Chromatron
Encyclopedia
The Chromatron is a color television cathode ray tube
design invented by Nobel prize
-winner Ernest Lawrence
and developed commercially by Sony
, Litton Industries
and others. The Chromatron offered brighter images than conventional color television systems using a shadow mask
, but a host of development problems kept it from being widely used in spite of years of development. Sony eventually abandoned it in favor of their famous Trinitron
system using an aperture grille
.
") that rotated in front of an otherwise conventional black and white television tube. Because they broadcast separate signals for the different colors, all of these systems were incompatible with existing black and white sets. Another problem was that the mechanical filter made them flicker unless very high refresh rates were used. In spite of these problems, the US Federal Communications Commission selected a sequential-frame 144 frame/s standard from CBS
as their color broadcast in 1950.
RCA
worked along different lines entirely, using the luminance-chrominance system introduced by Georges Valensi
in 1938. This system did not directly encode or transmit the RGB signals; instead it combined these colors into one overall brightness figure, the "luminance
". Luminance closely matched the black and white signal of existing broadcasts, allowing it to be displayed on existing televisions. This was a major advantage over the mechanical systems being proposed by other groups. 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, but the limited resolution of existing sets made this invisible in practice. On color sets the signal would be noticed, decoded back into RGB, and displayed.
Although Valensi's system had enormous benefits, it had not been successfully developed because it was difficult to produce the display tubes. Black and white TVs used a continuous signal and the tube could be coated with an even painting of phosphor. With Valensi's system, the color was changing continually along the line, which was far too fast for any sort of mechanical filter to follow. Instead, the phosphor had to be broken down into a discrete pattern of colored spots. Focusing the right signal on each of these tiny spots was beyond the capability of electron gun
s of the era, and RCA's early experiments used three-tube projectors, or mirror-based systems known as "Triniscope
".
. 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. Three guns, arranged in a triangle, were all aimed at the holes. 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. Since each of the guns aimed at the hole from a slightly different angle, the spots of phosphor on the tube could be separated slightly to prevent overlap.
The disadvantage of this approach was that for any given amount of gun power, the shadow mask filtered out the majority of the signal. To ensure there was no overlap of the signal on the screen, the dots had to be separated and covered perhaps 25% of its surface. This led to very dim images, requiring much greater power in order to provide a useful picture. Moreover, the system was highly dependent on the relative angles of the beams between the three guns, which required constant adjustment by the user to ensure the guns hit the correct colors. In spite of this, the technical superiority of the RCA system was overwhelming compared to the CBS system, and was selected as the new NTSC standard in 1953. The first broadcast using the new standard occurred on New Year's Day in 1954, when NBC broadcast the Tournament of Roses Parade
.
In spite of this early start, only a few years after regularly scheduled television broadcasting had begun, consumer uptake of color televisions was very slow to start. The dim images, constant adjustments and high costs had kept them in a niche of their own. Low consumer acceptance led to a lack of color programming, further reducing the demand for the sets in a chicken or the egg situation. In the United States in 1960, only 1 color set was sold for every 50 sets sold in total.
, a professor at University of California, Berkeley
best known as the father of the cyclotron
, patented a new solution to the color decoding problem. This system, the "Chromatron" or simply "Lawrence Tube", used an electronic focusing system in place of RCA's mechanical solution. The system consisted of a series of thin metal wires or plates placed about 1/2 an inch behind the phosphor screen. The wires were used to electrically focus the beams and bend them onto the correct phosphors, which were arranged in vertical stripes. The phosphor covered over 50% of the screen's area, whereas the contemporary shadow masks covered about 25%. This led to much brighter images using the same amount of power.
Each focusing element consisted of a pair of wires, and a conductive aluminum coating on the back of the phosphors. The screen was normally charged with a potential of 3000 to 4500 V between the wires and the aluminum, resulting in a curved electric field between the grid and the screen. 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. By varying the relative voltage between the two wires in each pair, the beam would be bent one direction of the other, allowing control over the color. Unlike a shadow mask, all of the signal eventually reached the screen, further reducing power requirements.
If the chrominance signal was missing, or deliberately ignored, the focusing system was disconnected and its power added to the gun. This produced a slightly stronger and unfocused beam, which hit all three colored strips and produced a B&W image. The spaces between the stripes meant the overall image would be about as bright as a conventional B&W set. A shadow mask set required all three guns to be powered to produce a B&W image, and since the color spots were small, their power had to be very high.
