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XVIII Airborne Corps

The XVIII Airborne Corps is a corps of the United States Army that has been in existence since 1942 and saw extensive service during World War II. The corps is designed for rapid deployment anywhere in the world and is referred to as "America's Contingency Corps." Its headquarters are at Fort Liberty, North Carolina.

Leadership
Its command group includes:
 * Commanding General: Lieutenant General Christopher T. Donahue
 * Deputy Commanding General: Brigadier General John P. Cogbill
 * Deputy Commanding General (Operations): Brigadier General Robert Pierre "Pete" Huet, Canadian Army
 * Chief of Staff: Colonel Adam Cobb
 * Command Sergeant Major: Command Sergeant Major Bryan D. Barker

World War II
The corps was first activated on 17 January 1942, five weeks after the entry of the United States into World War II, as the II Armored Corps at Camp Polk, Louisiana, under the command of Major General William Henry Harrison Morris, Jr. When the concept of armored corps proved unnecessary, II Armored Corps was re-designated as XVIII Corps on 9 October 1943 at the Presidio of Monterey, California.

XVIII Corps deployed to Europe on 17 August 1944 and became the XVIII Airborne Corps on 25 August 1944 at Ogbourne St. George, England, assuming command of the 82nd and 101st Airborne Divisions, as part of the preparation for Operation Market Garden. Prior to this time, the two divisions were assigned to VII Corps and jumped into Normandy during Operation Overlord, the Allied invasion of Normandy, as part of VII Corps.

Major General Matthew Bunker Ridgway, a highly experienced airborne commander who had led the 82nd Airborne Division in Sicily, Italy and Normandy, was chosen to command the corps, which then consisted of the 82nd and 101st Airborne Divisions and was part of the newly created First Allied Airborne Army.

The corps headquarters did not see service in Operation Market Garden, with the British I Airborne Corps being chosen instead to exercise operational command of all Allied airborne forces in the operation, including the 82nd and 101st Airborne Divisions.

Following the Battle of the Bulge, in which the corps played a significant part (and which, during the early stages of the battle, the corps was commanded by Major General James M. Gavin of the 82nd Airborne), all American airborne units on the Western Front fell under command of the corps. XVIII Airborne Corps planned and executed Operation Varsity, the airborne component of Operation Plunder, the crossing of the River Rhine into Germany. It was one of the largest airborne operations of the war, with the British 6th and U.S. 17th Airborne Divisions under command.

After taking part in the Western Allied invasion of Germany, the XVIII Airborne Corps, still under Ridgway, returned to the United States in June 1945 and was initially to take part in the invasion of Japan, codenamed Operation Downfall. However, the Japanese surrendered just weeks later and XVIII Airborne Corps was inactivated on 15 October 1945 at Fort Campbell, Kentucky.

World War II units

 * 1st Infantry Division — 26 January 1945 – 12 February 1945.
 * 4th Infantry Division
 * 8th Infantry Division — 26 January 1945 – 10 July 1945.
 * 17th Airborne Division — 12 August 1944 – 1 January 1945; 15 February 1945 – 24 March 1945.
 * 29th Infantry Division
 * 30th Infantry Division — 21 December 1944 – 3 February 1945.
 * 34th Infantry Division
 * 75th Infantry Division — 29 December 1944 – 2 January 1945; 7 January 1945.
 * 78th Infantry Division — 3 February 1945 – 12 February 1945.
 * 82nd Airborne Division — 12 August 1944 – 17 September 1944; 19 December 1944 – 14 February 1945; 30 April 1945 – 3 January 1946.
 * 84th Infantry Division — 20 December 1944 – 21 December 1944.
 * 86th Infantry Division — 5 April 1945 – 22 April 1945.
 * 89th Infantry Division
 * 97th Infantry Division — 10 April 1945 – 22 April 1945.
 * 101st Airborne Division — 12 August 1944 – 21 September 1944; 28 February 1945 – 1 April 1945.
 * 106th Infantry Division — 20 December 1944 – 6 February 1945.
 * 3rd Armored Division — 19 December 1944 – 23 December 1944.
 * 5th Armored Division — 4 May 1945 – 10 October 1945.
 * 7th Armored Division — 20 December 1944 – 29 January 1945; 30 April 1945 – 9 October 1945.
 * 13th Armored Division — 10 April 1945 – 22 April 1945.

Cold War
The Corps was reactivated at Fort Bragg on 21 May 1951 under the command of Major General John W. Leonard. Since then, the corps has been the primary strategic response force, with subordinate units participating in over a dozen major operations (listed below) in both combat and humanitarian roles, primarily in Central America and the CENTCOM area of responsibility.

In 1958 the XVIII Airborne Corps was given the additional mission of becoming the Strategic Army Corps. The corps was now tasked, in addition, to provide a flexible strike capability that could deploy worldwide, on short notice, without a declaration of an emergency. The 4th Infantry Division at Fort Lewis, Washington, and the 101st Airborne Division at Fort Campbell, Kentucky, were designated as STRAC's first-line divisions, while the 1st Infantry Division at Fort Riley, Kansas, and the 82nd Airborne Division at Fort Bragg were to provide backup in the event of general war. The 5th Logistical Command (later inactivated), also at Fort Bragg, would provide the corps with logistics support, while Fort Bragg's XVIII Airborne Corps Artillery would control artillery units.

The Corps deployed forces to the United States occupation of the Dominican Republic ('Operation Power Pack') in 1965.

The Corps deployed forces to the Vietnam War, including the entire 101st Airborne Division and the 3rd Brigade of the 82nd Airborne division.

In 1967 elements of the Corps were deployed to Detroit to suppress riots, and also to The Congo to support the government there and to rescue civilian hostages as part of Operation Dragon Rouge.

In 1982 the Corps first rotated elements to the Sinai Peninsula as part of the Multinational Force and Observers (UN) to guarantee the Camp David Peace Accords.

In 1983 elements of the Corps were deployed to the island of Grenada as part of Operation Urgent Fury, with the stated goal of reestablishing the democratically elected government.

In 1989 XVIII Airborne Corps, commanded by then LTG Carl Stiner, participated in the invasion of Panama in Operation Just Cause. Stiner served concurrently as Commander of Joint Task Force South.

Structure in 1989
At the end of the Cold War in 1989 the corps consisted of the following formations and units:

 * XVIII Airborne Corps, Fort Bragg, North Carolina
 * Headquarters & Headquarters Company
 * 18th Personnel Group
 * 18th Finance Group
 * 1st Battalion, 2nd Air Defense Artillery, Fort Stewart
 * 10th Mountain Division (Light), Fort Drum, New York
 * 24th Infantry Division (Mechanized), Fort Stewart, Georgia
 * 82nd Airborne Division, Fort Bragg, North Carolina
 * 101st Airborne Division (Air Assault), Fort Campbell, Kentucky
 * XVIII Airborne Corps Artillery, Fort Bragg
 * 18th Field Artillery Brigade (Airborne), Fort Bragg
 * Headquarters & Headquarters Battery
 * 3rd Battalion, 8th Field Artillery (24 × M198 155mm towed howitzer)
 * 5th Battalion, 8th Field Artillery (24 × M198 155mm towed howitzer)
 * 3rd Battalion, 27th Field Artillery (27 × M270 Multiple Launch Rocket System)
 * 1st Battalion, 39th Field Artillery (Airborne) (24 × M198 155mm towed howitzer)
 * 1st Field Artillery Detachment (Target Acquisition)
 * 18th Aviation Brigade (Airborne), Fort Bragg
 * Headquarters & Headquarters Company
 * 1st Battalion, 58th Aviation (Air Traffic Control)
 * 1st Battalion, 159th Aviation (General Support)
 * 2nd Battalion, 159th Aviation (Medium Lift)
 * 3rd Battalion, 159th Aviation (Attack)
 * 2nd Battalion, 229th Aviation (Attack) (former 2nd Battalion, 101st Aviation)
 * 20th Engineer Brigade (Airborne), Fort Bragg
 * 27th Engineer Battalion (Airborne)
 * 30th Engineer Battalion (Topographic)
 * 37th Engineer Battalion (Airborne)
 * 175th Engineer Company
 * 264th Engineer Company (Bridge)
 * 362nd Engineer Company
 * 16th Military Police Brigade (Airborne), Fort Bragg
 * 503rd Military Police Battalion (Airborne)
 * 35th Signal Brigade (Airborne), Fort Bragg
 * 25th Signal Battalion (Corps Area)
 * 50th Signal Battalion (Corps Command Operations) (Airborne)
 * 327th Signal Battalion (Corps Radio)
 * 426th Signal Battalion (Corps Area)
 * 525th Military Intelligence Brigade (Airborne), Fort Bragg
 * 224th Military Intelligence Battalion (Aerial Exploitation), Hunter Army Airfield, Georgia
 * 319th Military Intelligence Battalion (Operations)
 * 519th Military Intelligence Battalion (Tactical Exploitation) (Airborne)
 * 1st Corps Support Command (Airborne), Fort Bragg
 * subordination formations and units

Desert Storm
In 1991, XVIII Airborne Corps participated in the Persian Gulf War. The corps was responsible for securing VII Corps' northern flank against a possible Iraqi counterattack. Along with the 82nd and 101st Airborne Divisions, 24th Infantry Division and 3rd Armored Cavalry Regiment, XVIII Airborne Corps also gained operational control of the French 6th Light Armor Division (LAD) (which also included units from the French Foreign Legion).

During Operations Desert Shield and Desert Storm, XVIII Airborne Corps Artillery consisted of the 3d Battalion, 8th Field Artillery; 5th Battalion, 8th Field Artillery; and the 1st Battalion (Airborne), 39th Field Artillery. The living quarters for these three units were situated between the 82d Airborne Division and the Special Forces at Fort Bragg. Of the three units, only 1-39th was airborne qualified and served as the only fully airborne deployable 155 mm Field Artillery unit in history. The 1-39th FA and 3-8th FA were key components of the thrust into Iraq in the first Gulf War, providing fire support for the French Foreign Legion and the 82nd Airborne Division.

The 5th Battalion, 8th Field Artillery also served in a major support role for 82d and French troops during the Gulf War. It consisted of three individual batteries. Batteries A and B were Airborne-qualified, while Battery C was air assault. Batteries A and B were assigned to Fort Bragg, North Carolina and Battery C was assigned to Fort Campbell, Kentucky. All of the battalions were subsequently re-flagged during the years following the Gulf War.

Task Force 118 had flown the OH-58D Kiowa Warrior off naval vessels during Operation Prime Chance in the 1980s, operating against Iran in the Persian Gulf. It was redesignated the 4th Squadron, 17th Cavalry on 15 January 1991. During the Gulf War of 1991 it was part of the 18th Aviation Brigade.

Major formations, 1950–2006
The 82nd and 101st Airborne Divisions have served with the corps since the 1950s. The 24th Infantry Division (Mechanized) was 'reflagged' as the 3rd Infantry Division (Mechanized) in April 1996.

 * 7th Infantry Division (Light)
 * 10th Mountain Division (Light Infantry)
 * XVIII Airborne Corps Artillery
 * 18th Field Artillery Brigade
 * 1st Sustainment Command (Theater)
 * 35th Signal Brigade
 * 18th Aviation Brigade (no longer active)
 * 20th Engineer Brigade
 * 525th Battlefield Surveillance Brigade
 * 108th Air Defense Artillery Brigade
 * 16th Military Police Brigade
 * 44th Medical Command
 * 163rd Ordnance
 * additional smaller, National Guard, and Reserve units

21st century
The Corps headquarters was deployed to Afghanistan from May 2002 – 2003, and became Combined Joint Task Force 180 for the deployment.

