Beam-index tube
Encyclopedia
The beam-index tube is a color television
cathode ray tube
design, using phosphor stripes and active-feedback timing, rather than phosphor dots and a beam-shadowing mask
as developed by RCA
. Beam indexing offered much brighter pictures than shadow-mask CRTs, and only a single electron gun
rather than three, making it easier to build and reducing power consumption.
Philco
led development of the beam-indexing concept in a series of developments they called the "Apple" CRT. In spite of lengthy development, they were never able to manufacture a cost-competitive indexing tube, and eventually abandoned the concept. The system was re-introduced as the Uniray in the 1970s. Improvements in electronics greatly reduced the cost of implementing beam indexing, which became cost competitive with conventional sets. Several Japanese companies used it for a variety of specialist purposes, the best-known being the Sony Indextron series. The system also saw some military use, due to its low sensitivity to magnetic interference.
screen has a uniform coating of phosphor
that emits white light when struck by electron
s. The beam from an electron gun
at the back of the tube is deflected (most commonly) by the varying fields from magnetic coils so it may be directed at any point on the screen.
A color CRT is patterned with three phosphors, one for each additive primary (red, green and blue (RGB)). Three electron guns separately excite each phosphor with the appropriate color signal. Some arrangement is needed to assure that the beam from the red gun strikes only the red phosphor, the green gun the green phosphor, and the blue the blue.
RCA solved this problem with a shadow mask
, a metal plate with holes that ensured the beams hit only the correct phosphors. However, the mask blocked about 85% of the beam, which reduced the CRT's maximum brightness. Much effort was put into developing alternate ways of directing the electron beams to the correct phosphor that would not block as much of the beams. The ideal system would be a single gun that switched to the appropriate color signal as it passed over the corresponding phosphor. This is called beam indexing.
There were several possible ways to implement beam indexing. RCA worked on a system with charged wires that pulled the beams slightly toward them, with stripes of colored phosphors above them. The problem was that the wires had to be placed very close to each other and powered with high voltages, which made it very difficult to keep the signals from leaking from wire to wire. Development was abandoned when the shadow mask proved successful. Ernest Lawrence
developed a similar system known as Chromatron
that used a grid of fine wires behind the screen to electrically deflect the beam as it approached the screen, but it suffered from the same basic problem as RCA's approach. In spite of years of development, no one was able to produce a commercially viable version. Sony's attempt to produce a practical Chromatron inspired the development of their Trinitron
aperture grille
system.
, where high-speed electrons will entrain electrons from a surrounding material, creating a pulse of additional current. Philco's engineers aimed to use this pulse to time the passage of the beam within the tube, with sufficient accuracy to produce accurate color. By comparing the time of the pulse to the color clock, the beam could be modulated to produce the proper amount of power while passing over the appropriate color. Only one electron gun was needed, its power adjusted on the fly to produce the separate red, green and blue intensities. Unlike the shadow mask, where small dots of phosphor are used, the apple tube used vertical stripes and a separate "index" stripe for timing.
Several different arrangements of components, materials and electronics were used while researching this approach during a ten year development period, during most of which time it was kept secret. The most common system, first publicly demonstrated in 1956, used stripes of magnesium oxide
deposited on the back of aluminum as the indexing system. In order to ensure the electronics had enough time to respond to the indexing signal and adjust the color, a separate "pilot beam" was generated from the gun and positioned to lead the main "writing beam" by a small distance within the tube. When the indexing beam hit the magnesium oxide, a shower of electrons was given off, which were collected by a conductive coating of carbon
deposited on the inside of the tube. The low power pilot beam had just enough power to dimly light the tube to a just-visible even background intensity.
Since both the pilot and writing beams hit the index stripes, two signals would be generated as the beams swept across the tube. In order to distinguish between them, the pilot beam was modulated with a varying signal timed so that it was at maximum power only when it would be in the approximate location of the index stripes. The frequency of the modulating signal was a function of the tube geometry; on a 21" inch tube the index stripes were positioned 0.51 inches apart, a single horizontal sweep takes about 53 microseconds, so the signal had to be modulated at 7.4 MHz.
