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List of mayors, lord mayors and administrators of Sydney

The Right Honourable the Lord Mayor of Sydney is the head of the Council of the City of Sydney, which is the local government area covering the central business district of Sydney in the State of New South Wales, Australia. The Lord Mayor has been directly elected since 1995, replacing the previous system of being internally elected annually by the Councillors, and serves a four-year term. The most recent election was held on 4 December 2021, at which the incumbent Lord Mayor, Clover Moore, was re-elected to a fifth term. The Lord Mayor is assisted in their work by a Deputy Lord Mayor, who is elected on an annual basis by the elected councillors.

Office history
The office of the Mayor of Sydney along with the City of Sydney was created on 20 July 1842 pursuant to the Sydney City Incorporation Act 1842 by Governor Sir George Gipps. Prior to the first municipal election, the governor nominated magistrate Charles Windeyer to serve as interim mayor. The first council, consisting of 24 aldermen elected across six wards, was declared elected on 3 November 1842 and first met in the George Street Market Building (now the site of the Queen Victoria Building) on 9 November and elected John Hosking as the first elected mayor of Sydney.

The title of Mayor (in full: The Right Worshipful the Mayor ) was elevated to "Lord Mayor" on 23 November 1902 by King Edward VII, and as part of this process received the honorific The Right Honourable, a title which attaches to the title of Lord Mayor and not to the individual holding the office. In December 1915, the Parliament of New South Wales passed the Sydney Corporation (Election of Mayor) Act, 1915 which amended the 1902 act to allow for the governor to appoint the lord mayor should the council be unable to elect a candidate on or before 30 December of any year. This occurred three times, in 1916, 1920 and 1934.

The office of lord mayor, along with the City of Sydney, was governed by the Sydney Corporation Act, 1932 until the passing of the Local Government (Areas) Act 1948, which placed Sydney under the terms of the Local Government Act 1919, which governed all other local governments in the state. This meant that the election of lord mayor (until 1971 in December of each year, and then in September) marked the beginning of the term, instead of the previous system, where the lord mayoral term began on 1 January and expired on 31 December. When the City of Sydney Act 1988 was passed, the City of Sydney was once again governed under a separate law, but the election of lord mayor did not change until the Local Government Legislation Amendment Act 1995, which allowed for popular direct elections from 1995.

Vestments of office
As head of the council, the lord mayor is entitled to wear the chains and robes of office, as befitting the ancient status of lord mayor of a large city. In 1902 the Sydney Chamber of Commerce commissioned the first link of a mayoral chain. In 1903, the governor of New South Wales, Sir Harry Rawson presented the first lord mayor, Thomas Hughes, with the chain of office. It features the coat of arms of the Sydney Chamber of Commerce and the Stock Exchange and a pendant depicting the coat of arms of Sydney. Successive mayors each added a medallion, on which was embossed their term of office. By 1945, this practice had ended because of the size and weight of the chain. Today, the chain is worn with the robes of office only for rare civic ceremonies, a smaller collar being worn for most civic duties.

The original civic robe for the mayor of Sydney in 1842 was purple, trimmed with ermine and worn with a court dress hat. The current robes worn by the lord mayor and deputy lord mayor are black, trimmed with ermine, and worn with bicorne hat, lace jabot and white gloves. They are worn rarely and only at major civic functions. Recently, it has become the custom not to wear the robes.

List of deputy lord mayors
The position of Deputy Lord Mayor was made a permanent council position when the Local Government (Areas) Act 1948 placed the City of Sydney under the main body of local government legislation. Prior to 1 January 1949, "Deputy" Lord Mayors were occasionally elected to act for the council during times of absence or illness of a sitting Lord Mayor, but the position was not permanent under the Sydney Corporation Act 1932 or any previous acts. The following individuals have been elected as Deputy Lord Mayor of the City of Sydney:

List of town clerks, general managers, and chief executive officers
The first Town Clerk of Sydney was appointed on 3 September 1842 on a provisional basis by the Governor, pending the election of aldermen. When the council was dismissed in December 1853 and replaced by a board of three commissioners, the post of town clerk was left vacant. The Local Government Act, 1993 removed the requirement that the administrative head of a council be a "Town or Shire Clerk" and specified that the head was to be known as the General Manager. The Sydney City Council had previously recognised the changing nature of role in appointing their first General Manager in December 1992. In May 2005, the title of General Manager was changed to Chief Executive Officer (CEO).

Election results
In 1995, the Local Government Legislation Amendment Act 1995 amended the City of Sydney Act 1988, to allow for popular direct elections of the Lord Mayor from September 1995.


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OCBC Bank (Hong Kong)

OCBC Bank (Hong Kong) Limited, formerly Wing Hang Bank Limited and OCBC Wing Hang Bank Limited, is a licensed bank with its head office in Hong Kong. Since 15 October 2014, Wing Hang Bank has been a wholly-owned subsidiary of the Oversea-Chinese Banking Corporation (OCBC) headquartered in Singapore. The acquisition of Wing Hang has given OCBC a network of about seventy branches spanning Hong Kong, Macau and mainland China to add to OCBC's existing operations in Hong Kong and China.

History

Y K Fung established Wing Hang Ngan Ho in 1937 in Guangdong to engage in money changing. Its early years were difficult due to the turbulent political and economic conditions in China. In 1941, the firm established a subsidiary, Banco Weng Hang, in Macau.

In 1945, Wing Hang Ngan Ho re-established itself in Hong Kong with a capital of HK$300,000 and a staff of nineteen. The firm prospered during the post-war boom and was incorporated in 1960 as Wing Hang Bank.

In 1973, the Irving Trust Company of New York acquired a majority interest in Wing Hang. In 1979, the Head Office Building was re-developed to provide modern facilities for its operations.

In 1988, the Bank of New York merged with Irving Bank Corporation after a year-long takeover bid by the Bank of New York. In July 1993, Wing Hang Bank listed its shares on the Hong Kong Stock Exchange. In August 2004, Wing Hang completed the merger with Chekiang First Bank. In January 2007, the bank acquired Inchroy Credit Corporation, a major financial institution engaged in the hire purchase and lease financing business.

In July 2007, The Bank of New York Company Inc. merged with Mellon Financial Corporation to form The Bank of New York Mellon Corporation. That same year, Wing Hang established Wing Hang Bank (China).

Acquisition by OCBC
Singapore's OCBC Bank acquired Wing Hang in 2014 for S$6.23 billion. Under the Hong Kong Companies Ordinance, OCBC Bank, with 97.52 percent of Wing Hang's shares, compulsorily acquired the bank on 29 July 2014. OCBC Wing Hang was subsequently delisted after the acquisition was completed.

On 1 October 2014, Wing Hang Bank was re-branded as OCBC Wing Hang to reflect its integration into the OCBC family. On 3 July 2023, OCBC unveiled a unified brand across its core markets, including Hong Kong and Macau, solidifying OCBC's One Group approach to capitalize on the ASEAN-Greater China opportunity. In Hong Kong, "OCBC Wing Hang Bank Limited" has changed its name to "OCBC Bank (Hong Kong) Limited" and in Macau, "Banco OCBC Weng Hang, S.A." has changed its name to "Banco OCBC (Macau), S.A.". "Wing Hang" is no longer in the legal names of both OCBC's Hong Kong and Macau subsidiaries.

OCBC has also launched a new unified logo for its banking entities. The logo retains the classic Chinese junk ship, which has been featured in every iteration of its logo since the bank was founded in 1932. The bank has also launched a new tagline: For now, and beyond (心所向, 行致远 / 心所向, 行致遠).

Board of directors
The board comprises the chairman, one executive director, one non-executive directors and three non-executive independent directors.

 * Chairman: Khoo Cheng Hoe Andrew
 * Executive director:
 * Wang Ke – Chief Executive
 * Non-executive directors
 * Wong Pik Kuen Helen
 * Non-executive independent directors
 * Chim Wai Kin
 * Chong Chuan Neo
 * Hui Leung Wah, Herbert

Operations
OCBC Bank (Hong Kong) Limited is the holding company and the principal operating company of the group. It provides banking and related financial services through the holding bank and its subsidiaries in Hong Kong and China.

In its Hong Kong operations, it runs two wealth management centers, five premier banking centers, with a total of twenty-five branches across Hong Kong.

Its wholly-owned subsidiary in mainland China, OCBC Bank Limited (OCBC China), has a network of branches in Shenzhen, Guangzhou, Shanghai, Beijing, Chengdu, and Zhuhai. Through its other subsidiaries and affiliated companies, the Group provides nominee, deposit-taking, offshore banking, hire purchase, consumer financing, insurance, and share brokerage services.

Subsidiaries
As of 30 April 2024, OCBC Bank (Hong Kong) Limited has five major subsidiaries:
 * OCBC Bank Limited (OCBC China)
 * Banco OCBC (Macau), S.A.
 * OCBC Securities Brokerage (Hong Kong) Limited
 * OCBC Insurance Brokers (Hong Kong) Limited
 * OCBC Nominees Services (Hong Kong) Limited

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

title: OCBC Bank (Hong Kong)


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Williamson amplifier

The Williamson amplifier is a four-stage, push-pull, Class A triode-output valve audio power amplifier designed by D. T. N. Williamson during World War II. The original circuit, published in 1947 and addressed to the worldwide do it yourself community, set the standard of high fidelity sound reproduction and served as a benchmark or reference amplifier design throughout the 1950s. The original circuit was copied by hundreds of thousands amateurs worldwide. It was an absolute favourite on the DIY scene of the 1950s, and in the beginning of the decade also dominated British and North American markets for factory-assembled amplifiers.

The Williamson circuit was based on the 1934 Wireless World Quality Amplifier by Walter Cocking, with an additional error amplifier stage and a global negative feedback loop. Deep feedback, triode-connected KT66 power tetrodes, conservative choice of standing currents, and the use of wide-bandwidth output transformer all contributed to the performance of the Williamson. It had a modest output power rating of $15 Watts$ but surpassed all contemporary designs in having very low harmonic distortion and intermodulation, flat frequency response throughout the audible frequency range, and effective damping of loudspeaker resonances. The 0.1% distortion figure of the Williamson amplifier became the criterion for high fidelity performance that remains valid in the 21st century.

