Piet's Home-built Television

Fully revised and extended page

Television development at Philips, part 1 1936-1949

One of the childhood memories I have is on the home-built television receiver of my father Piet Hooijmans. A large (and heavy!) grey metal box with a very small picture screen. I must have been 5 years old, when on a Saturday afternoon around 1963 my father switched on the television set. I vividly remember images of a horse race, probably at nearby Duindigt in Wassenaar. It was the last time I've seen the set working, but it has always been carefully preserved. Later when I studied electronics myself I opened it once in a while, but never had the time nor the means to dive into it. It has always fascinated me. Now I have the time. The first thing that triggered me was the exotic EQ40 valve of which my father always talked about as the "enneode". This has resulted in my page on the history of the EQ40/EQ80.
Next I wanted to trace back the history of the home-built TV itself, although I was hampered by a severe lack of information about it. When starting to dive into the Internet I quickly discovered that the home-built set was tightly linked to the development of the first televisions in general, and that the activity of the Radiobuizen Lab where Piet Hooijmans worked had an important influence on the direction of these developments. The intended story on his home-built TV thus quickly became the integral story of the development of the first televisions at Philips. Or at least an effort to reconstruct it, since it is a much more complex story than it may seem. It will involve multiple departments, multiple standards, multiple models and valve choices, official prototypes, in-official do-it-yourself models, and the first commercial products. It is a reconstruction based on available data, which at least on the level of actual television sets and valves is very extensive thanks to forums like Radiomuseum.org, the Nederlandse Forum voor Oude Radios, UK Vintage Radio and others. And although my friend Ronald Dekker has already done a lot of pre-work on the internal Philips organisation at the time for his EF50 story, there are still many gaps related to the internal Philips activities. My analysis, which now roughly covers the period 1936-1956, is thus also based on my interpretation of facts and developments, and consequently a "living story" since never complete nor 100% correct. At the same time it is a "story in development", since I continue to receive fresh inputs that help to fill in the gaps. In this context especially the extensive knowledge and the rare collection of first generation TV's of Jac Janssen has been of tremendous value.

The first electronic Television standards, 1935-1940

To understand the post-war television developments it is necessary to take a brief look at what happened before 1940. After first experiments in the 1920s and early 1930s with mechanical Nipkov disk based systems, development of so-called electronic TV systems started during the mid 1930s. At this time the lead in television broadcast developments was disputed by the US (especially RCA), the UK (driven by the BBC) and Nazi Germany, although at a more modest level France, Italy, Poland and the USSR were also active. These years were characterized by a "race to higher line number", because the number of lines from which the TV image was build up is a primary indicator of the picture quality. The initial mechanical standards had pushed the line number up to 180, with a last effort by the UK Baird corporation to push it to 240 lines, where the latter system could be characterized as "half-electronic". One of the first consequences when systems moved from mechanical to electronic was the introduction of inter-laced scanning. With this method a picture was built up from two half pictures: the first one containing the odd lines, the second placing the even lines in between. This provided more stability thanks to better synchronization, and would become the standard until today for all TV broadcast. (Only PC monitors later re-introduced progressive scanning, and therefore were not compatible with TVs). Because the vertical picture frame rate was always locked to the AC power frequency (60Hz in the US, 50Hz in Europe and most of the rest of the word) the full interlaced picture rate was thus always half that frequency: 25 pictures/s in Europe, 30 pictures/s in the US. The line rate, the number of lines displayed per second, is the multiple of the field rate (25 or 30) and the line number.

The basis of all electronic television broadcast standards: interlaced scanning. A first field writes the odd (blue) lines, a second field the odd (red) lines that fall exactly in between the even lines. Scanning is from left to right, the diagonal lines are the so-called fly-back traces, during which the display is blanked such that they are not visible. Note that because of the two half lines the total number of full lines is always odd (essentially N-1).

The Alexandra Palace BBC transmitting tower in central London. It transmitted at a picture carrier of 45MHz and 41,5MHz sound. [BBC]

1936 was the year that a number of new standards were introduced. In the US RCA launched a 343-line system, which was used for limited field trials in New York (transmitting from the Empire State Building), Philadelphia and Los Angeles. Germany used the 1936 Berlin Olympic Games to demonstrate its half-electronic 180-line standard, using intermediary film rolls which were then electronically scanned for transmission. In parallel experimental transmissions were made using the new 375-line all-electronic system, using the new Telefunken Ionoscope camera tube. In Berlin-Witzleben a first transmitter station was installed, using a 42,9MHz picture carrier. Using long distance cable of the Reichspost the signal was also distributed to major cities across Germany for local transmission. After the Games transmissions continued, with viewing rooms in post offices. During the 1936 Radiolympia consumer electronics show in London, the BBC started test transmissions using both the Baird 240-line film-transfer semi-electronic and Marconi-EMI 405-line electronic systems, which were transmitted alternately. In November 1936 the BBC started official transmissions from the Alexandra Palace transmitter, still using both standards during different hours. But the trials were very conclusive, and January 1937 the BBC stopped the 240-line system and switched to the 405-line standard that would remain the British TV standard until the mid 1960s.

The next step was again made by RCA, which launched a 441-line standard in 1937 based on the earlier 343-line field trials in LA. By 1938 commercial sets were brought to the market and in 1939 a major official launch was made during the New York World's Fair. Almost the moment it was launched in the US, in 1937, Germany adopted it, albeit at the 25Hz frame rate, although it took till 1938 to have real transmissions. The Nazi regime saw television as a powerful propaganda tool and stimulated a broad roll-out, for which they forced the joint German set makers to develop the Einheitsfernsehempfanger (standard TV receiver), the same approach as the Volkswagen car. Volume roll out of the set was stopped due to the outbreak of war, though, in September 1939. The 441-line standard was also adopted by Italy and Russia, the latter based on an exchange with RCA of TV equipment. France in the meantime made a characteristic step to high quality television by launching a 455-line system, using a 30kW transmitter on the Eiffel Tower in Paris. However, available sets were expensive, and when transmissions stopped at the outbreak of war in September 1939 there were only 300 sets in use. Although the transmitters were destroyed before the evacuation of Paris in June 1940, the occupying German forces re-installed a transmitter, but now based on the German 441-line system. It started transmitting in 1943, and when later that year the German transmitting station in Berlin was destroyed by Allied bombing, the Paris transmitter was for a year the only TV transmitter in Europe. To close the pre-war overview, where the European countries all stopped TV development due to the outbreak of war, the still neutral US continued its path towards commercial TV broadcast. In 1939 the National Television Standardisation Committee (NTSC) was established. After quite some evaluation, lobbying and politics it decided for a 525-line standard, with as main innovation the use of Frequency Modulated (FM) audio, allowing a much better sound quality. It was officially announced as the US standard in March 1941, but after Pearl Harbour and entry of the war the US Government forbid all effort on commercial TV, also bringing US TV developments to an effective stop. Nevertheless the 525-line NTSC became the only TV transmission standard that was formally still alive at the end of the war, and as such became a reference point for many post-war developments.

Transmitter test image of the Berlin TV transmitter.

The 1939 Einheitsempfanger, here a Telefunken-produced model. This was probably the most modern TV at the time: very compact, 22cm diagonal cathode ray direct view picture tube, 16 valves. [Wikimedia]

Overview of the TV broadcast standards used between 1935 and 1941. Only (semi)-electronic standards actually used for formal (test) transmissions are listed. In the column "Sound carrier" parallel refers to systems with sound transmission and reception independently. Positive sound carrier distance refers to sound above picture carriers, negative sound-below-picture.

Pre-War Philips Television activities, 1936-1939

Where was Philips in all this? Clearly the company was not a leading player, although active in all countries mentioned above. Between 1935 and 1939 Philips Gloeilampenfabrieken (Incandescent Lightbulb Factories), as it was officially called, was already active in promoting and demonstrating television, although these activities were rather limited. Philips Research was in principle the centre for new developments with the magnitude of television. From the beginning, however, the general enthusiasm for television within the Philips Research management was lukewarm at best. In this period television was only a research activity, and thus driven by the Natuurkundig Laboratorium (NatLab) at the Strijp complex in Eindhoven. Especially its emblematic director Prof.Dr. Gilles Holst (1886-1968) didn't see the need for or potential of television, where his main arguments against it were a lack of programs and the size of a television set with an acceptable screen diameter. On the latter point it is fair to say that cathode ray tubes at the time were still fairly narrow, typically 22cm screen diameters, although 30cm tubes existed. The problem was especially the then limited deflection angle, which would give on extrapolation enormous picture tubes for larger screen sizes. It was therefore decided that at least the Philips television receivers were to be based on rear projection systems. So despite the reservations, activities continued.

The work on projection TV concepts was thus concentrated in the NatLab research organization. The pre-war activities were done in two groups: transmitter work in the Advanced Radio group by the famous Dr. Balthasar van der Pol (1889-1959), led by Jan van der Mark. Van der Pol had obtained fame with the first short wave transmission link to the Netherlands East Indies in 1927, as well as his work on non-linear relaxation behaviour of circuits, which had led to the famous "Van der Pol"-equations. He also discovered the "White Noise" phenomena. At the time van der Pol himself was working on ionospheric propagation. He and van der Mark already worked together since the mid twenties, when they built an electrical model of the heart, that could be used for heart rhythm analysis.

The receiver was developed in the group of Dr.Ir. Herre Rinia (1905-1985). Rinia was one of the first NatLab employees, joining in 1922 and working for van der Pol on amongst others the first pentode valves. He was very much involved in the definition and development of the projection TV concept, such as the optics. Probably after the war he took over the research group on television receivers from Oosterhuis. One of the engineers in the group of Rinia was Dr. Johan Haantjes (1908-1978), who joined the NatLab in 1937 and worked on magnetic deflection circuits and broadband amplifiers. Another interesting person was Freek Kerkhof, a radio amateur who had built a Nipkov-disk based television at home as early as 1927, and who started experimental television transmissions from his Eindhoven bed room in 1936. Kerkhof joined Philips in 1932, working closely with Haantjes on the receiver while continuing to be a very active amateur in his free time. Later, in the components groups of the NatLab M.C. Teves worked on inonoscope registration tubes and M. Wolf on display picture tubes. All in all it must have been some 15-20 people working on television in Research, a very small number compared to the activities in especially the US, the UK and Germany.

The first serious management discussions on television took place in 1934, triggered by the ionoscope camera development at RCA and the fact that Telefunken and EMI, major competitors, had taken over this concept. Later that year van der Pol and Rinia visited RCA, and came back with stories of the major developments on TV there. Although Holst continued to resist, Loupard, the commercial member of the Board of Directors, demanded a test transmitter, following the initiative announced by the BBC. By April 1935 the order for constructing a television transmitter was given, and by November that year it started functioning from atop a building on the Eindhoven Strijp complex. In parallel an experimental receiver was built, based on a direct-view oscilloscope electrical deflection picture tube. Although neither the first nor unique it was at least a state-of-the-art 180-line system. Van der Mark was the author of the system article on the 180-line TV system published in the very first volume of the Philips Technical Review in 1936 and the first Philips publication on television.

Gilles Holst, first director and founder of the NatLab.

Balthasar van der Pol

Herre Rinia

Johan Haantjes, for a long time leader of the television receiver activities at the NatLab. [Philips Koerier 1962]

The very first Philips TV transmitter on the roof of the Strijp Veemgebouw. [Eindhoven in Beeld]

Freek Kerkhof with one of his earliest Nipkov-disk based television systems. [dBNL]

Some of the Philips NatLab key players in early television. From left Erik de Vries, producer of the experimental programs demonstrating a camera, prof. Holst, director of the NatLab, van der Pol, group leader of the TV transmission group and van der Mark, group leader of the TV receiver group, around 1936. [NatLab site Hagenbeuk]

Block diagram of the Philips 180-line TV transmitter that was installed in Eindhoven end of 1935. [Philips Technical Review, Vol1, No1, pp.16-21, 1936]

The very first Philips 180-line TV system was still very basic, built with the means available at the time. It used an early ionoscope, probably purchased although it could also be a first NatLab design. The transmitter frequency was around 43,2MHz for video only and around 500W transmit power, it seems sound was not transmitted. The system was primarily used for technical experiments, but also for demonstrations to state committee investigating the introduction of TV broadcast in the Netherlands, and Dutch journalists. (The system was deemed too immature and non-differentiating to show it to the foreign press).

Interestingly, at this very same time a 180-line TV set claimed to be from Philips turns up in Germany! Although some sources link the very nice console set to the company CHF Müller in Hamburg, this was in fact fully owned by Philips since 1926, although, as so often in the case of Philips acquisitions, it continued to use its original brand name. Details on the origin nor the design of the set are known, and it could have been an Eindhoven based design (unlikely given all lack of references), a local Hamburg Valvo design or even an externally sourced chassis with only a cabinet design by the company Müller/Valvo/Philips. Given that after the coming to power of the NSDAP the German Philips activities were kept at arms length from Eindhoven, and this TV development must almost certainly have been a local activity.

The mysterious 1935 180-line TV console from CHF Müeller and Philips. It was shown at the 1935 Funkausstellung (Radio Show) and must have been used to receive the experimental TV transmissions during the 1936 Berlin Olympic Games. [Early Television.org]

The first ionoscope-based television camera developed in the Philips NatLab, 1935. [Early Television.org]

Images from a the prototype Philips 180-line TV system. On the left a shot out the window looking at one of the NatLab buildings on the Eindhoven Strijp-S complex. [PTR 1937]

Picture from Wireless World September 25, 1936, showing the first ionoscope TV camera in action.

Another picture of the 1935 Philips 180-line TV, this time without screen doors but otherwise the same cabinet. [Early Television]

The same Philips 180-line set as on the left picture, but this time with the cabinet removed. No deflection coils are visible, so the picture tube is most likely an electro-static deflection type. [Early Television]

In 1936 Philips showed a 375-line TV set for the new German transmission standard. It looks like a TV-radio combo with direct viewing screen. No details are known.