The original modulating signal was then compared with the amplified return signal from the secondary emission process, producing a net output that varied in phase by the difference in position between the estimated and real position of the beam. This phase signal was then sent into the conventional color decoder, adjusting the chroma on the fly. The writing beam, positioned to sweep the spaces between the indexes while the pilot beam was on them, received the chroma signal so that its power was modulated to produce the correct amounts of color when it was on top of those stripes. By the time it reached the index stripe the pilot's modulating signal would be at its minimum, and the strong signal given off by the writing beam would simply be ignored.
In order to ensure the positioning of the pilot and writing beams remained as constant as possible, the apple tube used a unique electron gun arrangement. The beams were produced from a single anode and two closely spaced cathodes, resulting in the beams traveling in slightly different directions. They were then magnetically focused so they crossed at a point, where an aperture was used to clear up the signal to produce a sharp-edged elliptical beam pattern. The deflection coils were positioned around the aperture, so by having both beams pass by the deflection coils while superimposed, the deflection of both was equal. The beams then spread out again on the far side of the aperture, where a second focussing arrangement ensured both were traveling parallel to each other.
The electrons emitted from the index stripes were low-power, and thus traveled at low speed to the pickup point at a "button" on the rear of the tube. Since the travel time was a significant factor, the timing of the phase comparison had to be adjusted as the beam swept the face of the tube – at the sides of the tube the electrons were close to the tube pickup, but when the beams were in the middle of the tube they had a longer distance to travel.
Actually building the apple tube's electronics proved to be difficult. The fast response needed to adjust the color signal based on the index was difficult to build using the tube-based electronics of the era, and the apple tube's electronics were thus much more expensive than conventional shadow mask sets. Their demonstration unit had eight more tubes that a similar shadow mask system, which at that time represented a significant cost. Additionally, the secondary emission did not provide a sharp signal, and crosstalk between the pilot and writing beams was always a problem.
. He replaced the electron emitter of the Philco design with a new material that gave of x-rays. These were received by scintillator
s at the back of the tube, beside the guns. As the light speed was independent of power and essentially instant compared to the timing needed for the indexing, the new design allowed the elimination of the complex timing circuitry of the original design.
Given all of the problems that the apple tube was having, Philco engineers adopted the design as the "advanced apple" tube. Their version used a new material that gave off ultraviolet
light in place of the x-rays, and replaced the scintillators with a single photomultiplier tube. The flashes of light given off by the index stripes were amplified by the photomultiplier and then sent into the color decoder as normal. Delays in the timing circuitry itself were taken care of by slightly adjusting the position of the index stripes on the tube. This eliminated much of the circuitry associated with the index timing, and led to a lower-cost chassis.
However, it also introduced the photomultiplier, a complex tube of its own that was at that time still in its developmental infancy and relatively expensive. After some development the company was able to reliably produce advanced apple systems, but the cost of production was too high ($75 per tube, over $525 in year 2005 dollars) and tooling ($15 million, $110 million year 2005) made the system unattractive.
Development of the system was also picked up by Sylvania
and Thorn Electrical Industries
in the UK, who published about what they called the "Zebra tube" in 1961. They were apparently successful in their work, but as no color television standard effort was making headway at the time, no commercial versions were forthcoming from this development either.
s dramatically changed the complexity and cost equations of the advanced apple indexing system, and the introduction of all-in-one timing systems implemented as integrated circuits did the same on the chassis side of the system. What was once a useful but impractical device became cost effective by the early 1970s.
Sunstein produced a prototype Uniray system using an original Philco tube and new electronics, and started shopping the concept around in 1972. There was some effort to license the system to Japanese companies, most of whom had licensed the shadow mask from RCA and were facing stiff competition from Sony
's newly introduced Trinitron
system. Several companies started development of Uniray based televisions in the later 1970s, and several different products were introduced in the 1980s.
