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130-544: The KWR-37 weighed 100 pounds (45 kg) and contained some 500 subminiature vacuum tubes , whose leads were soldered to printed circuit boards . Each flip-flop in the KW-37 required three tubes, placing an upper bound on the total number of stages in any shift registers used at 166. Squeezing so much logic in such a small and rugged package was quite a feat in the 1950s. Each KWT-37 filled an entire relay rack with five stacked modules. A precision time reference occupied

260-430: A galvanometer , but this method involves breaking the electrical circuit , which is sometimes inconvenient. Current can also be measured without breaking the circuit by detecting the magnetic field associated with the current. Devices, at the circuit level, use various techniques to measure current: Joule heating, also known as ohmic heating and resistive heating , is the process of power dissipation by which

390-453: A rectifier . Direct current may flow in a conductor such as a wire, but can also flow through semiconductors , insulators , or even through a vacuum as in electron or ion beams . An old name for direct current was galvanic current . Natural observable examples of electric current include lightning , static electric discharge , and the solar wind , the source of the polar auroras . Man-made occurrences of electric current include

520-494: A wire . In semiconductors they can be electrons or holes . In an electrolyte the charge carriers are ions , while in plasma , an ionized gas, they are ions and electrons. In the International System of Units (SI), electric current is expressed in units of ampere (sometimes called an "amp", symbol A), which is equivalent to one coulomb per second. The ampere is an SI base unit and electric current

650-494: A DC power supply , as a demodulator of amplitude modulated (AM) radio signals and for similar functions. Early tubes used 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

780-649: 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

910-411: A circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of either positive or negative charges, or both, a convention is needed for the direction of current that is independent of the type of charge carriers . Negatively charged carriers, such as the electrons (the charge carriers in metal wires and many other electronic circuit components), therefore flow in

1040-501: 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

1170-405: A common lead-acid electrochemical cell, electric currents are composed of positive hydronium ions flowing in one direction, and negative sulfate ions flowing in the other. Electric currents in sparks or plasma are flows of electrons as well as positive and negative ions. In ice and in certain solid electrolytes, the electric current is entirely composed of flowing ions. In a metal , some of

1300-416: A definition of current independent of the type of charge carriers, conventional current is defined as moving in the same direction as the positive charge flow. So, in metals where the charge carriers (electrons) are negative, conventional current is in the opposite direction to the overall electron movement. In conductors where the charge carriers are positive, conventional current is in the same direction as

1430-586: 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

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1560-572: A fatal weakness. KWR-37s fell into North Korean hands when the USS Pueblo was captured in 1968. New keying material was issued to ships throughout the world to limit the ongoing damage. In 1985 it was revealed that the Walker spy ring had been selling key lists and cards to the Soviet Union for decades. KW-37 systems were taken out of service by the early 1990s. The received input to

1690-505: 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 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

1820-431: 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 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

1950-447: A localized high current. These regions may be initiated by field electron emission , but are then sustained by localized thermionic emission once a vacuum arc forms. These small electron-emitting regions can form quite rapidly, even explosively, on a metal surface subjected to a high electrical field. Vacuum tubes and sprytrons are some of the electronic switching and amplifying devices based on vacuum conductivity. Superconductivity

2080-400: 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

2210-428: A metal wire is connected across the two terminals of a DC voltage source such as a battery , the source places an electric field across the conductor. The moment contact is made, the free electrons of the conductor are forced to drift toward the positive terminal under the influence of this field. The free electrons are therefore the charge carrier in a typical solid conductor. For a steady flow of charge through

2340-404: A millimetre per second. To take a different example, in the near-vacuum inside a cathode-ray tube , the electrons travel in near-straight lines at about a tenth of the speed of light . Any accelerating electric charge, and therefore any changing electric current, gives rise to an electromagnetic wave that propagates at very high speed outside the surface of the conductor. This speed is usually

