In a letter to the editor, IET Fellow Dr Geoff Towler refers to the ‘from the vaults’ feature on page 26 of issue 30 of Member News…
In this article Dr Towler redresses the balance and describes the individuals and their efforts in bringing the latest television technology to the 1948 London Olympics.
Tedham and McGee developed the Emitron around 1932.This was used at the opening of the BBC 405 line monochrome television service on the 2 November 1936. It was a vast improvement over the early Baird system that relied on a Nipkow disc. This mechanical device is feasible for low-definition television, (e.g. 30 lines), but is not suitable for higher definition because it has no storage and it becomes extremely inefficient. This is because it throws away most of the available light in the ratio of the pixel area to the total image area. Even for a 30-line system it can result in more than 99.9 per cent of the available light being thrown away.
The Emitron used a photoemissive storage mosaic, which enabled much more of the light to be used. Even so, the Emitron was not terribly sensitive and Gerhard Lubszynski developed a Super Emitron, by applying pre-storage gain in front of the storage mosaic. This achieved about a ten times increase in sensitivity and was first used on Armistice Day 1937. The Super Emitron enabled West End plays to be televised without any additional lighting. The first play to be televised from a West End theatre was ‘When we are married’ by JB Priestly in 1938.
However, both the Emitron and the Super Emitron did not achieve the theoretical sensitivity that should have been obtained by integrating the light over the entire frame period by means of the storage mosaic.
There was a second problem with Emitron and the Super Emitron of the pre-war period. This was a problem with shading of the image. Alan Blumlein found a solution to the shading problem by mixing into the video signal line and field electronic waveforms known as ‘tilt and bend’ signals to balance out the shading effects that could produce very non-uniform brightness in the image. This mixing had to be done manually by the ‘Tilt and Bend’ operator, who was usually a girl with alert concentration and acute observation.
Gerhard Lubszynski studied the scanning process in the Emitron and the Super Emitron and discovered that it was redistribution of electrons onto the storage mosaic that created the shading problem and the loss of sensitivity. This redistribution was the result of the camera tube operating in what came to be known as the anode potential stabilisation mode. Blumlein and McGee had filed a patent in 1934 to stabilise the photomosaic at cathode potential and preventing it reverting to anode potential by using a close spaced mesh at a low potential. Lubszynski had worked out the criteria necessary to achieve cathode potential stabilisation that would eliminate these problems by using orthogonal scanning in 1936.
Such a camera did not go into production before the war, and during the war the EMI staff were re-deployed for the war effort. McGee worked on infra-red imaging for night vision, and Blumlein, amongst other things, worked on H2 S radar. It was while carrying out airborne testing in a Halifax bomber on 7 June 1942 that Alan Blumlein was killed. A great loss in many fields.
When television started again after the war in 1946, production commenced on the new CPS Emitron. Unlike the Emitron that had the electron gun at an angle because of the reflective photomosaic, the CPS Emitron used a transmission photomosaic so that the storage photomosaic could be scanned orthogonally so that the cathode potential stabilisation criteria could be met.
The first is a photo from studio A at Alexandra Palace on the 2 November 1936 showing two Emitron cameras. Note the sloping of the case that accommodates the angled electron gun. The second photograph shows the Super Emitron camera with the case removed. The electron-optical image section can be seen as well as the angled electron gun. The main photograph, above, shows the new CPS Emitron camera at the Empire Pool Wembley at the 1948 Olympics. This shows that even at this first Olympics television broadcast, as has happened at every Olympics since, the television industry has always used the latest technology.
The CPS Emitron was first used on 20 November 1947 to televise the wedding of Princess Elizabeth.
Shoenberg demonstrated great boldness in 1931 at the height of the great economic depression by recruiting 114 engineers and scientists to engage in television research in the newly-formed EMI. The staff were engaged from some of the best laboratories in Europe, such as the Cavendish Laboratory in Cambridge, UK.
At the time, very similar work was going on at the Radio Corporation of America (RCA), but unlike Britain this did not lead to the setting up of a regular broadcasting service. There was, however, close resemblance between the Emitron and the Super Emitron with the iconoscope and the image iconoscope of RCA. It is probably not surprising that there are these similarities because Vladimir Zworykin who developed these camera tubes at RCA was a student in St Petersburg with Isaac Shoenberg. They were both students of Boris Rosing, widely regarded as the father of Russian television. His work was largely in mechanical television, but he did have an idea for electronic television.
Zworykin patented Rosing’s idea when he emigrated to the USA and first worked for Westinghouse. However, Westinghouse told him he was wasting his time, and he went to RCA after a chance meeting with David Sarnoff the founder.
EMI was formed in March 1931 by the merging of the Gramophone Company (HMV) with the Columbia Graphophone Company. Shoenberg was from the Columbia side of the business.
Alan Blumlein came from the Gramophone Company (HMV) the other side of the business to Shoenberg. He developed most of the 405 line television circuits and defined the video waveforms. Shoenberg gave Blumlein a roving commission within the EMI research laboratory. This gave him a legitimate reason to enquire about any research in any technological area. He was very prolific and filed a new patent on average every six weeks during his entire working life at EMI.
Gerhard Lubszynski was recruited from Telefunken in Germany where he was being persecuted by the Nazi regime. After his arrival in the UK circa 1933, the British government sent him to an internment camp on the Isle of Man as he was classed as an alien. It took Shoenberg some time to get him released.
James McGee joined Shoenberg from the Cavendish Laboratory Cambridge on 1 January 1932. He never intended to pursue a career in television research, hoping for something more academic. He had been a student of James Chadwick who discovered the neutron. However, it was in the midst of the depression and he took Chadwick’s advice, “I don’t think this television activity will come to much, but it is a job, and it will see you through the difficult patch, then you can start looking for a proper job.”
WF Tedham was the senior partner with McGee who developed the Emitron camera tube. Unfortunately the hectic pressure of work to meet the deadlines for the new television service caused him to suffer a nervous breakdown and eventually resign. He was, however, a very capable research worker.