Vacuum tube
A vacuum tube, electron tube,[1][2][3] valve (British usage), or tube (North America),[4] 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 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 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.[5]
These devices became a key component of electronic circuits for the first half of the twentieth century. They were crucial to the development of
In the 1940s, the invention of
Thermionic tubes are still employed in some applications, such as the
Not all electronic circuit valves / 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.
Classifications
One classification of thermionic vacuum tubes is by the number of active
Other classifications are:
- by frequency range (UHF, microwave)
- by power rating (small-signal, audio power, high-power radio transmitting)
- by filament type (indirectly heated, directly heated) and warm-up time(including "bright-emitter" or "dull-emitter")
- by characteristic curves design (e.g., sharp- versus remote-cutoff in some pentodes)
- by application (receiving, transmitting, amplifying or switching, rectification, mixing)
- specialized parameters (long life, very low microphonic sensitivity and low-noise audio amplification, rugged or military versions)
- specialized functions (light or radiation detectors, video imaging tubes)
- tubes used to display vacuum fluorescent displays, CRTs)
Vacuum tubes may have other components and functions than those described above, and are described elsewhere. These include as
Description
A vacuum tube consists of two or more
The earliest vacuum tubes evolved from
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 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.[10]
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 the
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 the plate. The vacuum tube is then known as a
History and development
The 19th century saw increasing research with evacuated tubes, such as the
Although
Amplification by vacuum tube became practical only with
Diodes
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 was also technical consultant to Edison-Swan.[17] 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 a printing instrument was needed. As a result of experiments conducted on Edison effect bulbs,[14] Fleming developed a vacuum tube that he termed the oscillation valve because it passed current in only one direction.[18] 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 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.[19] Later known as the Fleming valve, the oscillation valve was developed for the purpose of rectifying radio frequency current as the detector component of radio receiver circuits.[14][20]
While offering no advantage over the electrical sensitivity of crystal detectors,[21] 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.[22]
Triodes
In 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.[23] This von Lieben magnetic deflection tube was not a successful amplifier, however, because of the power used by the deflection coil.[24] 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.[25] By placing an additional electrode between the filament (cathode) and plate (anode), he discovered the ability of the resulting device to amplify signals. As 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 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 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 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.[26] The high-vacuum tubes could operate at high plate voltages without 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.[27]
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 the question of thermionic emission and conduction in a vacuum. Consequently, General Electric started producing hard vacuum triodes (which were branded Pliotrons) in 1915.[28] 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 '
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 is a current.[30] 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 (gm) 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 gm for 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 Rp or Ra. The Van der Bijl equation defines their relationship as follows:
The non-linear operating characteristic of 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 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
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, 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 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 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 a wide range of frequencies.
Tetrodes and pentodes
To combat the stability problems of the triode as a radio frequency amplifier due to grid-to-plate capacitance, the physicist
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 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 is the dynatron region[35] or tetrode kink and is an example of negative resistance which can itself cause instability.[36] 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 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 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[37] and became generally favored over the simple tetrode. Pentodes are made in two classes: those with 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.
Multifunction and multisection tubes
Superheterodyne receivers require a local oscillator and mixer, combined in the function of a single pentagrid converter tube. Various alternatives such as using 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 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 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 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 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, 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[38][39][40]) 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 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.[41]
Some otherwise conventional tubes do not fall into standard categories; the 6AR8, 6JH8 and 6ME8 have several common grids, followed by a pair of beam deflection electrodes which deflected the current towards either of two anodes.[42] 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.[43]
Beam power tubes
A beam tetrode (or "beam power tube") forms the electron stream from the cathode into multiple partially collimated beams to produce 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.[44][45] 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 the control grid, reducing control grid current.[46] 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.[47]
Beam power tubes offer the advantages of a longer load line, less screen current, higher transconductance and lower third harmonic distortion than comparable power pentodes.[48][49] Beam power tubes can be connected as triodes for improved audio tonal quality but in triode mode deliver significantly reduced power output.[50]
Gas-filled tubes
Miniature tubes
Early tubes used a metal or glass envelope atop an insulating bakelite base. In 1938 a technique was developed to use an all-glass construction[51] with the pins fused in the glass base of the envelope. This allowed the design of a much smaller tube profile, known as the miniature tube, having seven or nine pins. Making tubes smaller reduced the voltage where they could safely operate, and also reduced the power dissipation of the filament. Miniature tubes became predominant in consumer applications such as radio receivers and hi-fi amplifiers. However, the larger older styles continued to be used especially as higher-power rectifiers, in higher-power audio output stages and as transmitting tubes.
Sub-miniature tubes
Sub-miniature tubes with a size roughly that of half a cigarette were used in consumer applications as hearing-aid amplifiers. These tubes did not have pins plugging into a socket but were soldered in place. The "acorn tube" (named due to its shape) was also very small, as was the metal-cased RCA nuvistor from 1959, about the size of a thimble. The nuvistor was developed to compete with the early transistors and operated at higher frequencies than those early transistors could. The small size supported especially high-frequency operation; nuvistors were used in aircraft radio transceivers, UHF television tuners, and some HiFi FM radio tuners (Sansui 500A) until replaced by high-frequency capable transistors.
