EF50 the tube that helped to win the war

[CambridgeWorks]

http://www.dos4ever.com/EF50/EF50.html

I found this a very interesting site with lots of links to other sites likely to be of interest.
May take up a lot of your time, as I found it extremely interesting.
Robin

I have never seen one naked before.

[ppppenguin]

Following some links produce this interesting set of Youtube videos:
http://www.youtube.com/watch?v=pnCYe...eature=related

[Peter.N.]

I found this a fascinating and very informative article, very rarely does an account like this hold my interest but it has filled a great many gaps in my knowledge of the trade I worked in for 50 years or more - thanks

Peter

[murphyv310]

Excellent!

[Colin]

Thanks for posting this Robin. It's fascinating!

[Synchrodyne]

Thanks Robin, that's an excellent article.

I found a couple of the sidebar articles very interesting, too. One was on the advent of (highish frequencey) alternators for aircraft electrical systems in order to power radar systems (and other communications devices), and the other was on the origins of the Philips Rimlock valve series.

Cheers,

[dim-bulb]

Fascinating reading! Thanks for the link.

Bob

[M0FYA Andy]

A most fascinating paper - as is the whole website! Many thanks for the link.

Andy

[McMurdo]

An interesting read, though there are a few inaccuracies.

One example is the picture of a Heyford bomber used to test rdf principles, which isn't a Heyford. The Heyford was a giant biplane, no doubt picked because it was an easy target for RDF and almost obsolete so more easily utilized.

[ppppenguin]

Some fof the stuff in that article was taken from this excellent book: http://www.amazon.com/Radar-Days-Com.../dp/0852745907 Highly recommended.

Copies seem to be a bit expensive now but try Abebooks--UK as well as Amazon.

[Heatercathodeshort]

A great write up. This scan from the 'Wireless World' for the 16th February 1939 shows the original type with the hooked pins. I have never seen one of these early examples. John.

[DangerMan]

Yes, a good write up.
The Heyford was said to be chosen because (apart from availability) the wingspan was of the order of a half wavelength at the frequency used, thus giving a better reflection.
The Anson is correctly descibed as such in the same text, in Fig 3.4, and it's even the same photograph !

One thing that's not often known is that there are two fundamental types of EF50, not including the ones with hooked pins.
One type has a glass envelope that completely fills the metal can whereas the other has a smaller bulb firmly mounted into a thick aluminium base. Sometimes, if you open the can, these even say VR91 on top of the glass.
The latter construction type is more usual in american ones (e.g. Rogers, Sylvania), and seems much better controlled in terms of stray inductances and capacitances despite having nominally the same electrode assembly. Some Mullards are actually USA made and rebranded, and are of this type.

Perhaps this improved and more repeatable mechanical design is the origin of preferences for that type when EF50's were being hoovered up by amateurs...?

It's also worth knowing if you need to replace your EF50's and don't want to realign the set... simply fit the same variant as the one removed for "optimum" results where it matters.

I've never seen the hooked pin metalised version, either, but I'd sure like to.

Pete

[DangerMan]

Whilst we're discussing EF50's, another thing springs to mind.

I remember reading an article about them that describes the very first ones as having 8 pins, like an ordinary loctal. Not sure whether this was in the book about Pye (Radioman), an early BVWS article, or maybe somewhere else.
As far as I remember, the story was that the "liberated" parts were 9 pin types, so the valve was altered to use them and maybe it worked better for the change.

Not sure how true any of that is, but I don't recall there being a photograph of an 8 pin example...

Does anyone here know?

Pete

[M0FYA Andy]

I recall reading a story about the EF50 somewhere, I can't remember where or when.
This said that good examples of the EF50 were selected by testing for some particular radar application, and then identified by two black stripes painted across the top. I confess I have never seen one so marked, has anyone?

However the story then went on to say that these high performance examples were sought after in the post-war years, and were sold at a premium.

The 'enterprising' proprietor of one of the London government surplus shops just happened to have a nine-year old daughter who had a very steady hand with a fine paintbrush and a pot of black paint.........

I can't vouch for the authenticity of this story, but it does amuse me!

Andy

[DangerMan]

Hi Andy,
I've certainly heard the story and I believe she was not the only "artist" in town!!

I have some EF50's with the black stripes which were supposed to show better than average cathode current at saturation, for use in special jobs. EF50's are certainly very variable in some parameters.
The ones with the stripes do mostly work better than many others in my LV20 frame output, but the best of all is the most battered one I have got. It doesn't actually say Mullard or Philips on it, simply "Pentone".... so it's either one or the other of them (and it's red, with no black lines on top!).
After all this time, I'll never know whether some of the lined ones were "fakes" or have just had a hard life.

I have found the reference to an 8 pin "octal" (more likely "loctal") version, in EG Bowen's book "Radar Days".
On p78 he describes how the 250,000 glass bases "rescued" from Holland during the invasion "had nine pins not eight, and from that time onward the EF50 was assembled on a nine pin base, not the original octal base". Before p78, he specifically refers to EF50's as being on an octal base.

Anyone know any more, is it really true?

Pete

[PJL]

It's a great read and a charming story...but, it is difficult to beleive that the PYE strip and EF50 were the most critical components of the radar system. The Magnetron no doubt played a far more important role http://news.bbc.co.uk/1/hi/6331897.stm.

This reads more like marketing propoganda by Pye/Mullard to promote the technology and the huge stock of EF50 that remained after the war. I wonder how many EF50 were manufactured, when manufacturing stopped, and when they stopped being used in commercial production?

[Heatercathodeshort]

The 45mc/s R.F. strip employing the EF50 valve used in the 1946 Pye D16T television receiver is almost identical to the war time radar unit. 1949 appears to be the last year that EF50's were used in television receivers notably the Bush TV12 with it's incredibly well engineered and constructed R.F. deck, almost a work of art. J.

[Peter.N.]

I seem to remember that these 45mhz RF strips were available in the many government surplus stores in the '50s and were used for home TV construction along with a variety of ex air ministry CRTs, the VCR97 being about the most popular.

Peter

[DangerMan]

At the time the Pye strip was pressed into radar service, the development effort was for an airborne interception set operating at about 200Mhz, and the magnetron with its massive RF output was still to come.
So at the time, the transmitter power was quite limited, making an efficient receiver all the more necessary.

There's no doubt the magenetron was a fantastic invention for the job in hand, and would later revolutionise radar, but it was nothing like as versatile. A one trick pony maybe... but yes, what a pony.

Pete