Picture of the 405-line Philips television set demonstrated at the 1936 RadiOlympia show. Note that is the same set but not the same picture as that of the Berlin Radio Show. [Wireless World September 4, 1936]

In 1936 Philips was present at both the Berlin Radio Show as well as the London RadiOlympia, where they seemed to have shown the same set. In Berlin all German TV makers were present: Telefunken, Fernseh, Philips, Loewe, Lorenz and Te-Ka-De. Because at this time the line-rate was continuously changing to higher numbers, the Philips set was able to switch between 180 (the old German line number), 375 (the new German number) and 405 lines (for the UK electronic systems). It is said that switching between line-rates was done using a simple switch on the front panel. This was the set mounted in a Bauhaus-style metal tube frame, as confirmed by a picture in Wireless World. Not much is known of this set, so I'll simply copy the short description in Wireless World of September 4, 1936, which reports on the RadiOlympia exhibits. "Direct vision is also adopted in the Philips receiver; the black-and-white picture measures 8,5" by 7". The vision receiver is a superheterodyne with an HF stage followed by a two-valve frequency-changer. Three stages of IF amplification are used before the detector, and there is one LF stage. Electrostatic deflection is employed, and the time bases are of the hard-valve type; three valves are used in each, and three rectifiers are used for the power supply. For sound reception an eight-valve superheterodyne is provided, covering the 7-metre band in addition to medium and long-wave bands". Obviously the set was used in the 405-line mode in London. All this suggests, in contrast to what I thought earlier, that there was a much higher level of co-ordination across the different countries. Because there was nothing like an official Philips commercial TV policy yet, this can only have been organised through and by the NatLab Research organisation, and that despite the "constructive opposition" by its director Holst. But it is the only way to explain the availability of a single set covering both the old and new German norms, as well as the just emerging UK 405-line standard. One thing must have been sure at the same time: the sets were presented as prototypes, and not as commercial products, ready for sales.

In 1936 the commercial department of Philips revolted, triggered by the BBC experimental transmissions during the RadiOlympia show, and enforced a decision, overruling the head of Research Holst, that a more aggressive Commercial approach should be taken by Philips in promoting television, with the aim of selling sets. To start it was decided that two demonstration vans would be built for more aggressive promotion of television. The first van was delivered by September 1937, and looked much more mature than the original 180-line system in the NatLab studio. One van housed the larger picture transmitter and in a separate room the sound transmitter, both in professional racks. On two opposing corners of the van two 10m high antenna masts could be erected. The second van contained a fixed ionoscope camera, a film-to-TV converter and the control panels. New moveable cameras were developed too. Most of this equipment was developed by the NatLab groups. The receivers in contrast, although supported by the group of Rinia, were a joint development of the Apparatenlab (Set Development, the group responsible for all radio, record player and now also TV development) and the Mitcham, UK-based Mullard Labs. These receivers will be discussed in the next section. The vans and system were described in an article in the Philips Technical Review of January 1938 by van der Mark.
One very interesting fact is given in this 1938 publication. It literally says "The installation is suitable for the broadcasting of 25 pictures per second, with 405 or 567 lines per complete picture, while interlaced scanning is employed". This means that 8 years before the "formal" launch of the Philips 567-line standard, prototypes of this system had already been built. If true it made Philips the pre-war record holder on the number of lines used in experimental TV! It is strange that no further publicity has been given to this, but apparently there were good reasons for not doing so. In practise, in the 1938-39 years Philips joined the 405-line camp, mainly driven by its UK activities that were the frontrunner in this domain.

The transmitter van of the Philips Television Demonstration Caravan with deployed 10m high transmit antennas for the video and sound carriers. Right in front of the van one can see the thick cable coming from the other van. [Philips Technical Review Vol3 p1., 1938]

Interior view of the Philips transmitter van, looking at the picture transmitter. [PTR]

The new movable ionoscope-based TV camera. [PTR]

The movable camera in operation in front of the video processing van. [Eindhoven in Beeld]

In 1938 ir. P.R. Dijksterhuis, the head of the Apparaten Lab, where radio and television product development was done, warned the Philips management that in his view the television activities where too low level and unstructured, and would not lead to a strong Philips position in this domain. He proposed that the majority of the NatLab research activities should be devoted to television, including a strong focus on radio valves optimized for the application. The first was blocked by Holst, but it was agreed that the NatLab would step up the television activities in order to build a strong patent position, and valve activities were also increased.

After initial demonstrations in the Netherlands and Belgium, the two vans started touring through Europe, mainly visiting the capitals of the European countries that didn't have their own TV development. These were often seen as astonishing breakthroughs, attracting large crows and much publicity. For example in Romania demonstrations were given to King Carol II and his family, where the arrival of the King was broadcast live. When the 2nd World War broke out in September 1939 both demo vans were in Eastern Europe, one in Zagreb (Croatia) and one in Warsaw, Poland. The first one could be repatriated by sea, but the one in Poland had to be abandoned due to the fierce fighting in and around the Polish capital, the Philips crew was barely able to escape alive and return to Eindhoven. The remaining vans were parked on the Eindhoven Strijp complex and were subsequently destroyed in the December 6, 1942 RAF bombing raids on the Philips factories. The outbreak of war and the subsequent occupation of the Netherlands put an official stop to Dutch and Philips television developments. During the war all product development and system experiments on television were stopped, but theoretical work continued, albeit on a lower level. One of the topics was theoretical analysis of beam deflection in display tubes, an investment that would pay off in the following years. The single publications on TV-related developments was on a new transmitter implementation. The transmitter power was increased from the roughly 500W of the 1937 system to 9kW using new water-cooled PAW12/15 transmit pentodes. Initially (1942) this transmitter was still using full dual side bands (2x2,5MHz) of the signal, only later vestigial side band modulation would be introduced.

The same transmitter van. The limousine in front probably belongs to a Philips executive. [Eindhoven in Beeld]

Philips UK Televisions Tel6 and Tel61, 1936-1938

In 1936 the BBC started experimental television transmissions from the Alexandra Palace transmitter in central London, initially still transmitting using two standards: the 240-line mechanical one next to the new 405-line "electronic" standard as developed by EMI and Marconi and in turn based on the RCA developments in the US. The number of TV's sold at the time was of course very low, but around London the number of watchers steadily grew. Especially the sales department of Philips and its local subsidiary Mullard were pushing hard for an active role of the company in this new market, which was supported by Philips board member for Consumers Mr. Loupard. Philips was not present with a television set during the famous 1936 RadiOlympia consumer show in Olympia Hall, London, which saw the start of experimental 240 and 405-line transmissions. Further alarmed by the start of formal BBC transmissions by the end of 1936 it was therefore decided that Philips would present a prototype receiver at the 1937 annual RadiOlympia show. This set would be based on the rear projection concept that had been in development for a few years now in the Eindhoven NatLab, while the Eindhoven Apparatenlab and the Mitcham Mullard Lab would do the joint product development. Given the origin of the different designs it is logical to assume that the synchronization and deflection unit for the 25kV picture tube came from Eindhoven, while Mitcham did the bulk of the receive chains for both video and sound.

Advertisement for the typical Philips Miniwatt valves used in the early TV sets. The Mullard valves had similar form factor but were developed independently and exclusively used in the UK.

Block diagram of the Philips Tel6 rear projection television demonstrated at the 1937 RadiOlympia show in London, showing the valves used for each function. The set also contained a full radio chassis which took care of sound amplification.

This set, which in an overview of the RadiOlympia sets was called Tel6, was a rear projection receiver in a large cabinet, also containing a Philips 750A-model full band radio receiver chassis, bringing the total valves to 29. A few interesting features were:

It seems the set introduced some new valves designed specifically for the TV function, like the TSP4 RF/IF pentode and GT4H gas-filled triode. Others were the British equivalents of the European Philips valves: 2D4A=AB1, PenA4=AL3 or very similar (TH4A=ACH1). Interestingly, in Radiomuseum.org no other sets using the TSP4 and GT4H are known, only the contemporary Baird T5 used roughly the same TSP4-2DA4 IF video line up.
Video and sound only had the first RF amplifier in common, followed by separate down-converters and IF chains. IF frequencies were very low; 11,1MHz video and 7,6MHz sound.
After AM sound detection the audio signal was connected to the record player input of the radio which thus provided the audio output amplifier.
Both the frame and line time base generators used gassed filled GT4H triodes in the oscillators
The high voltage generator only used two high voltage rectifiers in a voltage doubling set-up, and not yet the fly-back concept with efficiency diodes that was only introduced towards the end of the forties. The high voltage was simply derived from the AC power supply using a high ratio transformer, yielding around 12kV. This was then rectified and doubled using the two diodes. A very dangerous construction, sometimes referred to as the "widow maker", because the voltage would not collapse when loaded like in the flyback circuit.
The projection picture tube was a 4" (11,4cm) high intensity MS11/1, the output of which was projected via a 45degree mirror onto the back of a glass sandwich 20x16" (50x40cm) projection screen. Because there was not yet corrective optics between the picture tube and the display screen, the front of the tube was concave (bent inwards) in order to provide an undistorted picture.

Given the exclusive use of Mullard valves, in combination with the UK being the only television market at the time, is it highly likely that the set was developed by the Mullard Labs, the UK subsidiary and local brand name of Philips. Clearly with support from the NatLab Research, but almost certainly not built in Eindhoven. The receiver concept was reported in the February 1937 Philips Technical Review by C. Richards (almost certainly from Mullard Lab in Mitcham), while the rear projection concept of the set was published by M. Wolf in the Philips Technical Review of August 1937.

A charming demonstrator of the Philips Tel61 on the 1938 RadiOlympia Show in London. [Daily Herald]

The set initially received a lot of positive attention and reviews, especially for the bright and large screen. (The next largest screens shown during the 1937 RadiOlympia were 13,5x10,75" (35x27cm) by GEC and Baird, so with more than twice smaller display area). Despite the fact that the set was removed from the show after only three days, a number of sets seems to have been sold, produced and delivered to customers. Unfortunately most of these had to be re-called due to field failures, with Philips even offering to reimburse the cost. The reason for all of this was the extremely short life time of the MS 11/1 projection tube. This was partly due to the high currents and voltages at which it was operating, and partly due to its sensitivity to breakdown. As soon as something would be wrong in the frame of line deflection drivers the result would be a horizontal or vertical line that would burn into the picture tube phosphors and destroy the tube. Having learned from this, during the 1938 RadiOlympia show Philips presented an improved set, the Tel61. Essentially it was the same platform but with three gas filled triodes as electronic relays that switched off the deflection and anode voltages to the picture tube in case of problems. The radio had been upgraded to the 753A. Another improvement was that the IF moved up to 13,2MHz for video and 9,7MHz for sound, values that would remain so for the next decade.

Three pictures of the 1937 and 1938 Radiolympia Philips UK television sets. On the left the 1937 model Tel6, showing the large 20x16" (50x40cm) screen. In the centre the interior view of the same TV, showing at the top the radio receiver and below small signal (left) and deflection/HV modules (right) with between them the picture tube module. On the right the 1938 Tel61 model, slightly more compact with a 18x14,5" (45x39cm) screen. Note that the picture screen dimension where 5:4 for the 405 line standard, only later they switched to 4:3. Furthermore, the Tel61 cabinet on the right clearly has a smaller width than the Tel6 on the left. [Images from review articles Television and Short Wave World Magazine October 1937 and September 1938, via TheValvePage.com]. In the centre below the picture tube used by these two sets, the MS11/1, with the clearly visible concave face. [PTR August 1937]

Block diagram of the Philips Tel61 rear projection TV as shown at the 1938 RadiOlympia show in London. The main difference with the Tel6 of the previous year were the CRT protection circuits.

Philips 2400, the direct view production set, 1939

For 1939 Philips had bigger plans, with the Apparaten (set manufacturing) organization stepping in to make the move to a first generation real production sets. The set up consequently saw a number of major changes against the Research-developed Tel6 and Tel61:

the switch to direct viewing, dropping the problematic rear projection with the unreliable MS 11/1 projection tube. Instead the brand new MW22-1 magnetic deflection 9"/22cm cathode ray tube was used. Especially the Mullard organization must have had a strong voice in this, given their preference to direct view sets;
only regular volume production valves were used from the Philips Miniwatt series;
the set introduced the brand new EE50 secondary emission all-glass pentode, a valve showing a very high transconductance (gain), thus allowing to substantially reduce the number of IF amplifier stages.
as a consequence the TV set has, while offering a very good performance, an extremely low number of valves: only 18;
for marketing optimization, at least four different sets are defined for the UK market: the 2405 (a 9" table model), 2407 (a 9" console model), 2412 (a 9" radio-TV console model), the 2409 (name not confirmed, a 12" console) and 2415 (idem 12" with radio). The radio used in the 2412 and 2415 was the 735A;
the sets were offered on a European scale. First launched in the UK, they were quickly also advertised in France, capable of both 405 and 455 lines. And in 1939 also pre-production of the model 2400/23 started in Italy, now adapted for 441 lines. Although there is so far no evidence this 441-line model was also introduced in Germany, it is remarkable that the 2405 table top model strongly resembles the mandatory German Einheitsempfänger. So I wouldn't be surprised that market was targeted too.

One of the most remarkable features of the pre-war models is the RF mixer-oscillator concept, where video and sound have their separate mixer heptodes, while the two oscillator triodes use a common tank circuit. [PTR 12-1939]

The EE50 was the first Philips valve with an all-glass base, after four years of development. These are pictures from the first public presentation of the valve, at the Internationale Fernseh Tagung in Zürich, Switserland, September 1938. [Dos4Ever.com]

The characteristic red metal capped EE50. The EF50 looked similar. [Radiomuseum.org]

In this context it is interesting to spend some attention to the EE50 development, which has been described in detail on Ronald Dekker's site, but deserves a summary here. The EE50 was the first major development of a new, smaller and cheaper radio valve construction, which was triggered by the introduction in 1934 of the RCA Acorn or Loktal tubes. Developments in the NatLab Research group of Johan Jonkers and the Radiobuizen division were slow, and the first prototype was only presented in September 1938. In the light of the earlier mentioned discussions on the importance and priority of television developments within Philips, it is remarkable that the first valves in the new 50-series were targeting television applications. The first was as mentioned the EE50, a secondary emission pentode developed in the group of Jonkers. This concept gave the valve an exceptionally high transconductance of 14mA/V, almost 3 times that of an ordinary contemporary pentode, thus substantially reducing the number of stages required for RF and IF amplification. However, the compromise for the high gain was higher noise, and in parallel the more standard pentode EF50 was developed with a transconductance of 6mA/V but better noise. This was the famous tube that was used in the 45MHz TV RF/IF strip of Pye in their 12C 1939 television, and then quickly copied and used by Watson-Watt and his team that were developing the Chain Home radar system. The EF50 thus became "the valve than won the war". Still, the technology of these new valves was fragile, and both the EE50 and EF50 went through a number of optimization cycles. First they had thick straight pins, which changed to thinner hooked pins to reduce cracks. But also these were not reliable and finally changed to straight thin pins. Also the top grid connection was eliminated and moved to a standard pin. Especially the EF50 was very much driven by the requirements of Pye, and included the adoption of the famous red metal shield over the glass housing.

