The Farnsworth Television and Radio Corporation was founded in 1938 according to
http://en.wikipedia.org/wiki/Philo_Farnsworth "In 1938, Farnsworth established the Farnsworth Television and Radio Corporation in Fort Wayne, Indiana, with E. A. Nicholas as president and himself as director of research." Also the same Wikipedia web-page states "Farnsworth Television and Radio Corporation was purchased by International Telephone and Telegraph (ITT) in 1951." There is an 1943 magazine advertisement for a similar Image Discector
http://www.earlytelevision.org/image...ector_1943.jpg So I would think early 1940s on your tube would be a close date? You can download the Farnsworth book that Wikipedia cites as reference at
http://www.earlytelevision.org/pdf/s...00everrich.pdf