2470-414: 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

2600-408: A particular band called the valence band . Semiconductors and insulators are distinguished from metals because the valence band in any given metal is nearly filled with electrons under usual operating conditions, while very few (semiconductor) or virtually none (insulator) of them are available in the conduction band , the band immediately above the valence band. The ease of exciting electrons in

2730-412: 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

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2860-509: 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

2990-461: A sigh of relief because the KWR-37 units were often unreliable and would occasionally fall out of synchronization timing, resulting in a loss of broadcast messages from the various fleet channels. Experiences operating the KWR-37 - a personal account from a retired US Navy fleet Radioman Vacuum tube A vacuum tube , electron tube , valve (British usage), or tube (North America)

3120-475: A significant fraction of the speed of light, as can be deduced from Maxwell's equations , and is therefore many times faster than the drift velocity of the electrons. For example, in AC power lines , the waves of electromagnetic energy propagate through the space between the wires, moving from a source to a distant load , even though the electrons in the wires only move back and forth over a tiny distance. The ratio of

3250-407: 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

3380-419: 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

3510-405: A surface, the current I (in amperes) can be calculated with the following equation: I = Q t , {\displaystyle I={Q \over t}\,,} where Q is the electric charge transferred through the surface over a time t . If Q and t are measured in coulombs and seconds respectively, I is in amperes. More generally, electric current can be represented as

3640-405: 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 the tube. The simplest vacuum tube, the diode (i.e. Fleming valve ), was invented in 1904 by John Ambrose Fleming . It contains only

3770-456: 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 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

3900-400: A very high plate voltage away from lower voltages, and accommodating one more electrode than allowed by 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

4030-429: 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

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4160-603: Is I , which originates from the French phrase intensité du courant , (current intensity). Current intensity is often referred to simply as current . The I symbol was used by André-Marie Ampère , after whom the unit of electric current is named, in formulating Ampère's force law (1820). The notation travelled from France to Great Britain, where it became standard, although at least one journal did not change from using C to I until 1896. The conventional direction of current, also known as conventional current ,

4290-551: Is a base quantity in the International System of Quantities (ISQ). Electric current is also known as amperage and is measured using a device called an ammeter . Electric currents create magnetic fields , which are used in motors, generators, inductors , and transformers . In ordinary conductors, they cause Joule heating , which creates light in incandescent light bulbs . Time-varying currents emit electromagnetic waves , which are used in telecommunications to broadcast information. The conventional symbol for current

4420-445: 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

4550-406: 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 a hot cathode for fundamental electronic functions such as signal amplification and current rectification . Non-thermionic types such as

4680-407: Is a flow of charged particles , such as electrons or ions , moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge carriers , which may be one of several types of particles, depending on the conductor . In electric circuits the charge carriers are often electrons moving through

4810-523: Is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature . It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden . Like ferromagnetism and atomic spectral lines , superconductivity is a quantum mechanical phenomenon. It is characterized by the Meissner effect ,

4940-411: Is arbitrarily defined as the direction in which positive charges flow. In a conductive material , the moving charged particles that constitute the electric current are called charge carriers . In metals, which make up the wires and other conductors in most electrical circuits , the positively charged atomic nuclei of the atoms are held in a fixed position, and the negatively charged electrons are

5070-683: Is current. Magnetic fields can also be used to make electric currents. When a changing magnetic field is applied to a conductor, an electromotive force (EMF) is induced, which starts an electric current, when there is a suitable path. When an electric current flows in a suitably shaped conductor at radio frequencies , radio waves can be generated. These travel at the speed of light and can cause electric currents in distant conductors. In metallic solids, electric charge flows by means of electrons , from lower to higher electrical potential . In other media, any stream of charged objects (ions, for example) may constitute an electric current. To provide

5200-423: Is in a nanowire , for every energy there is a state with electrons flowing in one direction and another state with the electrons flowing in the other. For a net current to flow, more states for one direction than for the other direction must be occupied. For this to occur, energy is required, as in the semiconductor the next higher states lie above the band gap. Often this is stated as: full bands do not contribute to