Philips 9" (22cm) direct view TV sets for the 405-lines UK market that were to be launched end of 1939. From left to right the 2412 radio-TV console, 2407 TV console and the 2405 table top models. [PTR 12-1939]

The electronics of the 1939 sets: from left to right the MW22 picture tube, the HV and deflection module, behind the small signal module and in front of that the deflection coils. [PTR 12-1939 and Tonino Giagnacovo]

French advertisement from 1939 of the Philips 2407, here as a 455-line version. The capability to receive TV sound is mentioned as a special feature! [Early Television]

French advertisement for the most luxurious model of the 1939 Philips TV series, the 2415. It featured the first MW31-1 12" picture tube and a full multi-band radio. [Early Television]

The technology behind the 2400 family has been mysterious for a long while. In an author-less article "compiled by C. Heller" in the Philips Technical Review of December 1939 the latest picture tube receiver was described, but without mentioning a single valve type. A circuit diagram of the 2407 is known, again without the mentioning of valve names. I've thought initially that the similarity with the Tel61 should have been high, but it has now become obvious, as mentioned in the introduction of this section, that the 2400 was an entirely redesigned chassis with a clear focus on low cost and good manufacturability. It is likely the platform was designed in the Eindhoven Apparatenlab on Strijp, although involvement of the Mullard lab is also quite logical. The fact that the Italian version was coded 2400/23, i.e. the basic platform name 2400 with the suffix 23 referring to Italy, is a strong indication in this direction.
Compared to the Tel61, the EE50 amplifier allowed to reduce the number of IF amplifier valves from five to two! The IF signal was so strong that after peak detection it could even be connected directly to the picture tube cathode, without the need for the usual video output power pentode. The detectors, three of them, also used the new miniature all-glass EA50 diode. The other remarkable valve is the EC50, a Helium-filled thyratron valve specifically designed for saw tooth oscillators. Most other valves, except those for power functions, were regular Miniwatt E-series valves used in high volume in radios. Only in retrospect it can be said that this low valve count was a major achievement: it would take 15 years before Philips produced another TV with 17 valves or less (the 17TD120 in 1954 with 16 valves, but also the first solid state diodes)!

The chassis was constructed in two parts, one for the deflection and high voltage generation and one for the small signal RF-IF-AF chains. The cabinets were typical for the time, and needed be sufficiently big to reflect the high price. As said earlier, the table top model 2405, intentionally or not, had a high resemblence with the mandatory German Einheitsfernsehemfänger design.

The Italian 441-line version of the 2400 family. [“La Televisione alla XI Mostra nazionale della Radio”, Radio Industria n.59 (september, 1939), pag.504-505. via Tonino Giagnacovo]

Block diagram of the Philips 2400 TV platform. The valves are based on the description of the 2400/23 Italian version, but almost certainly identical to those of the 2405 and 2407 UK and French versions.

Unique pictures of the assembly and testing of a small pre-series of Philips 2400/23 television sets in the Philips Monza radio factory near Milano, 1939. [Radio Industria No.67, p.248, 1939 via Tonino Giagnacovo]

The 2400 family was first shown in public during the August 1939 London RadiOlympia show, where they received good reviews. Production was ready to ramp when on September 1st war broke out. Germany invaded Poland, followed by Britain and France declaring war on Germany. The BBC immediately stopped all experimental television broadcasting and as a consequence all production plans in the UK and France were put on hold by Philips. Only in Italy activities continued, see pictures.
This effectively put a stop on most TV developments in Europe, although the Axis powers Germany and Italy continued a modest roll-out of their 441-line system at least symbolically, with ironically the Eifel tower transmitter in Paris being the most visible activity. It also meant the premature end of the Philips 2400 TV platform, which at least in terms of valve count and robustness looked so promising. It also effectively ended the life of the EE50 pentode in consumer applications, beyond 1939 there is only the Italian Magnadyne TM20 TV that is known to have used these valves. Its sister valve the EF50, in contrast, became the standard RF/IF amplifier tube for all UK radio and radar sets. In the days following the German invasion of Holland in May 1940 Philips brought a few truck loads of EF50s and its manufacturing equipment to the UK, where Mullard took up volume production.

Television Standards 1946-1948

During the first years after the war, 1945-1946, there were - in Western Europe - essentially only two countries with regular television transmission: Britain and France. In the background there was of course the US, where television transmission had started during the second half of the war years. It won't be a surprise that all three countries used different standards, summarized below:

The three relevant television broadcast standards in 1945-46.

The British 405 line standard and the French 441 line standard were both based on pre-war systems, from a time when achieving bandwidth was still a challenge. But by 1946 especially the 405 line system was considered as too low in resolution, and on larger screens the lines became visible. "Spot Wobble" was used as one option to smear out the lines, of course at the expense of vertical resolution. Although the French were transmitting the 441-line signals from the Eiffel Tower in Paris, it was clear that it would not be the targeted system for France. Based on this situation as a starting point, there were two more or less parallel development tracks in Europe.

The first was a British-French alignment. On the one hand the British were leading in Europe, with actual television transmissions starting in 1946 from the Alexandra Palace transmitter in London, and more transmitters being installed throughout the country in the years after. Britain openly had the intention to spread its standard towards the continent, to facilitate exchange of programs and to support British industry. However, in France the trend was clearly to higher resolution standards, initially a 1020 lines system was proposed, but by November 1948 French authorities decided for the competing 819 lines system. Compared to all other standards of that time this could be considered as high definition television, which was seen as part of the policy to push French technology excellence, of course at the price of high channel bandwidth and thus fewer transmitters per band. (There was place for only two channels in VHF-I, and most were consequently in VHF-III). Intensive discussions took place between the French and British television authorities, converging on the following plan: the French were to adopt the British 405-line system for the 45-80MHz VHF-I band, thus replacing the Eiffel Tower 441 line transmissions. In return the UK would adopt the 819 lines HDTV system for transmission in the VHF-III (160-210MHz) band once it would move there. Jointly this would then be the proposal into the CCIR (Comité Consultatif International du Radio, headquartered in Genève, Switzerland) standardization committee of the ITU.

Graphical depiction of the Philips 567-line interlaced TV standard with respect to frame and line synchronization. [Philips Report "Quelques données sur le système de télévision à 567 lignes ..", 1946/47 via Edvard Paling]

Graphical depiction of the Philips 567-line interlaced TV standard with respect to frequencies and modulation. [Philips Report "Quelques données sur le système de télévision à 567 lignes ..", 1946/47 via Edvard Paling]

The other track was building on the US NTSC system, in practice the best system then operating. Especially RCA was promoting the re-use of it standard in Europe, adapted from the 60 to 50Hz power supply frequency. And this is where Philips comes in! Although it is not possible to re-trace the history in all details yet, it is likely that Philips decided to build upon the US system due to its own presence in the US, potentially benefiting from a technical synergy between the two systems. As a consequence Philips developed a 567-line 50Hz (25 frames) standard, giving a line frequency of 567*25= 14.174Hz, close to the 15.750Hz of NTSC. At the same time I recently discovered that Philips already had worked on 567-line systems as early as 1937, see above. At that time 525-line NTSC had not been developed yet, which makes that link less plausible. In theory 567 lines in combination with 4:3 screen size would require a video bandwidth of 5,5MHz and a channel width of 7MHz. However, for maximum compatibility with NTSC a lot of that standards parameters were (later) taken over: 6MHz channel, 4,2MHz video bandwidth, negative modulation and an FM sound carrier 4,5MHz above the picture carrier. The lower video bandwidth resulted in a lower horizontal resolution, but delivered a very economical system and high synergy with the US system.

The 567-line standard was defined by a group of people in the research groups of van der Pol and Haantjes. On December 7, 1945 an internal NatLab report was written by J. van der Mark explaining the choices for the bandwidth and line rate. Philips was quite bullish about its standard, and seriously tried to promote it as the European standard to the surrounding countries. Johan Haantjes was the main promoter of television broadcast within Philips, and also the primary external contact to Dutch authorities, the PTT and potential broadcast corporations in Hilversum. He was likely also the representative proposing and promoting the Philips standard in the CCIR.

The only actual 567-line promotion material found is a Philips Report entitled "Quelques données sur le système de télévision à 567 lignes et sur le récepteur à projection" (Some information on the 567-line television system and the projection receiver). It is not numbered and not authored, which suggests it was intended for external use, in this case France and Belgium. The report discussed the main system choices, where it is interesting to see it gives many arguments against the positive modulation and AM sound used in the proposed French standards. It also shows the SG860 receiver which will be discussed further down. A last interesting observation is that Philips apparently had devised a logo for its 567-line TV standard, as shown on the cover.

Front page of the 19-page Philips report (in French) detailing the 567-line standard and prototype receiver. [Edvard Paling]

The four standards fighting for standardization in Western Europe 1947-48, plus the US NTSC reference, which had a considerable influence at least on the 567-line Philips proposal.

Philips rear projection TV, 1947

After the war, work on television was taken to a higher level again at the Natuurkundig Laboratorium. In 1946 its founder Holst retired, and was replaced by three directors each covering a fundamental group of activities: Hendrik Casimir for physics/devices, Evert Verwey for chemistry/materials and Herre Rinia for systems/electronics. This NatLab structure would exist for fifty years till well into the 1990s! One of the group leaders was Prof.Dr.Ir. Johan Jonker (1901-1963), who had between 1931 and 1936 had created the Radiobuizen Lab, which will be discussed later. After his return to the NatLab his group continued work on advanced valves, such as high frequency and high power transmission tubes including magnetrons, klystrons and travelling wave tubes, cathode ray tubes and camera tubes. His team was also responsible for the invention of the EQ40 enneode phi-detector as well as the E1T counting valve. In the sector of Rinia Haantjes took over the receiver group, while van der Pol continued to lead the transmitter activities until his retirement in 1949. That group was then taken over by van der Mark. Some time later all television research activities would be integrated under Haantjes, who led them till he became vice president in 1956.

As said earlier, the Philips television strategy was primarily built around projection TV. This was the concept that had been used for the 1937-39 demonstrations, and on which the research activities had been continued during the war years. When television started to gain momentum again after the war, Philips development activities continued based on this concept. After the definition of the 567-line standard, the next step was to build a prototype system around it. Many details of this prototype system are known through a number of publications in the research Philips Technical Review journal, with articles written by some of the key players introduced earlier:

PTR Vol7 1942, No5, pp.129-137, A nine kilowatt experimental television transmitter, M. van de Beek
PTR Vol10 1948, No3, pp.69-78, Projection Television Receiver I. The optical system for the projection, P.M. van Alphen and H. Rinia
PTR Vol10 1948, No4, pp.97-104, Projection Television Receiver II. The Cathode-Ray Tube, J. de Gier
PTR Vol10 1948, No5, pp.125-134, Projection Television Receiver III. The 25kV Anode Voltage Supply, G.J. Siezen and F. Kerkhof
PTR Vol10 1949, No10, pp.307-317, Projection Television Receiver IV. The circuits for deflecting the electron beam, J. Haantjes and F. Kerkhof
PTR Vol10 1949, No.12, pp.364-370, Projection Television Receiver V. The synchronization, J. Haantjes and F. Kerkhof.

The core of the receiver was the new high power picture tube, the MW6-1, a development of the pre-war MS11/1 [*]. It had a very high light output concentrated on a small frontal fluorescent screen with a diameter of just 6cm. This high light output was achieved with a high accelerating voltage of 25kV, which was quite exceptional for the time. Where exactly the MW6 was developed is not entirely clear. Given that a substantial article was published in PTR supports an origin in the NatLab, then most likely the group of Jonkers. However, the formal product code indicates it was developed as a real product in the valve division, possibly by Mullard in the UK. The first version of this tube was the MW6-1, which was used in the first SG860 TV, but quickly succeeded by the MW6-2 that would be used in all rear projection sets in the coming years.

[*] The product code for picture tubes was: 1st letter: D = Electrostatic deflection, M = Magnetic Deflection; 2nd letter S = Green, W = White medium persistence fluorescence; 6, 22, 31 = screen diagonal dimension in cm; -1 suffix is generational indicator.

The optical unit was clearly the most complex of the television receiver. The purpose was to project the image of the MW6-2 picture tube on much larger display screen with as little deformation and loss of light intensity as possible. For this a Schmidt optical system had been selected, the same as used in most astronomy telescopes. [In this context it is interesting to know that Philips also internally produced the 30cm telescope for the Philips Astronomical Observatory in Eindhoven (today the Dr A.F. Philips Sterrenwacht). This telescope was designed by Herre Rinia, who was also amateur astronomer!]. The picture was magnified roughly 6 times and rear-projected on a 32x40cm frosted glass projection screen. This was considered large enough to have multiple people in the same room watch the television program. The optical module was fairly compact in a roughly 30x30x30cm enclosed box, with only the MW6 foot sticking out for electrical connections. The light exited the box almost vertically through a glass plate window, which made cleaning easy and kept the optics dust-free. However, despite the high-intensity image output of the MW6 screen, the multi-element complex optical path (spherical mirror M1, plane mirror M2, corrective lens C, window D, followed by the 45degres mirror in the cover and finally the half-transparent projection screen) introduced quite some light losses, and although the picture had good resolution and - for the time - a large size, it was not very bright. (I've witnessed this on Jac Janssen's working SX861A!)

The electronics of the first TV set were very basic, and clearly based on the system designed during the previous years. It was thus almost entirely based on the E20/30 Miniwatt series, with valves such as the EBC33, ECH21, ECL21, EL34 and EL38. Only a few modern valves that had just been released like the EA40 efficiency diode and EY51 high voltage rectifier were used. Special attention was required for the 25kV high voltage supply for the MW6-1 and -2 anode, which was at the time a very high voltage for a consumer device. The third paper in the PTR series describes the blocking oscillator concept, followed by a cascaded rectifier stack.