Since the beam indexing adjusted the beam position as the beam was scanning across the tube, external magnetic fields had little effect on the image. This made the system particularly useful for avionics displays where the systems were subject to heavy interference from surrounding equipment. Rockwell International
received a patent in 1978 on this use. Ferranti
in the UK also offered a 4 by 3 inch beam-index tube as the mapping display in the Panavia Tornado
mid-life upgrade.
Hitachi
started development of the advanced apple system for television use, but instead used it for much more limited applications. The only widespread use was in the color viewfinders of handheld video tape recorder
s, first introduced in 1983 in a 1½ inch form. The single gun and brighter images for any given gun power levels meant that the indexed display was much more power efficient than conventional systems, allowing it to be used in battery powered applications that previously demanded B&W screens.
Sony also did some development with the Uniray concept, introducing a range of products under the "Indextron" trade name. Their first product was the FP-62 "Vidimagic" projection television system. The Indextron tube was so bright that it could directly project an enlarged image in a front projection television without the need for three separate tubes, which eliminated focusing problems. A second versions with built-in Betamax
VCR was sold as the PF-60. A better-known application was the KVX-370, a 4 inch "bedside" television with a built-in alarm clock and radio.
Sanyo used the bright images to make a new style of tube they called the "lollipop". It used an electron gun arranged at right angles to the display, extending down instead of to the rear. The result was a 3 inch display only 1½ inches deep, although it was several inches long. They demonstrated the system in a small television similar to the Sony Indextron.
was used to paint the stripes, and the beam strength is modulated in order to produce different colors.
Each RGB pattern was followed by a single stripe of UV phosphor on the inside face of the tube, where the light was not visible to the viewer. Light given off by this stripe was captured by a photomultiplier
tube on the outside of the tube that was positioned over a clear window in the tube surface. Light from the UV stripes was amplified and sent into the color decoder circuit.
The color decoder electrically subtracted the signal from the photomultiplier from the existing color burst signal. This resulted in a phase difference that advanced or retarded the modulation of the single beam. This way even if the beam was advancing too fast or too slow, the index system would adjust the timing on the fly to ensure proper colors were produced.
In order to ensure there was enough time for the electronics to make this adjustment, early models used a second beam that swept the screen slightly in advance of the first. Later sets did not need this adjustment and were able to correct by indexing off the preceding UV stripe. In order to receive a signal strong enough to index with, the beam had to be left on at all times, which reduced contrast ratio in relation to conventional tubes.
The beam-index tube bears some resemblance to two other types of television tubes which also used vertical stripes of colored phosphor instead of dots or grids. The Chromatron
used two sets of fine wires suspended behind the display area to electrically focus its single beam, one set of wires pulling the beam towards the red side and the other towards the blue. The grids were aligned so the beam would normally focus onto the green stripe in the middle, but by varying the relative voltage between the two the beam could accurately hit the colored stripes. In practice the wires were difficult to keep aligned with the phosphors, and gave off electrical noise that interfered with the radio receivers in a television application. It saw some use in military settings, but no commercial television use.
The other similar design is the Trinitron
. The Trinitron combined the vertical stripes of the beam-index and Chromatron tubes with a new single-gun three-beam cathode and a aperture grille
shadow mask. The result was a design with the mechanical simplicity of the shadow mask design and the bright images of the beam-index system. Trinitron was a major product for Sony for several decades, representing the high-point of conventional color TV displays until the widespread introduction of plasma display
s and LCD televisions in the 21st century.
Color television
Color television is part of the history of television, the technology of television and practices associated with television's transmission of moving images in color video....
cathode ray tube
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, using phosphor stripes and active-feedback timing, rather than phosphor dots and a beam-shadowing 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...
as developed by 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...
. Beam indexing offered much brighter pictures than shadow-mask CRTs, and only a single 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...
rather than three, making it easier to build and reducing power consumption.