XVIII Airborne Corps was deployed from January 2005 to January 2006 to Baghdad, Iraq, where it served as the Multi-National Corps – Iraq. Following its return, XVIII Airborne Corps and its subordinate units began the process of modernization and reorganization.

Under the previous Army Chief of Staff's future restructure of the Army, the corps headquarters of the XVIII Airborne Corps will lose its airborne (specifically parachute) certification as a cost-cutting measure—the same will occur to the divisional headquarters of the 82nd Airborne Division. This plan is designed to follow the U.S. Army's restructuring plan to go from being division-based to brigade-based. This will mean that the largest units that will be airborne – specifically parachute certified – will be at the brigade level. Even so, for traditional and historical reasons, the formation will continue to be called the XVIII Airborne Corps.

The divisions that fall under the XVIII Airborne Corps (as well as the other two corps in the Army) are in a period of transition, shifting from corps control to fall directly under FORSCOM, eliminating the corps status as a middle man. This ties in with the Army's broad modularity plan, as a corps can deploy and support any unit, not just the units subordinate to the corps. The 3d Infantry Division, the 10th Mountain Division (Light Infantry), and the 101st Airborne Division (Air Assault) have already changed over to direct FORSCOM control. The 82nd Airborne Division will transfer after the division returns from Afghanistan.

In August 2006, XVIII Airborne Corps traveled to South Korea to participate in Ulchi Focus Lens, a joint training exercise between the Republic of Korea Army and coalition forces stationed there.

In mid-April, 2007, the Department of the Army confirmed the next OIF deployment schedule, with XVIII Airborne Corps deploying to relieve III Corps as the MNC-I at Camp Victory, Baghdad, Iraq. XVIII Airborne Corps is scheduled to replace III Corps in November, 2007. The corps will deploy along with 1st Armored Division and 4th Infantry Division, as well as 1st Brigade Combat Team, 10th Mountain Division, and 1st BCT, 82nd Airborne Division.

On 21 December 2016, Stars and Stripes reported that in August the XVIII Airborne Corps deployed to Iraq for Operation Inherent Resolve, in December this included the XVIII Airborne Corps headquarters and the 1st Special Forces Command, which is deployed as the Special Operations Joint Task Force – Operation Inherent Resolve. The 18th Field Artillery Brigade deployed into Iraq with High Mobility Artillery Rocket Systems.

A Canadian Army General has served with the XVIII Corps since 2007.

XVIII Airborne Corps returned to Fort Liberty in October 2022 after a nine month deployment to Germany, in support of NATO and European Allies and partners. The mission was to provide a joint task force-capable headquarters in light of the 2022 Russian invasion of Ukraine.

Structure

XVIII Airborne Corps, Fort Liberty Other supporting units:
 * 3rd Infantry Division CSIB.png 3rd Infantry Division, Fort Stewart
 * 10th Mountain Division CSIB.jpg 10th Mountain Division, Fort Drum
 * 82nd Airborne Division CSIB.svg 82nd Airborne Division, Fort Liberty
 * Combat service identification badge of the 101st Airborne Division.png 101st Airborne Division, Fort Campbell
 * 3rd Sustainment Command CSIB.svg 3rd Sustainment Command (Expeditionary), Fort Liberty
 * 7SustainBdeSSI.jpg 7th Transportation Brigade, Fort Eustis
 * US Army 16th Military Police Brigade CSIB-without tab.png 16th Military Police Brigade, Fort Liberty
 * 18thFABDENOTAB.png 18th Field Artillery Brigade, Fort Liberty
 * 20EngrBdeCSIB.jpg 20th Engineer Brigade, Fort Liberty
 * 35th home.jpg 35th Signal Brigade, Fort Liberty
 * 44th Medical Command SSI.svg 44th Medical Brigade, Fort Liberty
 * 525 BfSB.svg 525th Expeditionary Military Intelligence Brigade, Fort Liberty
 * 52nd EOD Group SSI.svg 52nd Ordnance Group (EOD), Fort Campbell and Fort Liberty, part of 20th CBRNE Command
 * 108 ADA BDE SSI.svg 108th Air Defense Artillery Brigade, Fort Liberty, part of 32nd Army Air & Missile Defense Command
 * USAF - 18th Air Support Operations Group.png 18th Air Support Operations Group, Pope Field (United States Air Force unit responsible for coordinating corps tactical air support)

Operations
The corps has participated in a number of operations since then:
 * Operation Power Pack – Dominican Republic, 1965
 * Operation Urgent Fury – Grenada, 1983
 * Operation Golden Pheasant – Honduras, 1988
 * Operation Nimrod Dancer – Panama, 1989
 * Operation Hawkeye – U.S. Virgin Islands, 1989
 * Operation Just Cause – Panama, 1989
 * Operation Desert Shield – Saudi Arabia, 1990–1991
 * Operation Desert Storm – Saudi Arabia, Kuwait and Iraq, 1991
 * Operation GTMO – Cuba, 1991
 * Operation Hurricane Andrew – Florida, 1992
 * Operation Restore Hope – Somalia, 1992
 * Operation Uphold/Maintain Democracy – Haiti, 1994
 * Operation Vigilant Warrior – Kuwait, 1994
 * Operation Joint Forge – Bosnia, 1998
 * Operation Enduring Freedom – Afghanistan, 2002, 2014
 * Operation Iraqi Freedom – Iraq, 2003, 2005, 2008
 * Operation Unified Response – Haiti, 2010
 * Operation New Dawn – Iraq, 2011
 * Operation Inherent Resolve – Iraq and Syria, 2015–2016

Commanders
Individuals who have commanded XVIII Airborne Corps include:

 * LTG Matthew B. Ridgway, 1944 – 1945
 * Division inactive, 1945 – 1952
 * LTG John W. Leonard, 1952
 * MG Thomas F. Hickey, 1952 – 1953
 * MG Joseph P. Cleland, 1953 – 1955
 * MG Ridgely Gaither, 1955
 * LTG Paul D. Adams, 1955 – 1957
 * LTG Robert F. Sink, 1957 – 1960
 * MG Dwight E. Beach (acting), 1960
 * LTG Thomas J. H. Trapnell, 1960 – 1961
 * LTG Hamilton H. Howze, 1961 – 1962
 * LTG William C. Westmoreland, 1963 – 1964
 * MG Harry H. Critz (acting), 1964
 * LTG John W. Bowen, 1964 – 1965
 * BG John A. Seitz (acting), 1965
 * BG Roderick Wetherill (acting), 1965
 * MG Joe S. Lawrie (acting), 1965
 * LTG Bruce Palmer Jr., 1965 – 1967
 * MG Joe S. Lawrie (acting), 1967
 * LTG John L. Throckmorton, 1967
 * LTG Robert H. York, 1967 – 1968
 * LTG John J. Tolson, 1968 – 1971
 * LTG John H. Hay, 1971 – 1973
 * LTG Richard J. Seitz, 1973 – 1975
 * LTG Henry E. Emerson, 1975 – 1977
 * LTG Volney F. Warner, 1977 – 1979
 * LTG Thomas H. Tackaberry, 1979 – 1981
 * LTG Jack V. Mackmull, 1981 – 1984
 * LTG James J. Lindsay, 1984 – 1986
 * LTG John W. Foss, 1986 – 1988
 * LTG Carl W. Stiner, 1988 – 1990
 * LTG Gary E. Luck, 1990
 * MG William A. Roosma (acting), 1990
 * LTG Gary E. Luck, 1990 – 1993
 * LTG Henry H. Shelton, 1993 – 1996
 * LTG John M. Keane, 1996 – 1998
 * LTG William F. Kernan, 1998 – 2000
 * LTG Dan K. McNeill, 2000 – 2003
 * LTG John R. Vines, 2003 – 2006
 * LTG Lloyd Austin III, 2006 – 2009
 * LTG Frank Helmick, 2009 – 2012
 * LTG Daniel B. Allyn, 2012 – 2013
 * LTG Joseph Anderson, 2013 – 2015
 * LTG Stephen J. Townsend, 2015 – 2018
 * LTG Paul LaCamera, 2018 – 2019
 * LTG Michael Kurilla, 2019 – 2022
 * LTG Chris Donahue, 2022 – present

Notable members

 * John D. Altenburg, MG – Deputy Judge Advocate General of the U.S. Army.
 * Ralph Eaton, BG – 82nd Airborne Division and XVIII Airborne Corps Chief of Staff.
 * Michael C. Flowers, BG – Commander, Joint POW/MIA Accounting Command.
 * Michael T. Flynn, LTG – 25th National Security Advisor, Director of the Defense Intelligence Agency
 * Charles D. Gemar, LTC – US Astronaut.
 * Teresa King, SGM – First female Commandant of the U.S. Army Drill Sergeant Academy.
 * Stanley A. McChrystal, GEN – ISAF Commander.
 * Raymond T. Odierno, GEN – 38th Army Chief of Staff.
 * James Peake, LTG – Secretary of Veterans Affairs.
 * David Petraeus, GEN – ISAF Commander and Director of the Central Intelligence Agency.
 * David M. Rodriguez, GEN – Commander, U.S. Africa Command and FORSCOM.
 * Arthur D. Simons, COL – Led the Son Tay raid during the Vietnam War.
 * Michael Tomczyk, CPT – Computer entrepreneur and joint developer of the VIC-20.
 * Thomas R. Turner II, LTG – Commanding General of United States Army North.
 * James C. Yarbrough, BG – Commander, Joint Readiness Training Center at Fort Polk.
 * Wayne Eyre, GEN – Commander of the Canadian Army and Chief of Defence Staff.

title: XVIII Airborne Corps


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Yamato Province

Yamato Province (大和国) was a province of Japan, located in Kinai, corresponding to present-day Nara Prefecture in Honshū. It was also called Washū (和州). Yamato consists of two characters, 大 "great", and 和 "Wa". At first, the name was written with one different character (大倭), but due to its offensive connotation, for about ten years after 737, this was revised to use more desirable characters (大養徳) (see Names of Japan). The final revision was made in the second year of the Tenpyō-hōji era (c. 758). It is classified as a great province in the Engishiki.

The Yamato Period in the history of Japan refers to the late Kofun Period (c. 250–538) and Asuka Period (538–710). Japanese archaeologists and historians emphasize the fact that during the early Kofun Period the Yamato Kingship was in close contention with other regional powers, such as Kibi Province near present-day Okayama Prefecture. Around the 6th century, the local chieftainship gained national control and established the Imperial court in Yamato Province.

The battleship JAPANESE BATTLESHIP Yamato, the flagship of the Japanese Combined Fleet during World War II, was named after this ancient province.

Capital
During the Kofun period (300 to 538) and the Asuka period, many palace capitals were located in Kashihara, Asuka, and Sakurai. Yamato was the first central government of the unified country in the Kofun period. Heijō-kyō capital was placed in Nara City during the Nara period.

In the 14th century, the capital of the Southern Court was established in Yoshino and Anou.

Temples
The provincial temple for monks is popularly thought to have been Tōdai-ji, but it may have in fact been a different one in Kashihara. The one for nuns was Hokke-ji.

The primary shinto shrine was Sakurai's Ōmiwa Shrine, but there have been no records stating as such found at the shrine itself. There were no secondary shrines. The sōja (or principal Shinto shrine in the province) was Kokufu Shrine (Takatori, Takaichi, Nara).

