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29-473: In 1950, Hafler founded Acrosound with his colleague Herbert Keroes . This company was primarily in the business of designing and manufacturing transformers for tube amplifiers. Around this time Hafler and Keroes popularized the ultra-linear output-stage for audio amplifiers. However, the partnership did not last. In 1954 Hafler founded Dynaco with Ed Laurent . Hafler was instrumental in bringing affordable, high-quality audio kits to hobbyists, making his name

58-415: A common-cathode amplifier (where the output signal appears on the plate) may be operated as: The impression of any portion of the output signal onto the screen-grid can be seen as a form of feedback, which alters the behaviour of the electron stream passing from cathode to anode. By judicious choice of the screen-grid percentage-tap, the benefits of both triode and pentode vacuum-tubes can be realised. Over

87-770: A glass factory was built in 1955. In 1962 over 6,200 were employed and Mullard described the Blackburn works as "the largest valve manufacturing plant in Europe". By 1949 Mullard had produced a number of television sets, such as the MTS-521 and MTS-684. In 1951 Mullard was producing the LSD series of photographic flash tubes. Mullard had factories in Southport and Simonstone , both in Lancashire. The latter closed in 2004. There

116-448: A household word in the US audio community for many years. In the 1970s Hafler promoted "passive pseudo- quadraphonics ", an inexpensive method of recreating ambient sounds at the rear from ordinary stereophonic recordings. Known as the "Hafler hookup" or " Hafler circuit ", this consisted of two similar additional rear speakers, connected in series (typically 8 + 8 or 16 ohms total) between

145-583: A similar circuit. Mullard Mullard Limited was a British manufacturer of electronic components. The Mullard Radio Valve Co. Ltd. of Southfields , London, was founded in 1920 by Captain Stanley R. Mullard , who had previously designed thermionic valves for the Admiralty before becoming managing director of the Z Electric Lamp Co. The company soon moved to Hammersmith , London and then in 1923 to Balham , London. The head office in later years

174-403: A triode, beam tetrode or pentode based amplifier, are: The distributed load circuit may be applied to either push-pull or single-ended amplifier circuits. Note that the term 'ultra linear' was expressly reserved only for the condition of optimum tapping point. As Hafler and Keroes wrote: " Our patent claims cover the use of any primary tap in this circuit arrangement. However, we have restricted

203-438: A very narrow range of percentage-tapping, distortion is found to fall to an unusually low value—sometimes less than for either triode or pentode operation —while power efficiency is only slightly reduced compared with full pentode operation. The optimum percentage-tap to achieve ultra-linear operation depends mainly on the type of valve used; a commonly seen percentage is 43% (of the number of transformer primary turns on

232-872: Is now closed. The one in Hazel Grove, Stockport specialises in power semiconductor devices and is now Nexperia Manchester . The first transistors produced by Mullard were the OC50 and OC51 point-contact types in 1952, which were not widely used. In 1953 Mullard moved to junction transistors, beginning with the plastic-cased OC10 series. These were followed by the glass-encapsulated OC43...47, OC70/71, (released in 1957) and OC80 series (the output devices were metal encapsulated to facilitate heatsinking), which were produced in large numbers and copied by other companies, such as Valvo (another Philips subsidiary) and Siemens in Germany, and Amperex (another Philips subsidiary) in

261-424: The matrix decoders of the period, which attempted to reconstruct a surround sound field from a two channel recording. It had been observed that ambient sounds in a concert, such as applause or coughs from the audience, are generally received in a non-correlated phase by the stereophonic microphones , while sounds from the musicians are generally in a more or less synchronous phase. Thus, if rear speakers are fed with

290-554: The Dynaco business model, these products were available in both kit form and factory assembled. The units were acclaimed for their breakthrough sound quality and exceptional value, and are still highly prized today. Hafler made several different models of amplifiers and preamps over the years. Hafler products were also a solid foundation for improvements through later upgrades and modifications, installed both by DIY hobbyists and small specialist audio companies. Hafler sold his company to