Yet another advantage of the near-screen focusing was that the electron beam was bent to hit the phosphors on the tube's faceplate at right angles no matter what the angle of the beam was behind the focuser. This allowed the tubes to be built with much higher deflection angles than conventional tubes – 72 degrees as opposed to a more typical 45. Chromatron tubes thus had much less depth for any given horizontal size.
The Chromatron also had several disadvantages. One was that there was a fundamental ratio between the acceleration provided by the grid and the electron gun at the back of the tube; in order to ensure that the grid could successfully control the beam, it had to have a significant proportion of the overall power. Unfortunately the mechanical layout of the grid limited it to voltages of about 5000 V or less, which in turn limited the electron gun to relatively low powers around 8000 V. Thus the overall power in the Chromatron was less than in conventional tubes, offsetting its natural brightness to some degree.
The more pressing concern was the mechanical layout of the grid. Getting the fine wires to stay aligned with the strips of color on the screen proved to be the design's Achilles heel
. Nevertheless, Sony did succeed with its aperture grille, a related structure; they even had a high-resolution Trinitron working at a trade show.
set up "Chromatic Television Laboratories" to commercially develop the system, in partnership with Paramount Pictures
who provided development funding. They started producing the PDF 22-4 22 inch prototype tubes in 1952 and 1953, with a display area of 14 by 11 inches.
In practice the design proved to have serious problems. 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 latter was particularly annoying when used as the basis of a television, as the noise interfered with the radio receivers that picked up the broadcasts. 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. Development was still continuing in the early 1960s when their work was bought by Sony.
In spite of these problems, the promise of the Chromatron system was so great that a number of companies continued development of the system throughout the 1950s. The Chromatron design was also licensed for a variety of other uses; Litton Industries
used the Chromatron with a two-color display (blue-red) as the basis for an Identification Friend or Foe
system.
refused, apparently displaying an intense personal feeling that the shadow mask design was fundamentally flawed.
In March 1961 Ibuka, Akio Morita
and Nobutoshi Kihara
attended the IEEE trade show at the New York Coliseum
. This was Kihara's first visit to the U.S., and he spent considerable time wandering the show floor. At one small booth he saw the Chromatron being displayed, and hurried to find Morita and Ibuka to show them. When Morita saw the display he immediately started negotiating a meeting for the next morning to visit the Chromatic labs in Manhattan. 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."
In early 1963 Senri Miyaoka was sent to the Chromatic labs to arrange the transfer of the technology to Sony, which would lead to the closing of Chromatic. He was unimpressed with the labs, describing the windowless basement as "squalor". The American team was quick to point out the flaws in the Chromatron design, telling Miyaoka that the design was hopeless. By September 1964, a 17 inch prototype had been built in Japan, but mass-production test runs were demonstrating serious problems.
Ibuka remained a staunch supporter of the technology, and pressed ahead with the construction of a new factory to produce them at Osaki Station in Tokyo. This proved unwise, and in early runs only 1 to 3 tubes would be usable out of every 1,000 produced. The rest suffered from alignment problems, with the colors fading from one to another across the screen, impossible to fix after the tube was sealed. Usable tubes were quickly rushed to Sony showrooms in spite of the low yields, and Ibuka make the product Sony's top sales priority. This too proved unwise; the low yields meant that the production cost was about 400,000 yen, but Sony was forced to sell them at 198,000 yen ($500) in order to be competitive.
The production problems were never solved, and led to increasing tension between Ibuka and Morita. 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. Sony was clearly falling behind the rest of the market by following the Chromatron approach.
Ibuka finally announced that he would personally lead the search for an alternative system. His team of 30 engineers and physicists explored a wide variety of approaches in the search for a uniquely Sony system. 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. Miyaoka was attempting to leave work for a cello rehearsal, and rashly stated that it would work. The result was the famed Trinitron
system, which went on sale in 1968 to wide acclaim.
The phosphors were silk screened onto the back of the tube in strips 2 mils wide with 2 mil wide gaps between them, and then coated in aluminum to make the screen conductive. Since the grid had to be charged to relatively high voltages, the aluminum coating was fairly thick, which dimmed the image to some extent.