Improvements in construction and performance
The earliest vacuum tubes strongly resembled incandescent light bulbs and were made by lamp manufacturers, who had the equipment needed to manufacture glass envelopes and the
Indirectly heated cathodes
The desire to power electronic equipment using AC mains power faced a difficulty with respect to the powering of the tubes' filaments, as these were also the cathode of each tube. Powering the filaments directly from a
A superior solution, and one which allowed each cathode to "float" at a different voltage, was that of the indirectly heated cathode: a cylinder of oxide-coated nickel acted as an electron-emitting cathode and was electrically isolated from the filament inside it. Indirectly heated cathodes enable the cathode circuit to be separated from the heater circuit. The filament, no longer electrically connected to the tube's electrodes, became simply known as a "heater", and could as well be powered by AC without any introduction of hum.[52] In the 1930s, indirectly heated cathode tubes became widespread in equipment using AC power. Directly heated cathode tubes continued to be widely used in battery-powered equipment as their filaments required considerably less power than the heaters required with indirectly heated cathodes.
Tubes designed for high gain audio applications may have twisted heater wires to cancel out stray electric fields, fields that could induce objectionable hum into the program material.
Heaters may be energized with either alternating current (AC) or direct current (DC). DC is often used where low hum is required.
Use in electronic computers
Vacuum tubes used as switches made electronic computing possible for the first time, but the cost and relatively short
Advances using subminiature tubes included the Jaincomp series of machines produced by the Jacobs Instrument Company of Bethesda, Maryland. Models such as its Jaincomp-B employed just 300 such tubes in a desktop-sized unit that offered performance to rival many of the then room-sized machines.[56]
Colossus
Colossus I and its successor Colossus II (Mk2) were designed by Tommy Flowers and built by the General Post Office for Bletchley Park (BP) during World War II to substantially speed up the task of breaking the German high level Lorenz encryption. Colossus replaced an earlier machine based on relay and switch logic (the Heath Robinson). Colossus was able to break in a matter of hours messages that had previously taken several weeks; it was also much more reliable.[54] Colossus was the first use of vacuum tubes working in concert on such a large scale for a single machine.[54]
Tommy Flowers (who conceived Colossus) wrote that most radio equipment was "carted round, dumped around, switched on and off and generally mishandled. But I'd introduced valves into telephone equipment in large numbers before the war and I knew that if you never moved them and never switched them on and off they would go on forever". Colossus was "that reliable, extremely reliable". On its first day at BP a problem with a known answer was set. To the amazement of BP (Station X), after running for four hours with each run taking half an hour the answer was the same every time (the Robinson did not always give the same answer). [57][58] Colossus I used about 1600 valves, and Colossus II about 2400 valves (some sources say 1500 (Mk I) and 2500 (Mk II); the Robinson used about a hundred valves; some sources say fewer).[59]
Whirlwind and "special-quality" tubes
To meet the reliability requirements of the 1951 US digital computer Whirlwind, "special-quality" tubes with extended life, and a long-lasting cathode in particular, were produced. The problem of short lifetime was traced largely to evaporation of
The first such "computer tube" was Sylvania's 7AK7 pentode of 1948 (these replaced the 7AD7, which was supposed to be better quality than the standard 6AG7 but proved too unreliable).[61]: 59 Computers were the first tube devices to run tubes at cutoff (enough negative grid voltage to make them cease conduction) for quite-extended periods of time. Running in cutoff with the heater on accelerates cathode poisoning and the output current of the tube will be greatly reduced when switched into conduction mode.[60]: 224 The 7AK7 tubes improved the cathode poisoning problem, but that alone was insufficient to achieve the required reliability.[61]: 60 Further measures included switching off the heater voltage when the tubes were not required to conduct for extended periods, turning on and off the heater voltage with a slow ramp to avoid thermal shock on the heater element,[60]: 226 and stress testing the tubes during offline maintenance periods to bring on early failure of weak units.[61]: 60–61 Another commonly used computer tube was the 5965, also labeled as E180CC. This, according to an
The tubes developed for Whirlwind were later used in the giant
Heat generation and cooling
A considerable amount of heat is produced when tubes operate, from both the filament (heater) and the stream of electrons bombarding the plate. In power amplifiers, this source of heat is greater than cathode heating. A few types of tube permit operation with the anodes at a dull red heat; in other types, red heat indicates severe overload.
The requirements for heat removal can significantly change the appearance of high-power vacuum tubes. High power audio amplifiers and rectifiers required larger envelopes to dissipate heat. Transmitting tubes could be much larger still.
Heat escapes the device by black-body radiation from the anode (plate) as infrared radiation, and by convection of air over the tube envelope.[63]: 10 Convection is not possible inside most tubes since the anode is surrounded by vacuum.
Tubes which generate relatively little heat, such as the 1.4-volt filament directly heated tubes designed for use in battery-powered equipment, often have shiny metal anodes. 1T4, 1R5 and 1A7 are examples. Gas-filled tubes such as thyratrons may also use a shiny metal anode since the gas present inside the tube allows for heat convection from the anode to the glass enclosure.
The anode is often treated to make its surface emit more infrared energy. High-power amplifier tubes are designed with external anodes that can be cooled by convection, forced air or circulating water. The water-cooled 80 kg, 1.25 MW 8974 is among the largest commercial tubes available today.
In a water-cooled tube, the anode voltage appears directly on the cooling water surface, thus requiring the water to be an electrical insulator to prevent high voltage leakage through the cooling water to the radiator system. Water as usually supplied has ions that conduct electricity;
The screen grid may also generate considerable heat. Limits to screen grid dissipation, in addition to plate dissipation, are listed for power devices. If these are exceeded then tube failure is likely.