The Williamson amplifier was sensitive to selection and matching of passive components and valves, and prone to unwanted oscillations at infrasonic and ultrasonic frequencies. Enclosing four valve stages and an output transformer in a negative feedback loop was a severe test of design, resulting in a very narrow phase margin or, quite often, no margin at all. Attempts to improve stability of the Williamson could not fix this fundamental flaw. For this reason, and due to high costs of required quality components, manufacturers soon abandoned the Williamson circuit in favour of inherently more stable, cheaper and efficient three-stage, ultralinear or pentode-output designs.

Background

In 1925 Edward W. Kellogg published the first comprehensive theory of audio power amplifier design. Kellogg proposed that the permissible level of harmonic distortion can reach 5%, provided that distortion rises smoothly rather than abruptly, and that it generates only low-order harmonics. Kellogg's work became the de facto industry standard of the interwar period, when most amplifiers were employed in cinemas. Early sound film and public address requirements were low, and customers were content with crude but efficient and affordable transformer-coupled, class B amplifiers. The best theatre amplifiers, built by Western Electric around their 300A and 300B power triodes, far exceeded the average level but were expensive and rare.

By the middle of the 1930s Western Electric and RCA improved performance of their experimental audio equipment to a level approaching modern understanding of high fidelity, but none of these systems could be commercialized yet. They lacked sound sources of matching quality. Industry leaders of the 1930s agreed that the improvement of commercial amplifiers and loudspeakers would make sense only after the introduction of new physical media surpassing low-quality AM broadcasting and shellac records. The Great Depression, World War II and the post-war television boomconsecutively delayed this goal. Development of commercial audio equipment came to a standstill; the few enthusiasts seeking higher level of fidelity had to literally do it themselves. American DIYers experimented with novel beam tetrodes. Australians preferred traditional push-pull circuits built around directly-heated triodes and complex, expensive interstage transformers.

British school of thought led by Walter Cocking of Wireless World leaned to push-pull, class A, RC-coupled triode output stages. RC coupling, as opposed to transformer coupling, argued Cocking, extended the amplifier's bandwidth beyond the required minimum of 10 kHz and improved its transient response. Tetrodes and pentodes were undesirable due to higher harmonic distortion and higher output impedance that failed to control fundamental resonance of the loudspeaker. Cocking wrote that Kellogg's 5% distortion limit was too high for quality amplification, and outlined a different set of requirements - the first definition of high fidelity. Instead of Kellogg's single figure of merit (harmonic distortion), Cocking set three simultaneous targets - low frequency distortion, low harmonic distortion, and low phase distortion. In 1934 Cocking published his first Quality Amplifier design - a two-stage, RC-coupled triode class A amplifier that achieved no more than 2–3% maximum distortion without using feedback. Feedback appeared in his 1943 Wartime Quality Amplifier, built around American 6V6 beam tetrodes; however, both the input stage and the output transformer were placed outside the feedback loop. Cocking's Quality Amplifier family became the foundation of post-war British and Australian audio industry, including the Williamson amplifier.

Development
In 1943, in the middle of World War II, twenty-year-old Scotsman Theo Williamson failed mathematics exam and was discharged from the University of Edinburgh. Theo was not physically fit for military service, so instead the authorities drafted him for mandatory civilian work at Marconi-Osram Valve. In April 1944 Williamson transferred from production line to Applications Laboratory of the company, where he had enough free time for his own DIY projects. Management did not object, and by the end of 1944 Williamson had conceived, built and tested the amplifier that would soon be known as the Williamson amplifier. Another wartime projects, a novel magnetic cartridge, would be commercialized in 1948 as the Ferranti ribbon pickup.

Design targets
Following Cocking's ideas, Williamson devised a different, much stricter set of fidelity requirements:
 * 1) Negligible non-linear distortion (sum of harmonic distortion and intermodulation products) up to the maximum rated output, at all audible frequencies from 10 to 20000 Hz;
 * 2) Linear frequency response and constant output power at all audible frequencies;
 * 3) Negligible phase shift within the audible frequency range;
 * 4) Good transient response which, in addition to above frequency and phase requirements, demands perfectly constant gain when handling complex waveforms and transients;
 * 5) Low output impedance and, inversely, high damping factor. At the very least, output impedance of an amplifier must be lower than the loudspeaker impedance;
 * 6) Output power of 15–20W for reproduction of orchestral music via a dynamic loudspeaker, or $10 W$ for a horn loudspeaker.

Williamson reviewed contemporary amplifier configurations, and, just like Cocking, settled on a low distortion push-pull, class A, triode output stage. Unlike Cocking, Williamson believed that such a stage can deliver high fidelity sound only when the amplifier is governed by 20–30dB deep negative feedback loop (and thus the complete amplifier must have 20–30dB higher open loop gain to compensate the effect of feedback). Deep feedback inevitably causes sudden, harsh onset of distortion at overload but Williamson was content with this flaw. He argued that it is a price worth paying for an improvement in linearity at medium and high power levels. On the contrary, wrote Williamson, slow but steady rise of distortion to 3–5%, as advocated by Kellogg, is distinctly unwanted in a high fidelity system.

Prototypes and tests
Valve complement of the original Williamson amplifier was determined by scarce supply in wartime Britain. The two suitable and available output valves were either the PX25 triode, or a triode-connected KT66 beam tetrode. Williamson initially used the PX25, an already obsolete directly-heated triode introduced in 1932. In his second prototype, Williamson used the more efficient KT66, which became the valve of choice in post-war period. Powered from +500 V power supply, the KT66 prototype delivered 20 Watts at no more than 0.1% distortion. A less costly +425V power supply enabled 15 Watt output power at no more than 0.1% distortion; this arrangement became standard for the Williamson amplifier and defined its physical layout. The complete prototype system, including the amplifier, the experimental magnetic pickup and a Goodmans full-range speaker in an acoustical labyrinth enclosure, has proven to Williamson that a low distortion, deep feedback amplifier, indeed, sounded superior to amplifiers without feedback. The difference was particularly audible with the best available shellac records, despite the physical limitations of this low-fidelity format.

The prototypes impressed the Marconi management, who granted Williamson unlimited access to the company's test facilities and introduced him to the people from Decca Records. The latter provided Williamson with precious, exclusive test material - sample records of the experimental Decca ffrr system, the first true high fidelity medium in the United Kingdom. These records, which exceeded any preexisting media in sound quality, helped Williamson with fine-tuning his prototypes. He was certain that he was now firmly on the right track, but neither Marconi, nor its parent the General Electric Company were willing to invest in mass production of amplifiers for the civilian market. The design was not interesting to company lawyers either, because it did not contain anything patentable. Williamson merely put together well-known circuits and solutions.

Publication
In February 1946 Williamson left Marconi, moved to Edinburgh and joined Ferranti. A few months later a senior Marconi salesman, who sought new means of promoting the KT66 to general public, noticed Williamson's 1944 report about his amplifier prototypes, and sent it for publication to Wireless World. Chief editor H. F. Smith knew Williamson for his earlier contributions; he contacted the author directly and requested a detailed article written specifically for the DIY readers. Williamson promptly responded, but for unknown reasons the publication, originally slotted for 1946, was delayed until April–May 1947. While the paper was waiting for print, the magazine had published the new version of Cocking's Quality amplifier. Cocking, as the technical editor of Wireless World, certainly had precedence; according to Peter Stinson, he was sceptical about the Williamson amplifier, believing that his own design needed no further improvements.

By 1947 British industry had already released two amplifiers of comparable sound quality. Harold Leak announced production of his Leak Point One in September 1945; later in the same year Peter Walker published the first sketch of his distributed-load output stage that would become the Quad II production model. Leak and Walker tried to commercialize their ideas on the meagre post-war British market; their achievements were practically unknown outside of the United Kingdom. Williamson did the opposite: he donated his design to worldwide DIY community, thus securing lasting popular following.

In August 1949 Williamson, responding to letters from the readers, published the "New Version" of this amplifier. The article dealt extensively with construction, tuning and troubleshooting issues, however, its main objective was to address stability issues reported in letters from the readers. Apart from the additional frequency compensation network, a biasing potentiometer and a new, indirectly-heated rectifier valve that was not available in 1947, the circuit remained the same. In October 1949 – January 1950 and May 1952 Williamson published a series of articles on matching preamplifier stages and brief "Replies to Queries" concerning assembly and testing. A collection of articles published by Williamson in 1947–1950 was printed as a standalone 36-page brochure in 1952, with a second edition in 1953. The Williamson amplifier itself, as described in the August 1949 issue of Wireless World, remained unchanged.

Reception

The Williamson amplifier was an instant success. The publication coincided with the resumption of television broadcasting, the beginning of FM broadcasting, the release of the first high fidelity gramophone records (Decca ffrr and the LP record), and the "discovery" of the captured German Magnetophon. The high fidelity media that did not exist in the 1930s became a reality, and the public wanted playback equipment of matching quality. Off-the-shelf amplifiers available in 1947 were not fit for the task. At the same time, electronic components markets were flooded with military surplus, including cheap American 6L6 and 807 power valves. For a while, DIY construction was the only way to obtain high fidelity amplification. Thousands of amateurs began copying the Williamson design; the required transformers and chassis were soon provided by industry.

In September 1947 Australians R. H. Astor and Fritz Langford-Smith adapted the Williamson circuit for American 6SN7 and 807 valves; a 6L6 variant followed soon. British and Australian press was unanimously enthusiastic: "by far the best we have ever tested ... extraordinary linearity and lack of harmonic and intermodulation distortion", "amplifier to end [all] amplifiers", "absolute tops for obtaining natural reproduction" and so on. America lagged behind by about two years: first reviews appeared in the second half of 1949, and were just as complimentary. American companies adapted the circuit to locally available components, and soon began importing "premium" British valves and transformers, thus launching the market for British hi-fi in the United States. By the end of 1949 the Williamson amplifier became a universally recognized reference design, and a starting point for all valve designs employing global feedback.

The spread of DIY construction and the abundance of publications addressed to the amateurs had a solid economic reason: factory-made electronics of the 1940s were too expensive. The industry has not yet reorganized for mass production of affordable consumer products. Home construction of valve electronics was relatively simple and promised considerable savings. The number of home-made Williamson amplifiers is estimated at least in hundreds of thousands; they absolutely dominated the DIY scene in English-speaking countries. Stereo has not been commercialized yet; almost all surviving Williamson amplifiers are monaural. Each one differs in minor details, assembly quality is usually inferior to factory-made models. In the 21st century these monaural amplifiers are commonly sold at online auctions, but finding a matching pair is almost impossible.

