86-652: The Harwell computer , or Harwell Dekatron computer , later known as the Wolverhampton Instrument for Teaching Computing from Harwell ( WITCH ), is an early British computer of the 1950s based on valves and relays . From 2009 to 2012, it was restored at the National Museum of Computing . In 2013, for the second time, the Guinness Book of World Records recognised it as the world's oldest working digital computer , following its restoration. It previously held
172-490: A Computer Conservation Society project. The museum, a registered charity, invited members of the public and industry to sponsor the restoration of the Harwell computer by purchasing one of 25 shares at £4,500 each. In 2012, the restoration was completed successfully. A 9 by 7 feet (2.7 m × 2.1 m) painting of the machine, Portrait of a Dead WITCH was made by the artist John Yeadon in 1983. After being exhibited at
258-693: A European Space Agency training camp as part of a British Association of Planetaria conference. The Planetarium can be noticed if you look closely in the Minibrum Area. The museum shares the Millennium Point building with Birmingham City University , and is situated in the Eastside district. It lies near Aston University and the Gun Quarter – which was for many years the centre of world's gun-manufacturing industry. Immediately opposite are The Woodman ,
344-423: A World War I memorial event. Aside from projecting stars, digital planetariums can fill the dome with 360˚ of sound and video, and are therefore also known as immersive cinemas or ' fulldome ' theatres. The planetarium displays films about space and the night sky, the human body and undersea exploration , as well as music and light shows. In September 2014 it was used to provide a live link with Tim Peake at
430-410: A hot cathode for fundamental electronic functions such as signal amplification and current rectification . Non-thermionic types such as a vacuum phototube , however, achieve electron emission through the photoelectric effect , and are used for such purposes as the detection of light intensities. In both types, the electrons are accelerated from the cathode to the anode by the electric field in
516-404: A beam of electrons for display purposes (such as the television picture tube, in electron microscopy , and in electron beam lithography ); X-ray tubes ; phototubes and photomultipliers (which rely on electron flow through a vacuum where electron emission from the cathode depends on energy from photons rather than thermionic emission ). A vacuum tube consists of two or more electrodes in
602-550: A blower, or water-jacket. Klystrons and magnetrons often operate their anodes (called collectors in klystrons) at ground potential to facilitate cooling, particularly with water, without high-voltage insulation. These tubes instead operate with high negative voltages on the filament and cathode. Except for diodes, additional electrodes are positioned between the cathode and the plate (anode). These electrodes are referred to as grids as they are not solid electrodes but sparse elements through which electrons can pass on their way to
688-637: A blue glow. Finnish inventor Eric Tigerstedt significantly improved on the original triode design in 1914, while working on his sound-on-film process in Berlin, Germany. Tigerstedt's innovation was to make the electrodes concentric cylinders with the cathode at the centre, thus greatly increasing the collection of emitted electrons at the anode. Irving Langmuir at the General Electric research laboratory ( Schenectady, New York ) had improved Wolfgang Gaede 's high-vacuum diffusion pump and used it to settle
774-401: A certain sound or tone). Not all electronic circuit valves or electron tubes are vacuum tubes. Gas-filled tubes are similar devices, but containing a gas, typically at low pressure, which exploit phenomena related to electric discharge in gases , usually without a heater. One classification of thermionic vacuum tubes is by the number of active electrodes . A device with two active elements
860-498: A combination of a triode with a hexode and even an octode have been used for this purpose. The additional grids include control grids (at a low potential) and screen grids (at a high voltage). Many designs use such a screen grid as an additional anode to provide feedback for the oscillator function, whose current adds to that of the incoming radio frequency signal. The pentagrid converter thus became widely used in AM receivers, including
946-466: A common circuit (which can be AC without inducing hum) while allowing the cathodes in different tubes to operate at different voltages. H. J. Round invented the indirectly heated tube around 1913. The filaments require constant and often considerable power, even when amplifying signals at the microwatt level. Power is also dissipated when the electrons from the cathode slam into the anode (plate) and heat it; this can occur even in an idle amplifier due to
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#17330857727921032-579: A far superior and versatile technology for use in radio transmitters and receivers. At the end of the 19th century, radio or wireless technology was in an early stage of development and the Marconi Company was engaged in development and construction of radio communication systems. Guglielmo Marconi appointed English physicist John Ambrose Fleming as scientific advisor in 1899. Fleming had been engaged as scientific advisor to Edison Telephone (1879), as scientific advisor at Edison Electric Light (1882), and
