EF50

In the field of electronics, the EF50 is an early all-glass wideband remote cutoff pentode designed in 1938 by Philips. It was a landmark in the development of vacuum tube 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 and great efforts were made to secure a continuing supply of the device as Holland fell in World War II.

The vacuum tube itself is a 9-pin Loctal-socket device with short internal wires to nine short chromium-iron pins, making it suitable for Very High Frequency use.

The EF50 was preceded by RCA's acorn design and several other attempts, such as the “Stahlröhre” from Telefunken, to reduce inductance in the wire leads, all with some disadvantages. Philips had been working since 1934/5 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 already as far back as 1934/1935. It was indeed developed in view of possible television application."

Pye, a leading British electronics firm of the time, had pioneered television receiver design, and in the late 1930s wanted to market sets that would allow reception further and further from the single Alexandra Palace television transmitter. Encouraged by their 1937 success with a novel tuned radio frequency (TRF) design, Pye wanted a higher quality valve than they could produce themselves, and so talked to Mullard, 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 IF Strip, and created a stable television receiver that captured a good market – being able to receive transmissions at up to 5 times the distance than the competition.

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