5330-468: Is low, gases are dielectrics or insulators . However, once the applied electric field approaches the breakdown value, free electrons become sufficiently accelerated by the electric field to create additional free electrons by colliding, and ionizing , neutral gas atoms or molecules in a process called avalanche breakdown . The breakdown process forms a plasma that contains enough mobile electrons and positive ions to make it an electrical conductor. In

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5460-469: Is not heated and does not emit electrons. The filament has a dual function: it emits electrons when heated; and, together with 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

5590-410: 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

5720-455: Is opposite that of the chosen reference direction. Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance , one arrives at the usual mathematical equation that describes this relationship: I = V R , {\displaystyle I={\frac {V}{R}},} where I

5850-658: Is opposite to the velocity of the charges. In SI units , current density (symbol: j) is expressed in the SI base units of amperes per square metre. In linear materials such as metals, and under low frequencies, the current density across the conductor surface is uniform. In such conditions, Ohm's law states that the current is directly proportional to the potential difference between two ends (across) of that metal (ideal) resistor (or other ohmic device ): I = V R , {\displaystyle I={V \over R}\,,} where I {\displaystyle I}

5980-564: 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

6110-416: 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

6240-433: Is the current through the conductor in units of amperes , V is the potential difference measured across the conductor in units of volts , and R is the resistance of the conductor in units of ohms . More specifically, Ohm's law states that the R in this relation is constant, independent of the current. In alternating current (AC) systems, the movement of electric charge periodically reverses direction. AC

6370-400: Is the current, measured in amperes; V {\displaystyle V} is the potential difference , measured in volts ; and R {\displaystyle R} is the resistance , measured in ohms . For alternating currents , especially at higher frequencies, skin effect causes the current to spread unevenly across the conductor cross-section, with higher density near

6500-441: Is the form of electric power most commonly delivered to businesses and residences. The usual waveform of an AC power circuit is a sine wave , though certain applications use alternative waveforms, such as triangular or square waves . Audio and radio signals carried on electrical wires are also examples of alternating current. An important goal in these applications is recovery of information encoded (or modulated ) onto

6630-461: Is the rate at which charge passes through a chosen unit area. It is defined as a vector whose magnitude is the current per unit cross-sectional area. As discussed in Reference direction , the direction is arbitrary. Conventionally, if the moving charges are positive, then the current density has the same sign as the velocity of the charges. For negative charges, the sign of the current density

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6760-403: Is zero net current within the metal. At room temperature, the average speed of these random motions is 10 metres per second. Given a surface through which a metal wire passes, electrons move in both directions across the surface at an equal rate. As George Gamow wrote in his popular science book, One, Two, Three...Infinity (1947), "The metallic substances differ from all other materials by

6890-564: 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

7020-684: 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 ,

7150-429: 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

7280-480: 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

7410-482: 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

7540-405: The electrical conductivity . However, as a semiconductor's temperature rises above absolute zero , there is more energy in the semiconductor to spend on lattice vibration and on exciting electrons into the conduction band. The current-carrying electrons in the conduction band are known as free electrons , though they are often simply called electrons if that is clear in context. Current density

7670-487: 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

7800-467: 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

7930-458: The reference direction of the current I {\displaystyle I} . When analyzing electrical circuits , the actual direction of current through a specific circuit element is usually unknown until the analysis is completed. Consequently, the reference directions of currents are often assigned arbitrarily. When the circuit is solved, a negative value for the current implies the actual direction of current through that circuit element

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8060-418: The watt (symbol: W), is equivalent to one joule per second. In an electromagnet a coil of wires behaves like a magnet when an electric current flows through it. When the current is switched off, the coil loses its magnetism immediately. Electric current produces a magnetic field . The magnetic field can be visualized as a pattern of circular field lines surrounding the wire that persists as long as there