Tube packages
Most modern tubes have glass envelopes, but metal, fused quartz (
The internal elements of tubes have always been connected to external circuitry via pins at their base which plug into a socket. Subminiature tubes were produced using wire leads rather than sockets, however, these were restricted to rather specialized applications. In addition to the connections at the base of the tube, many early triodes connected the grid using a metal cap at the top of the tube; this reduces stray capacitance between the grid and the plate leads. Tube caps were also used for the plate (anode) connection, particularly in transmitting tubes and tubes using a very high plate voltage.
High-power tubes such as transmitting tubes have packages designed more to enhance heat transfer. In some tubes, the metal envelope is also the anode. The 4CX1000A is an external anode tube of this sort. Air is blown through an array of fins attached to the anode, thus cooling it. Power tubes using this cooling scheme are available up to 150 kW dissipation. Above that level, water or water-vapor cooling are used. The highest-power tube currently available is the Eimac 4CM2500KG, a forced water-cooled power tetrode capable of dissipating 2.5 megawatts.[65] By comparison, the largest power transistor can only dissipate about 1 kilowatt.
Names
The generic name "[thermionic] valve" used in the UK derives from the unidirectional current flow allowed by the earliest device, the thermionic diode emitting electrons from a heated filament, by analogy with a non-return valve in a water pipe.[66] The US names "vacuum tube", "electron tube", and "thermionic tube" all simply describe a tubular envelope which has been evacuated ("vacuum"), has a heater and controls electron flow.
In many cases, manufacturers and the military gave tubes designations that said nothing about their purpose (e.g., 1614). In the early days some manufacturers used proprietary names which might convey some information, but only about their products; the KT66 and KT88 were "kinkless tetrodes". Later, consumer tubes were given names that conveyed some information, with the same name often used generically by several manufacturers. In the US,
A system widely used in Europe known as the Mullard–Philips tube designation, also extended to transistors, uses a letter, followed by one or more further letters, and a number. The type designator specifies the heater voltage or current (one letter), the functions of all sections of the tube (one letter per section), the socket type (first digit), and the particular tube (remaining digits). For example, the ECC83 (equivalent to the 12AX7) is a 6.3V (E) double triode (CC) with a miniature base (8). In this system special-quality tubes (e.g., for long-life computer use) are indicated by moving the number immediately after the first letter: the E83CC is a special-quality equivalent of the ECC83, the E55L a power pentode with no consumer equivalent.
Special-purpose tubes
Some special-purpose tubes are constructed with particular gases in the envelope. For instance, voltage-regulator tubes contain various inert gases such as argon, helium or neon, which will ionize at predictable voltages. The thyratron is a special-purpose tube filled with low-pressure gas or mercury vapor. Like vacuum tubes, it contains a hot cathode and an anode, but also a control electrode which behaves somewhat like the grid of a triode. When the control electrode starts conduction, the gas ionizes, after which the control electrode can no longer stop the current; the tube "latches" into conduction. Removing anode (plate) voltage lets the gas de-ionize, restoring its non-conductive state.
Some thyratrons can carry large currents for their physical size. One example is the miniature type 2D21, often seen in 1950s
A specialized tube is the krytron, which is used for rapid high-voltage switching. Krytrons are used to initiate the detonations used to set off a nuclear weapon; krytrons are heavily controlled at an international level.
The photomultiplier tube is an extremely sensitive detector of light, which uses the photoelectric effect and secondary emission, rather than thermionic emission, to generate and amplify electrical signals. Nuclear medicine imaging equipment and liquid scintillation counters use photomultiplier tube arrays to detect low-intensity scintillation due to ionizing radiation.
The Ignatron tube was used in resistance welding equipment in the early 1970s. The Ignatron had a cathode, anode and an igniter. The tube base was filled with mercury and the tube was used as a very high current switch. A large current potential was placed between the anode and cathode of the tube but was only permitted to conduct when the igniter in contact with the mercury had enough current to vaporize the mercury and complete the circuit. Because this was used in resistance welding there were two Ignatrons for the two phases of an AC circuit. Because of the mercury at the bottom of the tube they were extremely difficult to ship. These tubes were eventually replaced by SCRs (Silicon Controlled Rectifiers).
Powering the tube
Batteries
The high voltage applied to the anode (plate) was provided by the
Early sets used a grid bias battery or
The "C battery" for bias is a designation having no relation to the "C cell" battery size.
AC power
Battery replacement was a major operating cost for early radio receiver users. The development of the
As a cost reduction measure, especially in high-volume consumer receivers, all the tube heaters could be connected in series across the AC supply using heaters requiring the same current and with a similar warm-up time. In one such design, a tap on the tube heater string supplied the 6 volts needed for the dial light. By deriving the high voltage from a half-wave rectifier directly connected to the AC mains, the heavy and costly power transformer was eliminated. This also allowed such receivers to operate on direct current, a so-called AC/DC receiver design. Many different US consumer AM radio manufacturers of the era used a virtually identical circuit, given the nickname All American Five.
Where the mains voltage was in the 100–120 V range, this limited voltage proved suitable only for low-power receivers. Television receivers either required a transformer or could use a voltage doubling circuit. Where 230 V nominal mains voltage was used, television receivers as well could dispense with a power transformer.