1118-400: A low potential space charge region between the anode and screen grid to return anode secondary emission electrons to the anode when the anode potential is less than that of the screen grid. Formation of beams also reduces screen grid current. In some cylindrically symmetrical beam power tubes, the cathode is formed of narrow strips of emitting material that are aligned with the apertures of
1204-615: A new building. The former museum closed in 1997, and Thinktank opened on 29 September 2001 as part of the £114-million Millennium Point complex. It was funded by Birmingham City Council, supported by the Millennium Commission . The area adjacent to the building is designated Eastside City Park . While many objects were put on display at Thinktank, others were stored at the Birmingham Museum Collection Centre , and some were brought out of storage. Although
1290-414: A pair of beam deflection electrodes which deflected the current towards either of two anodes. They were sometimes known as the 'sheet beam' tubes and used in some color TV sets for color demodulation . The similar 7360 was popular as a balanced SSB (de)modulator . A beam tetrode (or "beam power tube") forms the electron stream from the cathode into multiple partially collimated beams to produce
1376-412: A power consumption of 1.5 kW. Output was to either a Creed teleprinter or to a paper tape punch. The machine was decimal and initially had twenty eight-digit dekatron registers for internal storage, which was increased to 40 which appeared to be enough for nearly all calculations. It was assembled from components more commonly found in a British telephone exchange . The man who led the effort to rebuild
1462-412: A printing instrument was needed. As a result of experiments conducted on Edison effect bulbs, Fleming developed a vacuum tube that he termed the oscillation valve because it passed current in only one direction. The cathode was a carbon lamp filament, heated by passing current through it, that produced thermionic emission of electrons. Electrons that had been emitted from the cathode were attracted to
1548-506: A relatively low-value resistor is connected between the cathode and ground. This makes the cathode positive with respect to the grid, which is at ground potential for DC. However C batteries continued to be included in some equipment even when the "A" and "B" batteries had been replaced by power from the AC mains. That was possible because there was essentially no current draw on these batteries; they could thus last for many years (often longer than all
1634-407: A simple oscillator only requiring connection of the plate to a resonant LC circuit to oscillate. The dynatron oscillator operated on the same principle of negative resistance as the tunnel diode oscillator many years later. The dynatron region of the screen grid tube was eliminated by adding a grid between the screen grid and the plate to create the pentode . The suppressor grid of the pentode
1720-419: A small-signal vacuum tube are 1 to 10 millisiemens. It is one of the three 'constants' of a vacuum tube, the other two being its gain μ and plate resistance R p or R a . The Van der Bijl equation defines their relationship as follows: g m = μ R p {\displaystyle g_{m}={\mu \over R_{p}}} The non-linear operating characteristic of
1806-566: A theme, in general going from the past, in The Past (Level 0), through The Balcony (Level 1) and The Present (Level 2), to the future, in The Future gallery (Level 3). It has lost its theme as new items have been added. It is used to display stars as they would appear from on Earth at any point in time, and to simulate travel to the stars. On 4 August 2014 it was used to project the night sky as it would have appeared on 3 August 1914, as part of
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#17330857727921892-464: A vacuum inside an airtight envelope. Most tubes have glass envelopes with a glass-to-metal seal based on kovar sealable borosilicate glasses , although ceramic and metal envelopes (atop insulating bases) have been used. The electrodes are attached to leads which pass through the envelope via an airtight seal. Most vacuum tubes have a limited lifetime, due to the filament or heater burning out or other failure modes, so they are made as replaceable units;
1978-429: A wide range of frequencies. To combat the stability problems of the triode as a radio frequency amplifier due to grid-to-plate capacitance, the physicist Walter H. Schottky invented the tetrode or screen grid tube in 1919. He showed that the addition of an electrostatic shield between the control grid and the plate could solve the problem. This design was refined by Hull and Williams. The added grid became known as
2064-445: Is a current . Compare this to the behavior of the bipolar junction transistor , in which the controlling signal is a current and the output is also a current. For vacuum tubes, transconductance or mutual conductance ( g m ) is defined as the change in the plate(anode)/cathode current divided by the corresponding change in the grid to cathode voltage, with a constant plate(anode) to cathode voltage. Typical values of g m for