8190-509: The "crib" or the card reader by securing it onto pins and then firmly closing the card access door and then locking it with a key. Once the unit(s) were restarted, the key was placed back in the safe using two-person integrity (TPI) which was stringently enforced following the Walker spy investigation. In the early nineties when the KWR-37 units were retired from the navy and replaced by the more reliable and modern KWR-46's, fleet Radiomen breathed

8320-407: The 14's were fall out of sync as well. Each KG-14 could process one channel of the tone pack; most fleet units had six KG-14's, larger units even more. Typically, fleet units utilizing the KWR-37 units were outfitted with two devices for redundancy. Should one unit fail, the other one would already be online and patches via a high level, 60-milliamp patch panel would quickly be changed around so that

8450-413: 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

8580-401: The AC signal. In contrast, direct current (DC) refers to a system in which the movement of electric charge in only one direction (sometimes called unidirectional flow). Direct current is produced by sources such as batteries , thermocouples , solar cells , and commutator -type electric machines of the dynamo type. Alternating current can also be converted to direct current through use of

8710-485: 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

8840-466: The KW(R)-37 was in the form of a multiple broadcast (multicast) signal, consisting of many channels condensed into one tone pack which was deciphered at one stage by the KW(R)-37 and then the output was sent to several KG-14's which further deciphered the then split signals into each channel of the fleet broadcast. The KG-14 also received its timing signal from the KW(R)-37; if the 37 was out of sync, all

8970-585: The KWT-37 had a common fill device (CFD) for loading keys (or as NSA calls them cryptovariables ). The CFDs were similar to that first used in the KW-26 , accepting punched cards in Remington Rand format. The key was changed every day at 0000 hours GMT . The receivers were synchronized to the transmitter at that time. If a receiver ever got out of sync, say due to a power failure, an operator had to set

9100-462: 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 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

9230-400: 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

9360-435: 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 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

9490-479: 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 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

9620-402: The bottom, three key generators ( stream cyphers in civilian parlance) occupied the middle and an alarm panel occupied the top position. The outputs of the three key generators were combined in a voting circuit. If one of the units' output did not match the other two, an alarm was sounded and the output from the two units that did agree continued to be used. Each KWR-37 and each key generator in

9750-404: The cathode slam into the anode (plate) and heat it; this can occur even in an idle amplifier due to 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

9880-536: 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

10010-412: The charge carriers, free to move about in the metal. In other materials, notably the semiconductors , the charge carriers can be positive or negative, depending on the dopant used. Positive and negative charge carriers may even be present at the same time, as happens in an electrolyte in an electrochemical cell . A flow of positive charges gives the same electric current, and has the same effect in

10140-402: The charge carriers. In a vacuum , a beam of ions or electrons may be formed. In other conductive materials, the electric current is due to the flow of both positively and negatively charged particles at the same time. In still others, the current is entirely due to positive charge flow . For example, the electric currents in electrolytes are flows of positively and negatively charged ions. In

10270-534: The complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics . In a semiconductor it is sometimes useful to think of the current as due to the flow of positive " holes " (the mobile positive charge carriers that are places where

10400-425: 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. Electric current An electric current

10530-544: The correct voltages within radio antennas , radio waves are generated. In electronics , other forms of electric current include the flow of electrons through resistors or through the vacuum in a vacuum tube , the flow of ions inside a battery , and the flow of holes within metals and semiconductors . A biological example of current is the flow of ions in neurons and nerves, responsible for both thought and sensory perception. Current can be measured using an ammeter . Electric current can be directly measured with

10660-400: 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 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

10790-441: The current hour and minute on dials on the front panel. The KWR-37 would then "fast forward" through its key stream sequence until synchronization was re-established. Large numbers of fleet broadcast key cards had to be produced and distributed to every navy ship and many shore installations on a monthly basis, so many people had access to them. While the key cards were strictly accounted for, they were easy to copy. This proved to be

