Porta-Color
Encyclopedia
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
display introduced by RCA
. The original Porta-Color set remained in production from its introduction in 1966 until at least 1978, without changing its original tube-based chassis or making other major changes.
The name has been variously written, even in GE's literature as "Porta Color", "Porta-Color" and "Porta-color". The name may also refer to the specific television model, or less commonly, the style of television tube it used.
on the inside face. When excited by high-speed electron
s, the phosphor gives off light, typically white but other colors are also used in certain circumstances. An electron gun
at the back of the tube provides a beam of high-speed electrons, and a set of electromagnets arranged near the gun allow the beam to be moved about the display. The television signal is sent as a series of stripes, each one of which is displayed as a separate line on the display. The strength of the signal increases or decreases the current in the beam, producing bright or dark points on the display as the beam sweeps across the tube.
In a color display the uniform coating of white phosphor is replaced by dots or lines of three colored phosphors, producing red, green or blue light (RGB) when excited. When excited in the same fashion as a B&W tube, the three phosphors give off different amount of these primary color
s, which mix in the human eye to produce a single apparent color. In order to produce the same resolution as the B&W display, a color screen needs to have three times the resolution. This presents a problem for conventional electron guns, which cannot be focussed or positioned accurately enough to hit these much smaller individual patterns.
in 1950, with their shadow mask
system. The shadow mask is a thin metal foil with small holes cut into it, positioned so the holes lie directly above one triplet of colored phosphor dots. Three separate electron guns are individually focussed on the mask, sweeping the screen as normal. When the beams pass over one of the holes, they travel through it, and since the guns are separated by a small distance from each other at the back of the tube, each beam has a slight angle as it travels through the hole. The phosphor dots are arranged on the screen such that the beams hits only their correct phosphor.
The primary problem with the shadow mask system is that the vast majority of the beam energy, typically 85%, is lost "lighting up" the mask itself as the beam passes over the opaque sections between the holes. This means that the beams have to be greatly increased in power in order to produce an acceptable brightness when they do pass through the holes.
concept, but were never able to make it work as a basic color television, and started looking for alternate arrangements. GE eventually improved on the basic shadow mask system with a simple change to layout.
Instead of arranging the guns, and phosphors, in a triangle, their system arranged them side-by-side. This meant that the phosphors did not have to be displaced from each other in two directions, only one, which allowed them to be extended vertically to form short stripes instead of small dots. This simple change dramatically increased the painted area of the screen; a contemporary shadow mask design might have 25% of the screen surface covered by phosphor, but in the Porta-Color layout this was improved to about 50%. This doubled the brightness of the system with no other changes.
This change allowed GE to reduce the power of the guns, which led to reductions in size of the entire chassis. GE used the small size of their system as the primary selling feature. The original 28 pound set used a 11" tube and sold for $249, which was very inexpensive for a color set at that time. Introduced in 1966, the Porta-Color was extremely successful and led to a rush by other companies to introduce similar systems. By 1968 there was a wide variety of sets in the $200-$300 range, which led to the popularization of color television after over a decade of being largely ignored in the market.
GE produced the basic Porta-Color design well into the 1970s, even after most companies had moved to solid state
designs when transistor
s with the required power capabilities were introduced. The Porta Color II was their attempt at a solid state version, but did not see widespread sales. The basic technology, however, was copied into GE's entire lineup as product refresh cycles allowed. By the early 1970s most companies had introduced these "slot-mask" designs, including RCA.
television design the electron gun
s at the back of the tube are arranged in a triangle. They are individually focussed, with some difficulty, so that the three beams meet at a spot when they reach the shadow mask. The mask cuts off any unfocussed portions of the beams, which then continue through the holes towards the screen. Since the beams approach the mask at an angle, they separate again on the far side of the mask. This allows the beams to address the individual phosphor spots on the back of the screen.
GE's design modified this layout by arranging the electron guns in a side-by-side line instead of a triangle. This meant that after they passed through the mask they separated horizontally only, hitting phosphors that were also arranged side-by-side. Since the phosphors were no longer arranged around each other, they could be extended vertically and made much larger. The mask was similarly modified with slot-shaped holes instead of round ones, and was sometimes referred to as a "slot-mask".
Sony
's Trinitron
system is similar in concept, but introduced two additional improvements. Unlike the Porta-Color, Trinitron used a single gun with three cathode
s, which simplified the arrangement and eliminated focussing issues. Additionally, Sony extended the slots until they were the same vertical size as the entire screen, further improving the painted area, and thus the brightness to power figures.
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 was the first "portable" color television
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....
introduced in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. 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
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...
display introduced 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...
. The original Porta-Color set remained in production from its introduction in 1966 until at least 1978, without changing its original tube-based chassis or making other major changes.
The name has been variously written, even in GE's literature as "Porta Color", "Porta-Color" and "Porta-color". The name may also refer to the specific television model, or less commonly, the style of television tube it used.