319-663: The Mullard buildings was the manufacturing complex for Philips Radios. Mitcham was also home to the Mullard Application Laboratory. In the late 1930s Philips opened a plant in Blackburn , Lancashire, and during the Second World War some operations were moved there from Mitcham; by the end of the war, nearly 3,000 were employed. Tungsten and molybdenum wire were produced on-site from 1954, and

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348-856: The Rockford Corporation in 1987. Today, the Hafler company primarily makes products for the professional sound market. The Hafler brand was purchased by Canadian based Radial Engineering Ltd in 2014. Radial planned to re-launch the Hafler brand of high-fidelity audio products. Mike Belitz, CEO and President of Ultimate Support, in a venture with Vancouver, B.C. Private Equity Firm, Regimen Partners, have acquired Radial Engineering Ltd. and its diverse catalog of brands that include Primacoustic, Tonebone, Reamp, Hafler, Dynaco, Jensen Transformers and Iso•Max. David Hafler died from complications of Parkinson's disease in Philadelphia, Pennsylvania, at

377-468: The US patent 2218902. The particular advantages of ultra-linear operation, and the name itself, were published by David Hafler and Herbert Keroes in the early 1950s through articles in the magazine "Audio Engineering" from the USA. The special case of 'ultra linear' operation is sometimes confused with the more general principle of distributed loading. A pentode or tetrode vacuum-tube (valve) configured as

406-654: The USA. RF transistors were the OC170 and OC171. All these were germanium PNP transistors. Mullard's first silicon transistors were the OC201 to OC207, PNP alloy types using the standard SO-2 metal-over-glass construction such as the OC200 shown. From about 1960 Mullard switched to using the BC prefix for silicon, and AC for germanium, eliminating the confusion of part numbers. in the mid-1960s the first plastic packages were introduced. In 1964

435-437: The age of 84. Ultra-Linear Ultra-linear electronic circuits are those used to couple a tetrode or pentode vacuum-tube (also called "electron-valve") to a load (e.g. to a loudspeaker ). 'Ultra-linear' is a special case of 'distributed loading'; a circuit technique patented by Alan Blumlein in 1937 (Patent No. 496,883), although the name 'distributed loading' is probably due to Mullard . In 1938 he applied for

464-531: The company and included the Southampton plant; GEC contributed their small factory in School Street, Hazel Grove, producing thyristors , rectifiers and power diodes . GEC pulled out of ASM Ltd in 1969. In 1972 production was moved to a newly constructed factory nearby on Bramhall Moor Lane. Both sites were later owned by NXP Semiconductors (formerly Philips Semiconductors ). The Southampton site

493-712: The company produced a prototype electronic desktop calculator as a technology demonstrator for its transistors and cold cathode indicator tubes. In 1957 Philips-Mullard helped to set up the Mullard Radio Astronomy Observatory (MRAO) at the University of Cambridge . In 1966 the Mullard Space Science Laboratory (MSSL) was opened near Dorking , Surrey as part of University College London . The Royal Society Mullard Award for young scientists and engineers

522-401: The development and production of integrated circuits . The plant was planned to be the biggest semiconductor facility in Europe, employing 3,000 people including 200 scientists and engineers. In 1962 Associated Semiconductor Manufacturers (ASM) Ltd was formed by Mullard and GEC to combine the semiconductor development and production facilities of the two companies; Mullard owned two-thirds of

551-640: The difference between the stereo channels, audience noises and echoes from the auditorium can be heard from behind the listener. In 1977, Hafler founded the David Hafler company in Pennsauken, New Jersey (a Philadelphia suburb). His first two products were the DH-101 preamplifier, followed a few months later by the DH-200 companion power amplifier. Added later was the rugged DH-500 stereo amplifier, which