10920-439: The current offline unit could be changed over to online status at a moment's notice, to ensure that there was no interruption of message traffic. Later in their life, when KWR-37 units were aged and worn, sometimes the circuit cards inside had to be reseated with a rubber mallet which helped ensure the cards were seated properly. Other problems with the KWR-37's were related to the startup times. Fleet radiomen, and those stationed in

11050-428: 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 was the invention of the thermionic vacuum tube that made these technologies widespread and practical, and created

11180-445: 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 the transistor . However, the cathode-ray tube (CRT) remained the basis for television monitors and oscilloscopes until

11310-546: 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 a certain sound or tone). Not all electronic circuit valves or electron tubes are vacuum tubes. Gas-filled tubes are similar devices, but containing

11440-410: The energy of the ground state, the state in which electrons are tightly bound to the atomic nuclei of the material, and the free electron energy, the latter describing the energy required for an electron to escape entirely from the material. The energy bands each correspond to many discrete quantum states of the electrons, and most of the states with low energy (closer to the nucleus) are occupied, up to

11570-417: 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; 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

11700-425: 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

11830-458: The fact that the outer shells of their atoms are bound rather loosely, and often let one of their electrons go free. Thus the interior of a metal is filled up with a large number of unattached electrons that travel aimlessly around like a crowd of displaced persons. When a metal wire is subjected to electric force applied on its opposite ends, these free electrons rush in the direction of the force, thus forming what we call an electric current." When

11960-419: 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 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:

12090-459: The flow of conduction electrons in metal wires such as the overhead power lines that deliver electrical energy across long distances and the smaller wires within electrical and electronic equipment. Eddy currents are electric currents that occur in conductors exposed to changing magnetic fields. Similarly, electric currents occur, particularly in the surface, of conductors exposed to electromagnetic waves . When oscillating electric currents flow at

12220-444: 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 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

12350-410: The heavier positive ions, and hence carry the bulk of the current. The free ions recombine to create new chemical compounds (for example, breaking atmospheric oxygen into single oxygen [O 2 → 2O], which then recombine creating ozone [O 3 ]). Since a " perfect vacuum " contains no charged particles, it normally behaves as a perfect insulator. However, metal electrode surfaces can cause a region of

12480-411: 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

12610-440: The length of the wire he deduced that the heat produced was proportional to the square of the current multiplied by the electrical resistance of the wire. P ∝ I 2 R . {\displaystyle P\propto I^{2}R.} This relationship is known as Joule's Law . The SI unit of energy was subsequently named the joule and given the symbol J . The commonly known SI unit of power,

12740-424: The metal into the vacuum. Externally heated electrodes are often used to generate an electron cloud as in the filament or indirectly heated cathode of vacuum tubes . Cold electrodes can also spontaneously produce electron clouds via thermionic emission when small incandescent regions (called cathode spots or anode spots ) are formed. These are incandescent regions of the electrode surface that are created by

12870-561: 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

13000-424: The moving electrons in metals. In certain electrolyte mixtures, brightly coloured ions are the moving electric charges. The slow progress of the colour makes the current visible. In air and other ordinary gases below the breakdown field, the dominant source of electrical conduction is via relatively few mobile ions produced by radioactive gases, ultraviolet light, or cosmic rays. Since the electrical conductivity

13130-431: 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,

13260-435: 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

13390-400: The opposite direction of conventional current flow in an electrical circuit. A current in a wire or circuit element can flow in either of two directions. When defining a variable I {\displaystyle I} to represent the current, the direction representing positive current must be specified, usually by an arrow on the circuit schematic diagram . This is called

13520-403: The opposite direction of the electric field. The speed they drift at can be calculated from the equation: I = n A v Q , {\displaystyle I=nAvQ\,,} where Typically, electric charges in solids flow slowly. For example, in a copper wire of cross-section 0.5 mm , carrying a current of 5 A, the drift velocity of the electrons is on the order of

