General Electric
General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...
's Porta-Color was the first "portable"
color television
Color television or Colour television is a television transmission technology that includes color information for the picture, so the video image can be displayed in color on the television set. It improves on the monochrome or black-and-white t ...
introduced in the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
in 1966.
The Porta-Color set introduced a new variation of the
shadow mask
The shadow mask is one of the two technologies used in the manufacture of cathode-ray tube (CRT) televisions and computer monitors which produce clear, focused color images. The other approach is the aperture grille, better known by its t ...
display tube. It had the
electron gun
An electron gun (also called electron emitter) is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy. The largest use is in cathode-ray tubes (CRTs), used in nearly ...
s arranged in an in-line configuration, rather than
RCA
The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Comp ...
's delta arrangement. The main benefit of the in-line gun arrangement is that it simplified the convergence process, and did not become easily misaligned when moved, thus making true portability possible. There were many variations of this set produced from its introduction in 1966 until 1978, all using GE's Compactron vacuum tubes (valves).
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.
History
Basic television
A conventional black and white television (B&W) uses a tube that is uniformly coated with a
phosphor
A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or vi ...
on the inside face. When excited by high-speed
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kn ...
s, the phosphor gives off light, typically white but other colors are also used in certain circumstances. An
electron gun
An electron gun (also called electron emitter) is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy. The largest use is in cathode-ray tubes (CRTs), used in nearly ...
at the back of the tube provides a beam of high-speed electrons, and a set of
electromagnets
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in t ...
arranged near the gun allow the beam to be moved around the display.
Time base generator A time base generator (also timebase or time base) is a special type of function generator, an electronic circuit that generates a varying voltage to produce a particular waveform. Time base generators produce very high frequency sawtooth waves spec ...
s are used to produce a scanning motion. 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 color model
The RGB color model is an additive color model in which the red, green and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three additiv ...
) when excited. When excited in the same fashion as a B&W tube, the three phosphors produce different amount of these
primary color
A set (mathematics), set of primary colors or primary colours (see American and British English spelling differences#-our, -or, spelling differences) consists of colorants or colored lights that can be mixed in varying amounts to produce a gamu ...
s, which mix in the human eye to produce an apparent color. To produce the same resolution as the B&W display, a color screen must have three times the resolution. This presents a problem for conventional electron guns, which cannot be focused or positioned accurately enough to hit these much smaller individual patterns.
Shadow mask
The conventional solution to this problem was introduced by
RCA
The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Comp ...
in 1950, with their
shadow mask
The shadow mask is one of the two technologies used in the manufacture of cathode-ray tube (CRT) televisions and computer monitors which produce clear, focused color images. The other approach is the aperture grille, better known by its t ...
system. The shadow mask is a thin steel sheet with small round 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 hit 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 as the beam passes over the opaque sections between the holes. This means that the beams must be greatly increased in power to produce acceptable brightness when they do pass through the holes.
The General Electric Porta-Color
Paul Pelczynski was the project leader in the conception and production of the General Electric Porta Color in 1966.
![Schlitzmaske](https://upload.wikimedia.org/wikipedia/commons/4/47/Schlitzmaske.jpg)
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
Penetron 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. Pene ...
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 much-simplified convergence adjustments of the three beams, compared to the conventional delta shadow mask tube. This differed sufficiently from RCA's design to allow GE to circumvent the patents. It is important to realize that the GE 11" tube still had round mask holes and phosphor dots, not rectangular ones as in the later slot-mask tubes. The innovation here was with the in-line guns as opposed to the triad arrangement.
This change, which allowed vastly simpler convergence measures, together with the use of GE's own Compactron multi-function vacuum tubes 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 an 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. GE continued refining this system, up until 1978, which marked the end of production of vacuum tube type television receivers.
GE produced the basic Porta-Color design well into the 1970s, even after most companies had moved to
solid state designs when
transistor
upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink).
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
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 the "slot-mask" designs, including RCA.
Description
![DeltaGun](https://upload.wikimedia.org/wikipedia/commons/d/d3/DeltaGun.svg)
In a conventional
shadow mask
The shadow mask is one of the two technologies used in the manufacture of cathode-ray tube (CRT) televisions and computer monitors which produce clear, focused color images. The other approach is the aperture grille, better known by its t ...
television design the
electron gun
An electron gun (also called electron emitter) is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy. The largest use is in cathode-ray tubes (CRTs), used in nearly ...
s at the back of the tube are arranged in a triangle. They are individually focused, 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 (the "in-line gun") instead of a triangle (the "delta gun"). This meant that after they passed through the mask they separated horizontally only, hitting phosphors that were also arranged side by side. Otherwise, the GE design retained the round dot structure.
Later, Sony changed the whole game, replacing the shadow mask with an aperture grille and the phosphor dots with vertical phosphor stripes. They cleverly implemented a single electron gun with three independent cathodes, later branded
Trinitron
Trinitron was Sony's brand name for its line of aperture-grille-based CRTs used in television sets and computer monitors. One of the first truly innovative television systems to enter the market since the 1950s, the Trinitron was announced in ...
, all of which greatly simplified convergence.
Toshiba then countered this with their slot-mask system, which was somewhat in-between the Trinitron and the original delta-mask systems.
Sony attempted to stop Toshiba from producing their in-line gun system, citing patent violations, but Toshiba won this battle, and the Toshiba tube eventually became the standard in most domestic television receivers.
Collecting General Electric Porta Color Televisions
Over the years, the Porta Color has attracted interest as an old (dead) technology to be rescued. Once considered throw-away items, the Porta Color has become a collectible item, being the last all-vacuum tube color television made in the US.
See also
*
Penetron 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. Pene ...
Further reading
* http://www.earlytelevision.org/ge_portacolor.html
References
Notes
Bibliography
* "Business News", ''Forbes'', Volume 97 (1966), pg. 122
* Bill Hartford
"Color for $200?" ''Popular Mechanics'', November 1968, pp. 122–127, 256
* Jim Luckett
"New TV tubes lock in better color pictures" ''Popular Mechanics'', May 1974, pp. 85–89
{{refend
General Electric
History of television
Television technology
Vacuum tube displays
Early color television