EF50: How many pins?

According to the words of  E.G. Bowen, the father of airborne radar in Great Britain, the prewar production of EF50 came with 8-pin B8G loktal base*. In 1939 TRF receivers from EMI, operating at 45MHz and intended for use in the new television system, were commonly used by the Bowen group as IF amplifiers, just after the RF mixer. Around April or May 1939 Mullard gave samples of the new tube, probably in a pre-production stage, to PYE Radio Company and they used them in their new 45MHz  TRF receivers. PYE supplied some chassis with 8-pin EF50 to the Bowen group. These TRF receivers performed much better, were smaller and lighter than the EMI ones. Therefore were standardized as IF amplifiers in the early airborne radar sets. The first successful installation of a system including the new IF amplifier can be dated around the end of July 1939. Then several more system were installed both for AI and for sea-search equipment.

The EF50 tubes, even if supplied by Mullard, actually were manufactured at the Philips Eindhoven facilities. At the time Mullard was not capable of manufacturing the tube base.

At the outbreak of WWII, when Germany started the occupation of the Low Country, a destroyer was hastily dispatched to The Hague to take out from Holland some 25,000 complete EF50 tubes and more than 250,000 bases. Unfortunately it was found that the bases from Holland all had nine pins. From that date Mullard started to assemble the EF50 with the 9-pin B9G base and, obviously, Pye rewired its receivers.

I guess that at least during the war, while Mullard had switched to the 9-pin base, Philips continued the production of the 8-pin EF50. Starting from a given date a different code should have been assigned to the 8-pin tube. Does anybody know more about this pin count change?

Regards, Emilio

*Ref: Radar Days by E.G. Bowen, Adam Hilger - Bristol
 

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Dear Emilio,

there is a website that covers the development of the EF/EE50 pretty neatly in the context of the development of the all-glass envelops. It's an interesting read since the text is accompanied by references and also features some downloads,

I leave the question status for a future answer to your original question.

The website is located here.

Regards
Mark

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Hello mr Emilio

I have served army as radar operator and we had 4 decomissioned British Thompson targeting radar units build in late 50s or early 60s. We called them 3mark (No3 Mk3 i think)

They where laying in abondaned part of base and they where equiped with hundreds of CV1091/EF50 tubes, only output tube was different make. Everything except output was runned with EF50, not only IF amps. From antenna to the CRT, hundreds of EF50. All 9 pins with special collar sockets.

All british made (branded Mullard and Chelmer).

There is interesting story about CV1091/EF50 and eqvivalents on; www r-type.org (national valve museum).

Hope this helps.

Regards Sinisa

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First of all, many thanks to Mark and to Sinisa for their very interesting contribution.

I am going to attach the partial reproduction from the book ‘Radar Days’, where the author talks of the eight-pin EF50. By the way the author is Dr. E. G. ‘Taffy’ Bowen, that developed airborne radar in Great Britain. Actually around April or May 1938 very early samples of EF50s had been used by Pye to design their TRF strips for 45MHz television receiver sets. Just adding a diode mixer, these strips were used as IF subassemblies in the airborne radar sets.

No doubt that Bowen actually found 8-pin EF50 tubes in the very early PYE strips. This is also confirmed in chapters 8 and 9 of the site suggested by Mark, where PYE television receivers and the Dr. Bowen work are extensively treated. Probably the answer is in the chapter 6 of the same site, where they talk of the development of all-glass tubes in Philips. Picture 6-3, C actually shows one of  the very early press-glass prototypes, coming with 8 hooked pins and the grid connected to the top cap. No wonder that for a short while some lots of EF50 engineering samples could have been delivered within this envelope. The retaining of the same code for both the 8 and 9-pin versions can be explained if the 8-pin tubes had been sampled to PYE before freezing their specs.

Anyway this is only a guess. For this reason I leave the thread open.
 

Regards, Emilio

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The question may be closed with the above info found by Mark. The only open doubt is if the tubes described by Bowen were also marked as EF50.

Thanks to all,

Emilio

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