Kami of Yamato

 * Minamoto no Shigetoki
 * Minamoto no Suetō
 * Utsunomiya Nobufusa
 * Oda Hidanaga
 * Oda Toshisada
 * Oda Tatsusada
 * Oda Tatsukatsu
 * Mitsuki Naoyori
 * Honjō Fusanaga
 * Tōyama Kagetō
 * Jushii-ge Nakai Masakiyo
 * Jushii-ge Matsudaira Tomonori
 * Jushii-ge Matsudaira Naotsune
 * Jugoi-ge Kanō Hisachika
 * Jushii-ge Matsudaira Naonobu
 * Jushii-ge Matsudaira Tsunenori
 * Jushii-ge Matsudaira Naoyoshi

Domains

 * Yagyū Domain
 * Kōriyama Domain
 * Koizumi Domain
 * Yanagimoto Domain
 * Kaijū Domain / Shibamura Domain
 * Kujira Domain
 * Uda-Matsuyama Domain
 * Takatori Domain
 * Okidome Domain
 * Tatsuta Domain
 * Tawaramoto Domain
 * Kishida Domain
 * Yamato-Shinjō Domain
 * Gose Domain
 * Yamato-Gojō Domain

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Yamato Province


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User:Libaax-Sankataabte

http://www.somaliaonline.com Camel Milk Threads

title: User:Libaax-Sankataabte


text:
User talk:Linkan

Hello Linkan and welcome to Wikipedia. A few tips for you:

 * Peruse Welcome, newcomers and associated pages
 * Sign talk page entries with ~, which is automatically converted to a name and date
 * Ask questions on Village pump
 * Have fun.

-- Tim Starling 08:16 18 Jun 2003 (UTC)

FIB Secreatry General
Do we have a new Secretary General? Anyway, I'll remove that line again. John Anderson 12:34, 30 March 2007 (UTC)

title: User talk:Linkan


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List of British heritage and private railways

This is a list of heritage, private and preserved railways throughout the United Kingdom, the Crown dependencies, and British Overseas Territories whether operational or closed, that are operated for charitable purposes or shareholder profit. Some also provide economic local transport. For rail museums, see List of British railway museums.

Many of the standard-gauge railways listed, including former branch lines and ex-mainline routes, were closed by British Railways under the Beeching Axe of the 1960s. Most have been restored and operate as heritage lines. A smaller number of lines were formerly industrial or colliery railways.

Many of these preserved railways are mentioned in national and international tour guides, and visits may form part of a school curriculum or feature in other studies, including civil engineering, mechanics, social, economic and political history, visual arts and drama.

This list also includes tramways. Nearly all tram services in Britain ended in the 1950s and early 1960s, leaving just Blackpool Corporation Tramways, although some big cities have since revived them in the late 20th century onwards.

This list includes those railways which has public open days and excludes those on private sites which are not advertised to the public.

Standard gauge

 * Colne Valley Railway, Castle Hedingham, Essex
 * Epping Ongar Railway, Ongar, Essex
 * Mid-Norfolk Railway, Dereham, Norfolk
 * Mid Suffolk Light Railway, Brockford, Suffolk
 * Nene Valley Railway, Wansford, Cambridgeshire
 * North Norfolk Railway, Sheringham, Norfolk

Railway centres and museums

 * Bressingham Steam and Gardens, Diss, Norfolk
 * East Anglian Railway Museum, Chappel & Wakes Colne Station, Essex
 * Mangapps Railway Museum, Burnham-on-Crouch, Essex
 * Railworld Wildlife Haven, Peterborough, Cambridgeshire
 * Whitwell & Reepham Railway, Reepham, Norfolk

Narrow gauge

 * Bressingham Steam and Gardens, Diss, Norfolk
 * Great Whipsnade Railway, Whipsnade Zoo, Bedfordshire
 * Leighton Buzzard Light Railway, Bedfordshire
 * Southend Pier Railway, Southend-on-Sea, Essex
 * Southwold Steamworks, Southwold, Suffolk
 * Waltham Abbey Royal Gunpowder Mills, Essex
 * Yaxham Light Railway, Norfolk – private site

Miniature gauge

 * Audley End Railway, Essex
 * Bure Valley Railway, Aylsham, Norfolk
 * Bushey Miniature Railway, Bushey, Hertfordshire
 * East Herts Miniature Railway, Ware, Hertfordshire
 * Eaton Park Miniature Railway, Norwich, Norfolk
 * Fancott Miniature Railway, Bedfordshire
 * Rex Express, Paradise Wildlife Park, Hertfordshire
 * Great Woburn Railway, Woburn, Bedfordshire
 * Wells & Walsingham Light Railway, Wells-next-the-Sea, Norfolk

Tramways

 * East Anglia Transport Museum, Lowestoft, Suffolk

Standard gauge

 * Battlefield Line, Shackerstone, Leicestershire
 * Ecclesbourne Valley Railway, Wirksworth, Derbyshire
 * Great Central Railway, Loughborough, Leicestershire
 * Great Central Railway (Nottingham), Ruddington, Nottinghamshire
 * Lincolnshire Wolds Railway, Ludborough, Lincolnshire
 * Midland Railway – Butterley, Derbyshire
 * Mountsorrel Railway, Mountsorrel, Leicestershire
 * Northampton & Lamport Railway, Pitsford and Brampton, Northamptonshire
 * Northants Ironstone Railway, Hunsbury Hill, Northamptonshire
 * Peak Rail, Matlock, Derbyshire
 * Rushden, Higham & Wellingborough Railway, Rushden, Northamptonshire

Railway centres and museums

 * Appleby Frodingham Railway, Scunthorpe, Lincolnshire
 * Barrow Hill Roundhouse, Barrow Hill nr Chesterfield, Derbyshire
 * Nottingham Heritage Railway, Ruddington, Nottinghamshire
 * Rutland Railway Museum, Cottesmore, Rutland

Narrow gauge

 * Billing Aquadrome Miniature Railway, Great Billing, Northamptonshire
 * Crowle Peatland Railway, Crowle, North Lincolnshire
 * Derbyshire Dales Narrow Gauge Railway, Rowsley, Derbyshire
 * Golden Valley Light Railway, Butterley, Derbyshire
 * Irchester Narrow Gauge Railway Museum, Irchester, Wellingborough, Northamptonshire
 * Lincolnshire Coast Light Railway, Skegness, Lincolnshire
 * Narrow Gauge Railway, Mountsorrel, Leicestershire
 * North Ings Farm Railway, Lincolnshire
 * Sherwood Forest Railway, Nottinghamshire
 * Steeple Grange Light Railway, Wirksworth, Derbyshire
 * Wicksteed Park Railway, Kettering, Northamptonshire

Miniature gauge

 * Cleethorpes Coast Light Railway, Lincolnshire
 * Mablethorpe Miniature Railway, Queens Park, Mablethorpe, Lincolnshire
 * Stapleford Miniature Railway, near Melton Mowbray, Leicestershire

Tramways

 * National Tramway Museum, Crich, Derbyshire

Standard gauge

 * Aln Valley Railway, Alnwick, Northumberland
 * Bowes Railway, Tyne and Wear
 * Derwent Valley Light Railway, Murton, North Yorkshire
 * East Lancashire Railway, Bury, Greater Manchester
 * Eden Valley Railway, Warcop, Cumbria
 * Embsay and Bolton Abbey Steam Railway, Embsay, North Yorkshire
 * Keighley & Worth Valley Railway, Haworth, West Yorkshire
 * Lakeside and Haverthwaite Railway, Haverthwaite, nr Staveley, Cumbria
 * Middleton Railway, Hunslet, West Yorkshire
 * North Tyneside Steam Railway, North Shields, Tyne and Wear
 * North Yorkshire Moors Railway, Pickering, North Yorkshire
 * Ribble Steam Railway, Preston, Lancashire
 * Stainmore Railway, Kirkby Stephen, Cumbria
 * Tanfield Railway, Marley Hill, County Durham
 * Weardale Railway, Stanhope, County Durham
 * Wensleydale Railway, Leeming Bar, North Yorkshire
 * Yorkshire Wolds Railway, Sledmere–Fimber, East Yorkshire

Railway centres and museums

 * Beamish Museum & Railway Centre, County Durham
 * Carnforth Railway Centre, Carnforth, Lancashire - private site
 * Crewe Heritage Centre, Crewe, Cheshire
 * Head of Steam, Darlington, County Durham
 * Leeds Industrial Museum, Armley, West Yorkshire
 * Locomotion, Shildon, County Durham
 * National Railway Museum, York, North Yorkshire
 * South Yorkshire Transport Museum, Aldwarke, Rotherham, South Yorkshire
 * Stephenson Railway Museum, West Chirton, Tyne and Wear

Narrow gauge

 * Eaton Hall Railway, Cheshire – private site
 * Heatherslaw Light Railway, Northumberland
 * South Tynedale Railway between Alston, Cumbria and Slaggyford, Northumberland
 * Threlkeld Quarry Railway, Cumbria
 * West Lancashire Light Railway, Hesketh Bank, Lancashire
 * Woodhorn Narrow Gauge Railway, Ashington, Northumberland

Miniature gauge

 * All in one Miniature Railway, Knutsford nr Allostock, Cheshire
 * Blackpool Zoo Railway, Blackpool, Lancashire
 * Brookside Miniature Railway, Poynton, Cheshire
 * Dragon Miniature Railway, Marple, nr Stockport, Greater Manchester
 * High Legh Miniature Railway, High Legh, Cheshire
 * Whistlestop Valley, Clayton West, West Yorkshire
 * Knowsley Safari Park Railway, Knowsley, Merseyside
 * Halton Miniature Railway, Runcorn, Cheshire
 * Lakeside Miniature Railway, Pleasureland Southport, Merseyside
 * North Bay Railway, Scarborough, North Yorkshire
 * Pleasure Beach Express, Blackpool Pleasure Beach, Lancashire
 * Pugneys Light Railway, Wakefield, West Yorkshire
 * Ravenglass & Eskdale Railway, Cumbria
 * Wirral Model Engineering Society, Royden Park, Wirral, Merseyside
 * Saltburn Miniature Railway, Saltburn, North Yorkshire
 * South Park Miniature Railway, Cheadle Hulme, Greater Manchester
 * Teesside Small Gauge Railway, Preston Park, Stockton-on-Tees
 * Walton Park Miniature Railway, Sale, Greater Manchester
 * Windmill Farm Railway, Bursough, Lancashire
 * Thorpe Light Railway, Whorlton, County Durham

Tramways

 * Beamish Museum, County Durham
 * Bradford Industrial Museum, Eccleshill, (nr Bradford), West Yorkshire
 * Heaton Park Tramway, Manchester, Greater Manchester
 * Shipley Glen Tramway, Shipley, West Yorkshire
 * Wirral Transport Museum and Heritage Tramway, Birkenhead, Merseyside

Standard gauge

 * Bluebell Railway, Sheffield Park, Sussex
 * Chinnor & Princes Risborough Railway, Chinnor, Oxfordshire / Princes Risborough, Buckinghamshire
 * Cholsey & Wallingford Railway, Wallingford, Oxfordshire
 * East Kent Railway, Shepherdswell, Kent
 * Isle of Wight Steam Railway, Havenstreet, Isle of Wight
 * Kent & East Sussex Steam Railway, Tenterden, Kent
 * Lavender Line, Isfield, East Sussex
 * Rother Valley Railway, Robertsbridge, East Sussex (line extension under construction)
 * Spa Valley Railway, Royal Tunbridge Wells, Kent
 * Watercress Line, New Alresford, Hampshire