Philco
Philco
Philco, the Philadelphia Storage Battery Company , was a pioneer in early battery, radio, and television production as well as former employer of Philo Farnsworth, inventor of cathode ray tube television...
led development of the beam-indexing concept in a series of developments they called the "Apple" CRT. In spite of lengthy development, they were never able to manufacture a cost-competitive indexing tube, and eventually abandoned the concept. The system was re-introduced as the Uniray in the 1970s. Improvements in electronics greatly reduced the cost of implementing beam indexing, which became cost competitive with conventional sets. Several Japanese companies used it for a variety of specialist purposes, the best-known being the Sony Indextron series. The system also saw some military use, due to its low sensitivity to magnetic interference.
Early Color CRTs
In conventional black and white (B&W) televisions, the CRTCRT
-Medicine:* Capillary refill time, the rate at with blood refills empty capillaries* Cognitive Retention Therapy, a dementia treatment* Cardiac resynchronization therapy, a treatment for heart failure** CRT-D, an implanted cardiac resynchronization device...
screen has a uniform coating of phosphor
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
that emits white light when struck by electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s. The beam from an 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...
at the back of the tube is deflected (most commonly) by the varying fields from magnetic coils so it may be directed at any point on the screen.
A color CRT is patterned with three phosphors, one for each additive primary (red, green and blue (RGB)). Three electron guns separately excite each phosphor with the appropriate color signal. Some arrangement is needed to assure that the beam from the red gun strikes only the red phosphor, the green gun the green phosphor, and the blue the blue.
RCA solved this problem with 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...
, a metal plate with holes that ensured the beams hit only the correct phosphors. However, the mask blocked about 85% of the beam, which reduced the CRT's maximum brightness. Much effort was put into developing alternate ways of directing the electron beams to the correct phosphor that would not block as much of the beams. The ideal system would be a single gun that switched to the appropriate color signal as it passed over the corresponding phosphor. This is called beam indexing.
There were several possible ways to implement beam indexing. RCA worked on a system with charged wires that pulled the beams slightly toward them, with stripes of colored phosphors above them. The problem was that the wires had to be placed very close to each other and powered with high voltages, which made it very difficult to keep the signals from leaking from wire to wire. Development was abandoned when the shadow mask proved successful. 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...
developed a similar system known as Chromatron
Chromatron
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...
that used a grid of fine wires behind the screen to electrically deflect the beam as it approached the screen, but it suffered from the same basic problem as RCA's approach. In spite of years of development, no one was able to produce a commercially viable version. Sony's attempt to produce a practical Chromatron inspired the development of their 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%...
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....
system.
Apple tube
Philco's approach to the problem of properly indexing the beam in relation to the phosphors relied on the process of secondary emissionSecondary emission
Secondary emission in physics is a phenomenon where primary incident particles of sufficient energy, when hitting a surface or passing through some material, induce the emission of secondary particles. The primary particles are often charged particles like electrons or ions. If the secondary...
, where high-speed electrons will entrain electrons from a surrounding material, creating a pulse of additional current. Philco's engineers aimed to use this pulse to time the passage of the beam within the tube, with sufficient accuracy to produce accurate color. By comparing the time of the pulse to the color clock, the beam could be modulated to produce the proper amount of power while passing over the appropriate color. Only one electron gun was needed, its power adjusted on the fly to produce the separate red, green and blue intensities. Unlike the shadow mask, where small dots of phosphor are used, the apple tube used vertical stripes and a separate "index" stripe for timing.
Several different arrangements of components, materials and electronics were used while researching this approach during a ten year development period, during most of which time it was kept secret. The most common system, first publicly demonstrated in 1956, used stripes of magnesium oxide
Magnesium oxide
Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds...
deposited on the back of aluminum as the indexing system. In order to ensure the electronics had enough time to respond to the indexing signal and adjust the color, a separate "pilot beam" was generated from the gun and positioned to lead the main "writing beam" by a small distance within the tube. When the indexing beam hit the magnesium oxide, a shower of electrons was given off, which were collected by a conductive coating of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
deposited on the inside of the tube. The low power pilot beam had just enough power to dimly light the tube to a just-visible even background intensity.
