US2202614A - Cathode ray transmitting tube - Google Patents

Description

May 28, 1940.

M. ABRAHAMSOHN CATHODE RAY TRANSMITTING TUBE U Filed July 10, 1937 INVENTOR MAX ABE/1H MSG/lb ATTORNEY Patentecl May 28, 1940 ATENT oFFicE CATHODE RAY TRANSMITTING TUBE Max Abrahamsohn, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application July 10, 1937,. Serial No. 152,931 In Germany July 23, 1936 3 Claims.

The invention is concerned with a picture transmission cathode ray tube with a mosaic plate of the Iconoscope type.

A picture transmission or television tube of this kind comprises a plate of insulation material whose face or surface bears a myriad of electrically conducting globules consisting, for instance, of silver. These mosaic elements are disposed at close proximity to one another and they are photo-sensitized. In practical use, an image of the object is projected upon the mosaic plate with the result that an electric pattern of the object in the form of a multitude of electrostatic charges is produced thereon, the size of the said charges corresponding to and being a function of the intensity or brightness of the picture elements or'units. The tube moreover has means adapted to produce a cathode ray beam or pencil and to throw or impact the same upon the photosensitized mosaic plate, the'said pencil or beam being then subjected to deflective actions by means of deflector devices so as to insure a scanning action (electron gun). During'the scanning process, the electrostatic charges which have accumulated in the elements of the mosaic plate or sequentially neutralized with the result that picture or video signals for transmission are produced.

The general construction of such an Iconoscope is indicated in Fig. 1. Confined inside the tube or bulb I of the cathode ray device is an electron projector or gun 2 which terminates in the electrode 3. The mosaic plate consists of a posterior plate 4 made of metal, of a mica plate 5 superposed thereon, and of a mosaic assembly 5 whose elements are constituted by silver'globules above referred to. 7 denotes the objective lens through which an image of the object to be transmitted by videosignals is projected upon the multicellular plate.

It will be evident that in Iconoscopes in which the scanning beam and the light fall on the mosaic plate from the same directionthe positions of the various mosaic-plate globules 6 to electrode 3 which. takes up the photo-electrons and the secondary emission electrons will diiTer. The result is that the operating conditions of different portions of the mosaic plate will be widely different from one another, in fact, the existence of such dissimilaritiesin the working conditions will be conducive to the production of undesirable signals known as stray or shadowing signals.

Now, the present invention discloses a form of construction in which, in a type of Iconoscope" as hereinbefore described, the operating conditions for all points of the mosaic plate are ren-' dered uniform. According to the invention, a wire net 8 (Fig, '1) is mounted anteriorly of the mosaic plate comprising parts 4, 5, and 6, said screen or net being united with the last electrode 3 of the electron gun so that a counter-electrode will be positioned at the same distance directly opposite each of the elements of the mosaic plate, said counter-electrode or cooperating electrode serving at the same time as a photo-anode and as a secondary emission anode. The connection between the said net or screen 8 and the electrode 3 is indicated at 9.

By this scheme the above mentioned diificulty will be obviated to a substantial degree. However, the said screen or net is liable to throw a shadow upon the multi-cellular mosaic plate, and this would be liable to cause trouble.

According to a further object of this invention, the said wire net or gauze is mounted at a distance from the mosaicplate which is a multiple of the size of the picture element upon the mosaic plate. This arrangement is illustrated in Fig. 2. Only the most essential parts are here shown, namely, the objective 1, the gauze or net 8, the mica plate 5 and the mosaic elements 6. If the said distance is chosen around 30 times the size of the picture element, in other words, equal to 1 centimeter, the shadow efiect, as can be seen from the paths of the rays, will be diminished to an extent sothat no undesirable effects will be occasioned, even if the size or width of the meshes assumed in Fig. 2 is still very small.

It will be seen that in an arrangement as here disclosed the dififerences in the length of paths of the rays are so inappreciab-le that the working conditions both for the photo-electrons as well as for the secondary electrons are or become nearly the same.

A further reduction of the risk of shadow effects of both the light and the electron rays can be secured, according to another object of the invention, by making the mesh widths of the wire gauze several times the size of the picture elements, say, from 20- or more times. This arrangement is illustrated schematically in Fig. 3.

The influence or effect of the wire net or gauze 8 brought upon the cathode rays, according to a still further object of the present invention, may

be totally eliminated and suppressed by choosing the distance between the wire gauze 8 and the mosaic plate 4, 5, 6, so great, and the angle be--v tween the axis of the electron gun 2 and the wire gauze so small, that the cathode ray pencil will skirt or pass the said wire gauze so that it will directly strike the mosaic plate. This arrangement is shown in Fig, 4.

What I claim is:

1. A cathode ray picture transmitting tube comprising electron gun structure including an electron source and a plurality of anode elements for developing an electron beam, a light responsive mosaic electrode member positioned within the tube with the light responsive elements of the mosaic in the path of the developed electron beam and at an acute angle to the electron gun axis, a wire gauze electrode element positioned without the path of travel of the scanning electron beam and supported adjacent the light responsive surface of the mosaic electrode member and a connection between the wire gauze electrode member and one of the anode electrodes of the electron gun whereby said wire gauze electrode element simultaneously serves as an anode for photo-electron emission and a secondary electron emission element for the light responsive surface of the mosaic electrode element.

2. The cathode ray picture transmitting tube claimed in claim 1 wherein the wire gauze electrode element is spaced from the light sensitive surface of the mosaic electrode element at a distance of at least thirty picture elements.

3. The cathode ray tube structure claimed in claim 1 wherein the wire gauze electrode element is spaced from the light responsive surface of the mosaic electrode at a distance of at least thirty picture elements and wherein the mesh size of the wire gauze is of the order of twenty times larger than a picture element.

MAX ABRAHAMSOHN.

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