Around this new Schmitt-optics display unit a television set was designed roughly based on the pre-war Tel61 and 2400 UK platforms. Like all post-war designs it replaced most of the pre-war valves by the EF50 and Ex30 octal valves. And it introduced of course the MW6-1 high intensity rear projection picture tube. As to the types and their order it becomes a bit tricky now, but it seems that the successive developments went as follows:

Research prototype
For low line numbers, either 405 and/or 441;
Straight TRF receiver, MW6-1 picture tube;
Narrow "Tel61-like" cabinet; 1946.
SG860A
A 405-line set for the UK standard, TRF, MW6-1 initially, later upgraded to MW6-2;
design ready October 1946, wide "Tel6-like" cabinet
SX861A
A 567-line set for the proposed Philips standard, new heterodyne receiver, MW6-2;
design ready first half 1947, same wide cabinet as SG860A

The sets followed the standard Philips naming convention, with S probably a new indicator for back-projection sets (which was never used after these three sets), 2nd letter for the country, first number a luxury indicator, 2nd number last digit of year of design release. At the same time Philips itself was mixing up the type names, because in the above-mentioned 567-line French report they describe the "SG860A for 567 lines" while pictures are of the NatLab prototype.

Visit to the NatLab TV group by board member Frits Philips (right) in 1946. He's probably looking to the rear projection optics assembly of the Research prototype (recognizable by its narrow cabinet, the two decorative patches left and right of the screen, and the lack of horizontal bars across the speaker). [Site NatLab Hagenbeuk].

As said, the NatLab had the lead in developing a prototype system, based on the new optical system and the MW6-1. It used a cabinet of roughly the same "narrow" shape as the pre-war Tel61, and can be seen in the above picture with Frits Philips. The same set appears in the French report promoting the 567-line standard, see below pictures. These show that, despite the title of the chapter claiming this is a "SG860A for 567 lines", we see a low line count receiver, with lower right the six EF50 TRF receiver identical to the one used in the SG860A. The deflection unit lower left contains the additional transformer and EY1 for the 300V Vg2 of the MW6-1. Interestingly, the deflection unit also contained two selenium rectifier diodes, the first known use of a semi-conductor in a Philips TV set! Also, the SG860A introduced the EA40 efficiency diode in the line deflection circuit, a major efficiency improvement. On the top level we see the BX660 three-band radio left and the power supply chassis right. The set worked on classical parallel connected 6,3V heaters, and the power supply thus contained an enormous and heavy supply transformer. Although there are some as yet unconfirmed rumours about a French SF651A version, and descriptions are missing or confusing, it is most likely we are looking at the SG860A 405-line prototype.

Three beautiful pictures of the NatLab SG860A 405-line prototype system, as shown in the report "Quelques données sur le système de télévision à 567 lignes et sur le récepteur à projection" (Some information on the 567-line television system and the projection receiver). Left the front view, still without tuning dial. Note the lower width of the cabinet compared with the later "real" SG860A. Centre the interior view showing clock-wise from top left around the central optical display assembly: the three-band radio, 4-band switch, power supply, TRF radio, 25kV high-voltage supply with the can containing three EY51's, and finally the deflection unit. The right picture shows the set with extended chassis racks for servicing. [Edvard Paling collection]

Block diagram of the Philips SG860 405-line prototype rear projection TV. Note the non-heterodyne TRF receivers for video and sound, the first generation MW6-1 display tube and the separate 25kV supply module. The MW6-1 gate2, which required a voltage 150V above the cathode potential of 250V, used a dedicated EY1 power supply rectifier and HV transformer.

The SG860A was in the course of 1946 transferred from the NatLab to the Apparatenfabriek, where a small series was produced. The official documentation of the SG860, testifying the official adoption by set development, has July 1946 as the first release date for the radio module, October 1946 for most of the circuit diagrams, and July 1947 for the parts lists, with further small updates throughout 1947. So it is fair to assume that this period from mid 1946 till mid 1947 was the time that the SG860 got "productized". The main change in the "product" SG860A was the wider cabinet, with the addition of three decorative protection bars across the speaker cover. The set also received its dedicated radio dial. Internally it was identical to the narrow cabinet NatLab set, apart from the wider space. It is doubtful if many (or any) of these sets was actually sold in the UK, since there are no commercial traces. It seems the set was not shown during the 1947 RadiOlympia show in London, where the focus was on the first really commercial TV sets 463A and 563A, based on the direct view picture tube.

The SG 860 A. All pictures in this section from Philips Technical Review Vol.10.

Philips SX861A, the first 567-line television, 1947

Immediately following the 405-line SG860A, developments were started of a 567-line version, which would become the SX861A. Conceptually it copied the SG860A, and many modules were component by component identical, although the receiver required adaptation to the new 567-line standard. It also introduced a number of new functional concepts:

The RF input became a classical heterodyne (pre-amplifier and mixer-oscillator) and was now common for video and sound, and only after the 2nd IF amplifier the sound IF was split off into its separate chain. To accommodate the 6MHz channel bandwidth for 567 lines the video IF was chosen at 19MHz, with the sound IF 4,5MHz lower at 14,5MHz;
The SX861A introduced FM sound demodulation, linked to the 567-line standard, and using a dual diode EB4 Foster-Seeley type FM demodulator;
The set copied the line fly-back concept with an EA40 efficiency diode, introduced with the SG860A. A second diode, an EA50, was added and limited the line deflection voltage;
The SX861A used the newer MW6-2 picture tube, replacing the MW6-1 of the SG860A. Therefore the EY1 for the g2 450V voltage was no longer required since g2 was now connected to 300V;
Like the SG860A it used the 25kV CRT supply module as developed for the Research prototype. A single EBC3 was used as protection circuit, switching off the MW6-2 electron gun in case of any malfunction in the deflection circuits. As mentioned this circuit also contained the two Selenium rectifiers. Because the 567 line output required higher voltages and more power than the SG860A 405 lines, an AZ41 power supply rectifier was added.

From the outside the SX861A looked identical to the SG860A. Internally the valve count added up to 35; 23 for the television core, 6 for the 25kV high voltage module and 6 for the BX660 radio. The set was of course not produced in series, given the lack of 567-line transmissions, but it was transferred, just like the SG860A, to the HIG Apparaten. Here it went through a formal product development and documentation process, with first document releases between September and November 1947, and upgrades continuing till February 1948. Some 20 were built by the Apparaten-fabriek as pre-series, and were used for the Philips experimental television transmissions that started in 1948. Most amazing is that one of these rare sets has survived the seventy years since then, and is restored in working condition by Jac Janssen.

The unique restored and working SX861A of Jac Janssen. [Jac Janssen private collection]

Backside interior view of the SG861, with centrally the black optical module. [Jac Janssen private collection]

The SG860/SX861 was also used for publicity at e.g. shows, such as the June 1948 Feria in Barcelona, Spain.

Block diagram of the Philips SX861A rear projection television plus radio. Only a small series of some 20 pieces was produced and used for field tests during the Philips Experimental Television transmissions, starting March 1948.

Despite the official focus on the rear projection concept, apparently direct view television was not totally neglected. It seems that, probably also for the experimental transmissions that were planned to start soon, a prototype series of direct view sets was built too. In the only known official documentation, an undated component list, it is called "direct-zicht console" (direct view console). Jac Janssen possesses such a unique set which we'll call the "TX660A", with the T referring to direct view sets and the 6 to indicate a more modest feature level (console but smaller cabinet, no radio) compared to the SG/SX860. The TX660A essentially was a modified SX861, with a few differences:

Because the MW22 picture tube only required 7kV anode voltage, the original rear projection HV unit was kept, but with just one EY51 in the high-voltage can;
The set still used the separate transformer plus EY1 g2-supply of the picture tube, which was necessary to set the g2 250V above the 200V cathode voltage. The picture tube was possibly a very first MW22-7. (Jac's set was later re-gunned to become a MW22-16, so it is impossible to ascertain what the original picture tube was);
The HV protection EBC3 for the picture tube was deleted;
There was no radio, but the EBL21 sound amplifier stage was re-used. An additional EF22 audio amplifier was added.

The "TX660A" was almost certainly designed around 1946, parallel to or immediately after the SX861. (Given the high innovation rate of television valves that we will see in the coming sections, if it would have been later undoubtedly more modern valves would have been used). It is plausible that during the Philips Experimental TV transmissions in 1948 at least a few of these sets have been deployed for field tests. With the SX861A rear projection platform and the TX660A direct view chassis the Eindhoven set development now had two reference designs that could and would be used for commercial developments in the HIG Apparaten.

The only official documentation confirming the existence of a direct view television set based on the SX861A. This is an example of the parts list for the time base. The descriptions fit almost perfectly to the "TX660A" owned by Jac Janssen. [Edvard Paling collection]

The only known survivor of the experimental direct view console set based on the SX861A, which we will call the TX660A until further notice. The cabinet resembles the 2407 from 1939. [Jac Janssen collection]

Interior view of the TX660A. The module with the two red EF50's upper right is not original and added later for 625 lines. Centre left the RF+IF module, centre right the deflection module. [Jac Janssen collection]

The same interior view, but with lowered chassis for servicing. The eight red EF50's are clearly visible on the new heterodyne RF-IF chassis. On the bottom of the console the power supply (left) and high-voltage module. [Jac Janssen]

Block diagram of the Philips "TX660A" experimental direct view television. The similarities with the SX861A are obvious.

First commercial TV sets, 1947-48

By this time, we speak 1946, the UK was the only serious television country in Europe. During the war years most companies in the UK, including Philips/Mullard, switched to military applications and had no resources to work on consumer applications. When the BBC resumed television broadcasting in July 1946, most manufacturers - with the exception of Pye, which had secretly developed a new platform during the war - had to start where they had stopped developments in 1939. The same was true for Philips, and the first family that was developed was thus heavily based on the 1939 Tel61 platform, the last one that had made it to production. In 1947 two models were launched, the 463A and 563A, the next year the 663A and 383A. Where it seems the 383A re-used the 2405 cabinet from 1939, the while the 663A looked very much like the Tel61, albeit without the projection screen. This family of TVs was based on the SX861A/TX660A chassis from Eindhoven. The intention of the Apparaten Lab was undoubtedly to have the design done in Eindhoven, and then transferred to Mitcham for local industrialization. However, the transfer from Eindhoven to Mitcham seems to have been problematic, Mitcham claiming that it was not good enough and requiring modifications. Looking at the final solution there area number of differences that often reflect the Mullard involvement:

This was the first post-war chassis not based on rear projection, but using direct view MW22 picture tubes. The 463, 563 and 383 used the new Philips MW22-7 9" picture tube, while the 663A was the first TV with the new 13" MW31-7 tube;
All new 20-series valves (ECH21, EBL21) were replaced by the older local favourites ECH35, EBL33 and EL33. It also introduced the first miniature Ex90 valve as video detector and interference suppressor in the sync separator, the EB91. (The EB91 in this platform is a bit of an enigma. According most official documentation this valve was launched in 1949 as part of the miniature Noval series. Since the four sets were shown at the RadiOlympia 1947 AND the official service documentation clearly lists this valve, something doesn't fit. As we will see further down it happened regularly that valves were used in internal development and reference designs well before public launch. I therefore tend towards the scenario that the EB91 was available in 1946-47 for internal set development and that there is no conflict in timing);
The sound IF was clearly a local Mullard Labs pre-occupation, where they consistently deviated from the concepts developed in Eindhoven. So where the SX8161/TX660A already used a common RF-to-IF down-conversion for video and sound, the 383A chassis used separate mixer-oscillators for the video and sound paths. This is an architecture not seen in any other Philips set. Although the number of valves was identical for the RF-IF chain, the 383A solution (6x EF50, 2x ECH35) was more expensive than in the TX660A (7x EF50, 1x ECH21);
In the 563A and 663A, the models with a radio option, the radio bands re-used the TV chain while adding an EF39 pre-amp and EM34 magic eye tuning indicator;
The EA40 efficiency diode in the line output driver was not yet introduced, while the picture tube anode voltage generation required two HVR2 rectifiers, instead of the single EY51 in the SX861A.

The chassis of these TV's was made from two modules, one for small signal and one for the deflection and high-voltage generation. Twese two modules were either placed next to each other (like in the 463A and 383A) or on two levels (563A and 663A).

From left to right: the 563A, with on top the radio dial [TVHistory.TV]; a January 1949 advertisement for the 383A [The Valve Page]; A picture of the Philips 663A [Pinterest]; interior view of the upper half of the 663A with the small signal chassis [SSPL Prints]; The 383A and 663A used the same two chassis blocks. In the 383A they were mounted next to each other as shown, in the 663A on two levels. [Philips 383A and 663A Service Manual via The Valve Page]

The main argument in the complaints of the Mitcham Mullard Lab was that the Eindhoven designed prototypes were not properly measured for the 405-line transmissions, due to a lack of test signals. Which seems a bit strange, given that Eindhoven had built 405-line transmitters as early as 1937. It is hard to imagine they didn't have some sort of test signal generators in the Apparaten Lab. Nevertheless the argument gained momentum, and after the frictional development of the 463-563-383-663 chassis the centre of gravity of product design for UK sets moved to Mitcham. My guess is that they had already started the development of a local chassis in Mitcham, because in the same year the 520A or Mullard MTS521 appeared. It seems that the objective was to design a TV as cheap as possible, which effectively meant with the lowest number of preferably simple valves. It deviated quite a bit from the 463-chassis:

Only two combi valves (CCH35 and EBC33). It used, like the 463, only EF50 and Ex30 valves. No recent EB91, although a first EB41 was used, and the EY51 introduced;
It used the unique and never again seen concept of a dedicated oscillator valve (the triode section of a CCH35) for all bands: three radio and TV. But whereas the radio/sound chain used the hexode section of the CCH35 as mixer, in the video chain an EF50 was used in that role. The LO signal was magnetically coupled into the RF path, both the RF and LO appearing on the g1 of the mixer;
Assuming the numbers are correct, the IF frequencies were a mere 100kHz higher than so far used in UK sets: 13,3MHz Vision IF and 9,8MHz sound IF;
Other peculiar concepts are the frame and line time bases, both being realized with a single power pentode. So no separate oscillators, but self-oscillating pentodes, a concept I haven't seen in any other Philips set;
To compensate for the much higher IF bandwidth, the sound chain had an additional EF50 when in TV mode, which was by-passed in radio mode;
The 520A had no mains transformer and used series heater chains. The radio and TV 0,2A heater chains were separated, the first and driven by the UY21, the second by the PZ30. The picture tube had a separate small transformer for its heater supply. In radio mode the TV heater chain was disconnected and to avoid any voltages on the picture tube the cathode connection of the line output opened.