2150-489: Is a diode , usually used for rectification . Devices with three elements are triodes used for amplification and switching . Additional electrodes create tetrodes , pentodes , and so forth, which have multiple additional functions made possible by the additional controllable electrodes. Other classifications are: Vacuum tubes may have other components and functions than those described above, and are described elsewhere. These include as cathode-ray tubes , which create
2236-597: Is a science museum in Birmingham , England . Opened in 2001, it is part of Birmingham Museums Trust and is located within the Millennium Point complex on Curzon Street, Digbeth . The Birmingham Collection of Science & Industry was started in the mid-19th century, initially consisting of collections of weapons from the gun trade and the Birmingham Proof House . The Birmingham Museum & Art Gallery opened in 1885, including science collections. In 1951,
2322-488: Is capable of running for long periods unattended and the time spent performing useful computations is a large proportion of the total time available". The design was noted for its reliability because in the period from May 1952 until February 1953 it averaged 80 hours per week running time. Dr Jack Howlett , Director of the Computer Laboratory at AERE 1948–61, said it "could be left unattended for long periods; I think
2408-410: Is not important since they are simply re-captured by the plate. But in a tetrode they can be captured by the screen grid since it is also at a positive voltage, robbing them from the plate current and reducing the amplification of the tube. Since secondary electrons can outnumber the primary electrons over a certain range of plate voltages, the plate current can decrease with increasing plate voltage. This
2494-551: Is the Loewe 3NF . This 1920s device has three triodes in a single glass envelope together with all the fixed capacitors and resistors required to make a complete radio receiver. As the Loewe set had only one tube socket, it was able to substantially undercut the competition, since, in Germany, state tax was levied by the number of sockets. However, reliability was compromised, and production costs for
2580-416: Is the dynatron region or tetrode kink and is an example of negative resistance which can itself cause instability. Another undesirable consequence of secondary emission is that screen current is increased, which may cause the screen to exceed its power rating. The otherwise undesirable negative resistance region of the plate characteristic was exploited with the dynatron oscillator circuit to produce
2666-556: The Edison effect , that became well known. Although Edison was aware of the unidirectional property of current flow between the filament and the anode, his interest (and patent ) concentrated on the sensitivity of the anode current to the current through the filament (and thus filament temperature). It was years later that John Ambrose Fleming applied the rectifying property of the Edison effect to detection of radio signals, as an improvement over
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2752-661: The plate ( anode ) when the plate was at a positive voltage with respect to the cathode. Electrons could not pass in the reverse direction because the plate was not heated and not capable of thermionic emission of electrons. Fleming filed a patent for these tubes, assigned to the Marconi company, in the UK in November 1904 and this patent was issued in September 1905. Later known as the Fleming valve ,
2838-429: The screen grid or shield grid . The screen grid is operated at a positive voltage significantly less than the plate voltage and it is bypassed to ground with a capacitor of low impedance at the frequencies to be amplified. This arrangement substantially decouples the plate and the control grid , eliminating the need for neutralizing circuitry at medium wave broadcast frequencies. The screen grid also largely reduces
2924-469: The 6GH8 /ECF82 triode-pentode, quite popular in television receivers. The desire to include even more functions in one envelope resulted in the General Electric Compactron which has 12 pins. A typical example, the 6AG11, contains two triodes and two diodes. Some otherwise conventional tubes do not fall into standard categories; the 6AR8, 6JH8 and 6ME8 have several common grids, followed by
3010-482: The 6SN7 , is a "dual triode" which performs the functions of two triode tubes while taking up half as much space and costing less. The 12AX7 is a dual "high mu" (high voltage gain ) triode in a miniature enclosure, and became widely used in audio signal amplifiers, instruments, and guitar amplifiers . The introduction of the miniature tube base (see below) which can have 9 pins, more than previously available, allowed other multi-section tubes to be introduced, such as
3096-475: The Museum of Science and Industry opened at Elkington Silver Electroplating Works , Newhall Street. Over the following years, the museum acquired individual artefacts, as well as entire collections, that were related to local industry and the history of science and technology. Birmingham City Council decided in 1995 to relocate the museum when it was given an opportunity by the Millennium Commission to construct
3182-537: The Oxford Mathematical Institute ran a competition to award it to the college that could produce the best case for its future use. The competition was the idea of John Hammersley , who had worked at AERE previously. The competition was won by the Wolverhampton and Staffordshire Technical College (which later became Wolverhampton University ) where it was used to teach computing until 1973. The computer