Basic television
A conventional black and white television (B&W) uses a tube that is uniformly coated with a phosphorPhosphor
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...
on the inside face. When excited by high-speed 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 phosphor gives off light, typically white but other colors are also used in certain circumstances. 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 provides a beam of high-speed electrons, and a set of electromagnets arranged near the gun allow the beam to be moved about the display. The television signal is sent as a series of stripes, each one of which is displayed as a separate line on the display. The strength of the signal increases or decreases the current in the beam, producing bright or dark points on the display as the beam sweeps across the tube.
In a color display the uniform coating of white phosphor is replaced by dots or lines of three colored phosphors, producing red, green or blue light (RGB) when excited. When excited in the same fashion as a B&W tube, the three phosphors give off different amount of these primary color
Primary color
Primary colors are sets of colors that can be combined to make a useful range of colors. For human applications, three primary colors are usually used, since human color vision is trichromatic....
s, which mix in the human eye to produce a single apparent color. In order to produce the same resolution as the B&W display, a color screen needs to have three times the resolution. This presents a problem for conventional electron guns, which cannot be focussed or positioned accurately enough to hit these much smaller individual patterns.
Shadow masks
The conventional solution to this problem was introduced by RCARCA
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...
in 1950, with their 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...
system. The shadow mask is a thin metal foil with small holes cut into it, positioned so the holes lie directly above one triplet of colored phosphor dots. Three separate electron guns are individually focussed on the mask, sweeping the screen as normal. When the beams pass over one of the holes, they travel through it, and since the guns are separated by a small distance from each other at the back of the tube, each beam has a slight angle as it travels through the hole. The phosphor dots are arranged on the screen such that the beams hits only their correct phosphor.
The primary problem with the shadow mask system is that the vast majority of the beam energy, typically 85%, is lost "lighting up" the mask itself as the beam passes over the opaque sections between the holes. This means that the beams have to be greatly increased in power in order to produce an acceptable brightness when they do pass through the holes.
Porta-Color
General Electric (GE) had been working on a variety of systems that would allow them to introduce color sets that did not rely on the shadow mask patents. Through the 1950s they had put considerable effort into the PenetronPenetron
The penetron, short for penetration tube, is a type of limited-color television used in some military applications. Unlike a conventional color television, the penetron produces a limited color gamut, typically two colors and their combination...
concept, but were never able to make it work as a basic color television, and started looking for alternate arrangements. GE eventually improved on the basic shadow mask system with a simple change to layout.
Instead of arranging the guns, and phosphors, in a triangle, their system arranged them side-by-side. This meant that the phosphors did not have to be displaced from each other in two directions, only one, which allowed them to be extended vertically to form short stripes instead of small dots. This simple change dramatically increased the painted area of the screen; a contemporary shadow mask design might have 25% of the screen surface covered by phosphor, but in the Porta-Color layout this was improved to about 50%. This doubled the brightness of the system with no other changes.
This change allowed GE to reduce the power of the guns, which led to reductions in size of the entire chassis. GE used the small size of their system as the primary selling feature. The original 28 pound set used a 11" tube and sold for $249, which was very inexpensive for a color set at that time. Introduced in 1966, the Porta-Color was extremely successful and led to a rush by other companies to introduce similar systems. By 1968 there was a wide variety of sets in the $200-$300 range, which led to the popularization of color television after over a decade of being largely ignored in the market.
GE produced the basic Porta-Color design well into the 1970s, even after most companies had moved to solid state
Solid state (electronics)
Solid-state electronics are those circuits or devices built entirely from solid materials and in which the electrons, or other charge carriers, are confined entirely within the solid material...
designs when transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
s with the required power capabilities were introduced. The Porta Color II was their attempt at a solid state version, but did not see widespread sales. The basic technology, however, was copied into GE's entire lineup as product refresh cycles allowed. By the early 1970s most companies had introduced these "slot-mask" designs, including RCA.
Description
In a conventional 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...
television design the 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 at the back of the tube are arranged in a triangle. They are individually focussed, with some difficulty, so that the three beams meet at a spot when they reach the shadow mask. The mask cuts off any unfocussed portions of the beams, which then continue through the holes towards the screen. Since the beams approach the mask at an angle, they separate again on the far side of the mask. This allows the beams to address the individual phosphor spots on the back of the screen.
GE's design modified this layout by arranging the electron guns in a side-by-side line instead of a triangle. This meant that after they passed through the mask they separated horizontally only, hitting phosphors that were also arranged side-by-side. Since the phosphors were no longer arranged around each other, they could be extended vertically and made much larger. The mask was similarly modified with slot-shaped holes instead of round ones, and was sometimes referred to as a "slot-mask".
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 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 is similar in concept, but introduced two additional improvements. Unlike the Porta-Color, Trinitron used a single gun with three cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
s, which simplified the arrangement and eliminated focussing issues. Additionally, Sony extended the slots until they were the same vertical size as the entire screen, further improving the painted area, and thus the brightness to power figures.