The set was split into two chassis; one for the sound plus the video RF and IF, probably up to and including the EB41 video detector. This chassis was mounted upside down from the cabinet top, with special valve clips for the 30-series valves to prevent them from falling down. The bottom chassis contained all deflection and high voltage circuitry.
It seems that the 520A/MTS521 was a one-off exercise, developed separate from its 465-family contemporaries, nor re-used in any other Philips or Mullard TV set.

The Philips 520A, showing the radio dial on the top. [TVHistory.TV]

Interior view of the Philips 520A, with the radio/sound plus video RF/IF chassis hanging upside down. The red cilinders are EF50 valves. [UK Vintage Radio Forum]

Philips Experimental Television (PET), 1948

In order to bring television promotion and publicity to the next level, Philips decided it was time to start actual broadcast transmissions of television programs. Because there was no organization able to organize and execute this, it ended up as a 100% Philips activity. To start a transmitter was installed on the roof of one of the tall buildings of the massive Strijp-S factory complex in Eindhoven. On the southernmost distribution centre building (the so-called "Veemgebouw") of the Apparaten factories a lattice tower was erected, on top of which two antennas were mounted, one for the picture transmitter and one for the sound transmitter. Note that at this time the video and audio baseband signals were not yet combined into one composite television signal, with the sound carrier at 4,5MHz as was done later. In that case the composite baseband signal is in one step modulated on the picture carrier, with a guaranteed frequency distance between picture and sound carrier. By the time of the experimental transmissions picture and sound were transmitted by two separate transmitters, that had to be precisely controlled in terms of frequency separation and power level. In most systems the sound transmission power was 4 times (6dB) lower than the picture carrier. The video transmitter was called PAB3, the sound transmitter PAG3 (my guess is the abbreviations stand for Philips Apparaten Beeld and Philips Apparaten Geluid). The video transmitter had an effective transmit power of 20kW, giving a normative reception range of 30-40km. The picture transmission frequency was 63,25MHz, sound was at 67,75MHz, as mentioned earlier both with vertical polarization.

Only the next requirement were programs to be broadcast. To this end a very small one room 5x11m studio was created on the ground floor of the NatLab, opposite the street of the transmitter building. The studio room was so small that apparently it had to be entered through the window, the door being blocked by all equipment. Especially the cameras were still massive. Programs were organized and filmed by Eric de Vries, who had already been involved with the television demonstrations before the war. A variety of programs was transmitted, often a mix of flower arranging, child care instruction, music, comedy and other forms of risk-free information and entertainment. Much later, in 1950, the first life soccer match registration of the local derby PSV-Eindhoven would be transmitted, which generated much more enthusiasm. It should be remembered that the television experiments were not just to test the electronics of the system, but also to explore what television could mean to the public, which programs could be relevant and what the viewing experience of the viewers was. After all it was an entirely new medium! Philips had requested a radio licence for television transmission from the Dutch PTT, which they received March 18, 1948. The same day the first experimental transmission was made of what was now called Philips Experimentele Televisie (Philips Experimental Television, PET). The first transmission was announced by Bep Schäfer, a Philips secretary, as "Goedenavond, dames en heren. Hier is Philips Experimentele Televisie met de eerste uitzending. Beeld en geluid over de zenders PAB3 en PAG3...". Regular transmissions started April 1st, 1948, three times a week for 2-3 hours.

The Philips Experimental Television PET transmit tower on the "Veemgebouw", the central distribution center and the southernmost building on the Strijp-S complex in Eindhoven. [Eindhoven in Beeld]

Aerial picture of the southern part of the Eindhoven Strijp factory complex of Philips, looking north. The white encircled low-rise section in the foreground is the Natuurkundig Laboratorium (NatLab), with in one of the left-most buildings the PET studio. The long high-rise buildings running along the central axis of the complex belong to the Apparaten organization, and contain both the radio and television development as well as factories. On its western-most building indicated by the arrow the PET transmitters were located. [PTR Vol.13 1951]

The transmission monitoring and control equipment in the PET studio. The man standing right is Wil van Vlerken, who was involved with Philips experimental TV already before the war. [Eindhoven in Beeld]

PET studio during a television program transmission. Behind the camera left Eric de Vries, on the right Bep Schaefer doing the announcements. [DBNL]

The third element of the PET system were of course the receivers. To this end some tens of the SX861A rear projection and TX660A direct view experimental receivers were placed in the homes of mostly higher Philips management and local dignitaries. That both types of receivers were deployed is reported in an article in Radio Wereld on April 8, 1948, quting:
"The receiver models shown consisted of two models (one for direct viewing on the front of a cathode ray tube, and one with projection) are no devices made in a laboratory, [but real production sets]." The actual number produced differs, however, some sources saying 20, others 75. People with a receiver set were asked to fill in questionnaires about both the system, perceived performance as well as feedback on the programs.
Next to the officially distributed Philips receivers quickly a serious number of radio amateurs started building experimental receivers, and the PET receptions were received up to 150km from Eindhoven. During a big electronics show in Groningen in November 1948 the PET transmissions were received too, a distance of 220km. Very quickly circuit diagrams and instructions for home-built receivers were published in e.g. the "Electron" publication of Veron, the Vereniging for Radio Amateurs in Nederland.

Philips Protelgram, 1946-1949

The optics of the Philips Protelgram, essentially identical to the Schmitt-optics module developed by Research for the SG860 and SX861 TVs. [Philips-Norelco Protelgram 160 Service Manual]

But Philips didn't invest in all these developments just for fun or for the love of science; it wanted to do business. The first opportunity seemed to be the US. There television was booming since its introduction in 1943. Per month some 10.000 sets were produced, which were for a large part based on projection concepts similar to the one developed in the NatLab for the Philips 567-line system. But one of the main advantages of the 567-line standard was the synergy with the 525-line NTSC system, from which it was derived. The optical engine of the SG860A/SX861A receivers presented earlier could therefore be used with only minor adaptations in an NTSC television receiver. (The MW6-2 picture tube was registered in the US as 3NP4). Already in 1947 it was thus decided that the optical engine would be produced in the US under the name "Protelgram" and sold by the local Philips organization Norelco. A production facility at Dobbs Ferry (New York, since 1943 the Philips US headquarters)) took up production, and in 1948 Norelco started promoting its projection television module. Because at the time Philips didn't have its own television manufacturing organization in the US, only the optical engine plus its 25kV supply was sold in different versions as the Protelgram unit; Model 161A for 13x10"displays with rounded corners, Model 160A for 16x12" square displays, and Model 162A for movie-type projection on large screens. It needed be combined with a regular television chassis for signal reception and the deflection signal generation. The unit was used in amongst others the Scott 6T11A and Emerson television sets. From the Protelgram Service Manual as well as the 1948 Norelco advertisement it can be seen that the box is almost completely identical to the one presented in the Philips Technical Review in the same year. This means that the Research module was taken almost directly into production, which has proven over again to be a very risky approach, because the product had not been properly engineered. The same was true with the Protelgram module, and the production in Dobbs Ferry experienced many serious manufacturing issues, limiting the output of the fab to only 200 units per week. As a consequence customers massively cancelled orders, creating a serious business crisis.

The two modules that jointly formed the Protelgram function sold by Philips-Norelco: on the right the (dis-assembled) optical projection module, on the left the 25kV high-voltage supply box. [Philips-Norelco Protelgram 160 Service Manual]

The more fundamental killer of Protelgram, however, was not the complexity of the design, but the development of larger direct view picture tubes. Especially RCA, as the largest US TV player, invested in picture tubes with wider deflection angles. In 1946 it had introduced the 10BP4 10" round picture tube with a 50 degrees deflection angle. In 1948 the slightly larger 12" 12LP4 was introduced and in 1949 the 16" 16GP4. In 1946 most television models were still rear projection (with systems similar to the Philips Protelgram), in 1948 the mix rear projection-direct view was already 50:50, but by 1950 almost all RCA sets were based on the 16" direct view picture tubes.

This didn't go unnoticed to the Philips management. On March 5, 1948 ir. J.A.J. Bouman, head of the HIG Apparaten, sent the following alarming telegram from the US to his colleagues in Eindhoven:
"Try to stop development work broadcast-receivers and concentrate all efforts on television stop Television is our biggest chance stop Protelgram is all-right but we have to work on follow up like hell! stop Write on all doors and walls and blackboards TELEVISION stop Make everyone television crazy stop We have enough people to do the job but most of them work on the wrong items stop There really is only one item: TELEVISION stop The only actual television front we have at the moment is right here in U.S.A. stop
We are able to force it if we are ready to fight AND TO KEEP FIGHTING! stop Mobilise Eindhoven please stop No time to lose TELEVISION IS MARCHING ON HERE AND FROM HERE OVER THE WHOLE WORLD stop The only question is: WHO MARCHES ON WITH TELEVISION, PHILIPS OR THE OTHERS? stop THE OTHERS ARE ALREADY MARCHING! PHILIPS EINDHOVEN, TAKE THE LEAD ! fullstop''

For all clarity, in his telegram Bouman, when referring to "Television", meant direct viewing picture tube-based receiver sets. Although some people involved later disputed the decision was only due to Boumans' telegram, fact is that a rapid switch-over started to steer development activities toward direct view television. This is where the HIG Elektronenbuizen comes in, which fortunately had started work on picture tubes already.
The Protelgram situation didn't improve much, while the television-lobby also started to work against its concept. After 2,5MioHfl investments, a considerable sum at the time, the Philips Board took its losses and decided to stop Protelgram in September 1949. However, concepts can be persistent and we'll see rear projection television coming back later.

The Radiobuizen-Lab

The development of television was tightly linked to the development of new valves. All post-war Radio Valve activities within Philips were concentrated in the HIG Elektronenbuizen (Division Electron Valves) initially led by Dr. Theodoor Tromp (1903-1984), until he became member of the management board of Philips. Also in the Philips Board remained the "patron" of the radio valve division. This included all manufacturing plants but also the valve development in Eindhoven. From 1946 onwards this was done in the Radiobuizen Lab, located on the 3rd floor of the "Witte Dame" (White Lady) building along the Emmalaan in Eindhoven. (The building still stands in almost perfect condition, although no longer owned by Philips. It now houses the Eindhoven City Library, the well-known Design Academy and apartments). Originally the activities had been split into two groups, the "Proefafdeling" (Sample Department) which was able to prototype all new valves, and the "Elektronisch Laboratorium" (Electrical Laboratory), responsible for specifying the valves, measuring them and making application reference designs. Since 1946, to improve the up till then notoriously bad co-operation, these two groups were combined into the single Radiobuizen-Lab organization under ir Gerrit Alma (1902-1997). Alma worked with Philips on the development of radio valves since 1929, and was one of the leading and most experienced managers in this domain. He seems to have been a very pleasant person, nice to work for, totally non-political and good for his departments. Under Alma were two dedicated labs: Radiobuizen Lab 1 with a focus on valve definition and their application, and Radiobuizen Lab 2 under ir. G. van Beusekom responsible for the valve design and engineering.

Under Alma the Radiobuizen-Lab continued to grow, hiring engineers that were to play leading roles in the coming developments and the further growth of the valves business. One of them was ir Klaas Rodenhuis, a young Delft graduate who joined Philips in 1941 and would later lead the Professional Valves section of the Radiobuizen-Lab 1, before moving to Hamburg in 1959 to become head of Philips-Valvo. A second was Dr Bert Dammers (1910-1968), who started at the NatLab Research in 1937, almost certainly working in the group of Jonkers. Around 1946 he was asked by Tromp to join the Radiobuizen-Lab 1 to lead the Consumer Valves section in Alma's organization. Dammers was to become the expert in valve-based application circuit design, and at the same time also the person defining combination valves, to optimize the application with the minimum number of valves. Between 1948 and the mid 1950's Dammers published large numbers of application notes, publications and book chapters related to valve applications, especially in the emerging television receiver domain. He also had very good relations with the valve engineering teams in the factories, as well as with the set development organizations of the HIG Apparaten in the many different countries where Philips was active. It was often Dammers who made the road trips to the different countries to explain the latest television valves and application trends to both the internal organization as well as set making customers of the valve sales organization, often talking to large audiences.

[Most of the data on the Radiobuizen-Lab organization in above section is based on the research of my friend Ronald Dekker, also a valve aficionado and creator of the by now famous DOS4ever valve tester.]

Dammers in turn hired young assistants for much of the practical work involved with valve and application measurements. And one of them was my father, Piet Hooijmans (1918-2006). While working in Amsterdam as telegraph operator for the Dutch PTT on the long-distance connections, he had finished a professional training in electronics. Since Philips was expanding and could not find sufficient engineers locally in the province Noord-Brabant, there was quite some advertising, to which Piet reacted. He was invited to Eindhoven for interviews in February 1947, a very harsh winter and it took quite some effort and time to reach Eindhoven. But apparently the interview was successful, because on May 1st, 1947 he started in the Radiobuizen Lab 1, working for Mr Dammers.

It looks that the Consumer Valves group worked essentially on three applications: radio receivers (mainly AM but with FM reception in development), amplifiers (for microphones, record players and later tape recorders) and television. From the available reports it seems that the application activities were exclusively using the E40 Rimlock series of valves up till end of 1948 or the beginning of 1949, at which moment a new series of Noval E80 and P80 valves was released. The Radiobuizen Lab application notes then also switch to the Noval series. Regularly articles were published in the Electronic Application Bulletin (EAB) of the HIG Elektronenbuizen, introducing new valves in combination with recommended circuit applications. The consumer group and its valves will play an important story in the coming story on the development of television. In parallel the professional group of Rodenhuis worked on such valves as thyratrons, X-ray, RF transmitters, gas filled switching valves etcetera.

Dr Theodoor Tromp, in 1946-50 head of all Philips Radio Valve activities.

ir Gerrit Alma, head of the Radiobuizen Laboratory.

ir Klaas Rodenhuis, leading the Professional Valves group in the Radiobuizen-Lab.

Dr Bert Dammers, leading the Consumer Valve group of the Radiobuizen-Lab. All above pictures courtesy Ronald Dekker.

Piet Hooijmans, young assistent engineer in the Consumer Valves group of the Radiobuizen-Lab.