3268-464: The magnetic detector . Amplification by vacuum tube became practical only with Lee de Forest 's 1907 invention of the three-terminal " audion " tube, a crude form of what was to become the triode . Being essentially the first electronic amplifier , such tubes were instrumental in long-distance telephony (such as the first coast-to-coast telephone line in the US) and public address systems , and introduced
3354-468: The quiescent current necessary to ensure linearity and low distortion. In a power amplifier, this heating can be considerable and can destroy the tube if driven beyond its safe limits. Since the tube contains a vacuum, the anodes in most small and medium power tubes are cooled by radiation through the glass envelope. In some special high power applications, the anode forms part of the vacuum envelope to conduct heat to an external heat sink, usually cooled by
3440-518: The transistor . However, the cathode-ray tube (CRT) remained the basis for television monitors and oscilloscopes until the early 21st century. Thermionic tubes are still employed in some applications, such as the magnetron used in microwave ovens, certain high-frequency amplifiers , and high end audio amplifiers, which many audio enthusiasts prefer for their "warmer" tube sound , and amplifiers for electric musical instruments such as guitars (for desired effects, such as "overdriving" them to achieve
3526-522: The 1984 Leicestershire Schools and Colleges show and subsequently purchased by Newbridge High School , Coalville , Leicestershire. Within two years of that school becoming a private academy school , the painting was sold at auction in 2015 to an undisclosed private buyer. It was discovered on the wall of the Jam Street Cafe Bar in Manchester. Kaldip Bhamber, who has a fine arts degree, was unaware of
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3612-413: The 19th century, telegraph and telephone engineers had recognized the need to extend the distance that signals could be transmitted. In 1906, Robert von Lieben filed for a patent for a cathode-ray tube which used an external magnetic deflection coil and was intended for use as an amplifier in telephony equipment. This von Lieben magnetic deflection tube was not a successful amplifier, however, because of
3698-481: The Audion for demonstration to AT&T's engineering department. Dr. Harold D. Arnold of AT&T recognized that the blue glow was caused by ionized gas. Arnold recommended that AT&T purchase the patent, and AT&T followed his recommendation. Arnold developed high-vacuum tubes which were tested in the summer of 1913 on AT&T's long-distance network. The high-vacuum tubes could operate at high plate voltages without
3784-400: The allied military by 1916. Historically, vacuum levels in production vacuum tubes typically ranged from 10 μPa down to 10 nPa (8 × 10 Torr down to 8 × 10 Torr). The triode and its derivatives (tetrodes and pentodes) are transconductance devices, in which the controlling signal applied to the grid is a voltage , and the resulting amplified signal appearing at the anode
3870-409: The base. There was even an occasional design that had two top cap connections. The earliest vacuum tubes evolved from incandescent light bulbs , containing a filament sealed in an evacuated glass envelope. When hot, the filament in a vacuum tube (a cathode ) releases electrons into the vacuum, a process called thermionic emission . This can produce a controllable unidirectional current though
3956-536: The cathode, no direct current could pass from the cathode to the grid. Thus a change of voltage applied to the grid, requiring very little power input to the grid, could make a change in the plate current and could lead to a much larger voltage change at the plate; the result was voltage and power amplification . In 1908, de Forest was granted a patent ( U.S. patent 879,532 ) for such a three-electrode version of his original Audion for use as an electronic amplifier in radio communications. This eventually became known as
4042-492: The control grid, reducing control grid current. This design helps to overcome some of the practical barriers to designing high-power, high-efficiency power tubes. Manufacturer's data sheets often use the terms beam pentode or beam power pentode instead of beam power tube , and use a pentode graphic symbol instead of a graphic symbol showing beam forming plates. Museum of Science and Industry, Birmingham Thinktank, Birmingham (formerly known as simply Thinktank )
4128-513: The displayed aircraft to their production, locally. Among the new exhibits are a leather flying helmet previously belonging to Helen Kerly , one of only two British civilian women commended for flying during the Second World War . Thinktank, Birmingham Science Museum has a big collection of stationary steam engines. The following are some examples of them: Thinktank has four floors of over 200 hands-on exhibits and artefacts. Each floor has
4214-418: The electrode leads connect to pins on the tube's base which plug into a tube socket . Tubes were a frequent cause of failure in electronic equipment, and consumers were expected to be able to replace tubes themselves. In addition to the base terminals, some tubes had an electrode terminating at a top cap . The principal reason for doing this was to avoid leakage resistance through the tube base, particularly for