Transformer-less power supplies required safety precautions in their design to limit the shock hazard to users, such as electrically insulated cabinets and an interlock tying the power cord to the cabinet back, so the line cord was necessarily disconnected if the user or service person opened the cabinet. A cheater cord was a power cord ending in the special socket used by the safety interlock; servicers could then power the device with the hazardous voltages exposed.
To avoid the warm-up delay, "instant on" television receivers passed a small heating current through their tubes even when the set was nominally off. At switch on, full heating current was provided and the set would play almost immediately.
Reliability
One reliability problem of tubes with oxide cathodes is the possibility that the cathode may slowly become "
The heater's failure mode is typically a stress-related fracture of the tungsten wire or at a weld point and generally occurs after accruing many thermal (power on-off) cycles. Tungsten wire has a very low resistance when at room temperature. A negative temperature coefficient device, such as a thermistor, may be incorporated in the equipment's heater supply or a ramp-up circuit may be employed to allow the heater or filaments to reach operating temperature more gradually than if powered-up in a step-function. Low-cost radios had tubes with heaters connected in series, with a total voltage equal to that of the line (mains). Some receivers made before World War II had series-string heaters with total voltage less than that of the mains. Some had a resistance wire running the length of the power cord to drop the voltage to the tubes. Others had series resistors made like regular tubes; they were called ballast tubes.
Following World War II, tubes intended to be used in series heater strings were redesigned to all have the same ("controlled") warm-up time. Earlier designs had quite-different thermal time constants. The audio output stage, for instance, had a larger cathode and warmed up more slowly than lower-powered tubes. The result was that heaters that warmed up faster also temporarily had higher resistance, because of their positive temperature coefficient. This disproportionate resistance caused them to temporarily operate with heater voltages well above their ratings, and shortened their life.
Another important reliability problem is caused by air leakage into the tube. Usually oxygen in the air reacts chemically with the hot filament or cathode, quickly ruining it. Designers developed tube designs that sealed reliably. This was why most tubes were constructed of glass. Metal alloys (such as Cunife and Fernico) and glasses had been developed for light bulbs that expanded and contracted in similar amounts, as temperature changed. These made it easy to construct an insulating envelope of glass, while passing connection wires through the glass to the electrodes.
When a vacuum tube is overloaded or operated past its design dissipation, its anode (plate) may glow red. In consumer equipment, a glowing plate is universally a sign of an overloaded tube. However, some large transmitting tubes are designed to operate with their anodes at red, orange, or in rare cases, white heat.
"Special quality" versions of standard tubes were often made, designed for improved performance in some respect, such as a longer life cathode, low noise construction, mechanical ruggedness via ruggedized filaments, low microphony, for applications where the tube will spend much of its time cut off, etc. The only way to know the particular features of a special quality part is by reading the datasheet. Names may reflect the standard name (12AU7==>12AU7A, its equivalent ECC82==>E82CC, etc.), or be absolutely anything (standard and special-quality equivalents of the same tube include 12AU7, ECC82, B329, CV491, E2163, E812CC, M8136, CV4003, 6067, VX7058, 5814A and 12AU7A).[69]
The longest recorded valve life was earned by a Mazda AC/P pentode valve (serial No. 4418) in operation at the BBC's main Northern Ireland transmitter at Lisnagarvey. The valve was in service from 1935 until 1961 and had a recorded life of 232,592 hours. The BBC maintained meticulous records of their valves' lives with periodic returns to their central valve stores.[70][71]
Vacuum
A vacuum tube needs an extremely high vacuum (or hard vacuum, from X-ray terminology[72]) to avoid the consequences of generating positive ions within the tube. Residual gas atoms ionize when struck by an electron and can adversely affect the cathode, reducing emission.[73] Larger amounts of residual gas can create a visible glow discharge between the tube electrodes and cause overheating of the electrodes, producing more gas, damaging the tube and possibly other components due to excess current.[74][75][76] To avoid these effects, the residual pressure within the tube must be low enough that the mean free path of an electron is much longer than the size of the tube (so an electron is unlikely to strike a residual atom and very few ionized atoms will be present). Commercial vacuum tubes are evacuated at manufacture to about 0.000001 mmHg (1.0×10−6 Torr; 130 μPa; 1.3×10−6 mbar; 1.3×10−9 atm).[77][78]
To prevent gases from compromising the tube's vacuum, modern tubes are constructed with getters, which are usually metals that oxidize quickly, barium being the most common.[78][79] For glass tubes, while the tube envelope is being evacuated, the internal parts except the getter are heated by RF induction heating to evolve any remaining gas from the metal parts. The tube is then sealed and the getter trough or pan, for flash getters, is heated to a high temperature, again by radio frequency induction heating, which causes the getter material to vaporize and react with any residual gas. The vapor is deposited on the inside of the glass envelope, leaving a silver-colored metallic patch that continues to absorb small amounts of gas that may leak into the tube during its working life. Great care is taken with the valve design to ensure this material is not deposited on any of the working electrodes. If a tube develops a serious leak in the envelope, this deposit turns a white color as it reacts with atmospheric oxygen. Large transmitting and specialized tubes often use more exotic getter materials, such as zirconium. Early gettered tubes used phosphorus-based getters, and these tubes are easily identifiable, as the phosphorus leaves a characteristic orange or rainbow deposit on the glass. The use of phosphorus was short-lived and was quickly replaced by the superior barium getters. Unlike the barium getters, the phosphorus did not absorb any further gases once it had fired.