Since both the pilot and writing beams hit the index stripes, two signals would be generated as the beams swept across the tube. In order to distinguish between them, the pilot beam was modulated with a varying signal timed so that it was at maximum power only when it would be in the approximate location of the index stripes. The frequency of the modulating signal was a function of the tube geometry; on a 21" inch tube the index stripes were positioned 0.51 inches apart, a single horizontal sweep takes about 53 microseconds, so the signal had to be modulated at 7.4 MHz.
The original modulating signal was then compared with the amplified return signal from the secondary emission process, producing a net output that varied in phase by the difference in position between the estimated and real position of the beam. This phase signal was then sent into the conventional color decoder, adjusting the chroma on the fly. The writing beam, positioned to sweep the spaces between the indexes while the pilot beam was on them, received the chroma signal so that its power was modulated to produce the correct amounts of color when it was on top of those stripes. By the time it reached the index stripe the pilot's modulating signal would be at its minimum, and the strong signal given off by the writing beam would simply be ignored.
In order to ensure the positioning of the pilot and writing beams remained as constant as possible, the apple tube used a unique electron gun arrangement. The beams were produced from a single anode and two closely spaced cathodes, resulting in the beams traveling in slightly different directions. They were then magnetically focused so they crossed at a point, where an aperture was used to clear up the signal to produce a sharp-edged elliptical beam pattern. The deflection coils were positioned around the aperture, so by having both beams pass by the deflection coils while superimposed, the deflection of both was equal. The beams then spread out again on the far side of the aperture, where a second focussing arrangement ensured both were traveling parallel to each other.
The electrons emitted from the index stripes were low-power, and thus traveled at low speed to the pickup point at a "button" on the rear of the tube. Since the travel time was a significant factor, the timing of the phase comparison had to be adjusted as the beam swept the face of the tube – at the sides of the tube the electrons were close to the tube pickup, but when the beams were in the middle of the tube they had a longer distance to travel.
Actually building the apple tube's electronics proved to be difficult. The fast response needed to adjust the color signal based on the index was difficult to build using the tube-based electronics of the era, and the apple tube's electronics were thus much more expensive than conventional shadow mask sets. Their demonstration unit had eight more tubes that a similar shadow mask system, which at that time represented a significant cost. Additionally, the secondary emission did not provide a sharp signal, and crosstalk between the pilot and writing beams was always a problem.
Advanced Apple
Another solution to the indexing problem was introduced by David Goodman of New York UniversityNew York University
New York University is a private, nonsectarian research university based in New York City. NYU's main campus is situated in the Greenwich Village section of Manhattan...
. He replaced the electron emitter of the Philco design with a new material that gave of x-rays. These were received by scintillator
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
s at the back of the tube, beside the guns. As the light speed was independent of power and essentially instant compared to the timing needed for the indexing, the new design allowed the elimination of the complex timing circuitry of the original design.
Given all of the problems that the apple tube was having, Philco engineers adopted the design as the "advanced apple" tube. Their version used a new material that gave off ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
light in place of the x-rays, and replaced the scintillators with a single photomultiplier tube. The flashes of light given off by the index stripes were amplified by the photomultiplier and then sent into the color decoder as normal. Delays in the timing circuitry itself were taken care of by slightly adjusting the position of the index stripes on the tube. This eliminated much of the circuitry associated with the index timing, and led to a lower-cost chassis.
However, it also introduced the photomultiplier, a complex tube of its own that was at that time still in its developmental infancy and relatively expensive. After some development the company was able to reliably produce advanced apple systems, but the cost of production was too high ($75 per tube, over $525 in year 2005 dollars) and tooling ($15 million, $110 million year 2005) made the system unattractive.
