American television directory (1946)

TELESETS include large-image television screen, FM, standard broadcast, record changer and recording facilities. This model features a disappearing screen which tilts back into the teleset when it's not in use. Console models are designed in both classical and modern styles. BUILT-IN TELESET — The mechanism is concealed, leaving an 18-inch "direct view" screen vis¬ ible. A "direct view" picture, as distinguished from reflective and projection systems, is shown on the flattened, luminescent screen-face of a large picture receiving (cathode-ray) tube. focusing system. It would seem from this array of advantages that there is little question as to which is the most satisfactory, providing the audience is satisfied with an image no larger than 13 V2" x 18". A Disappearing Screen Of course there are some disadvan¬ tages to be recorded for direct-viewing television. There is a slight curvature of the screen which introduces some dis¬ tortion of the image. This is being largely overcome by flatter-faced tubes. Then there is the length of the tube which, mounted in the normal horizon¬ tal position, makes for a cabinet of awkward depth. The 20-inch tube is 31 inches long. However, we have ingeni¬ ously circumvented this awkwardness by mounting the tube in a swinging cradle so that it remains in the ver¬ tical position when the teleset is not in use, and is brought to the horizontal position only for actual viewing. With this tube-mounting we have reduced the cabinet depth to 24 inches or less. Considering the advantages of directviewing in greater detail, we find that the high light brightness of the 20-inch tube is in the order of 20 foot lamberts as compared with approximately 3.5 lamberts for the most efficient projec¬ tion system now in use. In both cases the picture size is considered to be 1314" x 18". The higher light brilliance means that the 20-inch teleset can be used satisfactorily in a brilliantly illu¬ minated room. An ambient light level as high as 5 foot lamberts can be tolerated without seriously impairing the picture quality. With the projection system only about .5 foot lamberts average ambient light can be tolerated. It is interesting to compare the brilliance of the picture on the 20-inch tube with that of normal commercial 35 mm. movies which aver¬ age between 6 and 10 foot lamberts. As regards brightness ratio or con¬ trast range, the 20-inch tube has a con¬ trast range of approximately 35, as compared with 17 for the projection system. This is an extremely important characteristic of the television picture since in many cases the lack of contrast gives viewers the impression of poor resolution. As to directivity (maximum viewing angle from the normal angle at which the apparent brightness decreases to 50% of its value in normal direction) we find that the 20-inch tube can be viewed from ±80°, whereas the projec¬ tion system can only be viewed from ±15°. It is, of course, possible to widen this angle somewhat in the projection system but in so doing the high light brightness will decrease from its al¬ ready low value. Life of Cathode-Ray Tubes In making these comparisons we have assumed an accelerating voltage on the 20-inch tube of 15 kilovolts, and 30 kilo¬ volts on the 5-inch flat-faced tube of the projection system. It is obvious that the lower accelerating voltage of the directviewing tube effects certain economies in the manufacture of the receiver. But aside from first costs, there is a marked difference in operating costs. With the 20-inch direct-viewing tube the spot size is sufficiently small to re¬ solve any 525-line television pattern or even higher, with a well-designed de¬ flection yoke, whereas care must be taken with the 5-inch projection tube to obtain full 525-line resolution. Forget¬ ting spot size for the moment, the reso¬ lution on the 5-inch tube is considerably reduced by light scattering on the fluo¬ rescent surface as well as on the transluscent screen. With the direct-viewing tube all elements are aligned within the glass envelope, as against the tube and optical system to be aligned in the pro¬ jection method. In order to focus the picture on the direct-viewing tube, it is only necessary to make an electrical ad¬ justment, whereas both electrical and optical adjustments are necessary in the projection system. Furthermore, unless the latter’s optical elements are properly protected, the picture is apt to deteriorate with age of equipment. Our organization has developed a projection unit that produces a 3' x 4' image on a suitable wall screen — more than four times as large as any pic¬ tures for home projection yet demon¬ strated. Our compact projector has a tested range of picture sizes from 18" x 24" to 414' x 6'. We believe this pro¬ jector has a place in the very large living room or playroom, and even far more so in the schoolroom, club, church, department store or other public place. Built-in Wall Telesets In a home desiring a large picture on the wall that can be viewed from dif¬ ferent parts of a fair-sized room, we favor the custom-built installation — a receiver built into the wall with the tube-screen suitably framed at any height desired. On the basis of bright, detailed, goodgradation pictures, at an attractive first cost and with low operating ex¬ penses, I hold that the direct-viewing teleset has exceptional advantages. But I am quick to admit that there is a place for the projection type set where cost is secondary to the desire for maximum screen sizes for the purpose of entertaining large groups in utmost comfort. 17