Getters act by chemically combining with residual or infiltrating gases, but are unable to counteract (non-reactive) inert gases. A known problem, mostly affecting valves with large envelopes such as
Transmitting tubes
Large transmitting tubes have carbonized tungsten filaments containing a small trace (1% to 2%) of thorium. An extremely thin (molecular) layer of thorium atoms forms on the outside of the wire's carbonized layer and, when heated, serve as an efficient source of electrons. The thorium slowly evaporates from the wire surface, while new thorium atoms diffuse to the surface to replace them. Such thoriated tungsten cathodes usually deliver lifetimes in the tens of thousands of hours. The end-of-life scenario for a thoriated-tungsten filament is when the carbonized layer has mostly been converted back into another form of tungsten carbide and emission begins to drop off rapidly; a complete loss of thorium has never been found to be a factor in the end-of-life in a tube with this type of emitter. WAAY-TV in Huntsville, Alabama achieved 163,000 hours (18.6 years) of service from an Eimac external cavity klystron in the visual circuit of its transmitter; this is the highest documented service life for this type of tube.[80] It has been said[who?] that transmitters with vacuum tubes are better able to survive lightning strikes than transistor transmitters do. While it was commonly believed that vacuum tubes were more efficient than solid-state circuits at RF power levels above approximately 20 kilowatts, this is no longer the case, especially in medium wave (AM broadcast) service where solid-state transmitters at nearly all power levels have measurably higher efficiency. FM broadcast transmitters with solid-state power amplifiers up to approximately 15 kW also show better overall power efficiency than tube-based power amplifiers.
Receiving tubes
Cathodes in small "receiving" tubes are coated with a mixture of barium oxide and strontium oxide, sometimes with addition of calcium oxide or aluminium oxide. An electric heater is inserted into the cathode sleeve and insulated from it electrically by a coating of aluminum oxide. This complex construction causes barium and strontium atoms to diffuse to the surface of the cathode and emit electrons when heated to about 780 degrees Celsius.
Failure modes
Catastrophic failures
A catastrophic failure is one that suddenly makes the vacuum tube unusable. A crack in the glass envelope will allow air into the tube and destroy it. Cracks may result from stress in the glass, bent pins or impacts; tube sockets must allow for thermal expansion, to prevent stress in the glass at the pins. Stress may accumulate if a metal shield or other object presses on the tube envelope and causes differential heating of the glass. Glass may also be damaged by high-voltage arcing.
Tube heaters may also fail without warning, especially if exposed to over voltage or as a result of manufacturing defects. Tube heaters do not normally fail by evaporation like lamp filaments since they operate at much lower temperature. The surge of inrush current when the heater is first energized causes stress in the heater and can be avoided by slowly warming the heaters, gradually increasing current with a NTC thermistor included in the circuit. Tubes intended for series-string operation of the heaters across the supply have a specified controlled warm-up time to avoid excess voltage on some heaters as others warm up. Directly heated filament-type cathodes as used in battery-operated tubes or some rectifiers may fail if the filament sags, causing internal arcing. Excess heater-to-cathode voltage in indirectly heated cathodes can break down the insulation between elements and destroy the heater.
Arcing between tube elements can destroy the tube. An arc can be caused by applying voltage to the anode (plate) before the cathode has come up to operating temperature, or by drawing excess current through a rectifier, which damages the emission coating. Arcs can also be initiated by any loose material inside the tube, or by excess screen voltage. An arc inside the tube allows gas to evolve from the tube materials, and may deposit conductive material on internal insulating spacers.[81]
Tube rectifiers have limited current capability and exceeding ratings will eventually destroy a tube.
Degenerative failures
Degenerative failures are those caused by the slow deterioration of performance over time.
Overheating of internal parts, such as control grids or mica spacer insulators, can result in trapped gas escaping into the tube; this can reduce performance. A getter is used to absorb gases evolved during tube operation but has only a limited ability to combine with gas. Control of the envelope temperature prevents some types of gassing. A tube with an unusually high level of internal gas may exhibit a visible blue glow when plate voltage is applied. The getter (being a highly reactive metal) is effective against many atmospheric gases but has no (or very limited) chemical reactivity to inert gases such as helium. One progressive type of failure, especially with physically large envelopes such as those used by camera tubes and cathode-ray tubes, comes from helium infiltration. The exact mechanism is not clear: the metal-to-glass lead-in seals are one possible infiltration site.
Gas and ions within the tube contribute to grid current which can disturb operation of a vacuum-tube circuit. Another effect of overheating is the slow deposit of metallic vapors on internal spacers, resulting in inter-element leakage.
Tubes on standby for long periods, with heater voltage applied, may develop high cathode interface resistance and display poor emission characteristics. This effect occurred especially in pulse and
Cathode depletion is the loss of emission after thousands of hours of normal use. Sometimes emission can be restored for a time by raising heater voltage, either for a short time or a permanent increase of a few percent. Cathode depletion was uncommon in signal tubes but was a frequent cause of failure of monochrome television cathode-ray tubes.[82] Usable life of this expensive component was sometimes extended by fitting a boost transformer to increase heater voltage.