The phosphors were pattered in an RGB-BGR-RGB pattern. The focusing grid was aligned so the beam would normally focus down onto the green strips in the middle of each pair of wires. To produce different colors, say blue, the beam would have to be pulled to the right for one pixel, and then to the left for the next. Since the adjacent stripes of phosphors shared one of the wires, this meant that a single voltage setting would produce the blue color on two adjacent pixels. Since a single frame of color television does not consist of a single color, the deflection system had to be continually varied as the beam moved across the screen.
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
design invented by Nobel prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
-winner Ernest Lawrence
Ernest Lawrence
Ernest Orlando Lawrence was an American physicist and Nobel Laureate, known for his invention, utilization, and improvement of the cyclotron atom-smasher beginning in 1929, based on his studies of the works of Rolf Widerøe, and his later work in uranium-isotope separation for the Manhattan Project...
and developed commercially by Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
, Litton Industries
Litton Industries
Named after inventor Charles Litton, Sr., Litton Industries was a large defense contractor in the United States, bought by the Northrop Grumman Corporation in 2001.-History:...
and others. The Chromatron offered brighter images than conventional color television systems using a shadow mask
Shadow mask
The shadow mask is one of two major technologies used to manufacture cathode ray tube televisions and computer displays that produce color images. The other approach is aperture grille, better known by its trade name, Trinitron. All early color televisions and the majority of CRT computer monitors...
, but a host of development problems kept it from being widely used in spite of years of development. Sony eventually abandoned it in favor of their famous Trinitron
Trinitron
Trinitron is Sony's brand name for its line of aperture grille based CRTs used in television sets and computer display monitors. One of the first truly new television systems to enter the market since the 1950s, the Trinitron was announced in 1966 to wide acclaim for its bright images, about 25%...
system using an aperture grille
Aperture grille
An aperture grille is one of two major technologies used to manufacture color cathode ray tube televisions and computer displays; the other is shadow mask....
.
Color television
Color television had been studied even before commercial broadcasting became common, but it was only in the late 1940s that the problem was seriously considered. At the time, a number of systems were being proposed that used separate red, green and blue signals (RGB), broadcast in succession. Most systems broadcast entire frames in sequence, with a colored filter (or "gelColor gel
A color gel or color filter , also known as lighting gel or simply gel, is a transparent colored material that is used in theatre, event production, photography, videography and cinematography to color light and for color correction...
") that rotated in front of an otherwise conventional black and white television tube. Because they broadcast separate signals for the different colors, all of these systems were incompatible with existing black and white sets. Another problem was that the mechanical filter made them flicker unless very high refresh rates were used. In spite of these problems, the US Federal Communications Commission selected a sequential-frame 144 frame/s standard from CBS
CBS
CBS Broadcasting Inc. is a major US commercial broadcasting television network, which started as a radio network. The name is derived from the initials of the network's former name, Columbia Broadcasting System. The network is sometimes referred to as the "Eye Network" in reference to the shape of...
as their color broadcast in 1950.
RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
worked along different lines entirely, using the luminance-chrominance system introduced by Georges Valensi
Georges Valensi
Georges Valensi was a French telecommunications engineer who, in 1938, invented and patented a method of transmitting color images so that they could be received on both color and black & white television sets....
in 1938. This system did not directly encode or transmit the RGB signals; instead it combined these colors into one overall brightness figure, the "luminance
Luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...
". Luminance closely matched the black and white signal of existing broadcasts, allowing it to be displayed on existing televisions. This was a major advantage over the mechanical systems being proposed by other groups. Color information was then separately encoded and folded into the signal as a high-frequency modification to produce a composite video
Composite video
Composite video is the format of an analog television signal before it is combined with a sound signal and modulated onto an RF carrier. In contrast to component video it contains all required video information, including colors in a single line-level signal...
signal – on a black and white television this extra information would be seen as a slight randomization of the image intensity, but the limited resolution of existing sets made this invisible in practice. On color sets the signal would be noticed, decoded back into RGB, and displayed.
