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|December 1947 Radio News|
|[Table of Contents] These articles are scanned and OCRed from old editions of the Radio & Television News magazine. Here is a list of the Radio & Television News articles I have already posted. All copyrights are hereby acknowledged.|
In the early days of television, what we today refer to as cathode ray tubes were called kinescopes. The kinescope on the receiving end displayed images generated by a tube called an iconoscope on the transmission end. Kinescopes had round faces onto which a rectangular picture was electronically drawn. Once manufacturing technology evolved sufficiently, it became possible to make them rectangular in order to save on material and to fit a larger picture in a smaller area. The real story in this article from my perspective is appreciating the ingenuity of the manufacturing engineers for an ability to develop machines that handle very complex operations. They were wonders of electromechanical manipulation. There were still some operations that needed human dexterity and decision making.
Television Tubes by the Thousands
By Frank E. Butler
A modern miracle of mass production is typified by the ingenious wedding of automatic machinery, technical skills, and quality-controlled materials.
The Age of television is at hand and to speed its progress toward perfection, groups of technical experts in widely divergent professions such as electronics, optics, and the glass industries are contributing their share of scientific knowledge and experience to this end.
The technological advance is so rapid, both in monochrome and color television transmission and receiving equipment, that pictures by both systems are now being shown with surprising realism and clarity. Only very little of this advanced development remains in the laboratory stage and this is sufficiently developed to insure its appearance in homes much sooner than most of us had expected.
The rapidity and skill with which this progress has been made by television laboratories and their confidence in the future of television is evidenced by the building of new plants and the designing of special machinery for the manufacture of equipment. Therefore a peep behind the scenes of television activity should prove of unusual interest at this time.
The heart of television is the iconoscope - the electronic device capable of detecting the image or scene of action that is to be televised through space, then subsequently translating the reflected light into electric impulses.
The kinescope is a similar electronic tube which reverses the above action whereby the televised impressions are transformed back into light to form a reproduced image or "picture" on the sensitive face of the tube. To create these two companion tubes, which must combine delicateness, ruggedness, and utmost sensitivity, requires the use of nimble fingers, keen eyes, highly developed skills, modern automatic machinery and the best techniques that can be devised by the several different industries involved in the manufacture of tubes.
The factory where these tubes are . produced must be fully air conditioned and the humidity level must be maintained at a predetermined level. In addition, the factory must also be equipped with dust filters in order to eliminate impurities which might affect the sensitive tube elements.
There are two kinds of kinescopes produced - one known as the electronic direct view type, and the other as the projection type. From the small kinescope which produces exceptionally brilliant images which are subsequently enlarged optically for projection on a viewing screen of a 7 1/2 x 10 or 18 x 24 foot theater size, to the largest kinescopes which have a 10 or 12 inch face from which the image is viewed directly (without enlargement), there are many precise and intricate operations which must be performed on both the tube elements and the glass bulb.
One of the first glass operations in the production of kinescopes or iconoscopes is to make the flare of the stem which holds the elements. This is done on the flare machine shown in Fig. 2. Here gas fuel is used to heat the glass parts as they index around the automatic machine, in various stages, to temperatures rangng from 600°C. to 900°C. After a small section has been cut off and the end flared, the bottom portion is heated by a special gas flame pattern which places the heat exactly where it is wanted at the proper temperature for flat pressing. Heating time is controlled by the speed at which the machine indexes from station to station.
A battery of automatic flare machines is used in making the glass stems in which the tube element supporting the lead-in wires are sealed. Specially designed gas burners, emitting predetermined flame patterns heat the glass tubing to various stages of viscosity in order that it may be flat pressed into a stem. All of the equipment that utilizes heat in any form for processing is efficiently hooded and ventilated to carry off excess heat and the products of combustion.
Fig. 6 - Next step is the insertion of the "button" in the side of the bulb by means of a gas-fired torch. Operator softens the glass, punctures a hole, and inserts button.
When this part has been formed, the lead-in wires to the tube elements are inserted and the assembled element units are placed on another automatic gas-fired machine where special flame patterns heat those parts of the stem to just the proper temperature and for just the correct time to effectively seal the wires into the glass stem. Annealing takes place immediately after the part has reached the last position on the machine. The unit is then ready for mounting the tube electrodes, after which it is prepared to be sealed into a bulb-blank, which resembles a large glass funnel with a long stem.
Fig. 7 - Baking on the colloidal graphite coaling requires approximately one and a half hours at 400°C in a gas-fired oven. A specially designed oven is used in this operation.
The bulb or kinescope blanks are subjected to many processes and operations; the first being a thorough washing, inside and out, after which they are placed in specially constructed racks in the "settling-room" Fig. 3. This room is constructed on its own foundation and the floor is composed of a heavy concrete slab floating on a layer of cork. There is no physical connection to any other part of the building, thus eliminating any transmission of vibration. A measured quantity of liquid containing a fluorescent substance is then placed in each tube. The preparation of this fluorescent solution requires a high degree of skill and accuracy. The operation is shown in Fig. 4.
Next, the coating, in suspension, is carefully and accurately poured into the kinescope bulb. See Fig. 5. Slowly, the solid, active fluorescent material settles on that part of the tube face on which the electrons react to produce the image. When the settling process is complete, the remaining liquid is carefully decanted.
