TELEVISION SIGNAL-GENERATING TUBES
R. J.. Reiman, Historian
Credit for inventing the first practical signal-generating, or pickup, tubes belongs to two electrical
engineers, Vladimir K. Zworykin and Philo T. Farnsworth. Zworykin's invention was the iconoscope,
which evolved into the imaging iconoscope, and Farnsworth's was the image dissector.
Vladimir K. Zworykin (1891-1982) was born in Russia as the son of an affluent ship-owning family.
He studied electrical engineering at the University of Petersburg where he became a student of Boris
Rosing, a pioneer in television picture tubes. Rosing disappeared during the Bolshevik Revolution
of 1917, but Zworykin was able to escape to the United States in 1919. He was employed by
Westinghouse as a research engineer, worked on the all-electronic television system, and was able
to demonstrate the invention of the iconoscope in 1923. The quality of the pictures, better than from
mechanical scanners, was poor, and funding was withheld until he received as audience with Sarnoff,
since Westinghouse was partly owned by RCA. Sarnoff, himself a Russian immigrant, listened to the
heavily-accented but impassioned description of the potential of the invention. "How much to develop
a successful tube?" was the question, and the answer of $100,000 was only off by $49,900,000.
Many Westinghouse engineers, including Zworykin, were transferred to the RCA plant at Camden,
New Jersey and Sarnoff promised financial support. Sarnoff purchased the Jenkin's Television
Company, maker of mechanical systems, in order to receive their patents. By 1932, Zworykin had
improved the iconoscope sufficiently to begin field tests. Although the sensitivity was low, it was
better than its competitor's dissector. A further improvement allegedly used an imaging section which
was similar to Farnsworth's dissector. After World War II, the image iconoscope, as the tube was
now called, was replaced by the image orthicon, a product of wartime research and this in turn by the
vidicon in 1954.
Philo T. Farnsworth (1906-1971) was born in Utah and educated at Brigham Young University where
he majored in engineering. He opened a radio store in 1926, displayed creative genius, and was able
to obtain financial backing. This led to his patent in 1927 of the image dissector. The image dissector
did not develop sufficient sensitivity to be more than moderately successful. Although never a
commercial success, its patent caused enough trouble for RCA that prolonged patent battles were
avoided by RCA agreeing to expensive cross-licensing agreements with Farnsworth.
Sarnoff was later to pay Farnsworth a gracious tribute before a Senate hearing: "It is only fair that I should mention this - an American inventor who I think has contributed, outside of RCA itself, more to television than anybody else in the United States, and that is Mr. Farnsworth of Farnsworth television system."