Development of the system was also picked up by Sylvania
Osram Sylvania
Osram Sylvania Inc. is the North American operation of lighting manufacturer Osram GmbH, which is owned by Siemens AG. It was established in January 1993, with the acquisition of GTE’s Sylvania lighting division by Osram GmbH....
and Thorn Electrical Industries
THORN Electrical Industries
Thorn Electrical Industries, Limited was an electrical engineering business. It was listed on the London Stock Exchange but it merged with EMI Group to form Thorn EMI in 1979...
in the UK, who published about what they called the "Zebra tube" in 1961. They were apparently successful in their work, but as no color television standard effort was making headway at the time, no commercial versions were forthcoming from this development either.
Uniray
After Philco gave up on the apple system, the rights were purchased by one of the engineers, David Sunstein. After many years he re-introduced the advanced apple design as the "Uniray". The introduction of low-cost photodiodePhotodiode
A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.The common, traditional solar cell used to generateelectric solar power is a large area photodiode....
s dramatically changed the complexity and cost equations of the advanced apple indexing system, and the introduction of all-in-one timing systems implemented as integrated circuits did the same on the chassis side of the system. What was once a useful but impractical device became cost effective by the early 1970s.
Sunstein produced a prototype Uniray system using an original Philco tube and new electronics, and started shopping the concept around in 1972. There was some effort to license the system to Japanese companies, most of whom had licensed the shadow mask from RCA and were facing stiff competition from 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....
's newly introduced 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. Several companies started development of Uniray based televisions in the later 1970s, and several different products were introduced in the 1980s.
Since the beam indexing adjusted the beam position as the beam was scanning across the tube, external magnetic fields had little effect on the image. This made the system particularly useful for avionics displays where the systems were subject to heavy interference from surrounding equipment. Rockwell International
Rockwell International
Rockwell International was a major American manufacturing conglomerate in the latter half of the 20th century, involved in aircraft, the space industry, both defense-oriented and commercial electronics, automotive and truck components, printing presses, valves and meters, and industrial automation....
received a patent in 1978 on this use. Ferranti
Ferranti
Ferranti or Ferranti International plc was a UK electrical engineering and equipment firm that operated for over a century from 1885 until it went bankrupt in 1993. Known primarily for defence electronics, the Company was once a constituent of the FTSE 100 Index but ceased trading in 1993.The...
in the UK also offered a 4 by 3 inch beam-index tube as the mapping display in the Panavia Tornado
Panavia Tornado
The Panavia Tornado is a family of twin-engine, variable-sweep wing combat aircraft, which was jointly developed and manufactured by the United Kingdom, West Germany and Italy...
mid-life upgrade.
Hitachi
Hitachi
Hitachi is a multinational corporation specializing in high-technology.Hitachi may also refer to:*Hitachi, Ibaraki, Japan*Hitachi province, former province of Japan*Prince Hitachi and Princess Hitachi, members of the Japanese imperial family...
started development of the advanced apple system for television use, but instead used it for much more limited applications. The only widespread use was in the color viewfinders of handheld video tape recorder
Video tape recorder
A video tape recorder is a tape recorder that can record video material, usually on a magnetic tape. VTRs originated as individual tape reels, serving as a replacement for motion picture film stock and making recording for television applications cheaper and quicker. An improved form included the...
s, first introduced in 1983 in a 1½ inch form. The single gun and brighter images for any given gun power levels meant that the indexed display was much more power efficient than conventional systems, allowing it to be used in battery powered applications that previously demanded B&W screens.
Sony also did some development with the Uniray concept, introducing a range of products under the "Indextron" trade name. Their first product was the FP-62 "Vidimagic" projection television system. The Indextron tube was so bright that it could directly project an enlarged image in a front projection television without the need for three separate tubes, which eliminated focusing problems. A second versions with built-in Betamax
Betamax
Betamax was a consumer-level analog videocassette magnetic tape recording format developed by Sony, released on May 10, 1975. The cassettes contain -wide videotape in a design similar to the earlier, professional wide, U-matic format...