Railway centres and museums

 * Buckinghamshire Railway Centre, Quainton, Aylesbury, Buckinghamshire
 * Chatham Historic Dockyard Railway, Kent
 * Didcot Railway Centre, Didcot, Oxfordshire
 * London Transport Museum, Covent Garden, Central London
 * Southall Railway Centre, Southall, West London- private site

Narrow gauge

 * Amberley Museum Railway, Amberley, West Sussex
 * Great Bush Railway, Tinkers Park, Hadlow Down, East Sussex
 * Bredgar & Wormshill Light Railway, near Sittingbourne, Kent
 * Exbury Gardens Railway, Beaulieu, Hampshire
 * Hayling Seaside Railway, Hayling Island, Hampshire
 * Hollycombe Steam Collection, near Liphook, Hampshire
 * Hythe Pier Ferry Railway, Hampshire
 * Old Kiln Light Railway, Rural Life Centre, Reeds Road, Tilford, Farnham, Surrey
 * Hampton & Kempton Waterworks Railway, Hanworth/Hampton, London.
 * London Museum of Water & Steam, Kew Bridge, Brentford, London
 * Mail Rail, short section of the former London Post Office Railway opened to public since 2017
 * Romney, Hythe & Dymchurch Railway, Kent
 * Sittingbourne & Kemsley Light Railway, Kent
 * Volk's Electric Railway, Brighton, East Sussex

Miniature gauge

 * Bekonscot Light Railway, Beaconsfield, Buckinghamshire
 * Blenheim Park Railway, Blenheim Palace, Oxfordshire
 * Beech Hurst Park Miniature Railway, Haywards Heath, West Sussex
 * Crowborough Miniature Railway, Crowborough, East Sussex
 * Eastleigh Lakeside Steam Railway, Hampshire
 * Frimley Lodge Park Railway, Surrey
 * Great Cockcrow Railway, Chertsey, Surrey
 * Harlington Locomotive Society, Hayes, Middlesex
 * Hastings Miniature Railway, Hastings Seafront, East Sussex
 * Ickenham Miniature Railway, Ickenham, London
 * Jocks Lane Miniature Railway, Bracknell, Berkshire
 * Leatherhead Model Railway, Leatherhead, Surrey
 * Littlehampton Miniature Railway, Littlehampton, West Sussex
 * Malden District Society of Model Engineers, Thames Ditton, Surrey
 * Moors Valley Railway, near Ringwood, Hampshire
 * Pinewood Model Railway, Pinewood, Crowthorne
 * Reading Society of Model Engineers, Reading Berkshire
 * Royal Victoria Railway, Southampton, Hampshire
 * Ruislip Lido Railway, Ruislip, London
 * South Downs Light Railway, Pulborough, West Sussex
 * Swanley New Barn Railway, Swanley, Kent
 * Watford Miniature Railway, Cassiobury Park, Watford, Hertfordshire
 * Woking Miniature Railway, Knaphill, Surrey

Standard gauge

 * Avon Valley Railway, Bitton, South Gloucestershire
 * Bodmin & Wenford Railway, Bodmin, Cornwall
 * Dartmouth Steam Railway, Paignton, Devon
 * Dean Forest Railway, Norchard, Gloucestershire
 * East Somerset Railway, Cranmore, Somerset
 * Helston Railway, Prospidnick, Cornwall
 * Plym Valley Railway, Marsh Mills, Plympton, Devon
 * North Dorset Railway, Shillingstone, Dorset
 * Somerset & Dorset Railway, Midsomer Norton, Somerset
 * South Devon Railway, Buckfastleigh, Devon
 * Swanage Railway, Swanage, Dorset
 * Swindon & Cricklade Railway, Blunsdon, Wiltshire
 * Tarka Valley Railway, Great Torrington, Devon
 * West Somerset Railway, Minehead, Somerset

Railway centres and museums

 * Bideford Railway Heritage Centre, Bideford, Devon
 * Bristol Harbour Railway, Bristol
 * Steam – Museum of the Great Western Railway, Swindon, Wiltshire
 * Yeovil Railway Centre, Yeovil, Somerset

Narrow gauge

 * Bicton Woodland Railway, Devon
 * Devon Railway Centre, Bickleigh, Devon
 * Exmoor Steam Railway, Devon – private site
 * Gartell Light Railway, Templecombe, Somerset
 * Launceston Steam Railway, Launceston, Cornwall
 * Lea Bailey Light Railway. Gloucestershire / Herefordshire border
 * Lynbarn Railway, Devon
 * Lynton & Barnstaple Railway, Woody Bay, Devon
 * Morwellham Quay Open Air Museum, Devon
 * Westonzoyland Pumping Station Museum, Somerset

Miniature gauge

 * Beer Heights Light Railway, Devon
 * Berkeley Light Railway, Gloucestershire
 * Exmouth Miniature Railway, Devon
 * Gorse Blossom Farm Railway, Devon
 * Lappa Valley Steam Railway, Cornwall
 * Longleat Railway, Wiltshire
 * Moors Valley Railway, Ashley Heath, Dorset
 * Perrygrove Railway, Coleford, Gloucestershire
 * Bickington Steam Railway, Trago Mills, Devon

Tramways

 * Seaton Tramway, Seaton, Devon

Standard gauge

 * Cambrian Heritage Railways, Oswestry and Llynclys, Shropshire
 * Chasewater Railway, Chasewater Country Park, Brownhills, Staffordshire
 * Churnet Valley Railway, Cheddleton, Staffordshire
 * Foxfield Railway, Blythe Bridge, Staffordshire
 * Gloucestershire Warwickshire Railway, Toddington, Gloucestershire and Broadway, Worcestershire
 * Severn Valley Railway, Bridgnorth, Shropshire and Kidderminster, Worcestershire
 * Telford Steam Railway, Horsehay, Shropshire

Railway centres and museums

 * Coleford Great Western Railway Museum, Coleford, Gloucestershire
 * Tyseley Railway Centre, Tyseley, Warwickshire
 * Winchcombe Railway Museum, Winchcombe, Gloucestershire

Narrow gauge

 * Amerton Railway, Staffordshire
 * Apedale Valley Light Railway, Chesterton, Newcastle Under Lyme, Staffordshire
 * Bromyard and Linton Light Railway, Bromyard, Herefordshire – private site
 * Moseley Railway Trust, Chesterton, Newcastle-under-Lyme, Staffordshire
 * North Gloucestershire Railway, Toddington, Gloucestershire
 * Perrygrove Railway, Gloucestershire
 * Rudyard Lake Steam Railway, Rudyard, Staffordshire
 * Statfold Barn Railway, Tamworth, Staffordshire

Miniature gauge

 * Broomy Hill Railway, Herefordshire
 * Downs Light Railway, Colwall, Worcestershire (also the oldest private miniature railway worldwide)
 * Echills Wood Railway, Kingsbury Waterpark, Warwickshire
 * Evesham Vale Light Railway, Evesham Country Park, Worcestershire
 * Weston Park Railway, Shropshire
 * Rainsbrook Valley Railway, Onley Lane, Warwickshire

Tramways

 * Black Country Living Museum, Dudley, West Midlands

East of England

 * Leiston Works Railway, Leiston, Suffolk (currently under construction)
 * Norfolk Orbital Railway, Holt, Norfolk
 * Southwold Railway, Blythburgh and Southwold, Suffolk
 * Wisbech and March Railway, Waldersea, Cambridgeshire

North of England

 * Poulton and Wyre Railway, Thornton–Cleveleys, Lancashire (under restoration)

South of England

 * North Somerset Railway, Radstock, Somerset
 * Tarka Valley Railway, Torrington, Devon
 * Vale of Berkeley Railway, Sharpness, Gloucestershire

Defunct
This is a list of former heritage railway attractions that are sadly defunct.
 * Ashford Steam Centre, Willesborough, Kent – closed in 1976.
 * Abbey Light Railway, Kirkstall, West Yorkshire – closed in 2012.
 * Brockham Railway Museum, Dorking, Surrey – closed 1982 (Stock moved to Amberley Museum Railway, West Sussex)
 * Bolebroke Castle Miniature Railway, East Sussex – closed 2012
 * Buxton Steam Centre, Derbyshire – closed in 1987, as Peak Rail moved to Darley Dale.
 * Cadeby Light Railway, Cadeby, Leicestershire – closed in 2005.
 * Chester Zoo monorail, Chester Zoo, Chester
 * Creekmoor Light Railway, Poole, Dorset – closed in 1973
 * Dinting Railway Centre, Derbyshire – closed in 1991, (Society moved to Ingrow (West) station on the KWVR, West Yorkshire.)
 * Dowty Railway Centre, Ashchurch, Gloucestershire – closed in the 1980s
 * Eastbourne Tramway, East Sussex – closed 1969, (moved to Seaton, Devon)
 * Electric Railway Museum, Warwickshire - closed in October 2017, (rolling stock relocated to other preserved railways across the UK).
 * Elsecar Heritage Railway, South Yorkshire - closed 2020.
 * Finmere railway station, Buckinghamshire (stock relocated after the land was developed for HS2).
 * Great Yorkshire Railway Preservation Society, Starbeck, North Yorkshire – closed in 1989 (Group moved to Murton, near York, to restore part of the former Derwent Valley Light Railway)
 * Lincolnshire Coast Light Railway, Humberston, Lincolnshire – closed 1985 - Rebuilt 2009 in Skegness.
 * Markeaton Park Light Railway, Rowsley, Derbyshire - closed in 2016, track lifted in 2017.
 * Marwell Wildlife Railway, Hampshire - closed in 2021 and track lifted by end of 2022.
 * Museum of British Transport, Clapham, South London – closed in 1973. Some exhibits moved first to Syon Park, West London and subsequently to Covent Garden to form London Transport Museum. Some exhibits moved to N.R.M. York.
 * North Downs Steam Railway, Dartford, Kent – closed in 1995 (society merged with Spa Valley Railway)
 * North Woolwich Old Station Museum, East London – closed in 2008
 * Queen Mary's Hospital Miniature Railway, Carshalton, South London - Closed in 1997
 * Ramsgate Tunnel Railway, Ramsgate, Kent – closed in 1965
 * Snibston Railway, Coalville, Leicestershire – closed on 31 July 2015 (as with the Discovery Museum, itself)
 * Southport Pier Tramway, Southport, Merseyside - closed 2015
 * Southport Railway Museum, Southport, Lancashire – closed in 1999 (Society moved to Preston Docks as the Ribble Steam Railway).
 * Stevington & Turvey Light Railway, Turvey, Bedfordshire – private site - closed in 2014.
 * Transperience, Low Moor, Bradford, Yorkshire – closed in 1997
 * Wells Harbour Railway, in Norfolk - closed in 2021
 * Westerham Valley Railway Association, Westerham, Kent – closed 1965 (merged with Kent and East Sussex Railway Preservation Society with a few items of stock transferred to KWVR.)

Northern Ireland
See List of heritage railways in Northern Ireland

Irish standard gauge

 * Downpatrick and County Down Railway, County Down

Railway centres and museums

 * Whitehead Railway Museum, Whitehead, County Antrim
 * Ulster Folk and Transport Museum, Cultra, County Down

Narrow gauge

 * Foyle Valley Railway, County Londonderry
 * Giant's Causeway and Bushmills Railway, County Antrim
 * Peatlands Park Railway, County Armagh

Defunct

 * Shane's Castle Railway, County Antrim – closed 1994 (stock moved to Giants Causeway and Bushmills Railway.)