Small-scale factory production in the United Kingdom began in February 1948; first big manufacturer, Rogers, announced production in October 1948. In the early 1950s the Williamson amplifier dominated factory production in both the United Kingdom and the United States; John Frieborn of Radio-Electronics wrote in 1953 that "since Williamson published the first description of his High-Quality Audio Amplifier, other audio designers had two apparent choices, beating him [Williamson] or joining him."

Specifications

 * Tube complement, 1947 version: 4x L63 (each equivalent to 6J5), 2x KT66, 1x U52 directly-heated rectifier. The 1949 version also provided for the use of 6SN7 or B65 double triodes, and replaced rectifier with the 53KU indirectly-heated type;
 * Output power and maximum distortion: 15W RMS at no more than 0.1% THD;
 * Intermodulation: not specified (Williamson did not have the necessary test equipment);
 * Frequency range: 10-20000Hz at ±0.2dB; 3-60000Hz at ±3dB;
 * Phase shift within 10-20000Hz: "never exceeds a few degrees" at the extremes of audio spectrum;
 * Noise and hum: -85 dBbelow maximum output, almost entirely consisting of mains frequency hum.

Topology
The Williamson amplifier is a four-stage, push-pull, class A triode valve amplifier built around a high quality, wideband output transformer. Its second (concertina-type phase splitter, V1B), third (driver, V2A and V2B) and fourth (output, V3 and V4) stages follow Cocking's Quality Amplifier circuit. The added first stage (V1A) is a dedicated error amplifier, which compensates for the loss of gain caused by negative feedback. Williamson optimized operating points of each stage for best linearity with sufficient overload reserve. The output stage is biased into pure class A; traditionally it used triode-connected beam tetrodes or pentodes. With American 807 or British KT66 valves (Williamson recommended the latter type) and specified power supply the amplifier delivered 15 watts of output power. Further increase in output, according to Williamson, required use of four output valves; his 1947 article mentions construction of a 70-watt prototype.

The plate of the first stage and the grid of the phase splitter are connected directly. This configuration, known since 1940, was still uncommon in 1947; American designers considered it a novelty even in the early 1950s. Phase splitter, driver and output stage are capacitively coupled. Cathode bypass capacitors are absent: Williamson, like Cocking before him, tried to linearize open-loop performance of each stage, and deliberately sacrificed gain for linearity; he was also concerned with potential low-frequency instability introduced by added capacitances. The circuit in either 1947 or 1949 variant contains no electrolytic capacitors; its power supply uses a CLC π-filter with two 8 μF paper capacitors, with a further LC filter feeding the first three stages.

Derivative designs of the 1950s often deviated from Williamson's recommendations while retaining his four-stage topology. According to Peter Stinson, this alone is not sufficient to be called a Williamson amplifier. A true Williamson amplifier must meet five criteria simultaneously:
 * 1) All four stages must use triodes; the output stage may use triode-connected tetrodes or pentodes;
 * 2) Output stage must operate in class A;
 * 3) Phase splitter must be directly coupled to the input stage;
 * 4) High-quality output transformer must conform to the original Williamson specification;
 * 5) Global negative feedback loop must be connected from transformer secondary to the cathode of the input triode, and be exactly 20 dB deep.

Feedback
The 20 dB (ten-to-one) feedback loop of the Williamson amplifier wraps around all four stages and the output transformer. According to Richard C. Hitchcock, "this is a severe test of design and is one of the outstanding features of the Williamson circuit." Williamson wrote that the depth of feedback can be easily increased from 20 to 30 dB, but the audible improvements of deeper feedback will be diminishingly low.

All frequency compensation components are located in the first and second stages of the circuit: their local smoothing RC filters subtly alter frequency response at infrasonic frequencies. An additional RC-filter in the first stage, introduced by Williamson in the 1949 version, prevents oscillations at ultrasonic frequencies. Feedback voltage divider is connected to the transformer secondary, thus feedback depth is dependent on loudspeaker impedance, and setting it at precisely 20 dB requires altering the divider ratio. The voltage divider is purely resistive, with no capacitive or inductive frequency compensation components. According to Williamson, a capacitor shunting the upper leg of the divider is only necessary for inferior-quality transformers; if the transformer matches requirements set by Williamson, the capacitor is useless.

Transformer
Williamson was confident that the output transformer is the most critical component in any valve amplifier. Even before applying global feedback, the transformer is liable for at least four types of distortion. Their causes cannot be addressed simultaneously, and the designer must make a compromise between conflicting requirements. Global feedback partially suppresses distortion, but also tightens requirements to the bandwidth of the transformer.

Stability theory predicted that an amplifier built to Williamson's specifications could only be stable if the bandwidth of its output transformer was no less than 2.5...160000 Hz. This was impractically wide for an audio amplifier, requiring an exceptionally large, complex and expensive transformer. Williamson, seeking a working solution, had to decrease phase margin to a bare minimum; even then, the required bandwidth had to be no less than 3,3...60000 Hz. Such a transformer, driven by a pair of triode-connected KT66, had to have primary winding inductance of at least 100 H, and leakage inductance of no more than 33 mH. These were extremely demanding specifications for the period, far exceeding anything available on the consumer market. The Williamson transformers had to be heavier, larger, more complex and more expensive than typical audio transformers, and yet they could only guarantee minimally acceptable stability. A wider phase margin, wrote Williamson, was highly desirable but required absolutely impractical values of primary inductance.

Overload behaviour
Valve amplifiers with capacitive coupling between the driver stage and the output stage do not clip in the same manner as transistor amplifiers (e.g. clamping output voltage to one of the supply rails). Instead, they choke when large signal swings intermittently attempt to bias the grids of the output valves above zero. Positively-biased grids begin conducting, but the coupling capacitors cannot delivered required current. Grid voltages do not reach target values, output waveform flattens.

Feedback attempts to overcome choking by increasing driver voltage swing, but fails because coupling capacitors cannot physically pass direct current. Resulting distortion pattern, as Williamson proved with photocopies of oscillograms and Lissajous curves, is "of the desirable type", i.e. with abrupt onset of distortion at the extremes of otherwise highly linear response curves.

Stability problem
The first attempts to build the Williamson amplifier revealed its tendency to oscillate due to very narrow phase margin. Astor and Langford-Smith, who gave the Williamson excellent ratings, reported that "for fairly large outputs at low frequencies a high frequency oscillation about 60 kC/s [kHz] would commence and be accompanied by a pulsed output of some other frequency". The Australians, armed with first-class test equipment, suppressed the 60 kHz oscillation with small capacitors on screen grids, but could not identify and suppress the cause of "some other" oscillations. Later, technicians of the United States Naval Research Laboratory examined seven different commercially available Williamson amplifiers, and found that all of them oscillated at infrasonic frequencies of 2...3 Hz. Replacement of output transformers affected stability only at audio and ultrasonic frequencies. The best transformers displayed perfectly flat frequency response from 10 to 100,000 Hz, but were also prone to infrasonic "breathing". The worst transformers displayed prominent ultrasonic resonances that, however, did not cause sustained oscillations. Some "ringed" at relatively low frequencies of 30 to 50 kHz, others extended into 500...700 kHz range.

Custom-built Williamson transformers were imperfect, but general-purpose, off-the-shelf transformers used by amateurs were far worse. Their resonances could only be tamed by narrowing the amplifier's bandwidth. The extent of stability problem in the DIY community remains unknown: the editors of Wireless Worlds were flooded with readers' letters, but preferred to redirect them to Williamson. What is known is that the inventor was compelled to revise and improve the design; he took a leave from his job at Ferranti and presented the second version of the Williamson in 1949. Williamson could not fix the fundamental stability problem; the "New version" was just barely stable. Independent analysis published in December 1950 proved that the revised Williamson amplifier remained prone to both infrasonic and ultrasonic oscillations.

According to the analysis, infrasonic open-loop response of the Williamson amplifier is shaped by three high-pass filters: two interstage RC filters, each with a cutoff frequency of 6 Hz, and the output stage RL filter, formed by the valves' output impedances and the transformer's primary inductance. At zero input signal, the nonlinear RL filter has a cutoff frequency of 3 Hz. This combination of cutoff frequencies, wrapped inside a 2030dB frequency loop, is unstable. Williamson tried to suppress it with a compensation network, also serving as a smoothing filter. The transformer's nonlinearity also improved stability: at high signal currents effective inductance of the primary increased, causing a decrease in cutoff frequency and a rise in phase margin. The simplest solution was to spread apart cutoff frequencies of the RC filters, provided that the output transformer conforms to the Williamson specification. For example, the 1952 Ultralinear Williamson by David Hafler and Herbert Keroes had these frequencies set at 1.3 and 6 Hz.

Precise analysis at ultrasonic frequencies is impossible due to the asymmetry of the phase splitter stage, and unknown parasitics and nonlinearities of the output stage. Depending on the chosen analysis model, open-loop response can be roughly approximated with a combination of either four or five low-pass filters. Different authors used different approaches and estimated somewhat different cutoff points of these filters, but in each case at least three of four or five cutoff frequencies were dangerously close to each other, which was a certain sign of instability. Williamson, again, fixed the problem with an RC compensation network, but even then phase margin remained dangerously low. DIYers had to tackle oscillations themselves: some added shunting capacitors to the screen grids, others tweaked layout and wiring, or deliberately narrowed the amplifier's bandwidth, negating the benefits of the original circuit.

Component problem

The Williamson amplifier was very sensitive to the quality and parameters of passive components and valves. Carbon and composition-type resistors generated excessive noise and caused harmonic distortion; American valves used as substitutes for the British types specified by Williamson, could not match their performance. Williamson warned that the KT66 has no direct substitutes, and should be preferred over any alternatives.

Amateurs who copied the Williamson amplifier were unable to identify and fix its critical weak points. An amateur armed with an analogue multimeter could "see" infrasonic oscillations by watching the instrument needle, but fixing high-frequency issues required an oscilloscope with bandwidth of at least 1 or 2MHz bandwidth. In the 1950s bandwidths of many commercial oscilloscopes were too narrow for the task, and even these models were too expensive for the DIYers.

