Thyratron Giant GE hydrogen thyratron, used in pulsed radars, next to miniature 2D21 thyratron used to trigger relays in jukeboxes A thyratron is a type of gas filled tube used as a high power electrical switch and controlled rectifier. A thyratron is basically a “controlled gas rectifier”. Triode, tetrode and pentode variations of the thyratron have been manufactured in the past, though most are of the triode design. Because of the gas fill, thyratrons can handle much greater currents than similar hard vacuum valves/tubes since in the ionized gas electron multiplication occurs (each electron leaving the cathode may generate 4 more electrons) by collisions of electrons with gas atoms, using the phenomenon known as a Townsend discharge. The average speed of the ions in the gas is much lower than that of the electrons, so that the ions may only account for 10% of the total current. Gases used include mercury vapor, xenon, neon, and (in special high-voltage applications or applications requiring very short switching times) hydrogen. Unlike a vacuum tube, a thyratron cannot be used to amplify signals linearly. In the 1920s, thyratrons were derived from early vacuum tubes such as the UV-200, which contained a small amount of argon gas to increase its sensitivity as a radio signal detector; and the German LRS Relay tube, which also contained argon gas. Gas rectifiers which predated vacuum tubes, such as the argon-filled General Electric “Tungar bulb” and the Cooper-Hewitt mercury pool rectifier, also provided an influence. Irving Langmuir and G. S. Meikle of GE are usually cited as the first investigators to study controlled rectification in gas tubes, about 1914. The first commercial thyratrons didn’t appear until around 1928. A solid-state device with similar operating characteristics is the thyristor, sometimes also known as the silicon controlled rectifier (SCR). The term “thyristor” was derived from a combination of “thyratron” and “transistor”. Since the 1960s thyristors have replaced thyratrons in most low- and medium-power applications. Contents    1 Construction and operation 2 Applications 3 Example of a small thyratron 4 Notes Construction and operation[edit] A typical hot-cathode thyratron uses a heated filament cathode, completely contained within a shield assembly with a control grid on one open side, which faces the plate-shaped anode. In the off situation the voltage on the control grid is negative with respect to the cathode. When positive voltage is applied to the anode, no current flows. When the control electrode is made less negative, electrons from the cathode can travel to the anode because the positive attraction from the anode prevails over the negative repulsion caused by the slightly negative voltage on the control grid. The electrons will ionize the gas by collisions with the gas in the tube and an avalanche effect results, causing an arc discharge between cathode and anode. The shield prevents ionized current paths that might form within other parts of the tube. The gas in a thyratron is typically at a fraction of the pressure of air at sea level; 15 to 30 millibars (1.5 to 3 kPa) is typical. For a cold cathode thyratron the trigger voltage on the control grid will typically be positive, and a flash over from control grid to cathode will initiate the arc discharge in the tube. Both hot- and cold-cathode versions are encountered. A hot cathode is at an advantage, as ionization of the gas is made easier; thus, the tube’s control electrode is more sensitive. Once turned on, the thyratron will remain on (conducting) as long as there is a significant current flowing through it. When the anode voltage or current falls to zero, the device switches off. Applications[edit] Rare Z806W relay tube used in elevators Low-power thyratrons (relay tubes and trigger tubes) were manufactured in the past for controlling incandescent lamps, electromechanical relays or solenoids, for bidirectional counters, to perform various functions in Dekatron calculators, for voltage threshold detectors in RC timers, etc. Glow thyratrons were optimized for high gas-discharge light output or even phosphorized and used as self-displaying shift registers in large-format, crawling-text dot-matrix displays. One miniature thyratron, the triode 6D4, found an additional use as a potent noise source, when operated as a diode (grid tied to cathode) in a transverse magnetic field. Sufficiently filtered for “flatness” (“white noise”) in a band of interest, such noise was used for testing radio receivers, servo systems and occasionally in analog computing as a random value source. Medium-power thyratrons found applications in machine tool motor controllers, where thyratrons, operating as phase-controlled rectifiers, are utilized in the tool’s armature regulator (zero to “base speed”, “constant torque” mode) and in the tool’s field regulator (“base speed” to about twice “base speed”, “constant horsepower” mode). Examples include Monarch Machine Tool 10EE lathe, which used thyratrons from 1949 until solid-state devices replaced them in 1984, 13EE and EE1000. For a brief period, an SCR-based “Monarch Sidney” drive was offered, which incorporated so-called SCR “power blocks”, but this model was quickly discontinued. The various national laboratories are still utilizing thyratron-based 10EE and 13EE/EE1000 machines and Richardson Electronics, as the successor to Electrons Inc, still makes the thyratrons which these machines utilize.