EF50
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In the field of
electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...
, the EF50 is an early all-glass wideband remote cutoff
pentode A pentode is an electronic device having five electrodes. The term most commonly applies to a three-grid amplifying vacuum tube or thermionic valve that was invented by Gilles Holst and Bernhard D.H. Tellegen in 1926. The pentode (called a ''tripl ...
designed in 1938 by
Philips Koninklijke Philips N.V. (), commonly shortened to Philips, is a Dutch multinational conglomerate corporation that was founded in Eindhoven in 1891. Since 1997, it has been mostly headquartered in Amsterdam, though the Benelux headquarters i ...
. It was a landmark in the development of
vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...
technology, departing from construction ideas of the time essentially unchanged from light bulb designs. Initially used in television receivers, it quickly gained a vital role in British
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
and great efforts were made to secure a continuing supply of the device as Holland fell in
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
. The EF50 tube is a 9-pin Loctal-socket device with short internal wires to nine short chromium-iron pins, making it suitable for
Very High Frequency Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves ( radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF ...
(VHF) use.


History

The EF50 was preceded by
RCA The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Comp ...
's
acorn The acorn, or oaknut, is the nut of the oaks and their close relatives (genera ''Quercus'' and '' Lithocarpus'', in the family Fagaceae). It usually contains one seed (occasionally two seeds), enclosed in a tough, leathery shell, and borne ...
design and several other attempts, such as the "Stahlröhre" (~steel tube) from
Telefunken Telefunken was a German radio and television apparatus company, founded in Berlin in 1903, as a joint venture of Siemens & Halske and the ''Allgemeine Elektrizitäts-Gesellschaft'' (AEG) ('General electricity company'). The name "Telefunken" app ...
, to reduce inductance in the wire leads, all with some disadvantages. Philips had been working since 1934–1935 on an alternative that would solve the problems of the other bases, and a design that could be produced cheaply and in large quantities. A presentation given by M.J.O. Strutt from the tube development group at Philips Research at the first "Internationale Fernseh-Tagung in Zürich" (international television conference in Zürich) described their work in September 1938. A few months later Professor J.L.H. Jonker, who had a leading role in the development of the EF50, published an internal Philips Research Technical Note, Titled: "New radio Tube Constructions". Jonker's role was confirmed decades later by Th. P. Tromp, head of radio-valve manufacturing and production: "Prof. Dr. Jonker (head of development lab of electronic valves in the mid thirties) was the originator of the EF50 and this development started as early as 1934–1935. It was, indeed, developed in view of possible television application."


Television requirements

Pye Ltd. Pye Ltd was an electronics company founded in 1896 in Cambridge, England, as a manufacturer of scientific instruments. The company merged with EKCO in 1960. Philips of the Netherlands acquired a majority shareholding in 1967, and later gained f ...
, a leading British electronics firm of the time, had pioneered television receiver design, and in the late 1930s wanted to market receivers that would allow reception further and further from the single
Alexandra Palace Alexandra Palace is a Grade II listed entertainment and sports venue in London, situated between Wood Green and Muswell Hill in the London Borough of Haringey. It is built on the site of Tottenham Wood and the later Tottenham Wood Farm. Origi ...
television transmitter. Encouraged by their 1937 success with a novel
tuned radio frequency A tuned radio frequency receiver (or TRF receiver) is a type of radio receiver that is composed of one or more tuned radio frequency (RF) amplifier stages followed by a detector ( demodulator) circuit to extract the audio signal and usually ...
(TRF) design, Pye wanted a higher quality valve than they could produce on their own, and so talked to
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 Admir ...
, which meant the research of Philips in Holland, plus some tweaking from Baden John Edwards and Donald Jackson from Pye (for example the metal shield), leading to the EF50 pentode that was needed in the Pye 45 MHz TRF design, and created a stable television receiver that captured a good market, being able to receive transmissions at up to five times the distance than the competition.