Other failures
Vacuum tubes may develop defects in operation that make an individual tube unsuitable in a given device, although it may perform satisfactorily in another application. Microphonics refers to internal vibrations of tube elements which modulate the tube's signal in an undesirable way; sound or vibration pick-up may affect the signals, or even cause uncontrolled howling if a feedback path (with greater than unity gain) develops between a microphonic tube and, for example, a loudspeaker. Leakage current between AC heaters and the cathode may couple into the circuit, or electrons emitted directly from the ends of the heater may also inject hum into the signal. Leakage current due to internal contamination may also inject noise.[83] Some of these effects make tubes unsuitable for small-signal audio use, although unobjectionable for other purposes. Selecting the best of a batch of nominally identical tubes for critical applications can produce better results.
Tube pins can develop non-conducting or high resistance surface films due to heat or dirt. Pins can be cleaned to restore conductance.
Testing
Vacuum tubes can be tested outside of their circuitry using a vacuum tube tester.
Other vacuum tube devices
Most small signal vacuum tube devices have been superseded by semiconductors, but some vacuum tube electronic devices are still in common use. The magnetron is the type of tube used in all microwave ovens. In spite of the advancing state of the art in power semiconductor technology, the vacuum tube still has reliability and cost advantages for high-frequency RF power generation.
Some tubes, such as
Cathode-ray tubes
The
The X-ray tube is a type of cathode-ray tube that generates X-rays when high voltage electrons hit the anode.[88][89]
Electron multipliers
A photomultiplier is a phototube whose sensitivity is greatly increased through the use of electron multiplication. This works on the principle of secondary emission, whereby a single electron emitted by the photocathode strikes a special sort of anode known as a dynode causing more electrons to be released from that dynode. Those electrons are accelerated toward another dynode at a higher voltage, releasing more secondary electrons; as many as 15 such stages provide a huge amplification. Despite great advances in solid-state photodetectors (e.g. Single-photon avalanche diode), the single-photon detection capability of photomultiplier tubes makes this vacuum tube device excel in certain applications. Such a tube can also be used for detection of ionizing radiation as an alternative to the Geiger–Müller tube (itself not an actual vacuum tube). Historically, the image orthicon TV camera tube widely used in television studios prior to the development of modern CCD arrays also used multistage electron multiplication.
For decades, electron-tube designers tried to augment amplifying tubes with electron multipliers in order to increase gain, but these suffered from short life because the material used for the dynodes "poisoned" the tube's hot cathode. (For instance, the interesting RCA 1630 secondary-emission tube was marketed, but did not last.) However, eventually, Philips of the Netherlands developed the EFP60 tube that had a satisfactory lifetime and was used in at least one product, a laboratory pulse generator. By that time, however, transistors were rapidly improving, making such developments superfluous.
One variant called a "channel electron multiplier" does not use individual dynodes but consists of a curved tube, such as a helix, coated on the inside with material with good secondary emission. One type had a funnel of sorts to capture the secondary electrons. The continuous dynode was resistive, and its ends were connected to enough voltage to create repeated cascades of electrons. The
Tektronix made a high-performance wideband oscilloscope CRT with a channel electron multiplier plate behind the phosphor layer. This plate was a bundled array of a huge number of short individual c.e.m. tubes that accepted a low-current beam and intensified it to provide a display of practical brightness. (The electron optics of the wideband electron gun could not provide enough current to directly excite the phosphor.)
Vacuum tubes in the 21st century
Industrial, commercial, and military niche applications
Although vacuum tubes have been largely replaced by solid-state devices in most amplifying, switching, and rectifying applications, there are certain exceptions. In addition to the special functions noted above, tubes still[update] have some niche applications.
In general, vacuum tubes are much less susceptible than corresponding solid-state components to transient overvoltages, such as mains voltage surges or lightning, the
Vacuum tubes are practical alternatives to solid-state devices in generating high power at
In military applications, a high-power vacuum tube can generate a 10–100 megawatt signal that can burn out an unprotected receiver's frontend. Such devices are considered non-nuclear electromagnetic weapons; they were introduced in the late 1990s by both the U.S. and Russia.[citation needed]
In music
Tube amplifiers remain commercially viable in three niches where their warm sound, performance when overdriven, and ability to replicate prior-era tube-based recording are prized: audiophile equipment, musical instrument amplifiers, and devices used in recording studios.[96]
Many guitarists prefer using valve amplifiers to solid-state models, often due to the way they tend to distort when overdriven.[97] Any amplifier can only accurately amplify a signal to a certain volume; past this limit, the amplifier will begin to distort the signal. Different circuits will distort the signal in different ways; some guitarists prefer the distortion characteristics of vacuum tubes. Most popular vintage models use vacuum tubes.[citation needed]
Displays
Cathode-ray tube
The
Vacuum tubes using field electron emitters
This section needs additional citations for verification. (May 2018) |
In the early years of the 21st century there has been renewed interest in vacuum tubes, this time with the electron emitter formed on a flat silicon substrate, as in integrated circuit technology. This subject is now called vacuum nanoelectronics.[100] The most common design uses a cold cathode in the form of a large-area field electron source (for example a field emitter array). With these devices, electrons are field-emitted from a large number of closely spaced individual emission sites.
Such integrated microtubes may find application in
As of 2014, NASA's Ames Research Center was reported to be working on vacuum-channel transistors produced using CMOS techniques.[101]
Characteristics
Space charge of a vacuum tube
When a cathode is heated and reaches an operating temperature around 1050° Kelvin (780 °C), free electrons are driven from its surface. These free electrons form a cloud in the empty space between the cathode and the anode, known as the space charge. This space charge cloud supplies the electrons that create the current flow from the cathode to the anode. As electrons are drawn to the anode during the operation of the circuit, new electrons will boil off the cathode to replenish the space charge.[102] The space charge is an example of an electric field.
