DAVID T. AMSTRONG
Vice -Pres., Electronics Research…
Is projection the TV of the future? To dale it is
the only Way to obtain a truly large- sized picture.
AMERICA is the land of competition.In the battle of survival of the fittest, woe to the fit or only more fit. This is as true in television
as it was in the case of evolution.Unfortunately, in the practice of many people the “good” becomes the enemy of the “best,” for they seem to say, “Since what we have now is good enough, let’s stay with it and let the better come along and make its own way in the world.”That attitude may be all right for
the average customer, but it is not all right for the enterprising service technician who wants to be in business tomorrow as well as today. He must learn to read the handwriting on the wall without being too critical of the typography. If one interprets the handwriting correctly, it seems that the only logical answer to the
problem of securing truly large -sized pictures is with projection units and that the next boom in television will be in this field. Sure, there are many who will protest that projection has made its appearance and did not “go over.” This is true only to a certain extent. Prices asked for the early projection units were high- ranging as they did from $650.00 up. This economic factor naturally limited the sale of these sets to a relatively small group of consumers. Like all television
receiver prices the price -tags on projection sets have been lowered to the point where the average- income family is now a potential customer.The trend today is obviously toward larger and larger pictures. The seven inch sets, so popular a year or so ago, are now obsolete. The time is coming when today’s ten and twelve inch receivers will have to make way for the newer sixteen and nineteen inch units. In fact the trend is so definitely in the direction of large pictures that one
well -known manufacturer is working on a thirty -inch cathoderay television tube.It’s a funny thing, but the company that made the very earliest cathoderay tubes and controls the basic patents, has been content recently to license other manufacturers to make the direct view tubes under their patents. They are concentrating on projection tubes entirely. If you think they are making a mistake, stick to direct view; but if you suspect they may be right, begin to think about
projection. Most technicians specialize. The author’s field is custom installations and we do about two or three a month, the year around. Actually it makes little
difference whether a client or prospect wants a direct view, RCA projection, or the Norelco Proteigram. We are in business to serve our customers. But at the same time we have the responsibility of providing the very best possible television service at prices our customers can afford. Therefore it pays us to look into the
new developments in the field and to offer the best of these to our discriminating clients. We have installed RCA direct view and projection, GE direct view and
projection, Du Mont, etc., and plans are now under way to use a number of the Norelco Proteigram units. There must be reasons. Figs. 2 and 3 show the fundamentals of the optical principle employed by RCA and the North American Philips Company. Custom building is expensive and presents many specialized and difficult problems. A custom installation is not flexible, for once it is installed there it remains. Thus, great care and much thought must be given to the placement
of the viewing screen. Custom – minded customers and prospects must like an installation, because the best possible advertisement comes from
satisfied customers who are proud of their installation and say so to their friends and guests. Formerly, one of the special problems involved in installation of a projection unit was the great amount of space taken up by the projection components alone. Heretofore, this has required 50 inches of straight line space and about 16 inches of diameter. A study of the required dimensions, shown in Fig. 2, clearly indicates this.
Then the supporting frame for the projection apparatus was bulky. In many instances it was difficult to find suitable depth to house such a unit.
The advent of Protelgram has been hailed by custom -installation technicians because outside of the standard chassis, which may be of the typical 630TS type, a minimum of space is necessary to install the two small additional components required for projection. Most of the basic units needed to operate the projection components are supplied by the 630TS chassis.