A few impressions of the Radiobuizen Lab in the Witte Dame on the Emmasingel in Eindhoven, probably from the early 1950's. Technicians wear a tie and white work jacket, bosses a suit and tie, which probably means that my father also walked around in such a white jacket. We see the engineers work on TV reference designs, which are built using folded metal frames with all large components (transformers, filters, all valves plus the picture tube) mounted on the top side, and all discrete components wired inside the frame. The same concept was used for the home-built TV's! [50 years Philips System Lab Eindhoven, 2002, via Oswald Moonen]

The "Witte Dame" (White Lady) building along the Emmasingel in Eindhoven, where the Radiobuizen Laboratory was housed on the 3rd floor. With the exception of the wall around the complex and the square brown building on the right picture, not much has changed on the look of the building, and today it is still as impressive as it was in the 1940's. [Ronald Dekker -DOS4Ever]

New Rimlock valves for television

Since 1946 the HIG Elektronenbuizen had been working hard on the roll-out of a new generation of radio valves: the Rimlock 40-series. Their main advantage was a much smaller size, pre-dominantly due to the new low-temperature all glass assembly process. Two major elements allowed this shrinking: 1. a method was found to have metal leads protrude through a glass footing without loss of vacuum inside the valve. This allowed for much smaller valve foot dimensions, which were standardized in the Rimlock base with eight pins equally spaced on a circle. 2. low temperature glass welding. This allowed the internal electron assembly to be mounted on the inner parts of the pins, where-after the glass encapsulation could be welded on the glass base plate at relatively low temperature without damaging the sensitive electron assembly. Philips used three standardized base dimensions: diameters of 22mm (Series A), 32mm (Series B) and 36mm (Series C). Only the 22mm Series A valves were formally called Rimlock. The first products brought to the market were the the Ux40 valves, using 0,1A heater current. These were pre-dominantly used in the modern small form factor radio sets that could be used in countries with 110V, 220V or even DC supply. The Rimlock series was announced in a Philips Technical Review article in October 1946, by Alma and Prakke. First products were released in 1947.

The three all-glass tube series of Philips introduced in 1947: left Series C (EFF50), Series B (ECH21) and Series A (UCH41). [PTR 10-1946]

The first series of Rimlock valves that were released specifically for radio sets. From left: triode-heptode UCH41, RF/MF pentode UF41, diode-pentode UAF41, power supply rectifier UY41 and and 9W power pentode UL41. [PTR 10-1946]

Where the 1946 PTR publication was a typical research story, focussing on the technical issues of the all-glass valve, the Rimlock series was introduced by the Radiobuizen organisation in publications of their Electronic Application Bulletin (EAB) in October 1946, followed by an updated family overview in December 1948 "Survey of the "MINIWATT" Rimlock E-valves". By this time the family had extended to some 14 E-valves (plus another 10 U-valves), which grouped in a number of application sub-families:
a) RF valves, mainly for radio
     EAF41, ECH41 and EF41
b) other radio valves necessary to make a set
     EL41, a 9W 10mA/V power pentode
     AZ41 (directly heated full wave rectifier, the only Rimlock valve without filament)
It is expressly stated that these E-valves are equivalent to the already existing U-series equivalents.
c) new valves
     ECH42 variable mu oscillator
     EAF42 very similar to the EAF41 but with g3 accessible with a separate pin
     EBC41 diode detector plus 70x triode amplifier
     EB41 for frequency discriminators
     EZ40 90mA full wave rectifier with high filament-cathode isolation
d) new valves for amplifiers, television and measurement equipment
     ECC40 for push-pull amplifiers, 2,7mA/V, 30x amplification
     EF40 1,85mA/V LF amplifier with sharp cut-off
     EF42 high slope 9,5mA/V especially for television receivers
e) battery supply power pentode
     EL42 6W pentode with only 200mW filament current

All these valves (either as E- or U-valve) with the exception of the EL42 will appear in the television designs of the period. Two non-Rimlock valves that were used additionally were the ECH21 triode-heptode (which because of its 9 electrodes did not fit in the Rimlock series A base, and used the series B base) and the EY51 high voltage rectifier diode. The EY51 was used inside the high voltage supply for the picture tube anode and didn't have a classical base. At the bottom two wires (cathode and heater) and at the top one wire (the anode) protruded from the glass bulb, which could be soldered with very short contacts.

The evlution of the pentode. From left to right the AF2 (1934), AF3 (1935), EF5 (1936) and EF41 (1947). [Radiomuseum]

The EA40 high voltage efficiency diode, one of the very first Rimlock valves.

The EY51 high voltage rectifier, without a classical base but only metal wires protruding from the glass bulb.

The MW22 picture tube

The last, but very important valve, was the picture tube. So although the focus of Philips television developments was on rear projection using the MW6-2 high intensity projection tube, the Elektronenbuizen division had been working on a direct view larger picture tube. Surprisingly this development had started already well before the war! As it seems Mullard, the London-based UK subsidiary of Philips which was acquired in 1927, developed a first 9"/22cm picture tube as early as 1938. This tube, the MW22-1, was used in the 405-line UK television system, both the Philips models 2405/07/12 from 1939 as well as e.g. the Pye televisions models 815 and 838. Mullard was sailing a quite independent course from the Eindhoven headquarters, and in contrast to the formal doctrine on projection television believed much more in the direct view concept. This concept was industrialized by RCA together with the glass-making company Corning. They had invented the concept where a metal cone could be welded to the curved glass front section. This required two technology steps: glass moulding and the glass-metal connection. Mullard probably licensed the technology and bought the sub-components (the moulded glass front plate and the metal cone) for assembly in its own valve factory.

Essentially there are two generations of MW22. The first one was the pre-war version, with a "hexode" electron gun assembly and a 5kV anode voltage. This assembly required a fairly high grid voltage of -60V (maximum light intensity) to -80V (black). The grid capacitance was still high at 13pF, limiting the bandwidth of the video signal.
The second generation, developed after the war, used the same glass balloon shape and dimensions, but had a re-designed internal constructions, of which apparently 2 existed. The MW22-3 had a "triode" electron gun like the MW6-2 projection picture tube, and although this tube was used in at least one UK television set in 1950, this doesn't seem to have become the standard solution. That was the concept as in the MW22-7. It had an improved electron gun assembly with less than half the grid capacitance (6pF), a much lower gate driving voltage (-11 to -35V) and higher brightness due to a higher anode voltage (7kV nominally, 9kV max). It used the same parallel 6,3V heater supply as the other Ex40 Rimlock valves.

The Philips Miniwatt MW22-3 22cm screen size magnetic deflection picture tube as it was shown in the official specification leaflet.

The MW22-7 came available in 1947, and was for the coming 2 years the standard picture tube in all Philips direct view television development sets. In parallel it was of course sold in the UK under the Mullard brand and used in multiple television sets of Ferguson (model 841T), Bush (model T91) and Pye (B16T and D16T), mostly sets introduced in 1948-49. Where the MW22-7 had the parallel 6,3V heater supply of the Ex40 series, the MW22-14 introduced 0,3A serial heater supply equivalent to the Ux40 series.

In parallel to the MW22 series also the MW31 was developed, with a 64 degrees deflection angle and a screen width of 31cm (12"). The story on its development, sub versions and availability is almost identical. Because the 31cm tube was certainly more difficult to produce, its actual application lags the MW22 by roughly a year. Also the first versions of the MW31 were already available before the war, since the 1939 models 2409 and 2415 used this 12" picture tube.

With this picture tube Philips now had all valves available to design direct view television receivers.

TX380, television sets based on the new Rimlock valves, 1948

At this time, we write end of 1947 to early 1948, matters become more complex. Philips is rolling out its limited scale NatLab-based 567-line experimental system, Protelgram is being introduced in the US, the UK television roll-out is picking up speed and needs Philips solutions, and in France Philips also wants to have sets that can receive the Eiffel Tower 819-line transmissions. After the initial work by the NatLab research, the centre of gravity needs to move to the HIG's. Two organizations therefore scale up television set development:

HIG Apparaten, which focuses on actual television receiver development. Central television development is in the Apparaten Lab (from here on AL, where "Apparaten" can best be translated by Devices) on the Strijp complex in Eindhoven, but in the big countries local development groups are active too. Especially in the UK, where the Philips subsidiary Mullard had a television development and production site in Mitcham. The official policy was that the platforms should come from Eindhoven, for local industrialization in the satellites. Not surprisingly the local "satellites" didn't like that concept.
HIG Elektronenbuizen, which focuses on reference designs of the new valves that are being developed and released. These developments, both of the valves and the reference designs, take place in the Radiobuizen Laboratorium (RBL) on the Emmasingel in Eindhoven. This organisation didn't suffer from the multi-site structure of the HIG Apparaten, but in turn doesn't produce sets themselves, so always needs to "sell" their concepts to HIG Apparaten or third party customers. Or phrased more bluntly: the reference designs of the Radiobuizen Lab are not necessarily taken into production.

In these two organizations essentially parallel tracks of television chassis developments took place, with a lot of exchange for system optimization. It is known that Bert Dammers, the head of the Consumer Valves group of the Radiobuizen Lab (the boss of my father) had a very good relation with the Apparaten Lab groups, and this resulted in regular introductions of circuit optimizations based on new valves. In the following I've tried to re-trace the main television platform developments up to the first volume sets. This is based on the use of valves and their functional circuits, on the naming of the products and on the date of publication of circuit diagrams or service documentation. Especially the Philips product naming convention is very helpful, since it indicates the year of design (see below explanation of the product codes).

The massive Apparatenfabrieken for radio and later also television manufacturing on the Eindhoven Strijp-S complex [Inoudeansichten.nl]

In the centre the not yet white painted "Witte Dame" building, housing the valve development and the Radiobuizenlab. The large brown building on the right is the Philips headquarters, the buildings behind the Witte Dame are mainly for light bulb manufacturing. [Pinterest]

It must have been around 1947 that real television product development started in earnest. As we will see later, it is highly likely that the Radiobuizen Lab and the Apparaten Lab really combined all their knowledge to define a state-of-the-art television platform based as much as possible on the latest and most compact valves available. Here the first subtleties came in.

The HIG Apparaten logically wanted to have product platforms that could be used in as many countries as possible. This involved flexibility in not only the television standards, but also the power supply, which still varied across countries between 110 and 220V, 25 and 50Hz and AC or DC. To create this flexibility the use of power supply transformers was avoided whenever possible, which meant that the 6,3V heater supply for E-series valves was not available either. As a consequence all AL-designed sets used U-series valves for serial heater connection at 0,1A current. So the Apparaten Lab set itself to designing a TV platform based on the valves they were using already for radios: the UF42, UAF42, UB41, UL41, UCH42 and UY41. The only dedicated television valves were the ubiquitous EA40 efficiency diode, the UL44 line/frame time base output amplifier and the EY51 high voltage rectifier.

The RBL in contrast focused on the application development, and although they made reference designs of complete sets they didn't focus on the power supply. In fact in the RBL they used standard power supply bench units supplying 250V and 6,3V, and the prototype units did not contain the power supply. See e.g. the reference design AM/FM receiver on the EQ40-page. As a consequence RBL reference designs always were based on E-series (6,3V) parallel heater supply valves. These designs were essentially the latest television design but with new valves inserted for performance optimization or valve count reduction. Examples are the EQ40, ECC40, EZ40 and EL43. It will be interesting to see which of the new valves of the RBL actually ended up in production televisions.

The naming convention of Philips Television receivers 1945-1950

Starting from the second half of the 1940's the television receivers of Philips were coded as follows: TX123A/00
1st letter: always T for Televisie (Television)
2nd letter: country code of the production (!) facility

X=Netherlands & Belgium
D= Duitsland (Germany)
F= France
G = Great Britain
I= Italy
W= USA

1st number: luxury/feature level

This was roughly
1 /2= low end, 3/4= standard, 5/6=luxury, 7/8= high end, often multi-function, 9 = top models

2nd number: year of development

the last digit of the year of development (not commercial introduction!); so e.g. 1947 gave 7

3rd number: product identifier

first product was 0, if next products were developed in the same year they obtained successive numbers

3rd letter: power supply

multiple options, including batteries and accumulators, but for early televisions the two relevant ones are:
A = mains AC supply only
U = universal mains, AC and DC possible

Suffix (two digits)

many different combinations. On the early sets these are seen:
00 = the basic first release
01, 02, ... = set upgrades/retrofits
15 = UK, 29 = French version, 68= Argentinian version etc.

This coding system survived for most products till around 1966 (!) with only few modifications/additions to accommodate the growing product diversity: when codes threatened to repeat (esp. due to the design year number after one decade) the 2nd letter and 1st digit were swapped. This happened mostly with Radios.
Not surprisingly the UK did not comply with the system since the letters TG were omitted (e.g. 383A being the first UK TV set).
Secondary brands always used modified product codes: Mullard TV was MTSxxx with xxx the Philips code plus one; Radiola in France initially inverted the Philips number (TF651A became RA156A).

Although started in 1947, the first television designs were ready in 1948, and thus the first generation televisions was coded as TX380 (with the 8 referring to product release in 1948). It is interesting to note that according to the product naming system the first digit 3 indicates it was positioned as a standard product, although given the price (85.000 old French Francs at the time) it could be considered a quite expensive product. All the more so because the product leaflet suggests the set also contained a full three-band radio receiver. The most logical explanation is that the screen size of 9" was already considered on the low side. For actual market introduction the most urgent version was for Great Britain (405-line system), the next France (still the 441-line system transmitting in Paris) and next the support of the fledgling Dutch (567-line system). The first market to introduce commercial TV sets for Philips was the UK, with the 465A and 565A launched in 1947, and their 1948 derivatives the 663A and 383A, as discussed in an earlier section. So next was a set for the French 41-line system.

The TF384A as it was called was the first to be based on the new Rimlock valves, with only the UCH21 and EY51 from another series. The design was based on the latest Philips valves and television reference design as used in the Radiobuizen Lab and Apparaten Lab, and it was apart from minor details identical to the RBL2 and the first TX594U designs. Because the latter two were designed for 567 lines instead of 441 lines, the TF384U could do with one IF amplifier less. And of course it didn't have an FM-based sound branch. Which brings us to the biggest oddity of this set: the sound concept. Here we have to realize that the TF384U was the last TV that was designed from the onset to deliver both television and multi-band radio reception. Using an existing radio chassis as e.g. in the UK sets was not possible due to the higher cost as well as the size constraints of the new table model cabinet. The unique solution was a sound branch integrated on the main chassis but electrically completely separate from the video branch. The receiver could be switched to radio or TV, where the TV sound IF was a unique low 1,5MHz. The video IF in contrast was the highest used to date in any Philips TV, 25,75MHz, which was almost certainly the same IF as used in the TX594U (27,5MHz) adapted downwards for the 441 lines. All in all this made the TF384A a unique set, as far as known this concept was not re-used in any other Philips TV.