4300-425: The exception of early light bulbs , such tubes were only used in scientific research or as novelties. The groundwork laid by these scientists and inventors, however, was critical to the development of subsequent vacuum tube technology. Although thermionic emission was originally reported in 1873 by Frederick Guthrie , it was Thomas Edison's apparently independent discovery of the phenomenon in 1883, referred to as
4386-403: The filament as the cathode; this is called a "directly heated" tube. Most modern tubes are "indirectly heated" by a "heater" element inside a metal tube that is the cathode. The heater is electrically isolated from the surrounding cathode and simply serves to heat the cathode sufficiently for thermionic emission of electrons. The electrical isolation allows all the tubes' heaters to be supplied from
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#17330857727924472-400: The high impedance grid input. The bases were commonly made with phenolic insulation which performs poorly as an insulator in humid conditions. Other reasons for using a top cap include improving stability by reducing grid-to-anode capacitance, improved high-frequency performance, keeping a very high plate voltage away from lower voltages, and accommodating one more electrode than allowed by
4558-411: The influence of the plate voltage on the space charge near the cathode, permitting the tetrode to produce greater voltage gain than the triode in amplifier circuits. While the amplification factors of typical triodes commonly range from below ten to around 100, tetrode amplification factors of 500 are common. Consequently, higher voltage gains from a single tube amplification stage became possible, reducing
4644-671: The machine (see below) put it in perspective to the BBC: "All together, the machine can store 90 numbers. The closest analogy is a man with a pocket calculator," Delwyn Holroyd, who led the restoration effort, tells the BBC in a video about the restoration. Although it could on occasions act as a true stored-program computer , that was not its normal mode of operation. It had a multiplication time of between 5 and 10 seconds, very slow for an electronic computer. As Ted Cooke-Yarborough wrote of his design in 1953 "a slow computer can only justify its existence if it
4730-550: The miniature tube version of the " All American Five ". Octodes, such as the 7A8, were rarely used in the United States, but much more common in Europe, particularly in battery operated radios where the lower power consumption was an advantage. To further reduce the cost and complexity of radio equipment, two separate structures (triode and pentode for instance) can be combined in the bulb of a single multisection tube . An early example
4816-431: The number of external pins (leads) often forced the functions to share some of those external connections such as their cathode connections (in addition to the heater connection). The RCA Type 55 is a double diode triode used as a detector, automatic gain control rectifier and audio preamplifier in early AC powered radios. These sets often include the 53 Dual Triode Audio Output. Another early type of multi-section tube,
4902-435: The number of tubes required. Screen grid tubes were marketed by late 1927. However, the useful region of operation of the screen grid tube as an amplifier was limited to plate voltages greater than the screen grid voltage, due to secondary emission from the plate. In any tube, electrons strike the plate with sufficient energy to cause the emission of electrons from its surface. In a triode this secondary emission of electrons
4988-523: The oscillation valve was developed for the purpose of rectifying radio frequency current as the detector component of radio receiver circuits. While offering no advantage over the electrical sensitivity of crystal detectors , the Fleming valve offered advantage, particularly in shipboard use, over the difficulty of adjustment of the crystal detector and the susceptibility of the crystal detector to being dislodged from adjustment by vibration or bumping. In
5074-480: The painting provenance when she purchased it. John Yeadon has visited the painting at its new location. Vacuum tube A vacuum tube , electron tube , valve (British usage), or tube (North America) is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as a thermionic tube or thermionic valve utilizes thermionic emission of electrons from
5160-647: The plate current, possibly changing the output by hundreds of volts (depending on the circuit). The solid-state device which operates most like the pentode tube is the junction field-effect transistor (JFET), although vacuum tubes typically operate at over a hundred volts, unlike most semiconductors in most applications. The 19th century saw increasing research with evacuated tubes, such as the Geissler and Crookes tubes . The many scientists and inventors who experimented with such tubes include Thomas Edison , Eugen Goldstein , Nikola Tesla , and Johann Wilhelm Hittorf . With
5246-471: The plate, it creates an electric field due to the potential difference between them. Such a tube with only two electrodes is termed a diode , and is used for rectification . Since current can only pass in one direction, such a diode (or rectifier ) will convert alternating current (AC) to pulsating DC. Diodes can therefore be used in a DC power supply , as a demodulator of amplitude modulated (AM) radio signals and for similar functions. Early tubes used