A few minor circuit changes which may be readily performed by the average service technician will convert such
a chassis to operate as an excellent projection unit. In fact, the changes are so simple that we have rigged up a small portable assembly for demonstration purposes. This assembly contains a viewing screen, the optical box, and the high voltage unit, the basic parts necessary for this projection system. In addition, a separate power supply and a picture tube protection circuit have been incorporated. A schematic of this circuit is shown in Fig. 4. Another circuit for the production of the necessary video output voltage has also been included for use with such receivers as do not have the required 90 volts peak -to -peak to insure adequate modulation of the high cut -off tubes. This is not generally necessary as any standard 630TS chassis that can drive a 10BP4 or the 12LP4 has sufficient
output and power supply to drive the projection unit. However, since the demonstration unit might be called upon to perform “miracles,” all the necessary circuits to meet any demand presented by any television receiver in the field have been included. The special video output circuit is detailed in Fig. 6. This circuit is typical of that required and has adequate bandwidth for good definition. Be sure that the receiver to be adapted for projection work has an i.f. system capable of passing the full 4.5 mc. band if good results are to be obtained. A receiver with a too narrow bandwidth will not give a sufficiently detailed picture. The actual video circuit changes needed will depend on the particular receiver. In many cases, the only changes necessary are the increase of the video bandpass. Choice of the
proper inductances and capacities will accomplish this in most cases. The values specified in Fig. 6 will serve as a guide in converting present amplifiers
if a complete new video section is not contemplated. This little gadget has been worth its cost many times over. Although it was originally designed to demonstrate the desirable features of the large pictures that are possible with only a few additions to an existing receiver, its use has grown and expanded. There is a minimum number of leads, usually five to seven, depending on the chassis being used, that must be connected to various points on the television chassis. All that is necessary is to expose the under side of the chassis and make connections with alligator clips, turn on the power, and the set is in operation. For safety’s
sake use alligator clips covered with rubber sleeves so that there is no possible danger of accidental short circuiting which could be dangerous and expensive. Use only clips that have positive grip which means high quality clips with powerful springs. You don’t want one of these clips to become dislodged, nor do you want a poor contact. The teeth should bite into the solder when the clips are attached. The frame is made of aluminum so as to be light in weight, neat in appearance,
and easy to fabricate.
The over -all dimensions are governed by the size of the screen. Since the screen used is 12×16 inches, the over -all dimensions
are 14x18x40 inches. A demonstration of this device excites much interest in the mind of a prospect for he can see the precise kind of picture he could have. At the
same time he can see the layout of the component parts and visualize how much space is required for a unitof this type.
This cuts down unnecessary questioning about the availability of placement space for the unit. He can see immediately just how much room must be provided for the installation. One important factor. In this gadget the beam is thrown directly on the viewing screen from the corrector lens. There is no intermediary mirror for folding the beam because a mirror introduces a slight loss of light and reduces the over -all optical efficiency somewhat. Plans are under way to build another unit with a folded beam, using a plane surface mirror because this is a fairly common type of installation. A further possibility has developed from the use of this type unit. Television can and should be built into new homes. Architects should be encouraged to think in terms of built -in projection television so that it will be
possible to have 40 inches over -all straightline distance for this purpose. In some instances it is possible to take an architectural sketch and work in an ideal television setup.
In many cases it is possible to conceal the optical projection box in a cabinet behind the walls. Another possibility is to build the television unit into the
utility room with a straight line 40 inch throw distance or it can be built into a closet on the other side of the living room wall. In this latter instance it would be necessary to use a plane surface mirror to fold the beam. The 40 inches required represent the total length from the bottom of the projection unit housing to the screen itself. The housing measures approximately 9 inches in height while the beam requires a throw of 31 inches. Such built -in projection gives the average family television at its best. When it is built into the structure there is a minimum cost for the installation because all the costs are concentrated on the installation per set. It is not necessary to tear down a partition, cut a hole in a wall, build up a bookcase, or provide some brica- brac shelves to make the television installation less conspicuous. Such extra building involves a cabinet maker, and, while it is the only type of construction possible in existing
structures, it is quite expensive. In a new installation there is no extra carpentry, plastering, or painting directly chargeable to the television receiver
because all of these become part of the final structure. Further, the work is done under the supervision of the architect or builder.
Now, for one of the main uses of this demonstration unit and the reason for which it was originally designed and built. Nobody wants to scrap an existing television receiver. With this Norelco Protelgram nobody has to. Take the case in point. A friend of the author had a fairly good direct view set using the 10BP4 tube and the standard 630TS chassis. The receiver was installed in his living room. Just beneath the living room was a large “whoopee” room in the cellar.