[dubious – discuss] High-power thyratrons are still manufactured, and are capable of operation up to tens of kiloamperes (kA) and tens of kilovolts (kV). Modern applications include pulse drivers for pulsed radar equipment, high-energy gas lasers, radiotherapy devices, particle accelerators and in Tesla coils and similar devices. Thyratrons are also used in high-power UHF television transmitters, to protect inductive output tubes from internal shorts, by grounding the incoming high-voltage supply during the time it takes for a circuit breaker to open and reactive components to drain their stored charges. This is commonly called a crowbar circuit. Thyratrons have been replaced in most low and medium-power applications by corresponding semiconductor devices known as thyristors (sometimes called silicon-controlled rectifiers, or SCRs) and triacs. However, switching service requiring voltages above 20 kV and involving very short risetimes remains within the domain of the thyratron. Variations of the thyratron idea are the krytron, the sprytron, the ignitron, and the triggered spark gap, all still used today in special applications, such as nuclear weapons (krytron) and AC-DC-AC power transmission (ignitron). Example of a small thyratron[edit] R.C.A. brand 885 Triode Thyratron The 885 is a small thyratron tube, using xenon gas. This device was used extensively in the timebase circuits of early oscilloscopes in the 1930s. It was employed in a circuit called a relaxation oscillator. During World War II small thyratrons, similar to the 885 were utilized in pairs to construct bistables, the “memory” cells used by early computers and code breaking machines. Thyratrons were also used for phase angle control of alternating current (AC) power sources in battery chargers and light dimmers, but these were usually of a larger current handling capacity than the 885. The 885 is a 2.5 volt, 5-pin based variant of the 884/6Q5. Notes[edit] Jump up ^ L.W. Turner,(ed), Electronics Engineer’s Reference Book, 4th ed. Newnes-Butterworth, London 1976 ISBN 0-408-00168-2, pages 7-177 and 7-180 Jump up ^ http://home.roadrunner.com/~mathematikos/Etymology/thyristor.pdf Jump up ^ “Sylvania: 6D4 Miniature triode thyratron data sheet” (PDF). Retrieved 25 13. Jump up ^ http://www.lathes.co.uk/monarch/page2.html Lathes.co.uk, retrieved 2012 – Applications

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Rare Z806W relay channel applied within elevatorsLow-power thyratrons (relay cylinders and actuate tubes) remained produced in the past for managing beaming lamps, electromechanical relays either solenoids, for bidirectional counters, to accomplish different purposes in Dekatron calculators, for voltage brink detectors in RC timers, etcetera. Glow thyratrons remained enhanced for elevated gas-discharge light yield either even phosphorized and applied like self-displaying move listings in large-format, crawling-text dot-matrix screens.One atomic thyratron, the triode 6D4, noticed an extra employ like a big sound origin, as controlled as a diode (grid connected to cathode) in a transverse magnetized area. Sufficiently filtered for ‘flatness’ (‘white noise’) in a group of attention, such sound was applied aimed at challenging broadcast receivers, servomechanism structures and sometimes in parallel data processing as a random worth origin.Medium-power thyratrons noticed applications in engine implement machine controllers, where thyratrons, working as phase-controlled rectifiers, are applied in the tool’s architecture controller (zero to ‘base speed’, ‘constant torque’ mode) and in the tool’s area controller (‘base speed’ to regarding twice ‘base speed’, ‘constant horsepower’ mode). Examples contain Monarch Machine Tool 10EE lathe, that applied thyratrons from 1949 till solid-state machines substituted them in 1984, 13EE and EE1000. For a brief time, an SCR-based ‘Monarch Sidney’ drive was presented, that integrated supposed SCR ‘power blocks’, however this type was swiftly ended. The different national laboratories are nevertheless applying thyratron-based 10EE and 13EE/EE1000 devices and Richardson Electronics, as the replacement to Electrons Inc, nevertheless produces the thyratrons that those devices use.[dubious – discuss]High-power thyratrons are nevertheless produced, and are capable of activity up to tens of kiloamperes (kA) and tens of kilovolts (kV). Modern applications contain beat drivers for pulsed radar outfits, high-energy gas lasers, radiotherapy machines, ace ace and in Tesla coils and alike machines. Thyratrons are as well applied within high-power UHF TV transmitters, to safeguard inductive yield cylinders from interior shorts, by basics the incoming high-voltage provision throughout the time it takes for a circle breaker to open and responsive parts to bleed their kept demands. This is normally named a crowbar circle.Thyratrons have been substituted in nearly all low and Medium-power applications by comparable semiconductor machines familiar like thyristors (sometimes named silicon-controlled rectifiers, either SCRs) and triacs. However, shifting facility needing voltages overhead 20 kV and including quite small risetimes stays in the domain of the thyratron.Variations of the thyratron thought are the krytron, the sprytron, the Ignitron, and the precipitated spark breach, altogether nevertheless applied this day in out of the ordinary applications, such like atomic weapons (krytron) and AC-DC-AC power conveyance (ignitron).