Voltage - Current characteristics of vacuum tube
All tubes with one or more control grids are controlled by an AC (
This relationship is shown with a set of Plate Characteristics curves, (see example above,) which visually display how the output current from the anode (Ia) can be affected by a small input voltage applied on the grid (Vg), for any given voltage on the plate(anode) (Va).
Every tube has a unique set of such characteristic curves. The curves graphically relate the changes to the instantaneous plate current driven by a much smaller change in the grid-to-cathode voltage (Vgk) as the input signal varies.
The V-I characteristic depends upon the size and material of the plate and cathode.[103] Express the ratio between voltage plate and plate current.[104]
- V-I curve (Voltage across filaments, plate current)
- Plate current, plate voltage characteristics
- DC plate resistance of the plate—resistance of the path between anode and cathode of direct current
- AC plate resistance of the plate—resistance of the path between anode and cathode of alternating current
Size of electrostatic field
Size of electrostatic field is the size between two or more plates in the tube.
Patents
- U.S. patent 803,684—Instrument for converting alternating electric currents into continuous currents (Fleming valve patent)
- U.S. patent 841,387—Device for amplifying feeble electrical currents
- U.S. patent 879,532—de Forest's three electrode Audion
See also
- Bogey value—close to manufacturer's stated parameter values
- Fetron—a solid-state, plug-compatible, replacement for vacuum tubes
- List of vacuum tubes—a list of type numbers.
- List of vacuum-tube computers
- Mullard–Philips tube designation
- Nixie tube—a gas-filled display device sometimes misidentified as a vacuum tube
- RETMA tube designation
- RMA tube designation
- Russian tube designations
- Tube caddy
- Tube tester
- Valve amplifier
- Zetatron
References
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- ^ Hoddeson L., Riordan M. (1997). Crystal Fire. New York: W. W. Norton & Co. Inc. p. 58. Retrieved Oct 2021
- ISBN 978-0-670-82698-8.
The electronics age may be said to have been ushered in with the invention of the vacuum diode valve in 1902 by the Briton John Fleming (himself coining the word 'electronics'), the immediate application being in the field of radio.
- ^ ISBN 0080966403.
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- doi:10.1049/jbire.1951.0074., p.571
- ISBN 9780852962183. Archivedfrom the original on 3 December 2016.
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- ^ Guthrie, Frederick (1876). Magnetism and Electricity. London and Glasgow: William Collins, Sons, & Company. p. 1.[page needed]
- ^ Thomas A. Edison U.S. patent 307,031 "Electrical Indicator", Issue date: 1884
- ^ a b c Fleming, J. A. (1934). Memories of a Scientific Life. London, UK: Marshall, Morgan & Scott, Ltd. pp. 136 - 143. Retrieved Nov. 2021.
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- ^ White, Thomas, United States Early Radio History, archived from the original on 18 August 2012
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- ^ Editors (Sept 1954) "World of Wireless" Wireless World p. 411. Retrieved Nov. 2021.
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- ^ Keen, R. (1922). Direction and Position Finding by Wireless. London: The Wireless Press, Ltd. p. 74. Retrieved Nov. 2021.
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- ^ Fleming, J. A. (1919). The Thermionic Valve and its Developments in Radiotelegraphy and Telephony. London, UK: The Wireless Press Ltd. p. 115. Retrieved Oct 2021
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- ^ Happell, Hesselberth (1953). Engineering Electronics. New York: McGraw-Hill. p. 88
- ^ Introduction to Thermionic Valves (Vacuum Tubes) Archived 28 May 2007 at the Wayback Machine, Colin J. Seymour
- ^ "Philips Historical Products: Philips Vacuum Tubes". Archived from the original on 6 November 2013. Retrieved 3 November 2013.
- ISBN 978-0-7506-8627-3.
- ^ Modjeski, Roger A. "Mu, Gm and Rp and how Tubes are matched". Välljud AB. Archived from the original on 21 March 2012. Retrieved 22 April 2011.
- ISBN 978-0-672-21983-2.
Amplification factor or voltage gain is the amount the signal at the control grid is increased in amplitude after passing through the tube, which is also referred to as the Greek letter μ (mu) or voltage gain (Vg) of the tube.
- ^ 6AG11 radiomuseum.org
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- ^ Donovan P. Geppert, (1951). Basic Electron Tubes, New York: McGraw-Hill, pp. 164 - 179. Retrieved 10 June 2021
- ^ Winfield G. Wagener, (May 1948). "500-Mc. Transmitting Tetrode Design Considerations" Proceedings of the I.R.E., p. 612. Retrieved 10 June 2021
- ^ Staff, (2003). Care and Feeding of Power Grid Tubes, San Carlos, CA: CPI, EIMAC Div., p. 28
- ^ GE Electronic Tubes, (March 1955) 6V6GT - 5V6GT Beam Pentode, Schenectady, NY: Tube Division, General Electric Co.
- ^ J. F. Dreyer, Jr., (April 1936). "The Beam Power Output Tube", Electronics, Vol. 9, No. 4, pp. 18 - 21, 35
- ^ R. S. Burnap (July 1936). "New Developments in Audio Power Tubes", RCA Review, New York: RCA Institutes Technical Press, pp. 101 - 108
- ^ RCA, (1954). 6L6, 6L6-G Beam Power Tube. Harrison, NJ: Tube Division, RCA. pp. 1,2,6
- ^ C H Gardner (1965) The Story of the Valve Archived 23 December 2015 at the Wayback Machine, Radio Constructor (See particularly the section "Glass Base Construction")
- ISBN 0-408-00168-2pages 7–2 through 7-6
- S2CID 41800914.