Articles by professional engineers dealing with analysis and fine tuning of the Williamson amplifier were published relatively late, when the original DIY enthusiasm had already faded - in 1952, 1957, 1961. Martin Kiebert, who built professional-grade Williamson amplifiers for his laboratory at Bendix Corporation, identified five sources of distortion caused by inferior components other than the transformer:

 * 1) Excessive noise and electromagnetic interference caused by noisy carbon or composition-type resistors and incorrect layout of the first stage. Replacement of resistors specified by Williamson with wirewound resistors could improve signal-to-noise ratio by $12 dB$. Replacement of 6SN7 with low-noise 12AY7 could gain another $12 dB$;
 * 2) Frequency and harmonic distortion caused by asymmetry of passive components in two sides of a push-pull circuit. Typical components of the 1950s had 20% tolerances, which was unacceptably high for the Williamson;
 * 3) The 6SN7 driver stage was often unable to properly swing the KT66 grids, causing excessive distortion. According to Kiebert, the American 5687 dual triode was clearly superior. According to Talbot Wright, the 6SN7 was not at fault - distortion was caused by incorrectly set standing current, and could be improved by a simple increase in bias voltage;
 * 4) Distortion in the feedback voltage divider. This critical function required low-distortion wirewound resistors;
 * 5) Distortion was clearly influenced by the choice of output valves, however, Kiebert could not identify any specific rules.

Kiebert rated the design positively but warned the readers that following Williamson's instructions is possible only in a laboratory environment. The amplifier reveals its potential only with expensive, properly matched components that were out of reach of an average amateur. Even a perfectly built and tested Williamson amplifier would sooner or later need valve replacement, which would very likely cause an unexpected rise in distortion.

Variants and derivatives

After 1950 the industry produced numerous derivatives of the Williamson amplifier, often deviating significantly from the principles outlined by its creator. In 1950 Herbert Keroes shunted common cathode resistor of his 807 amplifier with a large electrolytic capacitor which, according to Keroes, significantly reduced distortion at high output power. Contrary to recommendations by Cocking and Williamson, Keroes and his partner David Hafler used cathode shunt capacitors in most of their designs; by 1956 this approach became de facto industry standard. In the same 1956 Hafler used fixed bias in his EL34 Williamson. Later, fixed bias became a staple of Soviet and Russian Williamson-like designs that employed exotic output valves like the 6C4C directly-heated triode, the GU-50 generator pentode or the 6P45S horizontal deflection tetrode.

Throughout the 1950s, as prices of capacitors decreased, designers steadily increased their values. The original Williamson amplifier used $8 μF$ paper capacitors; by 1952 Kiebert uses $40 μF$ electrolytics; the 1955 reference design by Keroes used at least $250 μF$ bypass capacitors; the 1961 budget amplifier by Wright employed a total of $600 μF$. Designers of the commercial Bell2200 amplifier (1953) replaced direct coupling of the first two stages with capacitive coupling; the Stromberg-CarlsonAR-425 (also 1953) use a tetrode-mode output stage in an otherwise familiar Williamson topology. Both Bell and Stromberg-Carson modifications further worsened stability, and required additional frequency compensation. Designers of the BogenDB20 (1953) went even further, and combined global and local negative feedback loops with positive feedback in the output stage.

In December 1951 Hafler and Keroes began promoting the ultralinear stage - a method of distributing load between anode and screen grid of a pentode or tetrode, invented by Alan Blumlein in the 1930s. An ultralinear stage delivered 50% to 100% more output power than the same stage in triode connection, at roughly the same distortion, and cost less than a pure pentode or tetrode stage (the latter required a separate screen grid supply, the ultralinear did not need it). The first Ultralinear Williamson, employing a pair of 6L6 in a Williamson-like topology, delivered $20 W$; their second model, built around more powerful 807 tetrodes, delivered $30 W$. Very soon the American public acquired taste to high-power amplification, and the industry launched the "race for Watts". By 1955 Hafler and Keroes, now working separately, were offering 60-Watt models employing pairs of 6550 tetrodes or quartets of KT66s. Thus in less than a decade, step by step, the industry abandoned the principles set by Williamson, but continued to use his name as a convenient free trademark. In the 21st century it is even used for amplifiers without global negative feedback; the only thing they have in common with the true Williamson amplifier is the four-stage topology.

Following the success of Hafler and Keroes, American manufacturers like Eico, The Fisher, Harman/Kardon and Marantz disposed with "obsolete" power triodes and switched to ultralinear designs. Mullard, Britain's largest valve manufacturer and provider of reference designs to the European industry, publicly supported the novelty. Williamson's former employer, General Electric Company, followed suit and published a reference "30-Watt Williamson" design built around a pair of ultralinear-connected KT88. The original Williamson amplifier lost the race, just like alternative designs by Peter Walker and Frank McIntosh. In September 1952 Williamson and Walker (then business partners in the development of the Quad Electrostatic Loudspeaker) agreed that the ultralinear stage was, indeed, preferable in mass production. Williamson gradually stepped aside from audio engineering. He made his living by designing milling machines and flexible manufacturing systems, which later earned him election to the Royal Society, and never considered audio design a serious occupation for himself.

In 1956 most production amplifiers in North America followed the Ultralinear Williamson template, but in the next few years it was retired, too. The new three-stage reference design combined phase splitter and driver functions in one valve, and thus cost proportionally less than four-stage amplifiers. Hafler's Dynaco Stereo 70, which followed this topology, became the most produced valve amplifier in history. North American consumer market was flooded with millions of similar, almost identical amplifiers and receivers claiming 25 to 20W per channel, as well as clones of less powerful British designs like the Mullard 5-10. Advertisements claimed that these models performed as well as the original Williamson, with higher output power and with guaranteed stability. The customers could not verify these claims, and had to rely to listening tests, hearsay and expert advice. The problem was partially addressed by the concept of subjective listening, advanced by Hafler and Keroes back in 1951: "Excellent measurements are a necessary but not a sufficient condition for the quality of sound. The listening test is one of most importance... the most stringent test of all". By the end of the 1960s subjectivist approach was adopted by the audiophiles and marketing people, who eagerly forgot about the objective principles devised by Williamson in the 1940s.

Objectively, many deep-feedback valve designs of the 1950s matched or exceeded the 0.1% distortion rating of the Williamson amplifier, but none could significantly improve on this figure. Williamson had found that valve amplifier performance was limited mostly by the output transformer. Transistor amplifiers did not have this limitation, and yet it took around 15 years to bring their performance to the level attained by Williamson in 1947.

title: Williamson amplifier


text:
Le Theil

Le Theil may refer to several communes in France:

 * Le Theil, Allier, in the Allier département
 * Le Theil, Manche, in the Manche département
 * Le Theil, Orne, in the Orne département
 * Le Theil-Bocage, in the Calvados département
 * Le Theil-de-Bretagne, in the Ille-et-Vilaine département
 * Le Theil-en-Auge, in the Calvados département
 * Le Theil-Nolent, in the Eure département

title: Le Theil


text:
T-Bolan

T-Bolan is a Japanese rock band which debuted in 1991. Its members are vocal Arashi Moritomo, drummer Kazuyoshi Aoki, guitarist Takeshi Gomi, and bassist Hirofumi Ueno. The name of this band was inspired by T. Rex and its vocalist Marc Bolan.

Biography
The band was formed in 1990. Their 1991 song "Hanashitaku wa Nai" (lit. "I do not want to release you") became a hit song in the cable broadcast. After this success, the band released several hit songs and albums. Their 1993 song "Osaekirenai Kono Kimochi" (lit. "Inextinguishable This Heart") was used for the ending theme of Ichigo Hakusho (in which then-unknown Namie Amuro played a role). The single reached number 1 on the Japanese Oricon weekly charts, becoming their first number-one single. However, Moritomo suffered throat problems so his doctor advised that he should give up singing. Despite this, he was forced to perform a live concert on March 26, 1995. It became their last concert for the decade. After a long hiatus, the band officially disbanded in December 1999. In 2009, after nearly decade of treatment, Moritomo finally regained his voice, then started a solo career not under the band's same label, but by Avex. After hearing fans wishing for the group to reform however, Moritomo and the rest of T-Bolan agreed to reunite in late 2012 and are set to go on a nationwide tour of 16 cities beginning in October 2012. However the first attempt of reunion did not go well and the band went on hiatus for reasons of "each individual member walking their own paths". In 2017 the band has announced full resume of their music activities. They are active as of 2023.

Members

 * Arashi Morimoto (森友嵐士) - vocalist, lyricist, composer, arranger
 * Takashi Gomi (五味孝氏) - guitarist, composer, arranger
 * Hirofumi Ueno (上野博文) - bassist, arranger
 * Kazuyoshi Aoki (青木和義) - drummer, leader, arranger

title: T-Bolan


text: Category:Punctuation

title: Category:Punctuation


text:
Lockheed EC-121 Warning Star

The Lockheed EC-121 Warning Star was an American airborne early warning and control radar surveillance aircraft operational in the 1950s in both the United States Navy (USN) and United States Air Force (USAF).

The military version of the Lockheed L-1049 Super Constellation was used to serve as an airborne early warning system to supplement the Distant Early Warning Line, using two large radomes (a vertical dome above and a horizontal one below the fuselage). It replaced the TBM-3W used by the USN. Some EC-121s were also used for signal intelligence gathering. The EC-121 was introduced in 1954 and phased out in 1978, although a single specially modified EW aircraft remained in USN service until 1982.

The USN versions when initially procured were designated WV-1 (PO-1W), WV-2, and WV-3. The USAF Warning Stars served during the Vietnam War both as electronic sensor monitors and as a forerunner to the Boeing E-3 Sentry AWACS. USAF aircrews adopted its civil nickname, "Connie" (diminutive of Constellation) as reference, USN aircrews used the nickname "Willie Victor".