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#17330857727925332-405: The plate. The vacuum tube is then known as a triode , tetrode , pentode , etc., depending on the number of grids. A triode has three electrodes: the anode, cathode, and one grid, and so on. The first grid, known as the control grid, (and sometimes other grids) transforms the diode into a voltage-controlled device : the voltage applied to the control grid affects the current between the cathode and
5418-414: The plate. When held negative with respect to the cathode, the control grid creates an electric field that repels electrons emitted by the cathode, thus reducing or even stopping the current between cathode and anode. As long as the control grid is negative relative to the cathode, essentially no current flows into it, yet a change of several volts on the control grid is sufficient to make a large difference in
5504-399: The power used by the deflection coil. Von Lieben would later make refinements to triode vacuum tubes. Lee de Forest is credited with inventing the triode tube in 1907 while experimenting to improve his original (diode) Audion . By placing an additional electrode between the filament ( cathode ) and plate (anode), he discovered the ability of the resulting device to amplify signals. As
5590-448: The present-day C cell , for which the letter denotes its size and shape). The C battery's positive terminal was connected to the cathode of the tubes (or "ground" in most circuits) and whose negative terminal supplied this bias voltage to the grids of the tubes. Later circuits, after tubes were made with heaters isolated from their cathodes, used cathode biasing , avoiding the need for a separate negative power supply. For cathode biasing,
5676-427: The previous science museum was free to enter, Thinktank charges an entrance fee. In 2005 the museum underwent a £2 million upgrade, including the installation of a planetarium. By 2007 it had received over 1 million visitors. In April 2012, Birmingham Museums Trust took over governance and management responsibility for Thinktank, along with eight other sites. In March 2015, a new "Spitfire gallery" opened, relating
5762-523: The question of thermionic emission and conduction in a vacuum. Consequently, General Electric started producing hard vacuum triodes (which were branded Pliotrons) in 1915. Langmuir patented the hard vacuum triode, but de Forest and AT&T successfully asserted priority and invalidated the patent. Pliotrons were closely followed by the French type ' TM ' and later the English type 'R' which were in widespread use by
5848-425: The record was over one Christmas-New Year holiday when it was all by itself, with miles of input data on punched tape to keep it happy, for at least ten days and was still ticking away when we came back." It was the machine's untiring durability, rather than its speed, that was its main feature. Human mathematicians (a job role called a "hand-computer") could make calculations at a similar speed, but not continuously for
5934-474: The same lengths of time. Dr Howlett commented: One day EB ‘Bart’ Fossey, an excellent hand-computer (still with what used to be called the Atlas Computer Laboratory ), settled down beside the machine with his desk machine and attempted a race. He kept level for about half an hour working flat out, but had to retire, exhausted; the machine just ploughed on. In 1957, at the end of its life at Harwell,
6020-440: The suppressor grid wired internally to the cathode (e.g. EL84/6BQ5) and those with the suppressor grid wired to a separate pin for user access (e.g. 803, 837). An alternative solution for power applications is the beam tetrode or beam power tube , discussed below. Superheterodyne receivers require a local oscillator and mixer , combined in the function of a single pentagrid converter tube. Various alternatives such as using
6106-581: The title for several years until it was decommissioned in 1973. The museum uses the computer's visual, dekatron -based memory to teach schoolchildren about computers. The computer, which weighs 2.5 metric tons (2.8 short tons), was built and used at the Atomic Energy Research Establishment in Harwell , Berkshire . Construction started in 1949, and the machine became operational in April 1951. It
6192-455: The triode caused early tube audio amplifiers to exhibit harmonic distortion at low volumes. Plotting plate current as a function of applied grid voltage, it was seen that there was a range of grid voltages for which the transfer characteristics were approximately linear. To use this range, a negative bias voltage had to be applied to the grid to position the DC operating point in the linear region. This
6278-407: The triode. De Forest's original device was made with conventional vacuum technology. The vacuum was not a "hard vacuum" but rather left a very small amount of residual gas. The physics behind the device's operation was also not settled. The residual gas would cause a blue glow (visible ionization) when the plate voltage was high (above about 60 volts). In 1912, de Forest and John Stone Stone brought