Central Highlands

 * Keith & Dufftown Railway, Dufftown, Banffshire and Keith, Morayshire
 * Strathspey Railway, Aviemore, Highland

East Coast of Scotland

 * Bo'ness and Kinneil Railway, Bo'ness, Falkirk
 * Fife Heritage Railway, Leven, Fife
 * Caledonian Railway, Brechin, Angus
 * Royal Deeside Railway, Milton of Crathes, Aberdeenshire

South West Scotland

 * Scottish Industrial Railway Centre, Dunaskin - Waterside, East Ayrshire

Railway centres and museums

 * Museum of Scottish Railways, Bo'ness, Falkirk
 * Riverside Museum, Glasgow
 * Summerlee Museum of Scottish Industrial Life, Coatbridge, North Lanarkshire

Narrow gauge

 * Alford Valley Railway, Alford, Aberdeenshire
 * Almond Valley Light Railway, Livingston, West Lothian
 * Leadhills and Wanlockhead Railway, South Lanarkshire

Miniature railways

 * Craigtoun Miniature Railway, St Andrews, Fife
 * Ness Islands Railway, Inverness

Proposed

 * Waverley Route Heritage Association, Whitrope, Roxburghshire

Defunct

 * Isle of Mull Railway, Inner Hebrides – closed in 2011.
 * Kerr's Miniature Railway, Arbroath - closed in 2020.
 * Lochty Private Railway, Fife – closed in 1992.
 * Sanday Light Railway, Braeswick, Orkney – closed in 2006.

Standard gauge

 * Dolgarrog Railway, Conwy (under construction)
 * Bala & Ffestiniog Railway Heritage Trust, Maentwrog Road, Gwynedd (currently under restoration)

Narrow gauge

 * Glyn Valley Tramway, Chirk, Wrexham

Standard gauge

 * Garw Valley Railway, Pontycymer, Bridgend
 * Maerdy Heritage Railway, Maerdy, Rhondda Cynon Taf

Defunct

 * Butetown Historical Railway Society, Cardiff Bay – closed in 1997, moved to Barry Tourist Railway
 * Caerphilly Railway Society, Caerphilly Railway Works – closed 1996, moved to Gwili Railway
 * Gloddfa Ganol, Blaenau Ffestiniog - museum of narrow-gauge railways, closed in 1998, stock sold at auction
 * Swansea Vale Railway, Pentrechwyth – closed in 2009, (most of the track and rolling stock are now located on the Gwili Railway).
 * Penrhyn Quarry Railway, Bethesda, Gwynedd
 * Trawsfynydd and Blaenau Ffestiniog Railway, Closed and replaced by Bala & Ffestiniog Railway Heritage Trust

Derelict
See Rail transport in the Isle of Man.
 * Queen's Pier Tramway, Ramsey
 * Second Falcon Cliff lift, Douglas

Channel Islands

 * Alderney Railway, Alderney
 * Pallot Heritage Steam Museum, Jersey

Falkland Islands

 * Camber Railway, Stanley (defunct)


text:
Darkness

Darkness is defined as a lack of illumination, an absence of visible light, or a surface that absorbs light.

Human vision is unable to distinguish colors in conditions of very low luminance because the hue-sensitive photoreceptor cells on the retina are inactive when light levels are insufficient, in the range of visual perception referred to as scotopic vision.

The emotional response to darkness has generated metaphorical usages of the term in many cultures, often used to describe an unhappy or foreboding feeling.

"Darkness" may also refer to night, which occurs when the Sun is more than 18° below the horizon.

Perception
The perception of darkness differs from the mere absence of light that sometimes lead to afterimages. In perceiving, the eye is active, and the part of the retina that is unstimulated produces a complementary afterimage.

Physics
In terms of physics, an object is said to be dark when it absorbs photons, causing it to appear dim compared to other objects. For example, matte black paint does not reflect much visible light and appears dark, whereas white paint reflects much light and appears bright. For more information, see color. An object may appear dark, but it may be bright at a frequency that humans cannot perceive.

A dark area has limited light sources, making things hard to see. Exposure to alternating light and darkness (night and day) has caused several evolutionary adaptations to darkness. When a vertebrate, like a human, enters a dark area, its pupils dilate, allowing more light to enter the eye and improving night vision. Also, the light detecting cells in the human eye (rods and cones) will regenerate more unbleached rhodopsin when adapting to darkness.

One scientific measure of darkness is the Bortle scale, which indicates the night sky's and stars' brightness at a particular location, and the observability of celestial objects at that location.

The material known as Vantablack is one of the darkest substances known, absorbing up to 99.965% of visible light (at 663 nm if the light is perpendicular to the material), and was developed by Surrey NanoSystems in the United Kingdom. The name is a compound of the acronym VANTA (vertically aligned nanotube arrays) and the color black.

Technical
The color of a point, on a standard 24-bit computer display, is defined by three RGB (red, green, blue) values, each ranging from 0–255. When the red, green, and blue components of a pixel are fully illuminated (255,255,255), the pixel appears white; when all three components are unilluminated (0,0,0), the pixel appears black.

Artistic

Artists use darkness to emphasize and contrast the presence of light. Darkness can be used as a counterpoint to areas of lightness to create leading lines and voids. Such shapes draw the eye around areas of the painting. Shadows add depth and perspective to a painting. See chiaroscuro for a discussion of the uses of such contrasts in visual media.

Color paints are mixed together to create darkness, because each color absorbs certain frequencies of light. Theoretically, mixing together the three primary colors, or the three secondary colors, will absorb all visible light and create black. In practice, it is difficult to prevent the mixture from taking on a brown tint.

Literature

As a poetic term in the Western world, darkness is used to connote the presence of shadows, evil, and foreboding, or in modern parlance, to connote that a story is grim, heavy, and/or depressing.

Religion
The first creation narrative in Judaism and Christianity begins with darkness, into which is introduced the creation of light, and the separation of this light from the darkness (as distinct from the creation of the Sun and Moon on the fourth day of creation). Thus, although both light and darkness are included in the comprehensive works of God, darkness was considered "the second to last plague" (Exodus 10:21), and the location of "weeping and gnashing of teeth" (Matthew 8:12).

Erebus was a primordial deity in Greek mythology, representing the personification of darkness.

Philosophy
In Chinese philosophy, yin is the complementary feminine part of the taijitu and is represented by a dark lobe.

Poetry
The use of darkness as a rhetorical device has a long-standing tradition. William Shakespeare, working in the 16th and 17th centuries, made a character called the "prince of darkness" (King Lear: III, iv) and gave darkness jaws with which to devour love. (A Midsummer Night's Dream: I, i) Geoffrey Chaucer, a 14th-century Middle English writer of The Canterbury Tales, wrote that knights must cast away the "workes of darkness". In Divine Comedy, Dante described hell as "solid darkness stain'd".

Language
In Old English there were three words that could mean darkness: heolstor, genip, and sceadu. Heolstor also meant "hiding-place" and became holster. Genip meant "mist" and fell out of use like many strong verbs. It is however still used in the Dutch saying "in het geniep" which means secretly. Sceadu meant "shadow" and remained in use. The word dark eventually evolved from the word deorc.

title: Darkness


text:
Local homeomorphism

In mathematics, more specifically topology, a local homeomorphism is a function between topological spaces that, intuitively, preserves local (though not necessarily global) structure. If $$f : X \to Y$$ is a local homeomorphism, $$X$$ is said to be an étale space over $$Y.$$ Local homeomorphisms are used in the study of sheaves. Typical examples of local homeomorphisms are covering maps.

A topological space $$X$$ is locally homeomorphic to $$Y$$ if every point of $$X$$ has a neighborhood that is homeomorphic to an open subset of $$Y.$$ For example, a manifold of dimension $$n$$ is locally homeomorphic to $$\R^n.$$

If there is a local homeomorphism from $$X$$ to $$Y,$$ then $$X$$ is locally homeomorphic to $$Y,$$ but the converse is not always true. For example, the two dimensional sphere, being a manifold, is locally homeomorphic to the plane $$\R^2,$$ but there is no local homeomorphism $$S^2 \to \R^2.$$

Formal definition
A function $$f : X \to Y$$ between two topological spaces is called a if every point $$x \in X$$ has an open neighborhood $$U$$ whose image $$f(U)$$ is open in $$Y$$ and the restriction $$f\big\vert_U : U \to f(U)$$ is a homeomorphism (where the respective subspace topologies are used on $$U$$ and on $$f(U)$$).

Examples and sufficient conditions
Local homeomorphisms versus homeomorphisms

Every homeomorphism is a local homeomorphism. But a local homeomorphism is a homeomorphism if and only if it is bijective. A local homeomorphism need not be a homeomorphism. For example, the function $$\R \to S^1$$ defined by $$t \mapsto e^{it}$$ (so that geometrically, this map wraps the real line around the circle) is a local homeomorphism but not a homeomorphism. The map $$f : S^1 \to S^1$$ defined by $$f(z) = z^n,$$ which wraps the circle around itself $$n$$ times (that is, has winding number $$n$$), is a local homeomorphism for all non-zero $$n,$$ but it is a homeomorphism only when it is bijective (that is, only when $$n = 1$$ or $$n = -1$$).

Generalizing the previous two examples, every covering map is a local homeomorphism; in particular, the universal cover $$p : C \to Y$$ of a space $$Y$$ is a local homeomorphism. In certain situations the converse is true. For example: if $$p : X \to Y$$ is a proper local homeomorphism between two Hausdorff spaces and if $$Y$$ is also locally compact, then $$p$$ is a covering map.

Local homeomorphisms and composition of functions

The composition of two local homeomorphisms is a local homeomorphism; explicitly, if $$f : X \to Y$$ and $$g : Y \to Z$$ are local homeomorphisms then the composition $$g \circ f : X \to Z$$ is also a local homeomorphism. The restriction of a local homeomorphism to any open subset of the domain will again be a local homomorphism; explicitly, if $$f : X \to Y$$ is a local homeomorphism then its restriction $$f\big\vert_U : U \to Y$$ to any $$U$$ open subset of $$X$$ is also a local homeomorphism.

If $$f : X \to Y$$ is continuous while both $$g : Y \to Z$$ and $$g \circ f : X \to Z$$ are local homeomorphisms, then $$f$$ is also a local homeomorphism.

Inclusion maps

If $$U \subseteq X$$ is any subspace (where as usual, $$U$$ is equipped with the subspace topology induced by $$X$$) then the inclusion map $$i : U \to X$$ is always a topological embedding. But it is a local homeomorphism if and only if $$U$$ is open in $$X.$$ The subset $$U$$ being open in $$X$$ is essential for the inclusion map to be a local homeomorphism because the inclusion map of a non-open subset of $$X$$ yields a local homeomorphism (since it will not be an open map).

The restriction $$f\big\vert_U : U \to Y$$ of a function $$f : X \to Y$$ to a subset $$U \subseteq X$$ is equal to its composition with the inclusion map $$i : U \to X;$$ explicitly, $$f\big\vert_U = f \circ i.$$ Since the composition of two local homeomorphisms is a local homeomorphism, if $$f : X \to Y$$ and $$i : U \to X$$ are local homomorphisms then so is $$f\big\vert_U = f \circ i.$$ Thus restrictions of local homeomorphisms to open subsets are local homeomorphisms.