The next step in the manufacture of the tube is the insertion of a "button" in the side of the bulb. This operation, which is illustrated in Fig. 6, is performed by means of a gas-fired torch. The operator softens the glass, punctures a small hole and inserts the "button" or electrical contact which is then hermetically sealed in the tapered section of the bulb. The tube is then annealed at 450°C. by means of a continuous gas-fired radiant tube glass lehr where the cycle of passing through the heated air ranges from four to six hours, depending on the size of the tube.
The inside of the bulb is next coated with a colloidal graphite mixture which serves to carry off the electron charges after they bounce back from the screen. The grounded electrical circuit is through the "button" previously described. Next, this inner graphite coating is subjected to a baking cycle which is performed at temperatures of 400°C. for approximately one and a half hours. This operation is shown in Fig. 7.
The operator now applies a coating of non-reflecting carbon to the interior of the tube by means of a long handled brush (See Fig. 8). This coating keeps stray electrons from the picture screen.
Fig. 9 shows the operator adjusting the delicate electrical components that are to be inserted in the tube. At this stage of production, the prepared bulb is ready to be sealed to the glass stem which supports the internal elements, or electron gun. This operation takes place on a completely automatic gas-fired sealing machine (Fig. 10) where the elements are set in the tube, the flare and bulb are sealed, and the collet cut off. These operations take place as the tubes index around the machine to their respective stations where varying patterns of gas flames perform the successive operations on the glass. At the final station the excess neck of the bulb, or collet, is cut off when the No. 6 lime glass of which the kinescope blanks are made is heated to 1050°C. by a needle flame which produces a clean, sharp cut.
Fig. 11 shows a close-up view of the six needle gas flames which concentrate on the bulb neck where the collet is cut off as the tube revolves in the flame. The large gas burner, shown at the right of the photograph, performs the annealing operation. When the vacuum process has reached its final position, the tube is "tipped off" - an operation w h i c h seals the tube permanently and severs its connection to the vacuum pump.
After sealing, the tube progresses to an exhaust machine where an extremely high vacuum is developed. While on this machine, the glass bulb is heated by radiant heaters to its softening point to assist the vacuum pump in removing occluded moisture and gases. The electron gun and other internal elements are heated by high frequency induction methods and, at another stage in the process, working voltages are applied to the tube elements themselves.
After the tube has been evacuated and severed from the exhaust machine, the operator threads the lead-in wires into the socket base of the kinescope. This operation is shown in Fig. 12.
Final tests are then run on the complete kinescopes. The operator (Fig. 14) uses a special chart as a reference standard. Following this testing, the tubes undergo a 500-hour operational test (Fig. 13).
Larger television pictures obtainable in the projection system are the result of an optical development which is an outgrowth of a discovery revealed in 1932 by Bernard Schmidt, a research assistant in a German laboratory. At that time astronomical photography was unsatisfactory, due to spherical aberrations caused by the mirror used to reflect light from the stars and planets to the camera. By placing a "correcting lens" (corrector plate) between the mirror and the camera, Schmidt discovered that he obtained much clearer pictures. These plates, however, had to be ground by hand, and prior to the war there were only a few in existence because of the extreme difficulty of their manufacture. During the war, American scientists developed a new method for mass producing these "corrector plates" which were used in infrared viewing devices. Now, tens of thousands of these plates, embodying the same technique are being used for television reception. They are made by heating a flat piece of glass until it flows into the specially curved surface of a refractory on which the glass is placed. This mold is made of special composition that does not adhere to the glass and yet permits it to assume the desired curvature. One side of the glass is then ground and polished to a plane surface.
The mirror is aluminized in such a way that the reflectivity will be as high as possible. The problem of aluminizing large surfaces and producing an aluminum surface of the required durability was not simple, but it was solved .
Another contribution to the development of television receiving sets was the result of a war-time invention for producing glareless glass. This process makes possible the reception of clearer, sharper television pictures. The successful removal of light-consuming reflections from a television tube's glass face, which serves as the screen of a direct-viewing home television receiver, has been obtained through a new glare-removal technique which also produces images of greater clarity when applied to the optical system of the projection type. The technique was developed during the war to increase the efficiency of such military optical instruments as binoculars which gained over 60 percent in light transmission when reflections were reduced. Reflections are removed by directly coating the face of the television tube with a secret chemical composition. It is not necessary to disassemble the tube for the coating process or to apply the coating in the vacuum chambers used in earlier glare-removing techniques.
Fig. 14 - One of the test procedures used in checking the performance of kinescopes used in home television receiving sets.
The coating improves the reception of television pictures by: (1) Reducing reflections in the glass face of the tube caused by light sources in the room housing the receiver. (2) Reducing the intensity of false images caused by reflections from the outer surface of the image-producing fluorescent screen in the tube, thus increasing the sharpness of the images. (3) Reducing light losses from reflections, thus increasing the amount of light transmitted.
It is a tribute to glass craftsmen, machine designers, optical technicians, skilled operators, and electronic engineers that these relatively high temperatures, automatic operations, accurate optical amplification, and extreme electronic sensitivity can be used effectively in such narrow confines as the interior of television tubes - the iconoscope and the kinescope - an accomplishment which has been due to the efforts of these men of vision and still working in close cooperation.
Posted September 8, 2015