing confusion. So, for example, a pentode ’s transconductance of 2.2 mS might alternatively be written as 2.2 m℧ or 2200 μ℧ (most common in
95-445: Is the electric current through the object and V is the voltage (electrical potential difference) across the object. The unit siemens for the conductance G is defined by where Ω is the ohm , A is the ampere , and V is the volt . For a device with a conductance of one siemens, the electric current through the device will increase by one ampere for every increase of one volt of electric potential difference across
114-441: Is then said to be "triode-strapped" or "triode-connected". This is sometimes provided as an option in audiophile pentode amplifier circuits, to give the sought-after "sonic qualities" of a triode power amplifier. A resistor may be included in series with the screen grid to avoid exceeding the screen grid's power or voltage rating, and to prevent local oscillation. Triode-connection is a useful option for audiophiles who wish to avoid
133-690: The 7AK7 tube was expressly developed for use in computer equipment. After World War II, pentodes were widely used in TV receivers, particularly the successor to the EF50, the EF80. Vacuum tubes were replaced by transistors during the 1960s. However, they continue to be used in certain applications, including high-power radio transmitters and (because of their well-known valve sound ) in high-end and professional audio applications, microphone preamplifiers and electric guitar amplifiers . Large stockpiles in countries of
152-427: The 1930s) or 2.2 mA/V . The ohm had officially replaced the old " siemens unit" , a unit of resistance , at an international conference in 1881. Pentode A pentode is an electronic device having five electrodes . The term most commonly applies to a three-grid amplifying vacuum tube or thermionic valve that was invented by Gilles Holst and Bernhard D.H. Tellegen in 1926. The pentode (called
171-431: The 1960s to 1970s, during which time transistors replaced tubes in new designs. During the first quarter of the 21st century, a few pentode tubes have been in production for high power radio frequency applications, musical instrument amplifiers (especially guitars), home audio and niche markets. The simple tetrode or screen-grid tube offered a larger amplification factor, more power and a higher frequency capability than
190-416: The anode are repelled by the negative potential on the suppressor grid, so they can't reach the screen grid but return to the anode. The primary electrons from the cathode have a higher kinetic energy, so they can still pass through the suppressor grid and reach the anode. Pentodes, therefore, can have higher current outputs and a wider output voltage swing; the anode/plate can even be at a lower voltage than
209-465: The cathode hit the anode with more energy, knocking out more secondary electrons, increasing this current of electrons leaving the anode. The result is that in the tetrode the anode current I a is found to decrease with increasing anode voltage V a , over part of the characteristic curve . This property (Δ V a /Δ I a < 0) is called negative resistance . It can cause the tetrode to become unstable, leading to parasitic oscillations in
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#1732800908841228-401: The device. The conductance of a resistor with a resistance of five ohms, for example, is (5 Ω) , which is equal to a conductance of 200 mS. A historical equivalent for the siemens is the mho ( / ˈ m oʊ / ). The name is derived from the word ohm spelled backwards as the reciprocal of one ohm, at the suggestion of Sir William Thomson (Lord Kelvin) in 1883. Its symbol
247-403: The earlier triode . However, in the tetrode secondary electrons knocked out of the anode (plate) by the electrons from the cathode striking it (a process called secondary emission ) can flow to the screen grid due to its relatively high potential. This current of electrons leaving the anode reduces the net anode current I a . As the anode voltage V a is increased, the electrons from
266-470: The former Soviet Union have provided a continuing supply of such devices, some designed for other purposes but adapted to audio use, such as the GU-50 transmitter tube. A pentode can have its screen grid (grid 2) connected to the anode (plate), in which case it reverts to an ordinary triode with commensurate characteristics (lower anode resistance, lower mu, lower noise, more drive voltage required). The device
285-412: The link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=MHO&oldid=1010761336 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Mho The unit is named after Ernst Werner von Siemens . In English,
304-418: The output, called dynatron oscillations in some circumstances. The pentode, as introduced by Tellegen , has an additional electrode, or third grid, called the suppressor grid , located between the screen grid and the anode, which solves the problem of secondary emission. The suppressor grid is given a low potential—it is usually either grounded or connected to the cathode. Secondary emission electrons from
323-418: The potential of the cathode and prevents secondary emission electrons from the plate from reaching the screen grid. The addition of the suppressor grid permits much greater output signal amplitude to be obtained from the plate of the pentode in amplifier operation than from the plate of the screen-grid tube at the same plate supply voltage. Pentodes were widely manufactured and used in electronic equipment until
342-480: The same word siemens is used both for the singular and plural. Like other SI units named after people, the symbol (S) is capitalized but the name of the unit is not. For the siemens this distinguishes it from the second , symbol (lower case) s. The related property, electrical conductivity , is measured in units of siemens per metre (S/m). For an element conducting direct current , electrical resistance R and electrical conductance G are defined as where I
361-620: The screen grid yet still amplify well. Pentode tubes were first used in consumer-type radio receivers. A well-known pentode type, the EF50 , was designed before the start of World War II, and was extensively used in radar sets and other military electronic equipment. The pentode contributed to the electronic preponderance of the Allies. The Colossus computer and the Manchester Baby used large numbers of EF36 pentode tubes. Later on,
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