13650-528: 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

13780-502: The outer electrons in each atom are not bound to the individual molecules as they are in molecular solids , or in full bands as they are in insulating materials, but are free to move within the metal lattice . These conduction electrons can serve as charge carriers , carrying a current. Metals are particularly conductive because there are many of these free electrons. With no external electric field applied, these electrons move about randomly due to thermal energy but, on average, there

13910-413: The passage of an electric current through a conductor increases the internal energy of the conductor, converting thermodynamic work into heat . The phenomenon was first studied by James Prescott Joule in 1841. Joule immersed a length of wire in a fixed mass of water and measured the temperature rise due to a known current through the wire for a 30 minute period. By varying the current and

14040-399: 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

14170-448: 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,

14300-468: The process, it forms a light emitting conductive path, such as a spark , arc or lightning . Plasma is the state of matter where some of the electrons in a gas are stripped or "ionized" from their molecules or atoms. A plasma can be formed by high temperature , or by application of a high electric or alternating magnetic field as noted above. Due to their lower mass, the electrons in a plasma accelerate more quickly in response to an electric field than

14430-479: 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

14560-401: The rate at which charge flows through a given surface as: I = d Q d t . {\displaystyle I={\frac {\mathrm {d} Q}{\mathrm {d} t}}\,.} Electric currents in electrolytes are flows of electrically charged particles ( ions ). For example, if an electric field is placed across a solution of Na and Cl (and conditions are right)

14690-501: The semiconductor crystal is missing a valence electron). This is the case in a p-type semiconductor. A semiconductor has electrical conductivity intermediate in magnitude between that of a conductor and an insulator . This means a conductivity roughly in the range of 10 to 10 siemens per centimeter (S⋅cm ). In the classic crystalline semiconductors, electrons can have energies only within certain bands (i.e. ranges of levels of energy). Energetically, these bands are located between

14820-503: The semiconductor from the valence band to the conduction band depends on the band gap between the bands. The size of this energy band gap serves as an arbitrary dividing line (roughly 4 eV ) between semiconductors and insulators . With covalent bonds, an electron moves by hopping to a neighboring bond. The Pauli exclusion principle requires that the electron be lifted into the higher anti-bonding state of that bond. For delocalized states, for example in one dimension – that

14950-399: The shore transmitting stations, had to listen to an HF signal for coordinated universal time. Radiomen called this broadcast the "time tick," which gave them a sharp tone, signalling them to press the restart button so that the unit could then start up for " new day " or otherwise known as "HJ's" by the radiomen. This took place after the new day's crypto keylist card was properly inserted into

15080-419: The sodium ions move towards the negative electrode (cathode), while the chloride ions move towards the positive electrode (anode). Reactions take place at both electrode surfaces, neutralizing each ion. Water-ice and certain solid electrolytes called proton conductors contain positive hydrogen ions (" protons ") that are mobile. In these materials, electric currents are composed of moving protons, as opposed to

15210-440: 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

15340-443: The surface, thus increasing the apparent resistance. The mobile charged particles within a conductor move constantly in random directions, like the particles of a gas . (More accurately, a Fermi gas .) To create a net flow of charge, the particles must also move together with an average drift rate. Electrons are the charge carriers in most metals and they follow an erratic path, bouncing from atom to atom, but generally drifting in

15470-458: 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

15600-407: 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

15730-646: 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

15860-404: The tubes' heaters to be supplied from 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

15990-482: 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

16120-405: The vacuum to become conductive by injecting free electrons or ions through either field electron emission or thermionic emission . Thermionic emission occurs when the thermal energy exceeds the metal's work function , while field electron emission occurs when the electric field at the surface of the metal is high enough to cause tunneling , which results in the ejection of free electrons from

16250-406: The vacuum, a process called thermionic emission . This can produce a controllable unidirectional current though 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

16380-421: 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

16510-449: 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

16640-405: 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

16770-617: 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

16900-401: 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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