With so many overlapping and similar events happening not only in the US and UK, but at RCA, Westinghouse, General Electric and AT&T, writing this synopsis is a real challenge. That’s why, as this final part leads us into electronic television, I am only hitting the major events, and giving you links to fill in the glorious details. You will find them at the bottom of the page.

Surprise 1…We start with the first time the photo electric “eye” was actually put inside a light sealed box to make a television camera.

You can see that in the first photo (above), which is the AT&T “Direct Scanning System”. It was first demonstrated July 12, 1928 at the Bell Labs in New York, and was the first demonstration of outdoor television using sunlight and a scanning disc…something no other researcher had been able to do.

It was not revealed at the time, but the 50 hole, 3 foot disc system’s success was due to the new, Bell improved Case Thalofide photo electric cell.

On August 24, 1928, Philo Farnsworth gave a private demonstration of his all electronic system to Pacific Bell. The images on the
one-and-a-quarter by one-and-one-half inch blueish screen made images hard to identify, but the motion was easy to follow. Ten days later, he demonstrated it to the press in San Francisco. Reports were that “the basic principal of electronic TV had been proven and that perfection was just a matter of engineering”.

Surprise 2…Farnsworth applied for his first patent, which was on the Image Dissector tube January 7, 1929, but contrary to popular belief, he did not patent the first all electronic system. His patent did not specify a cathode ray receiving tube, as he was convinced that he could not patent such a basic device.

As I understand it, the real problem with Philo’s system was that due to some unlockable technical relationship between the Image Dissector output and the transmitted image, the size of the picture received was forever limited. That is, the only way to get a bigger picture on the receiving set was to massively increase the size of the Image Dissector tube.

Tests using a mechanical camera and an electronic receiving tube had been done as early as 1926 at Bell Labs, but half tones were not possible until improvements in the photo electric cells were made. That is why Bell’s Direct Scanning or Outside System was so important.

Finally in May of 1929, a 7” by 20” tube, fabricated by Corning Glass was given a willemite phosphor screen prepared by Zworykin’s group at Westinghouse. With it’s green phosphor screen, half of the goal of electronic television was accomplished. Here, half tones made a difference again, as part of the research Zworykin had done on the Westinghouse facsimile machine’s half tone transmission and reception was incorporated.

On November 13, 1928, Zworykin received an American patent on his improved all cathode ray television system. It was not until February of 1933 that RCA was able to demonstrate a fully electronic camera with Zworykin’s Iconoscope tube, which is shown below, with his recently developed spherical Iconoscope tube.
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At this link is a very thorough and photo filled article from Richard Brewster from our friends at the Early Television site.
http://www.earlytelevision.org/rca_story_brewster.html

Below is a video that takes us through the whole process…from Nipkow’s disc and Baird’s work, to Farnsworth and Zworykin. -Bobby Ellerbee

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