580-435: The live feeds to the front speakers. The crosstalk or loss of stereo separation in the front speakers was generally less than 2 dB , while the rear sound level in a typical recorded live performance was about 7 dB below the front, but clearly audible. The Dynaco QD-1 Quadaptor was based on this idea, adding a variable resistor to control the volume of the rear speakers. This passive method worked fairly well compared to

609-480: The plate-circuit) which applies to the KT88, although many other valve types have optimum values close to this. A value of 20% was recommended for 6V6GTs. Mullard circuits such as the 5-20 also used 20% distributed loading (but did not achieve ultra-linear operation), while LEAK amplifiers used 50%. The characteristics of the circuit which make distributed loading suitable for audio power amplifiers, when compared to

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638-663: The prefix PM, for Philips-Mullard, beginning with the PM3 and PM4 in 1926. Mullard finally sold all its shares to Philips in 1927. In 1928, the company introduced the first pentode valve to the British market. Mullard opened a new manufacturing plant at the end of New Road, Mitcham , Surrey in 1929. A second building was added in 1936. Both buildings had a very distinctive flat roof construction and were very similar to those at Philips' headquarters in Eindhoven , Netherlands. Co-sited with

667-467: The recession in the mid-1970s. To mark the 50th anniversary of the founding of the company, Mullard management decided to have a rose named after the company. Mullard's quest was simple, they wanted a world-beater, nothing less, so they contacted the renowned grower Sam McGredy IV in Northern Ireland. The naming fee of £10,000/$ 24,000 was a lot of money in 1970 and established a record fee for

696-526: The use of the term "Ultra Linear" to the conditions where the dynamic plate characteristic curves are most linear ". The "QUAD II" amplifier from QUAD uses a circuit in which the cathode has a portion of the output signal applied to it, and was referred to as "distributed load" by Peter Walker of QUAD. In the United States, McIntosh Laboratories used this technique extensively in their vacuum-tube power amplifiers. Audio Research Corp have also used

725-588: Was Mullard House at 1–19 Torrington Place, Bloomsbury , now part of University College London . In 1921, the directors were Sir Ralph Ashton (chairman), Basil Binyon of the Radio Communication Co, C.F. Elwell and S.R. Mullard (managing director). In 1923, to meet the technical demands of the newly formed BBC , Mullard formed a partnership with the Dutch manufacturer Philips . The valves (vacuum tubes) produced in this period were named with

754-404: Was a purpose-built plant, opened in 1957 for the manufacture of semiconductors . Production of germanium alloy transistors was transferred from Mitcham. At the same time the plant started the research, development and production of electro optical devices. Fabrication of planar devices on a mass production basis did not begin until 1966, when germanium sales were decreasing. 1967 saw the start of

783-862: Was also a sister factory at Belmont in Durham (closed in June 2005). Other factories included those at Fleetwood (closed in 1979) and Lytham St. Annes (closed in 1972). A feeder factory at Haydock closed in 1981. A small factory in Hove closed in the early 1970s. In the early 1980s, Mullard manufactured the SAA5050 , one of the first teletext character generator modules made in the UK. Mullard owned semiconductor factories in Southampton and Hazel Grove , Stockport, Cheshire. Southampton (Millbrook Trading Estate)

812-426: Was rated at 255 watts per channel and saw great success in home, studio, and live environments. The amplifiers were notable for their early use of new, more-powerful MOSFETs to enable much lower distortion at higher power, in a very economical fashion. The new designs were less vulnerable to thermal runaway , allowing them to operate reliably at higher power without requiring expensive protective circuitry. Following

841-661: Was set up in 1967. Philips continued to use the brand name "Mullard" in the UK until 1988. Mullard Research Laboratories in Redhill , Surrey then became Philips Research Laboratories. As of 2007, the Mullard brand has been revived by Sovtek , producing a variant of the ECC83 and EL34 . The Z Electric Lamp Co. continued business into the 1970s operating from premises in Thornton Heath , southern Greater London, manufacturing lamps of specialised design. However, it closed due to

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