Although Valensi's system had enormous benefits, it had not been successfully developed because it was difficult to produce the display tubes. Black and white TVs used a continuous signal and the tube could be coated with an even painting of phosphor. With Valensi's system, the color was changing continually along the line, which was far too fast for any sort of mechanical filter to follow. Instead, the phosphor had to be broken down into a discrete pattern of colored spots. Focusing the right signal on each of these tiny spots was beyond the capability of electron gun
Electron gun
An electron gun is an electrical component that produces an electron beam that has a precise kinetic energy and is most often used in television sets and computer displays which use cathode ray tube technology, as well as in other instruments, such as electron microscopes and particle...
s of the era, and RCA's early experiments used three-tube projectors, or mirror-based systems known as "Triniscope
Triniscope
The Triniscope was an early color television system developed by RCA. It used three separate video tubes with colored phosphors producing the primary colors, combining the images through dichroic mirrors onto a screen for viewing....
".
Shadow masks
RCA eventually solved the problem of displaying the color images with their introduction of the shadow maskShadow mask
The shadow mask is one of two major technologies used to manufacture cathode ray tube televisions and computer displays that produce color images. The other approach is aperture grille, better known by its trade name, Trinitron. All early color televisions and the majority of CRT computer monitors...
. The shadow mask consists of a thin sheet of aluminum with tiny holes photo etched
Photolithography
Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...
into it, placed just behind the front surface of the picture tube. Three guns, arranged in a triangle, were all aimed at the holes. 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. Since each of the guns aimed at the hole from a slightly different angle, the spots of phosphor on the tube could be separated slightly to prevent overlap.
The disadvantage of this approach was that for any given amount of gun power, the shadow mask filtered out the majority of the signal. To ensure there was no overlap of the signal on the screen, the dots had to be separated and covered perhaps 25% of its surface. This led to very dim images, requiring much greater power in order to provide a useful picture. Moreover, the system was highly dependent on the relative angles of the beams between the three guns, which required constant adjustment by the user to ensure the guns hit the correct colors. In spite of this, the technical superiority of the RCA system was overwhelming compared to the CBS system, and was selected as the new NTSC standard in 1953. The first broadcast using the new standard occurred on New Year's Day in 1954, when NBC broadcast the Tournament of Roses Parade
Tournament of Roses Parade
The Tournament of Roses Parade, better known as the Rose Parade, is "America's New Year Celebration", a festival of flower-covered floats, marching bands, equestrians and a college football game on New Year's Day , produced by the non-profit Pasadena Tournament of Roses Association.The annual...
.
In spite of this early start, only a few years after regularly scheduled television broadcasting had begun, consumer uptake of color televisions was very slow to start. The dim images, constant adjustments and high costs had kept them in a niche of their own. Low consumer acceptance led to a lack of color programming, further reducing the demand for the sets in a chicken or the egg situation. In the United States in 1960, only 1 color set was sold for every 50 sets sold in total.
Chromatron
In 1951 Ernest LawrenceErnest Lawrence
Ernest Orlando Lawrence was an American physicist and Nobel Laureate, known for his invention, utilization, and improvement of the cyclotron atom-smasher beginning in 1929, based on his studies of the works of Rolf Widerøe, and his later work in uranium-isotope separation for the Manhattan Project...
, a professor at University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
best known as the father of the cyclotron
Cyclotron
In technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...
, patented a new solution to the color decoding problem. This system, the "Chromatron" or simply "Lawrence Tube", used an electronic focusing system in place of RCA's mechanical solution. The system consisted of a series of thin metal wires or plates placed about 1/2 an inch behind the phosphor screen. The wires were used to electrically focus the beams and bend them onto the correct phosphors, which were arranged in vertical stripes. The phosphor covered over 50% of the screen's area, whereas the contemporary shadow masks covered about 25%. This led to much brighter images using the same amount of power.
Each focusing element consisted of a pair of wires, and a conductive aluminum coating on the back of the phosphors. The screen was normally charged with a potential of 3000 to 4500 V between the wires and the aluminum, resulting in a curved electric field between the grid and the screen. 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. By varying the relative voltage between the two wires in each pair, the beam would be bent one direction of the other, allowing control over the color. Unlike a shadow mask, all of the signal eventually reached the screen, further reducing power requirements.
If the chrominance signal was missing, or deliberately ignored, the focusing system was disconnected and its power added to the gun. This produced a slightly stronger and unfocused beam, which hit all three colored strips and produced a B&W image. The spaces between the stripes meant the overall image would be about as bright as a conventional B&W set. A shadow mask set required all three guns to be powered to produce a B&W image, and since the color spots were small, their power had to be very high.