Invariance of domain

Invariance of domain guarantees that if $$f : U \to \R^n$$ is a continuous injective map from an open subset $$U$$ of $$\R^n,$$ then $$f(U)$$ is open in $$\R^n$$ and $$f : U \to f(U)$$ is a homeomorphism. Consequently, a continuous map $$f : U \to \R^n$$ from an open subset $$U \subseteq \R^n$$ will be a local homeomorphism if and only if it is a locally injective map (meaning that every point in $$U$$ has a neighborhood $$N$$ such that the restriction of $$f$$ to $$N$$ is injective).

Local homeomorphisms in analysis

It is shown in complex analysis that a complex analytic function $$f : U \to \Complex$$ (where $$U$$ is an open subset of the complex plane $$\Complex$$) is a local homeomorphism precisely when the derivative $$f^{\prime}(z)$$ is non-zero for all $$z \in U.$$ The function $$f(x) = z^n$$ on an open disk around $$0$$ is not a local homeomorphism at $$0$$ when $$n \geq 2.$$ In that case $$0$$ is a point of "ramification" (intuitively, $$n$$ sheets come together there).

Using the inverse function theorem one can show that a continuously differentiable function $$f : U \to \R^n$$ (where $$U$$ is an open subset of $$\R^n$$) is a local homeomorphism if the derivative $$D_x f$$ is an invertible linear map (invertible square matrix) for every $$x \in U.$$ (The converse is false, as shown by the local homeomorphism $$f : \R \to \R$$ with $$f(x) = x^3$$). An analogous condition can be formulated for maps between differentiable manifolds.

Local homeomorphisms and fibers

Suppose $$f : X \to Y$$ is a continuous open surjection between two Hausdorff second-countable spaces where $$X$$ is a Baire space and $$Y$$ is a normal space. If every fiber of $$f$$ is a discrete subspace of $$X$$ (which is a necessary condition for $$f : X \to Y$$ to be a local homeomorphism) then $$f$$ is a $$Y$$-valued local homeomorphism on a dense open subset of $$X.$$ To clarify this statement's conclusion, let $$O = O_f$$ be the (unique) largest open subset of $$X$$ such that $$f\big\vert_O : O \to Y$$ is a local homeomorphism. If every fiber of $$f$$ is a discrete subspace of $$X$$ then this open set $$O$$ is necessarily a subset of $$X.$$ In particular, if $$X \neq \varnothing$$ then $$O \neq \varnothing;$$ a conclusion that may be false without the assumption that $$f$$'s fibers are discrete (see this footnote for an example). One corollary is that every continuous open surjection $$f$$ between completely metrizable second-countable spaces that has discrete fibers is "almost everywhere" a local homeomorphism (in the topological sense that $$O_f$$ is a dense open subset of its domain). For example, the map $$f : \R \to [0, \infty)$$ defined by the polynomial $$f(x) = x^2$$ is a continuous open surjection with discrete fibers so this result guarantees that the maximal open subset $$O_f$$ is dense in $$\R;$$ with additional effort (using the inverse function theorem for instance), it can be shown that $$O_f = \R \setminus \{0\},$$ which confirms that this set is indeed dense in $$\R.$$ This example also shows that it is possible for $$O_f$$ to be a dense subset of $$f$$'s domain. Because every fiber of every non-constant polynomial is finite (and thus a discrete, and even compact, subspace), this example generalizes to such polynomials whenever the mapping induced by it is an open map.

Local homeomorphisms and Hausdorffness

There exist local homeomorphisms $$f : X \to Y$$ where $$Y$$ is a Hausdorff space but $$X$$ is not. Consider for instance the quotient space $$X = \left(\R \sqcup \R\right) / \sim,$$ where the equivalence relation $$\sim$$ on the disjoint union of two copies of the reals identifies every negative real of the first copy with the corresponding negative real of the second copy. The two copies of $$0$$ are not identified and they do not have any disjoint neighborhoods, so $$X$$ is not Hausdorff. One readily checks that the natural map $$f : X \to \R$$ is a local homeomorphism. The fiber $$f^{-1}(\{y\})$$ has two elements if $$y \geq 0$$ and one element if $$y < 0.$$ Similarly, it is possible to construct a local homeomorphisms $$f : X \to Y$$ where $$X$$ is Hausdorff and $$Y$$ is not: pick the natural map from $$X = \R \sqcup \R$$ to $$Y = \left(\R \sqcup \R\right) / \sim$$ with the same equivalence relation $$\sim$$ as above.

Properties
A map is a local homeomorphism if and only if it is continuous, open, and locally injective. In particular, every local homeomorphism is a continuous and open map. A bijective local homeomorphism is therefore a homeomorphism.

Whether or not a function $$f : X \to Y$$ is a local homeomorphism depends on its codomain. The image $$f(X)$$ of a local homeomorphism $$f : X \to Y$$ is necessarily an open subset of its codomain $$Y$$ and $$f : X \to f(X)$$ will also be a local homeomorphism (that is, $$f$$ will continue to be a local homeomorphism when it is considered as the surjective map $$f : X \to f(X)$$ onto its image, where $$f(X)$$ has the subspace topology inherited from $$Y$$). However, in general it is possible for $$f : X \to f(X)$$ to be a local homeomorphism but $$f : X \to Y$$ to be a local homeomorphism (as is the case with the map $$f : \R \to \R^2$$ defined by $$f(x) = (x, 0),$$ for example). A map $$f : X \to Y$$ is a local homomorphism if and only if $$f : X \to f(X)$$ is a local homeomorphism and $$f(X)$$ is an open subset of $$Y.$$

Every fiber of a local homeomorphism $$f : X \to Y$$ is a discrete subspace of its domain $$X.$$

A local homeomorphism $$f : X \to Y$$ transfers "local" topological properties in both directions:
 * $$X$$ is locally connected if and only if $$f(X)$$ is;
 * $$X$$ is locally path-connected if and only if $$f(X)$$ is;
 * $$X$$ is locally compact if and only if $$f(X)$$ is;
 * $$X$$ is first-countable if and only if $$f(X)$$ is.

As pointed out above, the Hausdorff property is not local in this sense and need not be preserved by local homeomorphisms.

The local homeomorphisms with codomain $$Y$$ stand in a natural one-to-one correspondence with the sheaves of sets on $$Y;$$ this correspondence is in fact an equivalence of categories. Furthermore, every continuous map with codomain $$Y$$ gives rise to a uniquely defined local homeomorphism with codomain $$Y$$ in a natural way. All of this is explained in detail in the article on sheaves.

Generalizations and analogous concepts
The idea of a local homeomorphism can be formulated in geometric settings different from that of topological spaces. For differentiable manifolds, we obtain the local diffeomorphisms; for schemes, we have the formally étale morphisms and the étale morphisms; and for toposes, we get the étale geometric morphisms.

title: Local homeomorphism


text:
Talk:Amplifier

Example Circuit
The example circuit in the introduction needs a capacitor (or some other high-pass filter) connected between the collector and base of Q3 in order to provide frequency compensation. The circuit as drawn without the aforementioned capacitor has way too much open loop gain in the VA stage especially at high frequencies. This will cause distortion and instability. Relying solely on the Ccb or so called "Miller" capacitance of Q3 to provide adequate local negative feedback is usually considered a poor choice in design practice. — Preceding unsigned comment added by 24.218.178.56 (talk) 01:16, 30 December 2011 (UTC)

EDIT: It would also help if the diagram indicated that both bias diodes and both output transistors must be physically tied to the same spreader bar in order to provide proper thermal Vbe compensation and thus avoid thermal runaway in Q4 and Q5. — Preceding unsigned comment added by 24.218.178.56 (talk) 01:29, 30 December 2011 (UTC)

It also needs a capacitor in series with R7. Without it the output can not settle to mid-rail, which is required for maximum voltage swing and minimum distortion.88.247.150.46 (talk) 18:50, 9 November 2014 (UTC)

Class E/F
I've merged (from a different IP) and then completely rewritten the introduction to class E/F. i hope it clearer now. I've left the remaining description, although in my opinion it is not clear at all, and at time absolutely WRONG (seems to be a transcription from some source by someone who doesn't understand all the details). I recommend removing most of the remaining part in class E/F except my introduction ;)

I didn't remove any existing errors in the old text, because someone is stupidely reverting all my changes when i 'remove' anything... the blantant errors are: class E doesn't output square wave. it is possible to modulate the signal with class E. the text on class F is complete crap. i would remove it completely.

 * Your IP changed. See User talk:217.132.20.249 for your edits on electronic amplifiers.  You should just get an account. — Omegatron 22:25, 31 March 2006 (UTC)

The description of both classes is so poor that is incomprehensible. It misses the basic concepts while concentrating on secondary issues.

In Class-E amplifier the key is that $$L$$, $$C$$ and $$R_L$$ resonate at a frequency slightly higher than the carrier and with a well defined damping. The goal is to shape the voltage across the switch in such a way that it drops back to 0 just before the switch is closed. This minimizes losses in the switch as it always operates at zero current, zero voltage or both.

The function of $$L_0$$, $$C_0$$ is simply to filter out anything except the first harmonic of the carrier as usually we don't want to put any rubbish in the load (especially if that's an antenna). Other than that these devices are not a necessary part of the Class-E amplifier.

$$L_1$$ just provides a DC current (and power) to the circuit and does not contribute to the circuit operation at RF frequencies. Some implementations choose otherwise (i.e. $$L_1$$ performs the function of $$L$$) but the key is operation not the circuit structure.

Adding some voltage and current waveforms would make this section much clearer.

As for Class-F amplifier - again it misses the key idea, which is to block 3rd harmonic so that the voltage waveform across the active device becomes more rectangular, which reduces power losses (the device spends less time in transitions, where both voltage and current values are high).

Also, why not add the schematic of the Class-F amplifier? http://commons.wikimedia.org/wiki/File:Classe_F.svg — Preceding unsigned comment added by 60.37.105.127 (talk) 06:25, 23 September 2011 (UTC)

Class A amplifier problems
I think class A amplifier section is wrong. Firstly, a class A amplifier is not another name for an operational amplifier, as the text may suggest. And the diagram is misleading, drawing a BJT connected without any base-emitter current limiter. A BJT with a current generator in the emitter and a load in parallel is the standard way to depict it.

If people agree, I can modify the section.