VCR was sold as the PF-60. A better-known application was the KVX-370, a 4 inch "bedside" television with a built-in alarm clock and radio.
Sanyo used the bright images to make a new style of tube they called the "lollipop". It used an electron gun arranged at right angles to the display, extending down instead of to the rear. The result was a 3 inch display only 1½ inches deep, although it was several inches long. They demonstrated the system in a small television similar to the Sony Indextron.
Description
The optically indexed tube displayed images by lighting vertical stripes of colored phosphor arranged in a red-green-blue pattern. A single electron gunElectron 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...
was used to paint the stripes, and the beam strength is modulated in order to produce different colors.
Each RGB pattern was followed by a single stripe of UV phosphor on the inside face of the tube, where the light was not visible to the viewer. Light given off by this stripe was captured by a photomultiplier
Photomultiplier
Photomultiplier tubes , members of the class of vacuum tubes, and more specifically phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum...
tube on the outside of the tube that was positioned over a clear window in the tube surface. Light from the UV stripes was amplified and sent into the color decoder circuit.
The color decoder electrically subtracted the signal from the photomultiplier from the existing color burst signal. This resulted in a phase difference that advanced or retarded the modulation of the single beam. This way even if the beam was advancing too fast or too slow, the index system would adjust the timing on the fly to ensure proper colors were produced.
In order to ensure there was enough time for the electronics to make this adjustment, early models used a second beam that swept the screen slightly in advance of the first. Later sets did not need this adjustment and were able to correct by indexing off the preceding UV stripe. In order to receive a signal strong enough to index with, the beam had to be left on at all times, which reduced contrast ratio in relation to conventional tubes.
The beam-index tube bears some resemblance to two other types of television tubes which also used vertical stripes of colored phosphor instead of dots or grids. The Chromatron
Chromatron
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...
used two sets of fine wires suspended behind the display area to electrically focus its single beam, one set of wires pulling the beam towards the red side and the other towards the blue. The grids were aligned so the beam would normally focus onto the green stripe in the middle, but by varying the relative voltage between the two the beam could accurately hit the colored stripes. In practice the wires were difficult to keep aligned with the phosphors, and gave off electrical noise that interfered with the radio receivers in a television application. It saw some use in military settings, but no commercial television use.
The other similar design is the 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%...
. The Trinitron combined the vertical stripes of the beam-index and Chromatron tubes with a new single-gun three-beam cathode and a 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....
shadow mask. The result was a design with the mechanical simplicity of the shadow mask design and the bright images of the beam-index system. Trinitron was a major product for Sony for several decades, representing the high-point of conventional color TV displays until the widespread introduction of plasma display
Plasma display
A plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...
s and LCD televisions in the 21st century.
Patents
- U.S. Patent 2,307,188, "Television System", Alda Bedford/RCA, filed 30 November 1940, issued 5 January 1943
- U.S. Patent 2,752,418, "Color Television Indexing System", Richard Clapp/Philco, filed 3 November 1953, issued 26 June 1956
- U.S. Patent 2,910,615, "Photoelectric Control System for Color Television Receivers", Stephen Moulton et all/Philco, filed 31 May 1955, issued 27 October 1959
- U.S. Patent 4,159,484, "Multi-color, single gun, single grid/cathode beam index CRT display system", Lyle Strathman/Rockwell International, filed 1 May 1978, issued 26 June 1979
- U.S. Patent 4,232,332, "Color television receiver", Akira Toyama et all/Sony, filed 22 December 1978, issued 4 November 1980
- U.S. Patent 4,333,105, "Beam-indexing color television receiver", Masaro Kaku et all/Hitachi, filed 20 August 1980, issued 1 June 1982
Further reading
- Mark Heyer and Al Pinsky, "Interview with Harold B. Law", IEEE History Center, 15 July 1975