Chromatron

The Chromatron is a color television cathode ray tube design invented by Nobel prize-winner Ernest Lawrence and developed commercially by Paramount Pictures, Sony, Litton Industries and others.

At the time, a number of systems were being proposed that used separate red, green and blue signals (RGB), broadcast in succession.

Color information was then separately encoded and folded into the signal as a high-frequency modification to produce a composite video signal – on a black and white television this extra information would be seen as a slight randomization of the image intensity and just appear blurry, but the limited resolution of existing sets made this invisible in practice.

The shadow mask consists of a thin sheet of aluminum with tiny holes photo etched into it, placed just behind the front surface of the picture tube.

Stray electrons at the edge of the beam were cut off by the mask, creating a sharply focused spot that was small enough to hit a single colored phosphor on the screen.

Low consumer acceptance led to a lack of color programming, further reducing the demand for the sets in a chicken or the egg situation.

[4] In 1951 Ernest Lawrence, a 1939 Nobel Prize winner and professor at University of California, Berkeley best known as the father of the cyclotron, patented a new solution to the color decoding problem.

When the electron beam from the gun entered the region between the grid and the screen it was accelerated and focused down to a tiny spot, normally impinging on the green phosphor.

Since the focusing system had to quickly move the beam to generate the correct colors, very high voltages and powers had to be used, leading to arcing problems and radio frequency (RF) noise.

The University eventually abandoned their interest in Chromatron, but Paramount continued development as a system for displaying film during editing, which meant that the RF noise did not present a problem.

In addition, the output of the three video amplifiers switched the color information to hit each RGB stripe at the precise moments required.

Successor Chromatron tubes experimented with different color phosphors to obtain the correct combination of brightness and persistence.

Finally a rather large copper box or cage was mounted externally to the bell to reduce the remaining radiation from the grid coil.

Masaru Ibuka refused, apparently displaying an intense personal feeling that the shadow mask design was fundamentally flawed.

[4] In March 1961 Ibuka, Akio Morita and Nobutoshi Kihara attended the IEEE trade show at the New York Coliseum.

[9] By the end of the meeting the next day, Morita had secured a license to produce "a Chromatron tube and color television receiver utilizing it.

Ibuka remained a staunch supporter of the technology and pressed ahead with the construction of a new factory to produce them near Ōsaki Station in Tokyo.

In November 1966 Kazuo Iwama told Susumu Yoshida that the company was close to ruin, and that the team had to improve the yields by the end of the year, or the product would have to be cancelled.

Meanwhile, RCA was making great progress improving their shadow mask technology, and new entrants like General Electric's "Porta-Color" offered other advantages.

After reading several of the reports, Ibuka called 29-year-old physicist Miyaoka into his office along with Yoshida, and asked him if his single-gun approach could be made to work.

[1] The Sony KV 7010U CRT used the newly invented Trinitron gun combined with the Chromatron PDA wire grid instead of a shadow mask or aperture grill.

The basic concept that defined the Chromatron was the near-screen focusing system, which provided the beam resolution needed to accurately hit the individual colored phosphor strips.

Since the grid had to be charged to relatively high voltages, the aluminum coating was fairly thick, which dimmed the image to some extent.