Romano (talk) 16:06, 11 January 2011 (UTC)
 * I agree that the mention of op-amps is unhelpful, so just remove it. There is an "Operational amplifiers (op-amps)" section, and I do not think it needs any mention of "class". The diagram is problematic: yes, it's wrong, but exactly what alternative would be better? The point of the diagram is to give a very vague overview, while showing accurate i/o waveforms. I cannot think of any simple improvement that would not reduce its accessibility for general readers. There perhaps could be some mention like "bias circuit not shown", but the same applies to some extent in all the "class" diagrams. Johnuniq (talk) 00:48, 12 January 2011 (UTC)

Etymology of "Class A"
Who first used "Class A" "Class B" etc? —Preceding unsigned comment added by 96.224.72.5 (talk) 21:18, 12 May 2011 (UTC)

Valve vs. vacuum tube
The article uses both terms rather randomly and sometimes confusingly. It would clean things up if we chose one or the other. Can we do that? I don't care which really. --Kvng (talk) 01:38, 10 June 2011 (UTC)

A C distinction
The circuit diagrams for A and C are the same. Why do they differ? Is the transistor driven in another manner? Could someone write a sentence to clarify this? -- 178.83.12.182 (talk) 17:51, 20 September 2011 (UTC)
 * The tet does explain the difference. The waveforms would be more illustrative if they were properly referenced to 0 volts. It's hard to see how teh Class C amp can have an output that swings negative with respect to ground... --Wtshymanski (talk) 18:51, 20 September 2011 (UTC)

Added citation-needed for op-amp claim
I put a citation needed on the claim that most "quality" op amps have class A output stages. Op-amps, even very good ones, have push-pull output stages. When we use a word like "quality", we create the start of a No True Scotsman argument. What kind of quality? Can we put some kind of number on it? This is someone's opinion that op-amps have to have class A output stages to have good quality. Whoever believes this claim should be easily able to cite part numbers and data sheets to substantiate it, as well as other third-party documentation which shows that those op-amps are of superior quality: measured low noise and distortion figures, and other relevant qualities, like good power-supply rejection ratios, low offset currents and voltages, decent slew rates, etc. 192.139.122.42 (talk) 22:45, 2 October 2012 (UTC)

Class A can be implemented push/pull and still remain class A. This is not mentioned anywhere in the text, and adds to the confusion about op amps. — Preceding unsigned comment added by 66.14.154.3 (talk) 23:04, 25 January 2013 (UTC)

Article moved from Electronic amplifier
This article was moved from Electronic amplifier to Amplifier per Talk:Amplifier_figures_of_merit. Olli Niemitalo (talk) 07:54, 31 January 2013 (UTC)

 * This article is still sorting on "electronic amplifier". Is that what people want? Not sure what the best decision is here. Jason Quinn (talk) 04:48, 30 March 2013 (UTC)

amp always increase power?
This may be my being to pedantic but the article begins

"An electronic amplifier, amplifier, or (informally) amp is an electronic device that increases the power of a signal."

But I can imagine a circuit where the loaded voltage of a circuit is multiplied but then fed into a high impedance load so it draws very low power (consider attaching an amplifier to an oscilloscope, negligible power out of the amplifier but the voltage has increased.) Is it therefore accurate to say that it is power that is increased? RJFJR (talk) 16:14, 3 May 2014 (UTC)

 * Yeah, most definitions 1, 2, 3, 4,  5  don't seem to limit "amplifier" to devices that increase the power of a signal, but also include devices with voltage or current gain.  One that I like says "a device that uses an external power source to increase the strength or magnitude (power, voltage or current) of an electrical signal".  -- Chetvorno TALK 20:19, 7 June 2014 (UTC)

I entirely agree. Which is why I am changing the opening section of this article, to make this clear. — Preceding unsigned comment added by CatNip48 (talk • contribs) 14:57, 11 May 2023 (UTC)

History of amplification
The term Amplification redirects here. Wikipedia should include somewhere a history of the important concept of amplification. The invention of the amplifying vacuum tube (the Audion or triode) in 1906 created the field of "electronics" (the study of active (amplifying) electrical devices) and made possible all of information technology: long distance telephone lines, practical radio broadcasting, television, talking motion pictures, audio recording, telemetry, computers, networking, etc. I'm prepared to write such a history, but I don't know where it should go. This article is already bloated, and it focuses on a narrower topic: electronic amplifiers, rather than the concept of amplification in general. Gain focuses narrowly on definitions of voltage and power gain. Does anyone have any thoughts about where this history should go? Should there be a new Amplification or History of amplification article? -- Chetvorno TALK 07:57, 6 June 2014 (UTC)

 * I think your proposed information should go into amplification which would therefore be changed from a redirect into an article. Binksternet (talk) 14:30, 6 June 2014 (UTC)

 * Thanks, I think that's probably the best idea. Another possibility that occurred to me is to include it in the Electronics article, since the invention of amplifying devices was pretty much synonymous with the birth of electronics. -- Chetvorno TALK 20:27, 7 June 2014 (UTC)

I sick and tired of reading about ideal amplifiers. the problem with the explanation of Ideal amplifiers is it is poorly explained all for the sake of high fidelity this is true for books and websites on amplifiers as well as electronic website and webpages online I know there are simpler amplifiers out there that can be easier to explain  I once bought a electronics lab kit that had circuits you could build by connecting wires to springs that had electronic components attached to the springs one of the circuits was a basic real world simple amplifier that consisted of one npn transistor one capacitor one resistor a piezoelectric buzzer that double as a microphone a matching transformer and a piezoelectric earpiece although this simple real world amplifier had a lot hissing in it It's still was an amplifier even if it was not a ideal high fidelity one  I cannot find this basic simple amplifier or it's  explanation on the internet anywhere If human beings continual to give ideal explanations instead of real world explanations human beings will have to go back to living in caves this includes explanations  electronics and science   richardstephens99@yahoo.com  — Preceding unsigned comment added by 2001:558:6044:2:6D51:6199:568C:E550 (talk) 08:30, 30 August 2014 (UTC)
 * I know what you mean. Non-ideality is reality.  Like that broken "period" key on your keyboard that almost never works.  Dicklyon (talk) 00:36, 31 August 2014 (UTC)

Heart / nervous system
I deleted 'The amplifier is often described as the heart or the nervous system of a microphone or loudspeaker' since 86.29.7.158 (talk) 07:18, 20 April 2015 (UTC)
 * 1) in a lifetime of electrical & electronic engineering I've never heard anyone say it
 * 2) a newspaper is a long way from being a reliable or accurate source
 * 3) its typical journalistic fiction
 * Thanks. I see that the dubious text was added as part of a series of edits on 23 February 2015, and some of the other text should be examined. Johnuniq (talk) 09:47, 20 April 2015 (UTC)

The history of amplifiers is missing.
There should be a section dealing with the history of amplifiers, such as when the amplifier was invented. Blaylockjam10 (talk) 08:04, 28 June 2015 (UTC)

Sprucing this article up
I'm going to (slowly) start to clean this article up, feel free to help if you want to. The things I think need work:
 * What are we actually talking about? Is just a transistor an amplifier? Is a single op amp an amplifier? A transistor or op-amp with the surrounding circuitry to make it function? Is an entire audio power amplifier an amplifier? I suspect the answer to all these questions is yes, but we need to constrain the scope of the article: I think it would be best to write the article about circuit level or smaller (where circuit level is around the size of File:Amplifier Circuit Small.svg)
 * How are amplifiers categorised? Surely solid state/valve/magnetic isn't the same sort of categorisation as op-amp/fully differential or video/oscilloscope vertical/microwave? I propose splitting into categorisation by active device (solid state, valve, magnetic, negative resistance), {categorisation by architecture [wrong word?] (op-amp, differential amp, distributed)} (not sure about this) and examples of application specific amplifiers with their ideal properties (video, oscilloscope, microwave, instrument).
 * Reduce redundancy: some of the article repeats other parts - there are two sections containing functions of amplifier.
 * References: it would be nice to have more of the article referenced, including the bits that are (to experts) obvious

What does anyone think? I'm going to go ahead and start to implement some of these changes, feel free to either help or stop me! — crh 23    (Talk) 19:20, 18 June 2016 (UTC)
 * Basically, I'd like to get this up to the good article criteria. #1 should be achievable without too much effort, #2 is currently a fair way from achievement (see scientific citation guidelines, #3 is close, maybe needing a little more attention paid to summary style in some section (maybe not). I doubt #4 will be much trouble, nor will #5 (judging from recent activity, unless everyone suddenly gets very passionate about amplifier design). As to #6, we could do with a nice image to place at the top, maybe File:Operational amplifier.svg or something like File:LM741CN.jpg (which is already included in the page). — crh 23    (Talk) 20:53, 18 June 2016 (UTC)

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All amplifiers do/don't provide power gain
Today user:Chetvorno reverterd my edit. They provided as arguments: Incomprehensible for general readers (what is the "value" of a "signal"), has factual errors (all amps increase the power of a signal), is not an adequate summary of article I would like to discuss this here. First, the statement "all amps increase the power of the signal" seems incorrect to me. I will explain my reasoning with an example. Say I have a current source as input to a system (eg, photodiode). I would like to turn this into a voltage. To do such, I use a shunt resistor and feed the voltage over this resistor into a voltage amplifier with voltage gain of 100. For the sake of the example, let's say that I have a 1mA input current. I use a 5ohm shunt resistor. I find a voltage drop of 5mV. This would mean that the input signal is providing me with 1ma*5mV=5uW of power. My voltage amplifier has an output of Av*Vin=100*5mV=0.5V. If this is then fed into a second voltage amplifier stage, with a very high input resistance (as you desire with a voltage signal) of say 10Mohm (quite a reasonable number for say a MOSFET gate at a not-to-high frequency). This means we get a current of 0.5V/10Mohm=50nA. The power would hence be 50nA*0.5V=25nW. In other words, even though my amplifier has a voltage gain of 100, it has a negative power gain - we go from 5uW to 25nW of power. Unless you can disprove my calculations, I thus don't see why "not all amplifiers provide power gain" is a factual error.

As for your other arguments: I can agree with you on "value" of a "signal" being somewhat abstract, but this can be improved then by adding examples. The fact of the matter is that amplification is the increase of a value of a signal (and not neccesaraly power, we like to keep that as low as possible for as long as possible because power means heat), in the case of a voltage amplfifier it is the voltage of the input signal... I feel like the current introduction implies first that only voltage, current, transconductance and transimpedance amplifiers exist. At the same time, it also seems to suggest we only ever care about power, which is not correct (see my example above). Even if we come to the conclusion of my changed introduction being bad, I feel it still requires a rewrite. I would thus like to open discussion about this topic, to avoid getting into a revert war. Regards, TheUnnamedNewbie (talk) 10:05, 2 February 2017 (UTC)
 * I think that defining an amplifier as a device that increases the power of a signal is fairly well-motivated. The problem with defining something that can't increase the power of a signal as an amplifier is that it means you have to define a transformer as an amplifier, which I personally would be uncomfortable with. Indeed, we would have to call a boost converter an amplifier, which again doesn't seem right to me. — crh 23    (Talk) 17:10, 2 February 2017 (UTC)

 * I agree. Here is TheUnnamedNewbie's proposed introduction:
 * An amplifier, electronic amplifier or (informally) amp is an electronic device designed to increase the value of a signal. The amount of increase, as a ratio of the output signal over input signal is called the gain of the amplifier. The signal is often a voltage, electric current or power signal. The input and output signal must not necessaraly be of the same type. An amplifier is the opposite of an attenuator: while an amplifier provides gain, an attenuator provides loss.

 * Amplifiers are found both as separate pieces of equipment, such as a stereo amplifiers in audio applications, or as building blocks in larger systems. Amplifiers are one of the fundamental building blocks in electronics. Not all amplifiers are designed to provide a larger output power.
 * Here are my objections to it: As Crh23 says, engineering sources, , , ,  , ,     define an amplifier as a circuit which for some sources and loads can give power gain - the output power is greater than the input power.  It is an active circuit, not just any circuit which has voltage or current gain; otherwise a transformer would be an amplifier.  Thus the definition is in error.  Obviously, as in TheUnnamedNewbie's example above, with some sources and loads an amplifier will not have power gain - any amplifier with its output terminals left unconnected will have zero output power and thus no power gain.  The statement "Not all amplifiers are designed to produce a larger output power" is true, but the potential for power gain is an essential part of the definition, and thus all amplifiers require a power source.  The original intro included this essential stuff.