6364-638: The tube were much greater. In a sense, these were akin to integrated circuits. In the United States, Cleartron briefly produced the "Multivalve" triple triode for use in the Emerson Baby Grand receiver. This Emerson set also has a single tube socket, but because it uses a four-pin base, the additional element connections are made on a "mezzanine" platform at the top of the tube base. By 1940 multisection tubes had become commonplace. There were constraints, however, due to patents and other licensing considerations (see British Valve Association ). Constraints due to
6450-415: The tube. The simplest vacuum tube, the diode (i.e. Fleming valve ), was invented in 1904 by John Ambrose Fleming . It contains only a heated electron-emitting cathode and an anode. Electrons can flow in only one direction through the device – from the cathode to the anode. Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by
6536-478: The tubes) without requiring replacement. When triodes were first used in radio transmitters and receivers, it was found that tuned amplification stages had a tendency to oscillate unless their gain was very limited. This was due to the parasitic capacitance between the plate (the amplifier's output) and the control grid (the amplifier's input), known as the Miller capacitance . Eventually the technique of neutralization
6622-420: The vacuum known as the Edison effect . A second electrode, the anode or plate , will attract those electrons if it is at a more positive voltage. The result is a net flow of electrons from the filament to plate. However, electrons cannot flow in the reverse direction because the plate is not heated and does not emit electrons. The filament has a dual function: it emits electrons when heated; and, together with
6708-421: The voltage applied to the control grid (or simply "grid") was lowered from the cathode's voltage to somewhat more negative voltages, the amount of current from the filament to the plate would be reduced. The negative electrostatic field created by the grid in the vicinity of the cathode would inhibit the passage of emitted electrons and reduce the current to the plate. With the voltage of the grid less than that of
6794-468: The voltage on the grids. These devices became a key component of electronic circuits for the first half of the twentieth century. They were crucial to the development of radio , television , radar , sound recording and reproduction , long-distance telephone networks, and analog and early digital computers . Although some applications had used earlier technologies such as the spark gap transmitter for radio or mechanical computers for computing, it
6880-449: Was also technical consultant to Edison-Swan . One of Marconi's needs was for improvement of the detector , a device that extracts information from a modulated radio frequency. Marconi had developed a magnetic detector , which was less responsive to natural sources of radio frequency interference than the coherer , but the magnetic detector only provided an audio frequency signal to a telephone receiver. A reliable detector that could drive
6966-405: Was called the idle condition, and the plate current at this point the "idle current". The controlling voltage was superimposed onto the bias voltage, resulting in a linear variation of plate current in response to positive and negative variation of the input voltage around that point. This concept is called grid bias . Many early radio sets had a third battery called the "C battery" (unrelated to
7052-604: Was developed whereby the RF transformer connected to the plate (anode) would include an additional winding in the opposite phase. This winding would be connected back to the grid through a small capacitor, and when properly adjusted would cancel the Miller capacitance. This technique was employed and led to the success of the Neutrodyne radio during the 1920s. However, neutralization required careful adjustment and proved unsatisfactory when used over
7138-451: Was handed over to the computing group in May 1952 and remained in use until 1957. It used 828 dekatrons for volatile memory , similar to RAM in a modern computer, and paper tape for input and program storage. A total of 480 relays were used for sequence control and 199 valves (electronic vacuum tube) for calculations. The computer stands 2 meters high, 6 meters wide, and 1 meter deep with
7224-578: Was renamed as the WITCH, the Wolverhampton Instrument for Teaching Computing from Harwell. The WITCH was donated to the Museum of Science and Industry , Birmingham in 1973. After the museum closed in 1997, the computer was disassembled and stored at the Birmingham Museum Collection Centre . From September 2009, the machine was loaned to The National Museum of Computing in the site of Bletchley Park , where it began to be restored to working order as
7310-435: Was the invention of the thermionic vacuum tube that made these technologies widespread and practical, and created the discipline of electronics . In the 1940s, the invention of semiconductor devices made it possible to produce solid-state devices, which are smaller, safer, cooler, and more efficient, reliable, durable, and economical than thermionic tubes. Beginning in the mid-1960s, thermionic tubes were being replaced by
7396-401: Was usually connected to the cathode and its negative voltage relative to the anode repelled secondary electrons so that they would be collected by the anode instead of the screen grid. The term pentode means the tube has five electrodes. The pentode was invented in 1926 by Bernard D. H. Tellegen and became generally favored over the simple tetrode. Pentodes are made in two classes: those with
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