Radar uses

Hugh Dowding Air Chief Marshal Hugh Caswall Tremenheere Dowding, 1st Baron Dowding, (24 April 1882 – 15 February 1970) was an officer in the Royal Air Force. He was Air Officer Commanding RAF Fighter Command during the Battle of Britain and is generally c ...
had already seen the value of
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
for his
Air Defence system Anti-aircraft warfare, counter-air or air defence forces is the battlespace response to aerial warfare, defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It includes surface based, ...
. Developments progressed at
Bawdsey Manor Bawdsey Manor stands at a prominent position at the mouth of the River Deben close to the village of Bawdsey in Suffolk, England, about northeast of London. Built in 1886, it was enlarged in 1895 as the principal residence of Sir William C ...
from the mid-1930s; the early ground-based radar chains worked well but needed to be improved in accuracy, and Dowding saw the need for an airborne radar. At Bawdsey, Taffey Bowen had also needed a wideband
valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings ...
for Airborne Interception (AI) radar; he had just one working set. So he contacted Tom Goldup, a senior director of
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 Admir ...
, and "quite by chance in April or May of 1939" he heard of the Pye set from his old Professor at King's College, Edward Appleton. Visiting Pye, Bowen saw scores of what he sought, their 45MHz TRF chassis using the very new EF50, which he later described as "a valve that was to play almost as important a part in the radar war as the
magnetron The cavity magnetron is a high-power vacuum tube used in early radar systems and currently in microwave ovens and linear particle accelerators. It generates microwaves using the interaction of a stream of electrons with a magnetic field while ...
". The early Chain home radars chose 45 MHz as their
intermediate frequency In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier sign ...
so that they could take advantage of Pye's television front end with minimal modification. Pye's modified design was often referred to as the 'Pye 45 Megacycle IF strip'.


Flight from Holland

Because the EF50 had to come from Holland, yet was vital for the RDF (
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
), great efforts were made to secure a continuing supply as the risk of Holland being overrun increased. Mullard in England did not have the ability to manufacture the special glass base, for example, and just before Germany invaded Holland, a truckload with 25,000 complete EF50s and many more of their special bases were successfully sent to England. The entire EF50 production line was hurriedly relocated to Britain. On 13 May, the day before the Germans flattened Rotterdam in 1940, members of the Philips family escaped together with the Dutch government on the British
destroyer In naval terminology, a destroyer is a fast, manoeuvrable, long-endurance warship intended to escort larger vessels in a fleet, convoy or battle group and defend them against powerful short range attackers. They were originally developed in ...
HMS ''Windsor'', taking with them a small wooden box containing the industrial diamonds that were to be used to make the
die Die, as a verb, refers to death, the cessation of life. Die may also refer to: Games * Die, singular of dice, small throwable objects used for producing random numbers Manufacturing * Die (integrated circuit), a rectangular piece of a semicondu ...
s needed to make the fine tungsten wires in the valves.


Characteristics


Equivalents

To meet great wartime demand the EF50 was also made by Marconi-Osram (with the name Z90) and
Cossor A.C. Cossor Ltd. was a British electronics company founded in 1859. The company's products included valves, radios, televisions and military electronics. The company was purchased by Raytheon in 1961. Early history The story of A.C. Cossor Ltd ...
(their version named 63SPT) in the United Kingdom as well as Mullard (who were effectively using the Philips production line after it was moved from Holland). Versions were also made in Canada by
Rogers Vacuum Tube Company Rogers Vacuum Tube Company (formally named Radio Manufacturing Corporation Limited) was founded as the Standard Radio Manufacturing Corporation in 1925 by Edward Rogers (1900–1939) to sell Rogers "Batteryless" radios using vacuum tube technology. ...
and in the United States by Sylvania Electric Products. British military (Ministry of Aircraft Production Specification) and U.S. JAN type numbers assigned to the EF50 include: * ARP35 (Army Receiving Pentode 35) * VR91 (Original A.M. Name) * CV1091 (from 1943) * ZA3058 (Army) * ZC1051 or ZC/10E/92 (Army) * 10E/92 (Air Ministry) The tube was also assigned the GPO (PO)VT-207 type number, VT-250, and CV1578.Radio Museum, EF50
/ref> Valves of similar characteristics were produced with different bases, for example the later EF42 and 9-pin miniature (B9A) EF80.


References


See also

Mullard EF50 data sheet
{{Thermionic valves Vacuum tubes Philips products