 * Also the lead sentence leaves undefined the terms "value" and "signal". This sentence is going to be incomprehensible to the many non-technically-educated readers who come to the intro for a simple explanation. Yes, TheUnnamedNewbie, you could try to define them by giving examples, which will take a lot of space.  Why not simply use the words "voltage" and "current" as in the original sentence?  Also the intro does not touch on the history or different categories of amplifiers, so I don't think it meets the burden of MOS:INTRO to provide an "adequate summary" of the article.

 * I agree there was some unnecessary and/or awkward content in the original intro, such as the description of an amplifier as "modulating" a power supply, and division of amplifiers into voltage, current, transconductance and transimpedance amps, which should be corrected. But I think the original intro is a better place to begin. -- Chetvorno TALK 17:37, 2 February 2017 (UTC)

Class B Amplifier description is erroneous.
Class B has two active gain devices. One providing gain for for positive excursions of the signal from zero. The other providing gain for negative excursions. Each device theoretically operates for 180 degrees of the signal and is off for the other 180 degrees, effectively a rectifier for the signal. In practice, near zero signal level, both gain devices are off, which causes the output signal to be distorted.

The article is describing a class C amplifier, which has only one gain device and amplifies for 1/2 the period. This is probably because the cited source is a poor reference.

For example, an NPN transistor does not turn on and begin to amplify until the base voltage reaches the threshold voltage. Typically the threshold voltage is around .65 volts. Likewise, a PNP transistor turns on at -.65 volts. Thus when the input voltage is between -1 and 1 volts, significant distortion occurs as both devices are off. To correct the problem of the B amplifier, the AB amplifier was developed. The transistors are biased so that both are in their active zone when the input signal is near zero. --74.46.101.158 (talk) 16:33, 21 April 2017 (UTC)
 * In radio frequency applications, the amplifier load is a tuned circuit stage and so a single device can be used in Class B. The "ringing" effect of the tuned circuit fills in the missing portion of the waveform, if the Q factor is high enough. Such amplifiers are used in radio transmitters to increase the power of a modulated signal from an exciter to a level desired to feed a transmission antenna. --Wtshymanski (talk) 03:17, 22 April 2017 (UTC)
 * Almost. A single active amplifying device can be operated in class B (Classes A to C merely define the manner in which the stage is biased). Such an amplifier will only amplify the positive (or negative) parts of the input wave.  A class B amplifier can be used in RF applications where it energises a tuned circuit which oscillates with the full sine wave, though a class C biased stage is more likely to be encountered. For audio applications, it is wrong to state that a class B stage consists of two active devices. A class B "push-pull" amplifier consists of two class B stages, one to handle the positive parts of the input and one to handle the negative.
 * You have managed to make so much of the article incorrect and coupled with your inability to write good English, I have taken the brutal approach and just reverted the article to the point before you savaged it. Your standard of English is such that you should not be editing the English Wikipedia. 86.153.129.112 (talk) 13:18, 22 April 2017 (UTC)	Amplifier received a peer review by Wikipedia editors, which is now archived. It may contain ideas you can use to improve this article.

 * There were basically two things wrong with the article before I started editing it. First - the efficiency of class A amplifiers is 25% for capacitive and resistive coupling. This is normally the way this type of amplification class is used. But because it is used mainly in low power portions of a circuit, the efficiency hit is minimal, on the order of milliwatts. If, however, inductive or transformer coupling is not used on high power stages, the efficiency is 25% max. With inductive or transformer coupling it rises to 50%.  A cite for this information was given in the article.

 * Secondly, the references I looked at said that a class B amplifier has two active devices and operates in a push-pull mode. This change was also provided with a citation. Wtsham..ski made an edit after mine which indicated that class B may be single ended and provided and excellent cite. He also made the comment that you normally see class B with two active devices. I thought those changes to my edits were good.

 * So all in all, you revert back to the original leave the article with uncited information and with phrasing that misleads the reader on what class A and class B are.

 * Finally, I am a native speaker and I'm seeing no grammatical errors in my edits. If you're finding one,  please specify exactly the problem and discuss here. My IP address may have changed since yesterday's edit, but I am the guy who made the changes. --74.46.101.158 (talk) 15:49, 23 April 2017 (UTC)

 * This edit of yours changed perfectly good English into bad English.

 * Whilst most implementations of class B utilise two devices in push-pull, such an application consists of two devices both of which are operated in class B. It is thus wrong to claim that a class B amplifier can only have two active devices in it.  As has been stated above, a single class B device can be used in RF applications.  The current illustration of a class B stage correctly illustrates an transistor operating in class B.  The illustration that you moved into the class B section was of two class AB stages operating in push pull and was not the correct diagram as you claimed.

 * I don't understand your insistence that a class A amplifies has an efficiency of 25% max as this is precisely what the article stated before you changed it. It also notes that two class A stages used in push-pull has a maximum efficiency of 50% (which is the case even if they are not transformer coupled to the load - this is because one active device acts as the internal load (to the amplifier) for the other).  If you are able to draw out the Thevanin equivalent circuit for the amplifier stage and understand the maximum power transfer theorem, you would understand why this is the case.

 * This edit claimed to remove incorrect information which was in fact, entirely correct and half of it was covered in the preceding reference which you removed in an earlier edit (although you did provide a replacement, it was a poorer reference as it was not an online reference and therefore harder for anyone to verify). 86.153.129.112 (talk) 12:42, 24 April 2017 (UTC)

Overview, overview, overview
This is a deep subject. "Electronics Engineers' Handbook" has a 146 page chapter on amplifiers and oscillators, and *that* is still an overview (ok, so maybe 40 of those pages are about oscillators). Any specific details must be spun out to other articles, and this article should be only a 20,000 foot overview of the field. Even so, there's so much that hasn't been touched on here - stability, load lines, economics! Luckily a lot of the details are available already in other articles, we don't have to go on about tube sound here, for example, just point at it. --Wtshymanski (talk) 16:53, 7 May 2017 (UTC)

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Why mention carbon repeater in intro?
The 3rd paragraph of the introduction was recently changed from:
 * "The first practical electronic device that could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912."

to:
 * "After electro-mechanical signal repeaters, such as the Shreeve repeater of 1904, the first practical and entirely electronic device that could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912."

The reference to "electro-mechanical signal repeaters" is to speakers driving carbon microphones to make a crude electroacoustic amplifier, which had very limited use as telephone line repeaters during the first two decades of the 20th century.

While they are quite properly described in the History section, I think mentioning them in the introduction gives WP:UNDUE WEIGHT to this trivial dead-end technology. Carbon repeaters were truly horrible amplifiers, being insensitive, having sharp resonance peaks, DC offset problems, and introducing noise (the "carbon roar"). They were only used in a limited way in telephone lines, and had almost no usage in other applications of amplification. There are many more notable points about amplifiers in the article which should be mentioned in the introduction before mentioning this device. -- Chetvorno TALK 21:50, 3 June 2017 (UTC)
 * Agree. Dennis Brown - 2¢ 22:43, 4 June 2017 (UTC)

 * I also think it is blatant WP:UNDUE WEIGHT to put mechanical repeaters on a par with tubes by saying in the History section  "The Shreeve mechanical repeater and the vacuum tube were the only amplifying devices, other than specialized power devices such as the magnetic amplifier and amplidyne, for 40 years."  Even if it lingered on in a few specialty applications like hearing aids, the mechanical repeater was virtually obsolete by the early 1920s, replaced by tubes. -- Chetvorno TALK 03:20, 5 June 2017 (UTC)

Requested move 8 May 2020

 * The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review after discussing it on the closer's talk page. No further edits should be made to this discussion.

The result of the move request was: not moved (non-admin closure)  ~SS49~   {talk}  07:21, 16 May 2020 (UTC)

Amplifier → Electronic amplifier – Some people make the mistake of thinking that Electrical Amplifiers are the only type of amplifier, but please see Amplifier (disambiguation) - mainly Magnetic amplifier, Mechanical amplifier, Optical amplifier, Pneumatic amplifier 83.137.6.117 (talk) 10:41, 8 May 2020 (UTC)
 * Oppose per WP:PTOPIC. The ample entries for types of electronic amplifier indicate this is the most common meaning, and the |Optical_amplifier|Mechanical_amplifier|Pneumatic_amplifier|Amplifier_(disambiguation)|Amplifier page views only amplify the fact. The disambiguation page would need its hits amplified sevenfold to equal those of the other topics suggested: few readers are clicking through the hatnote to find the other meanings.
 * Incidentally, this request is malformed if (as I assume) the intent is to move the disambiguation page over per WP:NOPRIMARY. Nominators should request all associated moves explicitly. 178.164.139.126 (talk) 04:27, 10 May 2020 (UTC)

 * Comment. I'm wondering whether to include acoustic mirror at the DAB page, mainly because I can never remember what they are called and go searching for "sonic amplifier", "echo amplifier" and suchlike. (I found the term via a Google search for "concrete amplifier"). I do realise that they are not individually amplifiers. 178.164.139.126 (talk) 04:36, 10 May 2020 (UTC)
 * Oppose. Clear common name and primary topic. -- Necrothesp (talk) 15:02, 13 May 2020 (UTC)
 * Oppose per common name. Any confusion should be explained in the article. Johnuniq (talk) 00:42, 14 May 2020 (UTC)

 * The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Requested move 4 September 2023

 * The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review after discussing it on the closer's talk page. No further edits should be made to this discussion.

The result of the move request was: not moved. (closed by non-admin page mover) – Material  Works  20:11, 11 September 2023 (UTC)

Amplifier → Electronic amplifier – 1) The article opens with the hatnote: This article is about electronic amplifiers... 2) Then begins with an immediate disambiguation: An amplifier, electronic amplifier, ... 3) It is the main article of Category:Electronic amplifiers 4) The category Category:Amplifiers is subdivided into the two subcats Category:Electronic amplifiers and Category:Mechanical amplifiers, the latter of which has its own main article. Summary: All of the above indicates that the best title for this article is "Electronic amplifier" Gjs238 (talk) 16:11, 4 September 2023 (UTC) <div style="padding-left: 1.6em; font-style: italic; border-top: 1px solid #a2a9b1; margin: 0.5em 0; padding-top: 0.5em">The discussion above is closed. <b style="color: #FF0000;">Please do not modify it.</b> Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.
 * Oppose. The electronic sense still seems like the most common topic, in terms of what readers might be looking for--certainly more than mechanical, probably(?) more than biochemical--and what is named this without further qualification. WP:DAB says that therefore it can have the undisambiguated name (PRIMARYTOPIC), especially since the other variants seem to have easy nat-dab names available, and MOS says that providing at least some sort of pointer for readers to the other meanings is entirely appropriate. Has anything changed in the past three years since the last req-move? However, Category:Amplifiers should really have a third subcat for the biochemical sense, since almost all of the 28 pages in that higher-level cat are specifically about that subtopic. DMacks (talk) 16:22, 4 September 2023 (UTC)
 * Oppose. Electronic amplifiers are overwhelmingly the most commonly discussed and read-about amplifiers, making it sensible for amplifier without any qualifications to be an article about the electronic one. It's what a reader would expect to find here. The Quirky Kitty (talk) 18:34, 4 September 2023 (UTC)
 * Strong oppose and time to impose a moratorium until a much, much more convincing proposal is created. Red   Slash  21:45, 6 September 2023 (UTC)

title: Talk:Amplifier