Development
Since 1943, the Lockheed Constellation had been in USAAF service as the C-69. The use of the Constellation by the USN for patrol and airborne early warning duties was first investigated in 1949, when the USN acquired two Lockheed L-749 Constellations. First flown on 9 June 1949, the PO-1W carried large, long-range radars in massive radomes above and below the fuselage. As the radomes possessed considerably more side area, the vertical stabilizers of the PO-1W had to be enlarged. After the PO-1W (redesignated WV-1 in 1952) had proved that operating large radars on aircraft was possible, the USN ordered the WV-2 based on the L-1049 Super Constellation. The WV-1s were transferred to the Federal Aviation Agency in 1958–1959.

The WV-2/EC-121D was initially fitted with a dorsal AN/APS-45 height finder and a ventral AN/APS-20 search radar. These were later upgraded to AN/APS-103 and AN/APS-95 radars, although not simultaneously. The crew commonly numbered 18, six officers (two pilots, two navigators, and two weapons controllers) and 12 enlisted (two flight engineers, one radio operator, two crew chiefs, five radar operators, and two radar technicians). However, when North Korea shot down a Navy EC-121 in 1969, a crew of 31 was on board.

Orders were placed totaling 142 PO-2W Constellations based on the Lockheed L-1049 Super Constellation, with deliveries beginning in 1953. The PO-2W was redesignated WV-2 in 1954. In 1962, with standardization of aircraft designations within the Department of Defense, the WV-2 then became the EC-121K. In total, 13 of these were converted to WV-2Q electronic intelligence (ELINT) aircraft (becoming EC-121M in 1962). Nine were converted to WV-3 weather reconnaissance aircraft (WC-121N in 1962). The EC-121K was also operated by Training Squadron 86 (VT-86) at NAS Glynco, Georgia, for training of student naval flight officers destined to fly both the EC-121 and the Grumman E-2 Hawkeye. At NAS Glynco's closure, VT-86 transferred to NAS Pensacola, Florida, in 1973, the squadron's last EC-121 was also flown to NAS Pensacola, being stored in the collection of the National Museum of Naval Aviation, where it still remains. A single aircraft became an NC-121K, the electronic warfare variant assigned to Tactical Electronic Warfare Squadron 33 (VAQ-33) at NAS Key West, Florida. The aircraft was the last EC-121 in operational service, flying until 25 June 1982.

The USAF received 10 RC-121C and 74 EC-121D Warning Stars also based on the L-1049, beginning with diversions from the Navy contracts in October 1953. The 10 RC-121Cs became trainers, designated TC-121C. Between 1966 and 1969, 30 retired USN EC-121s were transferred to USAF and converted in EC-121Rs as sensor-monitoring aircraft. Of the 74 EC-121s, 42 were converted to the EC-121H upgrade beginning in 1962, and in 1969, 15 of the remaining EC-121Ds and seven of the EC-121Hs were further upgraded into the final operational variant, the EC-121T, serving as an AWACS prototype in Southeast Asia in 1972. Five EC-121Ds were modified to be broadcasting aircraft for psychological warfare operations, the predecessors of the EC-130 Commando Solo.

USN

WV-2s, redesignated EC-121s in 1962, served from 1954 to 1965 in two "barrier" forces, one off each coast of the North American continent. The barrier forces consisted of five surface picket stations each manned by radar destroyer escorts and an air wing of WV-2s/EC-121s that patrolled the picket lines at 1,000–4,000 m (3,000–12,000 ft) altitude in 6- to 20-hour missions. Their objective was to extend early warning coverage against surprise Soviet bomber and missile attacks as an extension of the DEW Line.

In April 1954, the first Lockheed Super Constellation (Model 1049C), WV-2 BuNo. 128323, was received at NAS Barbers Point by Airborne Early Warning Squadron One (VW-1).

The Atlantic Barrier (BARLANT) consisted of two rotating squadron detachments sourced from AEW Squadron Thirteen (VW-13) and AEW Squadron Fifteen (VW-15) from NAS Patuxent River, Maryland and one squadron, AEW Squadron Eleven (VW-11), permanently based at Naval Station Argentia, Newfoundland. Their mission was to fly orbits to the Azores and back. An additional AEW training unit was based at NAS Patuxent River for training flight crews and maintenance personnel.

BARLANT became operational on 1 July 1956, and flew continuous coverage until early 1965. The barrier was shifted to cover the approaches between Greenland, Iceland, and the United Kingdom (GIUK) barrier in June 1961. Aircraft from Argentia were staged through NAS Keflavik, Iceland, to extend coverage times.

The Pacific Barrier (BARPAC) received the first operational AEW squadron, Airborne Early Warning Squadron One (VW-1) and the first EC-121K aircraft. AEW Squadron Three followed with AEW Squadrons Twelve, Fourteen, and Sixteen. In January 1958 VW-1 and VW-3 relocated to NAS Agana, Guam, M.I. where VW-1 continued its AEW commitments and VW-3 operational commitment was divided between AEW and weather. BARPAC became operational with AEW Squadron Twelve (VW-12) based at NAS Barbers Point, Hawaii, operating from a deployment base at NAS Midway on 1 July 1958 and later expanded to include AEW Squadrons Fourteen (VW-14) and Sixteen (VW-16). Their orbits overlapped the radar picket stations of the ships of Escort Squadron Seven, from roughly Adak Island to Midway. Normally, five WV-2s/EC-121s were required at any single time to provide coverage over the entire line.

The Hawaiian barrier force operations were discontinued by September 1965, and their EC-121K aircraft were placed in storage. However, VW-1 continued operating until 1972, flying weather ops and supplying AEW to naval forces in the Gulf of Tonkin. USN C-121, EC-121, WC-12,1 and NC-121 operations continued until 1975 in seven other squadrons and until 1982 in an eighth. Some EC-121s were used in Vietnam, mirroring USAF EC-121 missions, but orbiting the Gulf of Tonkin, as that was the USN's assigned area.

Fleet Air Reconnaissance Squadron One (VQ-1) and Fleet Air Reconnaissance Squadron Two (VQ-2) operated EC-121M ELINT gathering aircraft at NAF Atsugi, Japan, and Naval Station Rota, Spain, respectively, until they transitioned to the EP-3B Orion and EP-3E Aries aircraft.

Weather Reconnaissance Squadron Four (VW-4) operated WV-3-cum-WC-121s between 1954 and 1975 as Hurricane Hunters, with its primary base at NAS Jacksonville, Florida, and a forward base at Naval Station Roosevelt Roads, Puerto Rico. Its Pacific counterpart, Weather Reconnaissance Squadron Three (VW-3) Typhoon Trackers was the operational weather squadron in the Pacific, flying from NAS Agana, Guam, tracking typhoons from 1955 to 1960. On June 30, 1960 Weather Reconnaissance Squadron Three, VW-3, disbanded and many of its aircraft (8 - BuNo. 145 series) and crews were absorbed by VW-1, which retained AEW designation and took on the weather commitments and the Title of "Typhoon Trackers" of VW-3. VW-4 later transitioned to WP-3A Orion.

Also operating C-121 and EC-121 aircraft was Oceanographic Development Squadron Eight (VXN-8) at NAS Patuxent River, Maryland, which employed the aircraft for specific projects (e.g., Project BIRDSEYE, MAGNET, ASWEPS etc.) for the Office of Naval Research until they were replaced by RP-3A and RP-3D Orion aircraft. VXN-8 also operated four additional NC-121 aircraft called the "Blue Eagles". These specially modified aircraft were equipped with complete radio and television transmitting equipment and studios for simultaneous broadcast of American and Vietnamese television and radio programs prior to the installation of ground stations during the Vietnam War. The aircraft flew nightly 7 days per week broadcasting such American TV programs as Combat, Have Gun-Will Travel, and Gunsmoke, along with other popular programs of the time in addition to Vietnamese programs recorded prior to each flight. Nightly American news broadcasts were transmitted live using an onboard TV studio and an Air Force newscaster bringing the latest news from home and the world. The "Blue Eagles" operated out of Saigon and Danang Air Bases for around 5 years commencing in 1965.

Air Development Squadron Six (VX-6, based at NAS Quonset Point, Rhode Island, also operated R7V aircraft, redesignated C-121J, in support of United States Antarctic Program operations until replaced by LC-130F Hercules aircraft.

The EC-121 was also operated by Training Squadron 86 (VT-86) at NAS Glynco, Georgia, for training student naval flight officers destined for the E-2 Hawkeye and by Tactical Electronic Warfare Squadron 33 (VAQ-33) for the Fleet Electronic Warfare Systems Group (FEWSG) at NAS Norfolk, Virginia, and later, following a squadron homeport change, at NAS Key West, Florida. At the time of its retirement on June 25, 1982, VAQ-33's NC-121K aircraft, Buno 141292 was the last NC-121K and the last of its type operated by the USN.

USAF
The USAF operated EC-121s between 1954 and 1978, with three wings at maximum employment and three independent squadrons as operations wound down. Until the Vietnam War, their primary mission was to provide complementary early warning radar coverage to the Pacific and Atlantic barriers by flying orbits 300 mi offshore from the continental United States in what were termed "contiguous barriers". The coverage orbits overlapped those of land-based early warning radars.

Initial deployment of EC-121Cs began with 551st Airborne Early Warning and Control Wing, based at Otis Air Force Base, Massachusetts. Operational on 21 December 1954, 551st AEWCW subsequently upgraded to EC-121D and later EC-121H Warning Stars.

Its Pacific counterpart was 552d Airborne Early Warning and Control Wing (AEWCW), based at McClellan Air Force Base, California, becoming operational on 1 July 1955. After the Cuban Missile Crisis in 1962, 552nd AEWCW also had administrative control of the 966th AEWCS, based at McCoy Air Force Base, Florida. The 966th had a dual mission - monitoring activity in Cuban airspace and flying Gold Digger missions (continuous tracks of U-2 surveillance missions).

The third air wing to operate EC-121s was 553rd Reconnaissance Wing, a Vietnam war organization activated in 1967 and based in Thailand until inactivation in 1970 (See BatCat below). In 1966, Lockheed modified 30 ex-USN Super Constellations (two EC-121P/WV-3 and 28 EC-121K/WV-2) aircraft to EC-121Rs for the specialized reconnaissance mission flown by the 553rd. Aircraft were delivered during the course of 1967. The 553rd RW flew over land and off the coast of Vietnam, over Laos and Cambodia, monitoring and retransmitting low-power signals. Usually, they orbited the Ho Chi Minh Trail in 8-hour shifts. As it was expensive to operate and it exposed a large crew to enemy fire, it was replaced in December 1970 by the much smaller (and eventually unmanned drone) QU-22 Pave Eagle sensor monitor.