- ^ a b c d From part of Copeland's "Colossus" available online Archived 23 March 2012 at the Wayback Machine
- ^ Randall, Alexander 5th (14 February 2006). "A lost interview with ENIAC co-inventor J. Presper Eckert". Computer World. Archived from the original on 2 April 2009. Retrieved 25 April 2011.
{{cite web}}
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- ^ Gannon 2006, pp. 255, 284.
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- ^ ISBN 3486856707.
- ^ Frost, H. B. (4 May 1953). "Memorandum M-2135: Some notes on current tube types" (PDF). MIT. p. 3. Archived from the original (PDF) on 28 March 2021. Retrieved 12 February 2024.
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- ^ "MULTI-PHASE COOLED POWER TETRODE 4CM2500KG" (PDF). Archived (PDF) from the original on 11 October 2016.
The maximum anode dissipation rating is 2500 kilowatts.
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- ^ National Valve Museum: audio double triodes ECC81, 2, and 3 Archived 7 January 2011 at the Wayback Machine
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- ^ Mazda Data Booklet 1968 Page 112.
- ^ Dushman, S. (1922) Production and Measurement of High Vacuum New York: General Electric Review. p. 174. Retrieved Nov. 2021
- ^ Hadley, C. P. (1962) "Oxide-Coated Emitters" New Jersey: Electron Tube Div., RCA. Electron Tube Design, p. 34. Retrieved 25 Oct 2021
- ^ Hicks, H. J. (1943) Principles and Practice of Radio Servicing 2nd ed. pp. 252. Retrieved 25 Oct 2021
- ^ Staff, (2003). Care and Feeding of Power Grid Tubes, San Carlos, CA: CPI, EIMAC Div., p. 68. Retrieved 25 Oct 2021
- LCCN 60-13843Retrieved Oct 2021
- ISBN 1483223558page 96
- ^ a b Thomas, C. H. (1962) "Getters" New Jersey: Electron Tube Div., RCA. Electron Tube Design, pp. 519 - 525 Retrieved 25 Oct 2021
- ^ Espe, Knoll, Wilder (Oct. 1950) "Getter Materials for Electron Tubes" New York: McGraw-Hill. Electronics pp. 80 - 86 Retrieved 25 Oct 2021
- ^ 31 Alumni. "The Klystron & Cactus". Archived from the original on 20 August 2013. Retrieved 29 December 2013.
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- ^ Tomer, R. B. (1960). pp. 34 - 35
- ^ Tomer, R. B. (1960). pp. 30 - 33
- ^ Analogue Oscilloscope: cathode ray oscilloscopeelectronics-notes.com
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- ^ Katzmaier, David. "Remember when TVs weighed 200 pounds? A look back at TV trends over the years". CNET.
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Further reading
- Eastman, Austin V., Fundamentals of Vacuum Tubes, McGraw-Hill, 1949
- Millman, J. & Seely, S. Electronics, 2nd ed. McGraw-Hill, 1951.
- Philips Technical Library. Books published in the UK in the 1940s and 1950s by Cleaver Hume Press on design and application of vacuum tubes.
- RCA. Radiotron Designer's Handbook, 1953 (4th Edition). Contains chapters on the design and application of receiving tubes.
- RCA. Receiving Tube Manual, RC15, RC26 (1947, 1968) Issued every two years, contains details of the technical specs of the tubes that RCA sold.
- Shiers, George, "The First Electron Tube", Scientific American, March 1969, p. 104.
- Spangenberg, Karl R. (1948). Vacuum Tubes. McGraw-Hill. LCC TK7872.V3.
- Stokes, John, 70 Years of Radio Tubes and Valves, Vestal Press, New York, 1982, pp. 3–9.
- Thrower, Keith, History of the British Radio Valve to 1940, MMA International, 1982, pp 9–13.
- Tyne, Gerald, Saga of the Vacuum Tube, Ziff Publishing, 1943, (reprint 1994 Prompt Publications), pp. 30–83.
- Basic Electronics: Volumes 1–5; Van Valkenburgh, Nooger & Neville Inc.; John F. Rider Publisher; 1955.
- Wireless World. Radio Designer's Handbook. UK reprint of the above.
- "Vacuum Tube Design"; 1940; RCA.
- Gannon, Paul (2006). Colossus: Bletchley Park's Greatest Secret. London: Atlantic Books. ISBN 1-84354-330-3.
- ISBN 978-0-7522-2189-2
External links
- The Vacuum Tube FAQ—FAQ from rec.audio
- The invention of the thermionic valve Archived 16 October 2012 at Archive-It. Fleming discovers the thermionic (or oscillation) valve, or 'diode'.
- "Tubes Vs. Transistors: Is There an Audible Difference?"—1972 AES paper on audible differences in sound quality between vacuum tubes and transistors.
- The cathode-ray tube site
- O'Neill's Electronic museum—vacuum tube museum
- Vacuum tubes for beginners—Japanese Version
- NJ7P Tube Database—Data manual for tubes used in North America.
- Vacuum tube data sheet locator
- Characteristics and datasheets Archived 13 January 2012 at the Wayback Machine
- Tuning eye tubes