Block diagram of the Philips TF384A television set for the French 441-line standard. Designed 1948, on the market 1949.

Drawing of the 1948 TF384A, showing the radio receiver dial plate at the bottom. This set was probably only produced in very small numbers, if t all. No survivors are known. [Philips leaflet via Radiomuseum.org]

The French model TF390A with its 9" screen. This set was first produced in 1949 in Eindhoven as the TX390/29 and exported to France, but then transferred to Suresnes for local production as TF390A. [Musée du Radio RTF]

TX390 upgraded platform, 1949

As described above, 1948 was the conversion year from the very first post-war chassis to the new Rimlock-valves state-of-the-art platform. The Mitcham 383A was still based on the old EF50 and E30 valves, while the TF384A indeed used the new valves but in combination with an immature sound chain. The 1949 TX390 chassis was the first entirely based on Rimlock valves, and the first to discard the concept of "TV is radio with pictures" and therefore the need to always have radio reception too. Furthermore, and strategically most important, the same basic platform was used for all three European TV segments: UK, France and the emerging proprietary 567-line Philips standard. A few of the main innovations of this new chassis were:

The new sound chain architecture, that would remain the standard for the coming years, was introduced. Here the RF mixer-oscillator performs down-conversion of the entire TV channel, so picture and sound simultaneously, resulting in a combined picture-sound IF. These are then split into the video and sound IF chains for separate filtering, amplification and detection. Of course the UK and French sets used AM sound detection, the 567-line chassis FM sound detection.
The last UCH21 was replaced by the UCH42 for frame and line time base oscillators.
In general a very limited set of valves was used: UF42 RF/IF amplifiers, UAF sound IF amplifiers and detectors, UB41 video detector, UL41/44 power amplifiers for sound, video and both frame and line drivers, UCH42 as time base oscillators plus the by now standard EA40 efficiency diode and EY51 high-voltage rectifier. As we will see this was the result of the intense cooperation between the Apparaten and Radiobuizen Labs.
The IF values were reduced back to what they had been before the TF384A: VIF/SIF of 13,0/9,0 (441 lines) or 13,4/9,9MHz (405 lines). The exception seems to have been the TX594U, which maintained the high 27,5/23MHz. Note that in both cases the LO frequency was below the RF, given that the transmitted sound carriers were also below the transmitted picture carriers. So for the French receivers of the 46MHz Paris Eiffel tower transmitter the LO was at 46-13=33MHz, for the UK Alexandra Palace 45MHz transmitter the LO was at 45-13,4=31,6MHz;
The chassis now consistently introduced a noise suppression circuit between the video detector and synchronization splitter, allowing better reception in case of weak or disturbed signals. This concept was first implemented in the 383 in a more experimental way;
With the serially fed heater supplies in the U-series valves there was no need for a supply transformer, and sets became fit for both AC and DC power supply, thus receiving the suffix U (for Universal supply).

The RF-IF line-up of the TX390, with B9 an UF42 pre-amplifier and B10 an UF42 self-oscillating mixer-oscillator. At the output of th mixer the sound-IF is immediately separated through S14-C69, thus reducing the bandwidth requirements for all following stages. This architecture would be the bases for the next two years.

Block diagram of the TF390 441-line set for France. Designed 1948, commercially launched 1949. First implementation of the new all-Rimlock architecture with the new standard sound IF chain. The TF402A, introduced one year later, was identical except for the new 31cm picture tube and two valve upgrades.

From this platform three first products were derived:

The TX390 and TF390 for the French 441-line system, followed by the TF402U and 502U later;
The 385A, 485U, 683U and 492U for the UK 405-line system;
The TX594U for the proposed 567-line system.

The French set was developed in Eindhoven, and initially also taken into production there as the TX390/29, with /29 indicating it was targeted at the French market. In fact this must have been the first real production TV set produced in the Eindhoven Apparatenfabriek. It seems this nice and compact set was not unsuccessful in the French market, since production was subsequently transferred to Suresnes, with the product becoming the TF390. This chassis was the last to be released with the MW22-7 picture tube, the newer designs introducing the MW22-14 for serial heater supply.

The audio chain of the TX/TF390 for standards with AM sound. B5 and B6 are UAF42's, B8 an UL41 power pentode. Note that the diode of B5 is not used. The diode of B6 takes care of AM peak detection. The detected signal is, after volume control with R24, fed to the pentode section of B6.

TX594, the first 567-line set, 1948

The next challenge was to develop from the same chassis a Dutch (and of course potentially European) version for the 567-line standard, with its higher line rate, higher bandwidths and FM sound standard. The official documentation has a first release date 24-7-1948, so design must have started end of 1947 with the deflection and high-voltage design clearly based on the TX380 platform, but already implementing the sound chain improvements of the TX390. However, although we know there was a design in July 1948, we don't have the details on it (yet), only those of a much later 1949 modification that will be discussed further down. The block diagram can thus only be speculated, but would most probably look as follows:

The block diagram of the first release of the TX594U for reception of the 567-line experimental PET transmissions. This block diagram is not 100% confirmed, but based on comparative analysis with TX380 and TX390 platforms adapted for FM detection.

Most remarkable is the fact that the FM sound detector does not yet use the EQ40, as recommended by the Radiobuizen Lab, but a classical Foster-Seeley detector based on a UB41 double diode. Because of the low detection gain this requires an additional UF42 sound amplifier before the power amplifier. Furthermore the TX594 seems to have introduced the much higher IF at double the value used so far: 27,5MHz VIF and 23,0MHz SIF. As already mentioned, the TF384A was the first to use these values in the first Philips commercial set for France. With three power rectifiers UY41 the total number of valves came to 23, the highest number of any direct view television set of the first generations. Around 150 pieces were built of the TX594U and distributed throughout Eindhoven, probably replacing most of the SX861A research sets that were called back. A number of sets might have gone to Denmark too, which was the only country opting for the 567-line standard. Philips supported local test transmissions in Denmark by supplying transmitter and receiver equipment. For reasons not entirely clear, the set, which was of the same design as the earlier TF384A, received the nickname "Hondje" (Doggie). Nevertheless, even despite the low volume, the TX594U will be in the annals of history as the first (almost) commercial television set in The Netherlands when it was launched end of 1948.

Philips TX594U, receiver for the 567-line Philips standard, as produced end of 1948 for reception of the Philips Experimental Transmission TV. Note the rather unusual reclined position of the picture tube. [Technisch Museum]

Backside of the TX594U. Note the high quality polished wooden housing, standard for TV's of the time. [Beeld en Geluid]

The last sets of the first generation, 1949

During 1948 and 1949 the TX390 platform was used as the basis for a number of last new products: the 385U for the British market, and the TF402 for the French market. They had 18 and 19 valves, respectively, and were based on the same platform architecture with only minor valve upgrades:

The most remarkable of those was the replacement of the good old EA40 efficiency diode, the very first Rimlock valve, by the more powerful UY41 that had already been used as power supply rectifier;
In the British sets the UL41 power pentode for the video and frame outputs was replaced by the UL46, a short-lived valve that was only used in the UK;
The British sets dropped one of the UAF42 sound IF amplifiers;
The British sets featured a video noise limiter for better reception under low signal conditions. For this half of the UB41 video detector was used;
As in the TX594U the UL41 video output amplifier in the TX402A was replaced by a lower power UF42.

One of the landmarks of these sets was the introduction of a new 12"/31cm picture tube: the MW31-14 or -17, giving an almost twice larger image. As we've seen earlier at roughly the same time this picture tube was used in the 663A, an old platform chassis. These tubes had the same characteristics as their MW22 predecessors, and didn't require any electronics changes. The 485U and TX402A both used the 31cm tube, later followed by the 683U. In parallel the 22cm picture tubes migrated to the MW22-14 and later -17.

And this in turn illustrates a next step in the growing maturity of the product: based on the same platform multiple models with different selling prices were introduced, especially in the British market where volumes were highest. In 1949 the 385U (mid end table top 9") and 683U (luxury console 9", also sold as the Mullard MTS684) were introduced, along with the 484U (mid end table top 12"). In 1950 the 492U followed (mid end table top 12"). In relation to the British market it should also be noted that in December 1949 the second transmitter station was activated at Sutton Coldfield near Birmingham, serving the Midlands. While Alexandra Palace in London was transmitting at 45MHz (picture, sound at 41,5MHz), the Birmingham transmissions were at 61,75/58,25MHz. Since the sets still did not contain a tuner, each television needed region-specific alignment of the RF-coils, and the set required modifying for receiving the other transmitter. Extensive change-over and alignment procedures are part of the Service Manuals.

With these products the TX390 platform came to the end of its (design) life, and no further derivatives were developed. Started in 1947 it had served its purpose, releasing the first sets in 1948 and establishing Philips as an emerging television player in the UK (through its Mullard branch), France and even The Netherlands. All television receivers launched in 1948-50 were thus based on this platform.

The interior of the Philips 385U 405-line set for the British market. On the right side in the back is the oil-filled high voltage unit with the two EY51's horizontally mounted on top of it. [Vintage Radio Forum]

The TF402A, the French version of the chassis and one of the first with a 12"/31cm screen. The 492U was the 405-line equivalent of the TF402A. [Antique-TV Blazianu]

Advertisement for the Philips 385U table-top model. [The Valve Page]

Block diagram of the British versions of the Philips TX390 television chassis: the 385U, 485U, 683U designed in 1948, introduced 1949 and the 492U from 1950. The sets were still single-channel without a tuner, so they had to be adapted for either London or Birmingham reception.

The variants of the 1949/50 UK television sets based on the 385U platform. On the left the 9"table top 385U, centre the table top 12"492U (identical to the TF402A shown above) and right the 485U 12"console model. [Philips Service Manual]

Backside view of the 492U TV set with the chassis partly removed. This is the 405-line UK version of the TF402A for 441 lines in France. [Restore by Matt on UK Vintage Radio Repair and Restoration forum]

Front-to-back top view of the 492U. On the right the RF-IF signal chain, on the left deflection and HV with centre-left the two EY51's on top of the HV transformer can. [UKVRR forum]

Back-to-front view of the 492U, with the picture tube mounted. The MW31-74 was never used in new TVs and probably a service solution. [UKVRR forum]

The last Philips TV model from the 1940 decade is at the same time a big question mark: the 799A. It was again a 12x16" (31x40cm) rear projection model, shown first at the 1949 RadiOlympia show, a large console also containing a full multi-band radio. Unfortunately no details are known so far, other than below pictures. The main question is which platform this chassis was based on: a late development of the SG860 original 405-line rear projection set from 1946/47, the TX390 direct view platform modified for rear projection, or a prototype of the Protelgram-based TX600 platform to appear in 1950. From the interior picture it looks like the high intensity display unit was not Protelgram, but without further documentation this is difficult to ascertain.

The Philips 799A UK rear projection TV in radio mode, with TV doors closed. [Early Television]

Rear interior view of the Philips 799A with upper left the radio, lower left the small signal chassis and right the deflection chassis and optics. [SSPL Prints]

The Philips 799A in TV mode, with opened door and control panel cover. Given the 30x40cm screen the total console size was around 100x100x40cm. [SSPL Prints]

Activities at the Radiobuizen Lab, 1947-49

While their colleagues at the Apparaten Lab were busy rolling out the TX380 and TX390 platforms and their British and French derivatives, the Radiobuizen Lab worked on the application of new valves. For this they used the latest AL platform as the starting point, based on which they would then change specific circuit blocks using the new valve. As mentioned when introducing the RBL they used - at least initially - exclusively the6,3V E-version of the Rimlock family.
The primary role of the consumer group (Dammers) in the RBL was to promote the application of the new Rimlock valves in consumer applications, which meant first and foremost radio, (record player) amplifiers and then the emerging television. As mentioned when introducing the Rimlock series the initial publication on the technical concept of the Rimlock all-glass base was in the research Philips Technical Review in 1946, but in the Electronic Application Bulletin (EAB) of 1949 the series was introduced on a practical application level. And since then there was a regular stream of specific valve introductions. The first one of these was on the EA40 efficiency diode for the line output amplifier and high voltage supply (EAB Vol.10 No.1 December 1948). The EA40 was in that sense successful, since used without exception in all first generation Philips television designs. The same was true for the EF42 and EY51, both designed specifically for television applications.

Normally it would be extremely difficult to trace back the activities of an organization like the RBL, but luckily I have three sets of schematics of television sets in the legacy of my father. These were the basis for the home-built televisions we will discuss in the next section. I have three of these schematics which I will call RBL1 to 3. They relate to the AL product designs as follows:

RBL1
This is a schematic dated 23-8-1948, signed by P. Huijser and titled "Schema van Televisie-ontvanger" (Schematic of television receiver). The concept is clearly based on the TX380, which was being developed at the same time.
Four different new valves were applied in this design:
- the EL43 power pentode, replacing the UL41. This valve never made it to volume production, and was superseded by the EL/UL44.
- the ECC40 dual triode, used in the frame and line time base oscillators, replacing the large and expensive UCH21.
- the EZ40 dual phase full wave supply rectifier. For this story the same holds as for the ECC40: a long career, but not in television sets. Cheap receivers would use a single EY/UY half wave rectifier, sets with full wave rectification mostly used the older but more powerful AZ50, which could handle as much current as three EZ40's.
- the EQ40 FM phi detector. This was clearly the most successful exercise of the RBL to get its reference designs adopted by the AL. In parallel to the RBL1 design the AL was working on the TX594U, their first FM receiver television set. However, the result - 6 valves - must have been considered disappointing, because the subsequent platform used the EQ40 design from the RBL. All details on the development and application of the EQ40 can be read here.
The main weakness of this design was the bad RF sensitivity, given that the antenna was directly connected to the hexode mixer input, with its intrinsically higher noise

From right to left the RF, IF, video detector, video amplifier and sync separator chain of the early 1948 Philips television platform in the RBL1 reference design. At the output of the 2nd EF42 the sound IF is tapped off towards the sound IF section. [Legacy Piet Hooijmans]

The most interesting from this list is the ECC40 as used in time base oscillators. In the same EAB edition as on the Rimlock series and the EA40 an article by J. Jager of the RBL discusses this double triode in time base oscillators with linearisation for feedback. One of the possible implementations in this article for a frame time base oscillator uses a transformer for feedback in what is called an intermittent or "squegging" oscillator, and invention by - who else - Bert Dammers, published in EAB of April 1946. This circuit is exactly identical to the one in the RBL1 reference design. Despite the RBL pushing the ECC40 in this role, the Apparatenlab apparently didn't follow them because they would move to the UCH42 instead in a blocking oscillator arrangement. The ECC40 had much more success in the amplifier and radio application, where at this time my father was working on. See e.g. the amplifier reference design report from Bert Dammers and Piet Hooijmans shown here, where the ECC40 is used as phase inverter in the single-to-balanced converter of a balanced push pull power stage with two EL41's. An article on this was published in EAB of March 1949. The ECC40 had a long and successful career of 10 years, including its professional variant E80CC. Interestingly there never was a UCC40 version.