The 551st AEWCW inactivated in 1969, while the 552d was reduced by a squadron in 1971. In July 1974, USAF redesignated 552d Airborne Early Warning and Control Wing as 552d Airborne Warning and Control Group when it was downsized to a single squadron. It inactivated in April 1976.

As the USAF prepared for deploying the E-3 Sentry in the later 1970s, it phased out EC-121 operations by the end of 1975. All remaining EC-121s transferred to Air Force Reserve, which formed the 79th AEWCS at Homestead Air Force Base, Florida, in early 1976. The active duty force continued providing personnel to operate the EC-121s on a 24-hour basis, assigning Detachment 1, 20th Air Defence Squadron to Homestead AFB as associate active duty crews to fly the AFRES-owned aircraft. Besides monitoring Cuban waters, these last Warning Stars also operated from NAS Keflavik. Final EC-121 ops ended in September 1978. Detachment 1 dissolved and 79th AEWCS was redesignated a fighter squadron on 1 October 1978.

In 1967, five EC-121s became operational with the 193rd Tactical Electronic Warfare Squadron of the Pennsylvania Air National Guard, responsible for psychological operations missions under project Coronet Solo. From July 1970 to January 1971, they rotated on 30- to 90-day temporary-duty deployments to Korat Royal Thai Air Force Base, Thailand, under the name Commando Buzz.

Vietnam War
EC-121s were used extensively in Southeast Asia between 16 April 1965, and 1 June 1974, particularly in support of Operation Rolling Thunder and Operation Linebacker/Linebacker II, providing radar early warning and limited airborne control of USAF fighter forces engaging MiG interceptors. Flying orbits over the Gulf of Tonkin and later over Laos, they were the forerunners of AWACS aircraft. The USN used a variant, the NC-121, in their Blue Eagle unit from 1965–1972. Blue Eagles were television- and radio-broadcasting airplanes. The Blue Eagles were based at NAS Patuxent River and were part of oceanographic squadron VXN-8.

Big Eye
At the onset of Rolling Thunder, the North Vietnamese had an advantage in that their radar coverage could detect most US strike aircraft flying at or above 5,000 ft virtually anywhere in the country, using a system that was difficult to jam. US forces countered with radar ships (Crown) in the Gulf of Tonkin and a ground site at Nakhon Phanom RTAFB, Thailand, but both systems were line-of-sight and suffered coverage gaps.

To increase coverage, the Seventh Air Force (7 AF) requested airborne radar support and the Air Defense Command (redesignated Aerospace Defense Command in 1968) was directed to set up the Big Eye Task Force. Five EC-121Ds and 100 support personnel of the 552nd AEWCW at McClellan AFB were deployed to Tainan Air Station, Taiwan, with four of the EC-121s sent on to a forward operating location at Tan Son Nhut Air Base, near Saigon, South Vietnam.

The EC-121s were designed for detection of aircraft flying over water, so ground clutter (spurious signal returns off of terrain features such as mountains) caused interference with their radar pictures. The crews, however, were experienced in tracking Soviet aircraft over Cuba and had developed a technique whereby an EC-121 flying at 50 ft to 300 ft above water could bounce a signal from its bottom-mounted APS-95 Search radar off the surface of the water and detect aircraft at medium altitudes out to 150 mi. Operating in pairs, one Big Eye EC-121 flew a 50 mi race track pattern approximately 30 mi offshore (Alpha orbit), with the orbit's center at 19.41667°N, 107.41667°W. The second one flew a track at 10,000 ft (Bravo orbit) farther from the coast, acting as a spare for the Alpha EC-121.

This provided a practical detection range of 100 mi, enough to cover the Hanoi urban area and the main MiG base at Phúc Yên. A major disadvantage of this arrangement, however, was that most MiG contacts were beyond the 70 mi range of the Big Eye's APS-45 Height Finder radar, so that they were unable to provide this data to USAF strike forces. Furthermore, technical shortcomings in the EC-121D's systems precluded either controlling a fighter intercept or identifying a specific flight under attack.

The missions from Tan Son Nhut AB began 21 April 1965, using callsigns Ethan Alpha and Ethan Bravo, which became standard. After refueling at Danang Air Base, Ethan Alpha made a wave-top approach to its orbit station, where it remained for five hours. Because of the threat of MiG interception, EC-121s were protected by a Lockheed F-104 Starfighter MiGCAP. If, for any reason, the MiGCAP could not rendezvous, the EC-121s cancelled their mission. Air-conditioning systems aboard the EC-121 were virtually useless in this profile, and the heat produced by the electronics, combined with the threat of being shot down, made Alpha orbit missions in particular very stressful. On 10 July 1965, in its first airborne-controlled interception, an EC-121 provided warning to a pair of USAF F-4C fighters, resulting in the shooting down of two MiG-17s.

The Big Eye Task Force remained at Tan Son Nhut until February 1967, when the threat of Viet Cong ground attacks prompted a move to Thailand.

College Eye
In March 1967, Big Eye was renamed College Eye Task Force (CETF) and relocated at Ubon Royal Thai Air Force Base. Because of the complexity of the aircraft and its systems along with the large support group it required, CETF could not be supported at the relatively small Thai bases. It moved to Udon RTAFB in July and to its final station at Korat RTAFB in October 1967. Seven of 26 EC-121s deployed from Otis AFB and arrived at Korat, on the 19th.

From April 1965 to early 1966 and beginning again in late 1967, the EC-121Ds also controlled a flight of MiGCAP fighters for unarmed support aircraft operating over the Tonkin Gulf. The EC-121Ds also served as an airborne communications relay center for strike aircraft to transmit mission results and position reports to Danang Air Control Center; directed operations of fighter escorts, MiGCAPs, Lockheed C-130 Hercules flare ships and A-26 strike aircraft along the North Vietnamese-Laotian border; provided radar and navigational assistance for combat search and rescue missions; and assisted fighters in finding tankers for emergency refueling.

In May 1966, the government of China formally protested an incursion by a Republic F-105 Thunderchief pursuing a North Vietnamese MiG it subsequently shot down 25 mi inside Chinese territory. A US board of inquiry recommended that College Eye also had to monitor the "no-fly zone" inside the North Vietnamese border with China, to provide alerts to US aircraft nearing the buffer zone and to report border crossing violations by US aircraft. This could not be done from the gulf, so a third orbit, Ethan Charlie, was created in Laos. After tests in June and August, regular missions began 24 August. Not enough EC-121s or crews were available to support three orbits twice daily, so the Laotian orbit was only flown every third day, with Ethan Bravo missions cancelled on those days. After 13 October 1966, the Charlie orbit was flown every day and the Bravo orbit suspended altogether. In April 1967, four more EC-121s were deployed, to Thailand on 29 May, making for a total strength of three College Eyes in Taiwan and six in Thailand.

In April 1967, USAF began fitting its entire EC-121 fleet with QRC-248 IFF transponder interrogators. QRC-248 had been developed to follow Soviet-export aircraft flown by the Cuban Air Force. The SRO-2 transponders installed in Soviet export MiGs enabled Cuban ground-controlled interception (GCI) radars to identify and control their fighters. A testbed EC-121 called Quick Look had flown with College Eye in January 1967 to test QRC-248 and found that North Vietnamese MiGs used the same transponder. QRC-248 accurately discriminated MiG radar returns from the myriad returns picked up during a mission and extended the range of low-altitude detection to more than 175 mi, covering virtually all important North Vietnamese target areas.

By May, all College Eyes had been fitted with QRC-248. Ethan Bravo's mission was changed from that of a backup for Ethan Alpha to being the primary QRC-248 listener, but College Eye was prohibited by the Joint Chiefs of Staff from actively "interrogating" MiG transponders, following a National Security Agency security policy protecting its "intelligence sources" (of which the QRC-248 was one), thus was restricted to waiting for North Vietnamese GCI to interrogate its aircraft. QRC-248 began regular use in July 1967, but by then North Vietnam's MiG force, which had suffered serious losses in May, had suspended its combat operations.

In the last week of August, however, after a period of intensive training and revision of tactics, the MiGs began engaging US strike forces again, scoring a number of kills. Then, Seventh Air Force finally obtained permission for the new Ethan Bravo mission EC-121 to actively interrogate with QRC-248 on 6 October. By 4 December, its success outweighed any value in flying the Ethan Alpha orbit, which was discontinued until July 1972.

On 1 March 1968, College Eye callsigns changed to Ethan 01, 02, 03 and 04. Ethan 03 (Laotian orbit) began "positive control" (airborne direction) of C-130 flareship flights and A-26 Invader night interdiction missions along the Ho Chi Minh Trail in Laos on 19 April 1968.

The task force was scaled back in July 1968, to four EC-121Ds and the Rivet Top testbed aircraft to allow for the basing of another College Eye detachment at Itazuke AB, Japan. The name of the task force was discontinued in October 1968, when it was redesignated a final time as Detachment 1 (Rotational), 552nd AEWCW. EC-121 deployments to Southeast Asia were discontinued in June 1970 in the expectation that they would no longer be used.

Rivet Top
In August 1967, while the College Eye Task Force was still based at Udon RTAFB, another prototype EC-121 variation began operations testing new equipment as Detachment 2 of the Tactical Air Warfare Center. Known as Rivet Top, this modified EC-121K (later redesignated EC-121M) carried the QRC-248 newly installed in the College Eye aircraft and also had electronic interrogators capable of reading two additional Soviet transponders, the SRO-1 and SOD-57. Its electronics were custom built rather than off-the-shelf. Its most important upgrade was the top-secret Rivet Gym installation. This consisted of the addition to the crew of Vietnamese-speaking intelligence specialists manning four voice communications intercept stations able to monitor all communications between the MiGs and their GCI controllers.

Despite this advantage, Rivet Top experienced two problems, reducing its effectiveness. Its operators did not have radar scopes to correlate intercepted conversations with specific flights of MiGs, thus could not determine which US aircraft might be under attack. Secondly, like QRC-248, Rivet Gym was an NSA SIGINT asset and subject to even more stringent rules protecting knowledge of its existence. Even when real-time warnings to US aircraft were finally permitted in mid-1972, fighter crews were not made aware of the source of the warnings and because EC-121 radio communications were poor, mandating the use of a radio relay aircraft that often failed, they tended to disregard the credibility of the source.