Yet another advantage of the near-screen focusing was that the electron beam was bent to hit the phosphors on the tube's faceplate at right angles no matter what the angle of the beam was behind the focuser. This allowed the tubes to be built with much higher deflection angles than conventional tubes – 72 degrees as opposed to a more typical 45. Chromatron tubes thus had much less depth for any given horizontal size.
The Chromatron also had several disadvantages. One was that there was a fundamental ratio between the acceleration provided by the grid and the electron gun at the back of the tube; in order to ensure that the grid could successfully control the beam, it had to have a significant proportion of the overall power. Unfortunately the mechanical layout of the grid limited it to voltages of about 5000 V or less, which in turn limited the electron gun to relatively low powers around 8000 V. Thus the overall power in the Chromatron was less than in conventional tubes, offsetting its natural brightness to some degree.
The more pressing concern was the mechanical layout of the grid. Getting the fine wires to stay aligned with the strips of color on the screen proved to be the design's Achilles heel
Achilles Heel
Achilles Heel may refer to:* Achilles' heel, a metaphor for a fatal weakness in spite of overall strength* Achilles Heel , music by Pedro the Lion* Achilles Heel , off Antarctica...
. Nevertheless, Sony did succeed with its aperture grille, a related structure; they even had a high-resolution Trinitron working at a trade show.
Commercial developments
The University of California, BerkeleyUniversity of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
set up "Chromatic Television Laboratories" to commercially develop the system, in partnership with Paramount Pictures
Paramount Pictures
Paramount Pictures Corporation is an American film production and distribution company, located at 5555 Melrose Avenue in Hollywood. Founded in 1912 and currently owned by media conglomerate Viacom, it is America's oldest existing film studio; it is also the last major film studio still...
who provided development funding. They started producing the PDF 22-4 22 inch prototype tubes in 1952 and 1953, with a display area of 14 by 11 inches.
In practice the design proved to have serious problems. 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
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
(RF) noise. The latter was particularly annoying when used as the basis of a television, as the noise interfered with the radio receivers that picked up the broadcasts. 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. Development was still continuing in the early 1960s when their work was bought by Sony.
In spite of these problems, the promise of the Chromatron system was so great that a number of companies continued development of the system throughout the 1950s. The Chromatron design was also licensed for a variety of other uses; Litton Industries
Litton Industries
Named after inventor Charles Litton, Sr., Litton Industries was a large defense contractor in the United States, bought by the Northrop Grumman Corporation in 2001.-History:...
used the Chromatron with a two-color display (blue-red) as the basis for an Identification Friend or Foe
Identification friend or foe
In telecommunications, identification, friend or foe is an identification system designed for command and control. It is a system that enables military and national interrogation systems to identify aircraft, vehicles, or forces as friendly and to determine their bearing and range from the...
system.
Sony's attempt
By 1961 Sony was a major Japanese vendor of black and white sets, but had no color television technology at all. Sony dealers were asking when they could expect a color set, and the sales division started putting pressure on engineering to simply license a shadow mask design from another vendor and start production. Masaru IbukaMasaru Ibuka
Masaru Ibuka was a Japanese electronics industrialist. He co-founded what is now Sony....
refused, apparently displaying an intense personal feeling that the shadow mask design was fundamentally flawed.
In March 1961 Ibuka, Akio Morita
Akio Morita
Akio Morita KBE was a Japanese businessman and co-founder of Sony Corporation along with Masaru Ibuka.-Early life:...
and Nobutoshi Kihara
Nobutoshi Kihara
Nobutoshi Kihara was an engineer at Sony, best known for his work on the original Walkman cassette-tape player in the 1970s and was commonly called Mr...
attended the IEEE trade show at the New York Coliseum
New York Coliseum
The New York Coliseum was a convention center that stood on Columbus Circle in New York City from 1956 to 2000. It was designed by architects Leon and Lionel Levy in a modified international style, and included both a low building with exhibition space and a 26-story office block.-History:The...
. This was Kihara's first visit to the U.S., and he spent considerable time wandering the show floor. At one small booth he saw the Chromatron being displayed, and hurried to find Morita and Ibuka to show them. When Morita saw the display he immediately started negotiating a meeting for the next morning to visit the Chromatic labs in Manhattan. 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."
