World Library  
Flag as Inappropriate
Email this Article


Article Id: WHEBN0000402178
Reproduction Date:

Title: Thyratron  
Author: World Heritage Encyclopedia
Language: English
Subject: List of vacuum tubes, Gas-filled tube, Colossus computer, Vacuum tube, Ignitron
Collection: Gas-Filled Tubes, Switching Tubes
Publisher: World Heritage Encyclopedia


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. Because of the gas fill, thyratrons can handle much greater currents than similar hard-vacuum tubes, since electron multiplication occurs in the ionized gas, the phenomenon called Townsend discharge. Gases used include mercury vapor, xenon, neon, and (in special high-voltage applications or applications requiring very short switching times) hydrogen.[1] Unlike a vacuum tube (valve), 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".[2] Since the 1960s thyristors have replaced thyratrons in most low- and medium-power applications.


  • Construction and operation 1
  • Applications 2
  • Example of a small thyratron 3
  • Notes 4
  • References 5
  • External links 6

Construction and operation

Most commonly used symbols in U.S.A. and in Europe of a thyratron (variations are usually related to the representation of the filament and the cathode)

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.


Rare Z806W relay tube used in elevators
Wynn-Williams' Scale-of-Two Counter using thyratrons. (With permission of the Cavendish Laboratory, University of Cambridge, UK.)

Low-power thyratrons (relay tubes and trigger tubes) were manufactured 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.

Another use of the thyratron was in relaxation oscillators.[3] Since the plate turn-on voltage is much higher than the turn-off voltage the tube has hysteresis and with a capacitor across it could function as a sawtooth oscillator. The voltage on the grid controlled the breakdown voltage and thus the period of oscillation. Thyratron relaxation oscillators were used in power inverters and oscilloscope sweep circuits.

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.[4] 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.

The miniature RK61/2 thyraton valves marketed in 1938 were designed specifically for radio control circuits, and were the major technical development which led to the wartime development of radio-controlled weapons and the parallel development of radio controlled modelling as a hobby.[5]

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.[6]

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

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.


  1. ^ 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.
  2. ^
  3. ^ Gottlieb, Irving (1997). Practical Oscillator Handbook. Elsevier. pp. 69–73.  
  4. ^ data sheet"6D4 Miniature triode thyratron"Sylvania: (PDF). Retrieved 25 May 2013. 
  5. ^ George Honnest-Redlich Radio Control for Models (1950) p. 7
  6. ^, retrieved 2012 July 27


  • Stokes, John, 70 Years of Radio Tubes and Valves, Vestal Press, NY, 1982, pp. 111–115.
  • Thrower, Keith, History of the British Radio Valve to 1940, MMA International, 1982, p. 30, 31, 81.
  • Hull, A. W., "Gas-Filled Thermionic Valves", Trans. AIEE, 47, 1928, pp. 753–763.
  • Data for 6D4 type, "Sylvania Engineering Data Service", 1957
  • J.D. Cobine, J.R. Curry, "Electrical Noise Generators", Proceedings of the I.R.E., 1947, p. 875
  • Radio and Electronic Laboratory Handbook, M.G. Scroggie 1971, ISBN 0-592-05950-2

External links

  • Article about switch tubes by John Pasley
  • Thyratron collection at the Virtual Valve Museum
  • Article on gas filled thyratrons
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.