The Rivet Top prototype moved to Korat RTAFB along with the College Eye Task Force in October 1967. Originally scheduled to return to the USA in February 1968, because of its value, it remained at Korat until 1969. Flying daily missions through its testing period, it began flying every-other-day missions over the Gulf of Tonkin after 31 March 1968, when Rolling Thunder operations were sharply scaled back. Rivet Gym installations were back-fitted to all College Eye EC-121s by the end of May 1968.

Operation Kingpin
Two EC-121Ds, newly modified with the Southeast Asia Operational Requirement 62 (SEAOR-62) electronics suite, but not yet operational as EC-121Ts, were ordered to Korat RTAFB in October 1970. Under the guise of being field tested, they were accompanied by a C-121G carrying additional crew members, the most experienced 552nd AEWCW technicians, and equipment necessary to maintain the new electronics. The SEAOR-62 package was supported by a digital data receiver ground terminal and by radio relay equipment transshipped by separate classified airlift. The EC-121Ts arrived in Thailand from McClellan AFB on 12 November.

The purpose of the deployment was to provide an integrated tactical data display with real-time inputs (similar to the Navy Airborne Tactical Data System equipping E-1B Tracer platforms of Task Force 77) in support of Operation Kingpin, a mission to rescue US prisoners of war held at Son Tay prison. Once at Korat, some equipment was tested for the first time because of emission restrictions in US airspace and the only available manuals and checklists were notes from early flight tests. Even so, both aircraft were operational by 17 November.

On 20 November 1970, two Warning Stars, using the callsigns Frog 01 and 02, respectively, took off 10 minutes apart at 22:00 from Korat to take station at the low-altitude Alpha orbit over the Gulf of Tonkin, with Frog 02 as a backup. The 17-man crews were advised in the air of the nature of the rescue mission and their role, providing MiG warning and directing USAF F-4 Phantom CAP intercepts. As Frog 01 began its climb to the higher Bravo orbit, it experienced a ruptured oil line forcing shutdown of one engine. As planned, Frog 02 became the primary aircraft when Frog 01 made an emergency landing at Danang.

The new equipment failed to function properly aboard Frog 02. The ground receivers at the command post in Danang failed to receive data and the APX-83 IFF processors would not display aboard the aircraft, despite repeated repairs. Their own radar monitors experienced excessive electronic noise and the jamming of North Vietnamese radars by nearby EKA-3B Skywarriors hindered efforts of the radar technicians to correct the problems. While unable to provide vectoring information to the F-4s escorting the mission, Frog 02 remained on station and relied on its Rivet Top voice intercept capability to provide supplementary data.

Disco
In October 1971, North Vietnamese MiGs, operating from forward bases opened after the end of Rolling Thunder, began a campaign to intercept Boeing B-52 Stratofortress missions over southern Laos. On 20 November, a MiG-21 launched air-to-air missiles at a B-52 that evaded by dropping flares. As a result, Warning Stars of Det. 1 returned to Korat RTAFB to provide radar support by flying the Laotian orbit again, using callsign Disco. Seven EC-121Ts, replacement aircraft for the earlier series, were based in Thailand and contained both QRC-248 and Rivet Top electronic suites.

When Operation Linebacker began on 10 May 1972, Disco was one of two principal GCI radars used by US forces, although it continued to be handicapped by poor radio communications. In addition, its slow-turning radar limited its value as a controller of fighters during MiG engagements, while the size of USAF raids during Linebacker nearly saturated its capabilities. Improvements made in the systems since 1968 enabled the operators to distinguish MiG types and a color code system for them entered the air operations vernacular: "Red Bandits" (Mig-17s); "White Bandits" (MiG-19s); "Blue Bandits" (MiG-21s), and "Black bandits" (MiGs low on fuel).

On 6 July 1972, as the result of seven F-4 Phantoms shot down in a two-week period, a second Disco track was initiated. Flown near the former Alpha orbit over the Gulf of Tonkin, its purpose was to gain better low-altitude coverage in the Hanoi area. At the end of the month, Disco was also integrated into Teaball control center, a highly classified system established to collate all signal intelligence on North Vietnamese air activity gathered by all sources, including nonmilitary. Disco was used as a conduit through which warnings and control vectors were given, but the delay in Teaball acquiring the information and relaying it through Disco (often using an unreliable radio relay KC-135A Combat Lightning aircraft operating under callsign Luzon) cancelled out its value for use in "real time", and the fact that its existence was kept from US aircrews damaged its credibility. Teaball received direct communications capability, but experienced transmission failures with frustrating frequency. Disco remained the primary backup controller, but its usefulness remained limited because it directly controlled only MiGCAP missions and could only provide its information to strike, chaff, and escort forces via the "Guard" frequency.

On 15 August 1973, Disco EC-121s flew their final combat mission and on 1 June 1974, Det.1 was permanently withdrawn from Southeast Asia. Between 1965 and 1973, the EC-121s flew 13,921 combat missions, more than 98,000 accident-free flying hours, assisted in the shoot-down of 25 MiGs, and supported the rescue of 80 downed flyers. No Big Eye, College Eye, or Disco aircraft were lost.

Batcat
During the Vietnam War, some 40 EC-121s were modified from USN WV-2 and WV-3 early warning Constellations for use with ground sensors to detect enemy troop movements along the Ho Chi Minh Trail and 25 were deployed to Korat RTAFB as a part of Operation Igloo White. The resulting EC-121R configuration was nicknamed the Batcat. Two Batcats were lost during the war, with the loss of 22 crewmen, one in a takeoff accident during a thunderstorm in April 1969, the other in September 1969, in a landing accident which also killed four Thai civilians.

Batcat EC-121s were camouflaged in standard tree-color Southeast Asia scheme, while the College Eye/Disco early warning aircraft were not. BatCat missions were 18 hours in length, with 8 hours on station at one of 11 color-coded orbits used during their five-year history, three of which were over South Vietnam, six over Laos, one over Cambodia, and one over the Gulf of Tonkin.

EC-121Rs were operated by the 553d and 554th Reconnaissance Squadrons of the 553d Reconnaissance Wing, between October 1967 and December 1970, with about 20 Batcats on hand at any time. The wing activated in December 1970 and the 554th RS relocated to Nakhon Phanom RTAFB to fly QU-22 sensor monitors nicknamed "Baby Bats". Initially with 11 aircraft, the 553rd RS continued operations for another year, gradually returning aircraft and crews to the USA. The final Batcat mission was in December 1971. The last remaining administrative and support personnel returned to Otis AFB in January 1972.

USN variants

 * WV-1. 2 prototypes, L-749A Constellation, designated PO-1W before 1952
 * EC-121K (WV-2). Main USN variant, designated PO-2W before 1952; 244 ordered, 142 produced (the rest to USAF).
 * JC-121K. One modified EC-121K used as a US Army avionics testbed
 * NC-121K. Unknown number modified as special mission aircraft
 * YEC-121K. One modified avionics testbed
 * EC-121L (WV-2E). One modified WV-2, testbed for rotating radar dome with an AN/APS-70 radar
 * EC-121M (WV-2Q). ELINT collection variant, 13 modified WV-2
 * WC-121N (WV-3. Weather reconnaissance variant, 8 modified WV-2
 * EC-121P. Unknown number modified from EC-121K as anti-submarine variant
 * JEC-121P. 3 EC-121P used by the USAF

USAF variants

 * RC-121C: 10 produced, initial USAF variant
 * JC-121C: 2 converted from C-121C and 1 TC-121C as avionics testbeds
 * TC-121C: 9 RC-121C modified before 1962 as crew trainers
 * EC-121D: 73 produced 1953–55 as main USAF variant and 1 converted from C-121C, originally designated RC-121D
 * EC-121D Quick Look: 1 testbed for QRC-248 IFF transponder interrogator
 * EC-121H: 42 USAF upgrades in 1962, 35x EC-121D and 7x WV-2s transferred from the Navy
 * EC-121J: 2 USAF EC-121D modified with upgraded electronics
 * EC-121M Rivet Top: 1 EC-121D testbed for Rivet Gym cryptologic linguist electronics suite, originally designated EC-121K
 * EC-121Q: 4 EC-121D modified with upgraded electronics for USAF Gold Digger missions
 * EC-121R: 30 EC-121K / EC-121P transferred to USAF in 1966–1967 and converted to Batcat sensor signal processor
 * EC-121S: 5 converted for Pennsylvania Air National Guard from USAF C-121 transports
 * EC-121T: Final USAF variant. A total of 22 T's were converted from 15x EC-121D and 7x EC-121H.
 * XW2V-1: Proposed naval development with new features such as 4 Allison T56-A8 turboprop engines, L-1649A Starliner wings and Bomarc missiles for defense. None built; was designated L-084 due to the large differences from its predecessors.