In early 1963 Senri Miyaoka was sent to the Chromatic labs to arrange the transfer of the technology to Sony, which would lead to the closing of Chromatic. He was unimpressed with the labs, describing the windowless basement as "squalor". The American team was quick to point out the flaws in the Chromatron design, telling Miyaoka that the design was hopeless. By September 1964, a 17 inch prototype had been built in Japan, but mass-production test runs were demonstrating serious problems.
Ibuka remained a staunch supporter of the technology, and pressed ahead with the construction of a new factory to produce them at Osaki Station in Tokyo. This proved unwise, and in early runs only 1 to 3 tubes would be usable out of every 1,000 produced. The rest suffered from alignment problems, with the colors fading from one to another across the screen, impossible to fix after the tube was sealed. Usable tubes were quickly rushed to Sony showrooms in spite of the low yields, and Ibuka make the product Sony's top sales priority. This too proved unwise; the low yields meant that the production cost was about 400,000 yen, but Sony was forced to sell them at 198,000 yen ($500) in order to be competitive.
The production problems were never solved, and led to increasing tension between Ibuka and Morita. 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
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
's "Porta-Color
Porta-Color
General Electric's Porta-Color was the first "portable" color television introduced in the United States. The Porta-Color set introduced a new display system that improved image brightness, allowing the set to operate at lower power than competing systems based on the almost universal shadow mask...
" offered other advantages. Sony was clearly falling behind the rest of the market by following the Chromatron approach.
Ibuka finally announced that he would personally lead the search for an alternative system. His team of 30 engineers and physicists explored a wide variety of approaches in the search for a uniquely Sony system. 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. Miyaoka was attempting to leave work for a cello rehearsal, and rashly stated that it would work. The result was the famed Trinitron
Trinitron
Trinitron is Sony's brand name for its line of aperture grille based CRTs used in television sets and computer display monitors. One of the first truly new television systems to enter the market since the 1950s, the Trinitron was announced in 1966 to wide acclaim for its bright images, about 25%...
system, which went on sale in 1968 to wide acclaim.
Description
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. The grid both focused the signal as well as guided it to the correct colors.The phosphors were silk screened onto the back of the tube in strips 2 mils wide with 2 mil wide gaps between them, and then coated in aluminum to make the screen conductive. Since the grid had to be charged to relatively high voltages, the aluminum coating was fairly thick, which dimmed the image to some extent.
The phosphors were pattered in an RGB-BGR-RGB pattern. The focusing grid was aligned so the beam would normally focus down onto the green strips in the middle of each pair of wires. To produce different colors, say blue, the beam would have to be pulled to the right for one pixel, and then to the left for the next. Since the adjacent stripes of phosphors shared one of the wires, this meant that a single voltage setting would produce the blue color on two adjacent pixels. Since a single frame of color television does not consist of a single color, the deflection system had to be continually varied as the beam moved across the screen.
See also
- Geer tubeGeer tubeThe Geer tube was an early single-tube color television cathode ray tube, developed by Willard Geer. The Geer tube used a pattern of small phosphor-covered three-sided pyramids on the inside of the CRT faceplate to mix together separate red, green and blue signals from three electron guns...
, another early color television CRT that is no longer used - Shadow maskShadow maskThe shadow mask is one of two major technologies used to manufacture cathode ray tube televisions and computer displays that produce color images. The other approach is aperture grille, better known by its trade name, Trinitron. All early color televisions and the majority of CRT computer monitors...
- Aperture grilleAperture grilleAn aperture grille is one of two major technologies used to manufacture color cathode ray tube televisions and computer displays; the other is shadow mask....
Patents
- U.S. Patent 2,692,532, "Cathode Ray Focusing Apparatus", Ernst O. Lawrence, University of California/Chromatic Television Laboratories (original Chromatron patent)
- U.S. Patent 2,866,094, "Symmetrical to Asymmetrical Signal Conversion Circuit", Hoffman Electronics
- U.S. Patent 3,368,105, "High Voltage Power Supply System for Cathode Ray Tubes Employing Protective Time Delay Means", Sony
Further reading
- "This is Color TV: A Look at the Record To See What's Ahead", TV Guide, June 26 to July 2, 1953, pp. 5–7
- Mark Heyer and Al Pinsky, "Interview with Harold B. Law", IEEE History Center, 15 July 1975
External links
- "Model PDF-22-4", Chromatic Labs brochure
- "Lawrence Experimental type CH-22", Thomas Electronics brochure (also has the 15GP22)
- "Model PDF-10-1X", Litton Industries brochure