The frame time base oscillator from the RBL1 circuit diagram, using a squegging oscillator with ECC40, the concept of which is hown in the right picture from the Electronic Application Bulletin. [EAB December 1948]

RBL2
This schematic is originally of exactly the same date and authorization as RBL1, but updated 3-3-1949.
It clearly bears resemblance with the TX390 platform, using the new two-stage RF input without the ECH42. And it also copied the synchronization separator from that design, replacing the ECH21 by the much cheaper EF40 (which is the only use of this valve in any of the schematics). The power supply also copied the powerful AZ50, replacing the three EZ40 power supply rectifiers.
Both the frame and line time base oscillators are still based on the ECC40, although the frame time base oscillator has been replaced by a simpler and more classical blocking oscillator. Although in the EAB article of Jager the "squegging" oscillator was presented as an improvement of the blocking oscillators, practical considerations have apparently led to falling back on the older and simpler design.

Given the date, early 1949, I originally considered the RBL2 as the then optimized design of a 567-line Philips-standard television, with 4,5MHz picture-to-sound carrier bandwidth and FM sound. With 21 valves it was an efficient design compared to the contemporary TX594U of the AL with its record 23 valves. Also compared to the TX390 for 405 and 441lines, the penalty for higher bandwidth and FM sound of only two valves should have been acceptable. It is then not unlogical to assume that this design would have been the basis for a real 567-line product development of the TX594U successor. However, as we will see next, the RBL2 design was almost certainly something else.

RBL2, the ultimate reference design for a 567-line television receiver based on Rimlock E-valves. [Legacy Piet Hooijmans]

RBL3
This an undated and unsigned schematic.
It is a receiver using the MW22-14, dating it to the 2nd half of 1948. It is - with the exception of the EQ40 - entirely based on U-series valves and has indeed most in common with the contemporary 385U and TF402A executions of the TX390 platform. It seems an effort to design a TV with minimal number of valves - 15 - which makes it a typical RBL activity.
This was achieved by a number of design tricks: one UF42 IF amplifier less than normal; no sound IF amplifiers; the triode section of the UCH21 used as peak detector; no separate line time base oscillator and only one EY51 booster. It all seems a bit too much squeezed out, and I have some doubts whether this set would have functioned properly. However interesting, I have no further traces of its application.

The Radiobuizen Lab RBL3 television receiver reference design with only 15 valves.

Based on their activities the HIG Elektronenbuizen published a continuous stream of application articles in their Electronic Application Bulletin. Most of these were a combination of introducing a new (Rimlock) valve and circuit optimization. The table below gives the overview, which shows that all new valves in the core of the RBL television reference designs were covered with a dedicated article: the EA40, ECC40, EF42 and of course the EQ40. Interestingly articles are not only from the Eindhoven RBL, but also from Mullard (Mr. Coxall) and the new Paris Lab (Mr. Chambes).

Television-related publications by engineers of the Philips Radiobuizen Lab in the Electronic Application Bulletin (EAB) of the HIG Radio Valves, 1949.

Test equipment

It is a bit of an excursion from the main story on television development, but it is nevertheless interesting to have a brief look at a side activity in the Radiobuizen Lab. Today it is hard to imagine with how minimal means the development teams of the day had to work. Only the most basic frequency generators, voltmeters and the oscilloscope were available. In many cases television sets could only be measured integrally using signals received off-air. Therefore it was e.g. very difficult to optimize a 525-line UK set in Eindhoven because there was no reception of British broadcast signals. Only around 1950 video test pattern generators appeared. Also in the Philips Electronic Application Bulletin regularly articles were published about new measurement equipment for the demanding new applications and circuitry. For example in EAB June 1950 was an article on "A simple oscilloscope for unit function response testing of networks", which was used to measure amplifier characteristics, ringing and filter responses. In later EAB articles measurements were referred to this equipment. Similarly in December "An instrument for recording the frequency drift of an oscillator" was presented. But these were only modest instruments compared to what came next; the valve tester and curve tracer.

Up till then valve testers were essentially voltage sources that could be applied to valve contacts to measure the anode current; nothing sophisticated. Operation was manual and analysing a valve took many readings. In order to speed up the analysis of the many new valves that were being developed by the Elektronenbuizen division, Dammers and his RBL team developed what looks like the first and most advanced automated curve tracer valve tester.

An article about this machine was published in the Philips Technical Review of April 1951, "The Electrical Recording of Diagrams with a Calibrated System of Coordinates" by Bert Dammers, van der Knaap and Uitjens, all three from the Radiobuizen Lab. For its time this was an incredible piece of test equipment, showing simultaneously on a cathode ray display multiple traces with fixed Vg steps, a calibrate horizontal and vertical grid and a movable cross-hair pointer to measure the exact voltages on specific points of a trace. It contained a stepped-pyramid voltage generator for the grid, an advanced timer assembly to time-interleave the different signals to the deflection plates and of course the sweepers for the curve tracer. The total device contained a stunning 200+ valves, making it almost a analogue mini computer avant la lettre. It is a clear illustration of how creative Dammers and his Radiobuizen Lab team were.

Front view of the curve tracer and valve tester. The engineer is looking to the cathode ray screen through a viewing cap. The large displays above are indicators for the cross-hair curve analysis. Each module was self-supporting, with its own power supply for easy replacement. [All pictures PTR 4-51 p.283]

Screen shots of the curve tracer while measuring the pentode section (left and center) and triod section (right) of an ECL80. All visible lines are displayed simultaneously, only the text is later added to the pictures.

Home-built television sets, 1948-1949

At this point we come to one of the most intriguing elements on this saga of early television development, and the original trigger for me diving into this: the home built television sets. As already explained, from March 1948 the Philips Experimentele Televisie (PET) was transmitting in Eindhoven, albeit for a very limited number of watchers. Originally some 20 SX861A research sets were handed out to dignitaries, towards the end of 1949 replaced or supplemented by some 150 TX594U's. As soon as the PET transmissions started amateurs all over the country started to build experimental home-built receivers, where it is not unlikely that quite some Philips engineers tried the same. Although it is so far not possible to trace back the decision, apparently the Philips management decided to allow some of its employees to build a television receiver at home, based on Philips components. There are strong indications this initiative originated from the Radiobuizen Lab, although it might later have allowed people from other organizations (Apparaten Lab and Research notably) to join. Piet Hooijmans, young RBL employee was one of them! Because the RBL1 schematic is the oldest in his files, I assume that is the one he started building on, which means the original set was built second half of 1948.

The home built activities were organized as follows. For efficiency reasons it was decided that everybody would work from the same reference designs; RBL1 as introduced above. Once an employee was allowed into the program he (there are no traces of she's in this story) would receive all material from Philips to build a TV according the design. This included, in order of material cost, all valves including the picture tube, the transformers and speaker, the passive components and the metal frame. Knowing the Philips culture, it was clearly not the intention that people worked on their TV during working hours, but after-work activities in the office were allowed. Most people - like my father -were unlikely to have all or any measurement equipment at home, and were thus forced to use the lab equipment. At least for Piet this shouldn't have been a problem, because he was still unmarried and - according to him - there was anyway nothing to do in post-war Eindhoven. The most complex part of the construction was the high voltage transformer, which was housed inside a metal can that was filled with oil (for isolation) and then soldered close. This was allowed to be done by the workshops during working hours. One interesting fact is the power supply transformer, number 7 in below picture. This is an extremely heavy component, in fact it creates quite some torsion in the entire set frame when lifted. This transformer was required in view of the 6,3V heater supply but also provided all other voltages. In Piet's notes it says "voedingstransformator (supply transformer) A3 161 21 app. SG860a" which suggests this is the same transformer as used in the SG860A receivers. An unexpected historical link!

No two home-built television receivers are of course identical. This one has a 22cm picture tube, a large HV cage covering the entire deflection unit, no loudspeaker and also the layout is different. [Private collection Jac Janssen]

Rear side interior view of the home-built television of my father Piet Hooijmans. Note the very high ressemblence with the official picture. [Private collection Pieter Hooijmans]

However, like so many activities started with the best intentions, also this one got out of hand. On March 2, 1949 Mr Alma, the head of the Radiobuizen Lab, issues below memorandum

                                                                               Radiobuizen Lab 1
                                                                               March 2, 1949

Announcement concerning the home building of television devices

Lately, some drawbacks have become clear related to the do-it-yourself construction of television devices.
A lot of working hours are spent on asking for and the giving of technical advice.
To avoid these problems in the future, it has been agreed that from on this technical advice will only be provided at defined time slots by defined experts.
The following gentlemen have declared themselves willing to act as so-called "television doctors":
Dammers
v.d. Knaap
Uitjens                       Tuesday and Friday 17.00- 17.30
Huyser
Cock
Everyone participating in the do-it-yourself project can address any of these doctors at the prescribed times for advice.
Furthermore it seems desirable to limit the period allowed for the construction of a device, e.g. half a year.
Only in exceptional cases it will be allowed to deviate from this, e.g. due to problems in component supply or illness.
Because the NV [Philips] has already supplied a considerable amount of material for the home built televisions, from now on, both for those already in the program but need new components for an extension, as well as for those who will start for the first time, permission will be required from undersigned.
Furthermore we beg the do-it-yourself people for considering not to disturb the workshops for trivialities like bolts and wires.
           In general, from now on no longer materials will be supplied for the construction of antennas, this will be limited to giving advice.

                                                                G. Alma

Draconic measures! The distribution list contains 36 names, including a number of managers. Although the majority has not been identified, they seem mostly from the RBL Fifth name from the bottom is NatLab group leader Haantjes, which might suggest some four researchers had joined the program. Al in all it seems some 25 people were already participating in the do-it-yourself television program. Including Piet Hooijmans on the fourth line (here erroneously written as Hooymans).

But apparently the first round of measures was not sufficient to get a grip on the program, because two months later Alma issued a second memo:

                                                                                      Radiobuizen Lab 1
                                                                                      May 11, 1949
                                                                                      Dr.A/EM

Additional announcement concerning the do-it-yourself construction of television devices.

From now on, as a rule only one new member will be admitted to the program each month.
The finished and under construction devices remain property of the NV [Philips].
Upon departure of a program member from the NV, the device should be handed in.
The program member shall, if necessary, allow the device to be at the disposal of the company for half of the time.
The device can be given on loan to the member for a period of maximum two years after completion; thereafter the member can opt to buy the device at a to-be-defined price.
Servicing of the device will be at the expense of the department.
Also for serious modifications of the device permission is required.

Eindhoven, May 11, 1949
G. Alma

It is beyond the scope of this page to dive into the details of the home built TV. In any case Piet Hooijmans finished its construction and got it all working, most probably towards the end of 1948. But he had it working and was allowed to take it home, where he invited two of his sisters to come over and watch the PET transmissions. When he left the Radiobuizen Lab early 1950 he was apparently allowed to keep it, whether he had to pay money as per point 5. of the last memo I don't know. But 67 years later the set is still in my possession.

What happened further with the program I don't know. But given the memo's it is not hard to imagine that it didn't live too long, and was stopped ultimately the introduction of operational TV reception in 1951.

Piet Hooijmans' home-built television set 1948-1949. [Private collection Pieter Hooijmans]

Continue reading Part.2 covering the years 1950-1955

References

See part 2.

Update history

First upload July 2017
August 2017
Added section on pre-war and immediate post-war UK sets as bridge to the SG860/SX861.
Re-written and extended the SX861 section based on all inputs from Jac Janssen.
Update block diagrams with some technical details (RF and IF frequencies, valve and semiconductor count).
Added table of content per page with clickable links to the chapters.
Added some nice pictures.
February 2019
I have come to the conclusion that for explaining the post-war developments it is necessary to understand the pre-war TV activities. After quite some extra research I've thus been able to re-write the pre-war section. As always many inputs from Jac Janssen.
Based on extensive analysis of the 1946-1949 post war sets and discussions with Jac, I have re-written these sections too, with a much more logical succession of the different sets and their inter-relation. Also corrected many errors related to valves used, IF frequencies, etcetera, so almost all TV block diagrams have been updated.
As a consequence I've given this chapter the new sub-title "1936-1949".
Many pictures added.
June 2019
Thanks to the site I was contacted by Edvard Paling, who's father Ton Paling started working on TV development at the NatLab in 1942. Edvard is also the owner of a (cannibalized) SX861A, but most interestingly also possesses a unique set of documents (circuit and assembly diagrams, parts lists) of the SG860A and SX861A, as well as the report in French promoting the 567-line standard and containing beautiful pictures of the Natlab SG860A prototype. His papers also gave the very first and so far unique confirmation of the 1947 "console direct zicht" receiver, of which Jac has a unique surviving example, which we've provisionally baptized the TX660A. Detailed analyses of this new data, together with Jac Janssen, has allowed me to further refine the sections on the SG860A-SX861A-TX660A sets.
November 2019
Have added interesting new details omn the 1936 Philips demos at the Berlin and London radio shows, based on articles in Wireless World from that year, I was pointed at by Peter Scott (who also has a nice page on pre-war TV).
Have added a few interesting pictures of the 405-line 492U which were shared on the UK Vintage Radio Repair forum.
March 2020
Tonino Giagnacovo from Rome, Italy, sent me a very interesting articles from the Italian magazine Radio Industria in 1939 and 1940. These contain the first detailed description of the 2400 TV family, the first direct view production chassis of Philips. This has allowed me to completely re-write a new section dedicated to this chassis. As a bonus he also included pictures of the early production of these sets in Monza.

Piet's Home-built TVorHow Philips developed Televisionpt.1 1936-1949