Active duty

 * 551st AEWCW – Otis AFB, Massachusetts
 * 960th AEWCS
 * 961st AEWCS
 * 962d AEWCS
 * 552d AEWCW – McClellan AFB, California
 * 963d AEWCS
 * 964th AEWCS
 * 965th AEWCS
 * 553d RW – Korat RTAFB, Thailand
 * 553d RS
 * 554th RS
 * 966th AEWCS – McCoy AFB, Florida
 * Det 1, 20th ADS – Homestead AFB, Florida

AFRES

 * 79th AEWCS (AFRES) – Homestead AFB, Florida

ANG

 * 193d TEWS (PA ANG) – Olmsted Air Force Base, later renamed Harrisburg Air National Guard Base, Pennsylvania

USN

 * AEW Wing Atlantic – NAS Patuxent River, Maryland
 * VXN-8 – NAS Patuxent River, Maryland
 * VW-2 (BarLant) -NAS Patuxent River, Maryland
 * VW-4 ("Hurricane Hunters") – NAS Jacksonville, Florida
 * VW-11 (BarLant) – NS Argentia, Newfoundland / NAS Patuxent River, Maryland
 * VW-13 (BarLant) – NAS Patuxent River, Maryland / NS Argentia, Newfoundland
 * VW-15 (BarLant) – NAS Argentia, Newfoundland / NAS Patuxent River, Maryland
 * AEWTULANT – NAS Patuxent River, Maryland
 * Naval CIC Officers School, later Training Squadron EIGHTY SIX (VT-86) – NAS Glynco, Georgia
 * AEW Wing Pacific – NAS Barbers Point, Hawaii
 * VW-1 ("Typhoon Trackers") – NAS Agana, Guam
 * VW-3 ("Typhoon Chasers") – NAS Agana, Guam
 * VW-12 (BarPac) – NAS Barbers Point, Hawaii
 * VW-14 (BarPac) – NAS Barbers Point, Hawaii
 * VW-16 (BarPac) – NAS Barbers Point, Hawaii
 * AewBarsRon 2 (Service/Support) – NAS Barbers Point, Hawaii
 * MatRon 1 (Support) – NAS Barbers Point, Hawaii
 * AewBarRonPac (amalgamation of VW-12, VW-14, and AEWBarRon 2) – NAS Barbers Point, Hawaii
 * VQ-1 – NAF Atsugi, Japan
 * VQ-2 – NS Rota, Spain
 * VAQ-33 – NAS Norfolk, Virginia / NAS Key West, Florida
 * VX-6 – NAS Quonset Point, Rhode Island

Accidents and incidents
A total of 20 Navy EC-121s were destroyed in accidents, with 113 aircrew deaths:
 * 15x WV-2/EC-121K; 3x WV-2Q/EC-121M and 2x WV-3/WC-121N

Another unarmed EC-121M was destroyed in one-sided combat. In April 1969, North Korean Air Force MiG-21 fighter-interceptors shot down an EC-121 in international airspace off the country's east coast, killing all of the crew of 31 on board.

The USAF had a total of 11 Warning Stars destroyed in accidents, killing 66 aircrew:
 * 2x RC-121C/TC-121C; 2x RC-121D; 3x EC-121H; 3x EC-121R and 1x EC-121T

3 EC-121Hs from the 551st AEWCW were lost on 11 July 1965, 11 November 1966 and 25 April 1967, respectively, resulting in 50 deaths, including the wing commander of the 551st AEWCW, Col James P. Lyle. The 2 Batcat EC-121R crashes resulted in 22 killed.

Surviving aircraft

 * EC-121T
 * On Display
 * AF Ser. No. 52-3418 – on display at the Combat Air Museum at Forbes Field (former Forbes AFB) in Topeka, Kansas. The aircraft was delivered to USAF in October 1954 as an RC-121D and redesignated an EC-121D in 1962. It was converted to an EC-121T, but the upper radome has been removed.
 * AF Ser. No. 52-3425 – on display at the Peterson Air and Space Museum at Peterson AFB in Colorado Springs, Colorado. Previously assigned to the 966th AEWCS at McCoy AFB, Florida and then the 79th AEWCS at Homestead AFB, Florida. It was delivered to Peterson AFB in October 1978.
 * AF Ser. No. 53-0548 – on display at the Yanks Air Museum in Chino, California. It was stored at Camarillo Airport (former Oxnard AFB) while the Yanks Air Museum was working to get it restored and to complete FAA paperwork for a ferry flight. The final maintenance efforts by Yanks Air Museum Restoration Director Frank Wright included a rebuild of engine #4 in early January 2012. 53-0548 departed Camarillo at 12:10PM on Saturday, 14 January 2012 for the 90-minute flight to Chino, where it will become a static display.
 * AF Ser. No. 53-0552 – on display at Tinker AFB, Oklahoma.
 * AF Ser. No. 53-0554 – on display at the Pima Air & Space Museum, adjacent to Davis-Monthan AFB in Tucson, Arizona.
 * AF Ser. No. 53-0555 – on display at the National Museum of the United States Air Force at Wright-Patterson Air Force Base near Dayton, Ohio. The College Eye EC-121D is fully restored and on display indoors. This aircraft was nicknamed "Triple Nickel" because of its serial number (53-555). On 24 October 1967, while operating over the Gulf of Tonkin, it guided a U.S. fighter by radar into position to destroy a North Vietnamese Air Force enemy fighter aircraft, a MiG-21. This was the first time a weapons controller aboard an airborne radar aircraft had ever directed a successful attack on an enemy aircraft. "Triple Nickel" was retired to the USAF Museum in 1971.
 * AF Ser. No. 52-3417 – in storage at the University of Montana – Helena College of Technology in Helena, Montana. The aircraft is the oldest surviving EC-121, and was delivered to the USAF as a RC-121D in September 1954, and upgraded to an EC-121T in 1970. It served with the Air Force Reserve at Homestead Air Force Base before being retired to Davis-Monthan Air Force Base in March 1976. In the early 1980s, the university purchased the aircraft from the Air Force for $10,000 and it was ferried to the university in July 1981. In spring 2009, it was declared surplus by the university and offered to any museum interested in preserving it. The aircraft was eventually acquired by the Evergreen Aviation and Space Museum in McMinnville, Oregon, and prepped for a ferry flight to Oregon. However, after the museum's parent company Evergreen International Aviation went bankrupt, the aircraft was acquired by the Castle Air Museum at the former Castle AFB in Atwater, California, for restoration. After that, many parts and materials were collected, and now it is completely restored and preserved.
 * EC-121K
 * On Display
 * BuNo 137890 – on display outside 552d Air Control Wing Headquarters, the home of E-3 AWACS operations for the USAF, at Tinker Air Force Base, in Oklahoma City, Oklahoma. The aircraft is one of two Warning Stars displayed in the markings as AF Serial Number 53-0552.
 * BuNo 141297 – on display at the Museum of Aviation at Robins Air Force Base, Georgia. It was flown to the museum in 1987 for display.
 * BuNo 141309 – on display as AF Serial Number 53-0552 at the Aerospace Museum of California at the former McClellan AFB, California. This is one of two Warning Stars painted as 53-0552.
 * BuNo 141311 – awaiting restoration at the Yankee Air Museum, Belleville, MI. Previously at Octave Chanute Aerospace Museum, Rantoul, Illinois.
 * BuNo 143221 – on display at the National Naval Aviation Museum at Naval Air Station Pensacola in Pensacola, Florida. The aircraft was acquired in flyable condition in 1973 from Training Squadron 86 (VT-86) at NAS Glynco, Georgia pending the closure of NAS Glynco and the squadron's relocation to NAS Pensacola. It is currently on display at the Sherman Field flight line annex of the museum.

title: Lockheed EC-121 Warning Star


text:
Expenditure minimization problem

In microeconomics, the expenditure minimization problem is the dual of the utility maximization problem: "how much money do I need to reach a certain level of happiness?". This question comes in two parts. Given a consumer's utility function, prices, and a utility target,
 * how much money would the consumer need? This is answered by the expenditure function.
 * what could the consumer buy to meet this utility target while minimizing expenditure? This is answered by the Hicksian demand function.

Expenditure function
Formally, the expenditure function is defined as follows. Suppose the consumer has a utility function $$u$$ defined on $$L$$ commodities. Then the consumer's expenditure function gives the amount of money required to buy a package of commodities at given prices $$p$$ that give utility of at least $$u^*$$,

 * $$e(p, u^*) = \min_{x \in \geq{u^*}} p \cdot x$$

where

 * $$\geq{u^*} = \{x \in \mathbb{R}^L_+ : u(x) \geq u^*\}$$

is the set of all packages that give utility at least as good as $$u^*$$.

Hicksian demand correspondence
Hicksian demand is defined by
 * $$h : \mathbb{R}^L_+ \times \mathbb{R}_+ \to P(\mathbb{R}^L_+)$$
 * $$h(p, u^*) = \underset{x \in \geq u^* }{\operatorname{argmin}}\ p \cdot x$$.

Hicksian demand function gives the cheapest package that gives the desired utility. It is related to Marshallian demand function by and expenditure function by
 * $$h(p, u^*) = x(p, e(p, u^*)). \,$$

The relationship between the utility function and Marshallian demand in the utility maximization problem mirrors the relationship between the expenditure function and Hicksian demand in the expenditure minimization problem. It is also possible that the Hicksian and Marshallian demands are not unique (i.e. there is more than one commodity bundle that satisfies the expenditure minimization problem); then the demand is a correspondence, and not a function. This does not happen, and the demands are functions, under the assumption of local nonsatiation.

title: Expenditure minimization problem


text:
Le Theil-Bocage

Le Theil-Bocage is a former commune in the Calvados department in the Normandy region in northwestern France. On 1 January 2016, it was merged into the new commune of Valdallière.

title: Le Theil-Bocage


text:
Le Theil-en-Auge

Le Theil-en-Auge (, literally Le Theil in Auge) is a commune in the Calvados department in the Normandy region in northwestern France.

title: Le Theil-en-Auge


text: Category:Peruvian footballers

title: Category:Peruvian footballers


text:
Strange particle

A strange particle is an elementary particle with a strangeness quantum number different from zero. Strange particles are members of a large family of elementary particles carrying the quantum number of strangeness, including several cases where the quantum number is hidden in a strange/anti-strange pair, for example in the ϕ meson. The classification of particles, as mesons and baryons, follows the quark/anti-quark and three quark content respectively. Murray Gell-Mann recognized the group structure of elementary particle classification introducing the flavour SU(3) and strangeness as a new quantum number.

title: Strange particle


text: Category:Bolivian footballers

title: Category:Bolivian footballers


text:
Second-in-command

Second-in-command (2i/c or 2IC) is a title denoting that the holder of the title is the second-highest authority within a certain organisation.

Usage
In the British Army or Royal Marines, the second-in-command is the deputy commander of a unit, from battalion or regiment downwards. This terminology is also used in many other Commonwealth armies and other nations. The equivalent appointment in the United States Army is the executive officer.

The second-in-command of a battalion or regiment is usually a major. The second-in-command of a company, squadron, or artillery battery (in which they are called the battery captain) is usually a captain (although infantry company second-in-commands were usually lieutenants until after the Second World War), the second-in-command of a platoon or troop is the platoon or troop sergeant, and the second-in-command of a section is usually a lance corporal.

In the Royal Navy and Commonwealth navies, the second-in-command of a vessel, regardless of rank, is known as the first lieutenant or executive officer.

Other uses
In common usage, the term refers to a deputy. Its basic meaning is "someone who relieves a commander".

title: Second-in-command