Ir. Th. P. Tromp                                                                                               Jan 16th 1979 

Sumatralaan 1


Mr. Bell

Lower Gate House



Mr Bell,


I joined Philips in 1927 (retired in 1969) and have been appointed in 1931 as head of the “Radio Valve Foreign Dept.” and early 1939 as head of “Radio Valve Department (development and manufacture) as well as supervisor of Radio Valve Factories abroad until the end of the war. I am therefore fully conversant with the history of the EF50.


I happened to know Mr. C.O. Stanley, whom I met a couple of times before the war together with Captain Mullard.  After the war Mr. Loupart and myself met Mr. Stanley also on several occasions as Pye was an important customer of Mullard/Philips for tubes.


Some of these discussions took place with Mr. S.S. Eriks as managing director of Mullard in England. Cathodian Southend is also known to me and I also met Mr. B.J. Edwards of PYE several times, mostly on valve matters and development.


The story on page 1 and 2 item 2 of your note attached to your letter to Mr. Philips is however not quite correct. The glass based valves mentioned by you originated at Philips during the thirties for a number of reasons. One of them being the fact that Telefunken brought out a steel valve (which we have also manufactured) and exerted enormous pressure (also politically) with regard to this development. I filed personally two patents on the glass base with iron-chrome lead-in wires and those patents were granted. Thos development formed the basis for a complete series of valves including the EF50 and amongst others the EL50 which was also a very important output stage pentode, which was also extensively used during the war. Mr Edwards was aware of these developments of Philips Eindhoven and valves were supplied to him, mostly via Mullard. It may be that he also worked on some prototypes, although PYE was, as you state correctly, not a valve manufacturer. It is, in my opinion however, incorrect to state that the EF50 was passed over by PYE to Mullard for production, as the EF50 originated from Philips and nowhere else.


The facts are these: 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. The British Military  Authorities and among them as you state correctly Prof. Appleton and Mr. R. Watson-Watt were interested in the EF50 for military applications. This must have been about 1938/1939. PYE, apparently, was a.o. the equipment maker who had to use this valve.  At that time, it was of course unknown to us for which applications PYE used this valve. Consequently, Philips Eindhoven supplied a quantity of the EF50 (and the EL50) via Mullard to Britain  and in parallel Mullard started a modest pilot production under supervision of Mr. F.A. Kloppert (head of Mullard radio valve factory in Mitcham) and Dr. O.S. Pratt, head of Mullards Development and Quality lab.


When the war broke out (Holland not being at war at that moment) pressure increased to put up large scale production in England.   


Early 1940 (and I do not remember whether it was February or March) I was, as head of the radio valve activities, instructed to go to England. The necessary security checks and arrangements were made and a visa was given (it was not easy at that time for a Dutchman to go to England).


During this visit I took along an existing sample of a special infra-red tube, which was developed by our research lab and of which only two samples were in existence. One sample was supplied to the Armed Forces Physical Lab near Noordwijk, and the other was brought by me to England. The first sample was destroyed by the armed forces during the night of the invasion on the 10th of May.


On a Saturday afternoon, after closing hours, Mr. Watson-Watt visited Mr Eriks’ office of Century House , Shaftsbury Avenue. I handed this tube over to Mr Watson-Watt together with all specifications and manufacturing details. The thought behind this was that the infra-red tube could be used for looking “across the Channel from Dover to the German gun emplacements at Calais, from where the bombarded England with heavy guns. After the war I learned that this tube was given to the General Electric Company (GEC)    for further engineering and manufacturing, and was successfully used for the purpose described above.


At that same meeting on Saturday afternoon, Mr Watson-Watt informed me that the British Government was most anxious to set-up a large scale production of EF-50 (and also EL50) in England and requested me, if possible, to supply Mullard with all the production equipment and special tools for these valves, together with a very large number of complete sets of components for the EF50. This to enable Mullard to start production of the EF50 in quantity already before they would be able to make their own components in large quantities for full-scale production at Mullard’s. It was therefore not PYE (who was of course highly interested in this valve for radar use as we learned later) but it was the British Government (though Mr. Robert Watson-Watt) who made the official request.


The first and second paragraph on page 2 of your letter to Mr. Philips are therefore not quite correct and complete. The request for Machines, Tools and Components was not formulated after the invasion of Holland (this would have been impossible in occupied Holland) but already in February or March 1940 , notwithstanding the fact that supplies from Eindhoven to Mullard took place long before.


Being the responsible manufacturer in Eindhoven, I followed up Mr. Robert Watson-Watt’s request and the complete shipment of everything took place in the night of 9-10 May when the Germans invaded our country. The steamer of the “Zeeland” Steamer Company which was carrying the machinery, Tools and Components on board was bombarded by German fighters,  but not hit and the consignment arrived safely in Harwich. Of course when the shipment was made after frantic efforts to speed up all supplies we did not know that we would be invaded on the same day of May the 10th, and it was sheer good luck that the shipment was made just before the invasion and that it could reach England safely.


 This is the full story of the EF50 which has been of paramount importance for winning “The Battle of Britain” and everything which followed afterwards. With regard to your question on information of what valves the Germans used in their radar I cannot inform you completely. After the invasion we were forced to start some manufacture of German tubes (which was heavily sabotaged), but I got the impression that they did not want to manufacture the more advanced valves in occupied Holland. The types we were given to make were already made for some years prior to the war at the Valvo radio valve factory in Hamburg.


As I have been active in the Dutch resistance during the war and had the possibility of making microfilms and sending them over to England though various routes, I have send over to London all the manufacturing specifications of these German Tubes. Later during the war, when a radio transmitter and radio telegraphist   was dropped from England, I obtained the possibility of sending secret coded telegrams to England, also related to Germany’s war production in the electronic field and the required quantities, which could be of importance to the Allies for assessing Germany’s war potential.