Light Tube Helps Radio (1925)

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Light Tube Helps Radio (1925) 
12.Jan.14 15:38
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Georg Richter (D)
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Georg Richter

Extracted from "Radio Digest" Vol.XV No.6 of November 14th, 1925. The author is yet unknown.


Light tube helps radio

New Hok-Up Will Benefit Air Pictures

Photo-Electric Cell Combined with Radio Amplifier Has Vast Possibilities

NEW YORK. — The photo-electric cell, which is used in turning light into electrical current in picture telegraphing, in talking films, in new types of phonographs, in television experiments and in many other processes, has been combined by V.K. Zworykin, a physicist of the Westinghouse Electric Research Laboratories, with the Radio vacuum tube amplifier forming a new scientific device of vast possibilities, which was exhibited publicly for the first time.

Variations of light falling on this instrument, which looks nearly the same as an ordinary Radio tube, instantly become variations of electrical current and are  amplified many thousandfold.

The photo-electric cell, which makes electricity out of light, is built into the standard Radio tube. One end of the Radio tube is coated on the inside with potassium or some other alkaline metal which throws off showers of electrons when light falls on it. Electron showers are electrical currents. The shower is feeble if the light is feeble, heavy if the light is strong. Any variation in light changes the intensity of the electron shower. The current which the light strikes out of the alkali metals is amplified before it leaves the tube.

Represents Three Years Work

Three years ago Zworykin got the idea of uniting the tube and the photo-electric cell. For the last year and a half he has been at work in the Westinghouse laboratories overcoming the practical difficulties. The instrument was so complex and sensitive that it was difficult to prevent any one part from interfering with the action of the others. For instance, if any of the filaments of the tube produced a light of its own, this would upset the whole apparatus, because the photo-electric cell would respond to that light, instead of to external light. Overcoming these difficulties, Zworykin exhibited yesterday a tube so sensitive to light changes that the smoke of a cigarette was utilized to ring a bell. The smoke came between a lantern and the Zworykin device. It intercepted enough light to lower the electrical current which the light from the lamp had been producing. The fall in current permitted a switch to close and rang the bell. Using the device in connection with a loud speaker, the inventor produced a howl by passing a wire one millimeter thick between the lantern and the cell.

Has Many Uses

The photo-electric cell is at present used in combination with the amplifying tubes for a great variety of

purposes, including the turning of printed words into musical sounds, so that the blind may read by ear; the steering of torpedoes, ships or automobiles by Radio; the transmission of pictures by wire and Radio; the attempt to transmit motion pictures by Radio; the reproduction of sound by phonographs which use films instead of wax records, and the measuring of the light of stars and planets.

When used in combination, the current which is produced by light 'in the photoelectric cell is led off to the vacuum tube and there amplified. This method requires the use of more apparatus and tends toward cumbersomeness. Zworykin's invention makes it possible to simplify apparatus in all processes which call for the conversion of light into electricity.

Mr. Zworykin said yesterday that the Westinghouse company was working on a process for transmitting pictures by Radio, and that this would be useful in this connection.

Optimistic on Television

Speaking of television, or the projection of motion pictures, on which several inventors' are working, Mr.Zworykin said: "All the processes that are needed for projecting motion pictures are in existence already. The theory is all right, but at present the apparatus would have to be endless, cumbersome and uncertain. But it will be simplified. It will take some years, but we will have eventually the instantaneous or near-instantaneous transmission of motion pictures."

The inventor said he thought the new combination tube was a step in the direction of television, but nothing more. One of the Zworykin patents covers a combination of his photo-electric and Radio tube with the interferometer invented by A. A. Michelson, the American astronomer. The interferometer is the most sensitive measuring instrument known.

Expects Extensive Patent

The Michelson invention is so sensitive that its performances can be disturbed by the slightest sound. The patent, which Zworykin is seeking to cover both his own combination of devices and the interferometer, is intended to give him the rights over any microphone that may be produced by the combination of all three.

"It might be possible," he said, "to combine the principles and produce the most sensitive microphone in the world. The interferometer responds to pressure by changes in its shadows, or interference fringes. It might be possible to arrange the grids of the photo-electric cell in such relation to the interference fringes so as to produce disturbances of current corresponding to the disturbances produced by the sound waves in the interferometer. The trouble is now that such a combination of instruments would react wildly and violently to sound. It would be necessary to find some way of controlling their oversensitivity. I covered this combination by patents, but of course, many things are patented which do not come to pass."

The physicist said that his invention could be used for measuring the light of stars  and  for recording continuously the light of variable stars: This is now being done by astronomers using the photo-electric  cell and the tube separately.

Another application is a burglar alarm, the gong being set in action when the burglar passes between a window and the photo-electric cell. It is said to have manifold uses in railroad signalling.


 

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