This direct view chassis was modified slightly and tied to the projection unit which was placed in the cellar. By utilizing the space between the
beams there was plenty of room to locate the optical box and the high voltage power supply. With straight line throw and no intervening mirror required to bend the beam, he was getting the best possible 16×12 inch projection picture. He still has his 10 inch direct view receiver, but by the flick of a switch he can turn off the voltage to the direct view tube and direct it to the projection unit for large picture projection in his “whoopee” room.
This is classed as a “dual system.”
It is possible to have a 10 or 12 inch direct view and switch over to the large size picture should the situation warrant. There may be times when a small family group would rather use the direct view tube or there may be other times when the projection picture would be preferable. With a conversion job like this both types of reception are possible. Then, if a tube goes in the middle of a good program, simply switch to the built -in “ace in the hole.” There is another excellent reason
why this dual system offers possibilities for the service technician or engineer. A television installation in a bar is an investment and the picture should be as good as possible. With a dual unit, involving both direct view and projection,
it is possible for the bartender to tune the program in at its best and then switch over to projection. All the controls are accessible to him without leaving his post. In a large bar, say 50 or 60 feet long, it ‘might be possible and desirable to
have two projector units, one at each end of the room. Both could be controlled by a single master tuner with some modifications; and nobody would be outside of the optimum viewing range. This “slave” system could be applied to a club which might find it desirable to have projection in various clubrooms for a hotel which wants to provide multiple installations in the better class rooms, or for a school which wants high quality television in a number of key locations, all to be operated from a master tuner. There are still other interesting features possible with the Protelgram system. It makes large scale projection possible with a quality of resolution, definition, brightness, and clarity that make a living room a telemovie center.
This latest television innovation has been incorporated in the Ansley unit shown in Fig. 1. This type of projection is television at its finest. The cabinet projector throws a 3×4 foot picture through a lens in the front of a “coffee table.” The controls are revealed by moving the top of the cabinet
forward about 6 inches. One of the advantages of this type of unit is that the television receiver is an unobtrusive piece of furniture because the cabinet by the side of the upholstered chair closely resembles a cabinet type coffee table. Probably the ultimate in simplicity and appeal in the use of Protelgram
is in a unit made by Avery Fisher, president of the Fisher Radio Company of New York City. He has gone into projection in a big way and has had tuner and sweep components designed and manufactured to fit into the unused space of the projection receiver. As a result, he has been able to produce a table model with over -all
dimensions of 253/a” long, 21″ deep, and 14″ high. The top lifts up to reveal a viewing screen.
The simplicity of the unit is manifest in the three controls, one for tuning in the various channels, another for brightness, and a third for vertical or horizontal focusing. Because the cost of the optical box and the high voltage unit is moderate, it is entirely possible that soon television receivers incorporating the Protelgram feature will be available at prices comparable to those now asked for 16 inch direct view receivers. Obviously you will get the best out of projection if you design “a special chassis to provide just the right output required for the optimum operation of the system. In their haste to cash in on something good, too many manufacturers have simply added Protelgram to existing cabinets and chassis. The waste of space and undesirable cable lead length which results have proven costly. By redesigning the tuner chassis, sweep chassis, and power supply to fill in all the space surrounding the optical box, it is possible to produce a compact unit. Some manufacturers are alert to the importance . of this new kind of television and have designed special circuits to feed the 3NP4 projection type kinescope. The service technician
who knows his circuits will readily appreciate the fact that there are no particular changes from standard design for television circuits. This circuit
represents straightforward television engineering up to the point of feeding the picture into the Protelgram system. In the Scott circuit recognition was given to the fact that the electrical focus of the Protelgram system changes the signal strength with brightness or contrast more sharply than with direct view receivers, and a focus control has been provided on front panel. This control might have been eliminated by controlling the maximum end of the brightness control
by introducing a screwdriver – actuated or service control, which would limit the amount of brightness available to a point at which the focus control need not be shifted. The Scott circuit also provides the proper input d.c. voltage to the Philips 25 kc. high voltage unit. A 6SN7 tube is used as a protection tube to
cut off the high voltage to the 3NP4 in the event of failure in the sweep circuits. This is good engineering since the screen on the picture tube
face will be burned if the electron beam is concentrated on it in a narrow line for even a few seconds.
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