US2378875A - Cathode ray television tube - Google Patents

Description

June 19, 1945.

J. s. \(AN SANT CATHODE RAY TELEVISION TUBE Filed March so, *1942 14200121 014 7 Jafin/ 5. Vanaarzf Patented June 19, 1945 CATHODE RAY TELEVISION TUBE John S. Vansant, Huntingdon Valley, Pa., assignor to Philco Radio and Television Corporation, Philadelphia, Pa., a corporation of Delaware Application March 30,1942, Serial No. 436,875

Claims.

This application relates 'to cathode ray tubes and more particularly to cathode ray tubes employed in television receivers.

In the cathode ray tubes which have been used in television receivers up to the present time, it has been the practice to cover theentire face of the tube with fluorescent material and to employ some form of mask externally of the tube to cover that portion of the tube on which the Picture does not appear. It has also been necessary to mask the edges of the picture itself since normally the edges are ragged in appearance and tend to detract from the artistic value of the picture.

The use of an external mask may have any of several detrimental effects depending on the amount ofpicture masked out and the angle from which the picture is viewed. Since it is impossible to accurately cover the part of the tube on which the picture does not appear, the mask reduces to some extent thesize of the picture which may be seen. Furthermore, if the picture is viewed from an angle the effect of (parallax enters in because the fluorescent screen is on the inside surface of the thick glass face of the tube. When the screen is viewed from one side the mask covers a portion or the picture on that side and allows the ragged edge of the picture to show oh the other. Masks also have the highly ob- .lectionable eflect of picking. up light from the cathode ray tube screen and from th room,

thereby causing a bright border around the picture which detracts greatly from the contrast of the /picture. Moreover, light which is reflected from the mask and back to the screen further reduces this contrast.

' The primary object of this invention is to devise a television picture tube which requires no mask to delineate the visible picture area, and which, notwithstanding the absence of a mask, ischaracterized in that the outline of the reconstituted picture is sharply defined.

Other objects of the invention will beapparent to those skilled in the art from the following description and accompanying drawing," in which Fig. 1 is a side elevatlonal view of a cathode ray tube constrlijizted according to the invention, with a portion cent screen;

Fig. 2 is aface view of the end of the tube;

Fig. 3 is a side elevational view of the tube parts during the construction the tube; and

Fig. 4 is a face view 0 the mask employed according to the invention. I

Referring first to Figs. 1 and 2, there is shown oken away to show the fluoresflt over the inner surface of the face 2.

a cathode ray tube I having a circular transparent glass face 2 on which there is a fluorescent screen 3 of rectangular shape. In the operation of the tube, the rectangular screen 3 is excited to luminescence by an electron stream projected from an electron gun within the tube and deflected by suitable deflecting means (not shown), as will be well understood. In the illustration the screen 3 is shown as having arectangular shape but it is to be understood that the screen may be made to have any desired shape in accordance with the invention.

prior to their being joined along the dotted line- 6 of Fig. 1. The screen is formed on the face of part 5, prior to the joining of the parts, as

follows. The inside of part 5 is first completely a cleaned. to make it chemically free from any foreign matter. Following this, a mask 1 e. g. of paper, celluloid, or other material, suchas shown in Fig. 4, is dropped into part 5 so as to The mask is preformed so that it conforms in size and-shape with the site and shape crime 2, and an opening is formed therein corresponding to the size and shape of the screen desired. This mask should be made of a material which is chemically inert, e. g. chemical filter paper or othermaterial which will leave no residual deleterious matter. The material used for the mask, in addition to being chemically inert, may desirably have physical characteristics which permit it to be easilyrolled or bent, and which permit it to adhere snugly to the glass face at every point of contact. The mask should preferably be not deformable in its own plane, however, for anydeformation may result in the shape of the screen being distorted. .The mask may be rolled up for insertion in the part 5 in the case of the conical form shown, or it may be dropped in flat in any case where the shape of part 5 permits, it being understood that the tube may take any desired form. A small amount of distilled water may: then be introduced and allowed to wet the mask so as to cause it to adhere to the surface of the glass,-as shown in Fig. 3.- water is then poured out, and an air jet may-be used tea the inside of part 5 and the mask until the glass is dry but the mask is still sufllciently wet to adhere to face 2. The tube is screen. 7

The. excess The first step in the application of the screen is to appl a binding material uniformly over the exposedinner face surface. Any suitable bindtions of the preferred screen application method described above may be used without departing fromthe scope of the invention.

ing material may be employed, for example a dilute solution vof sodium silicate (commercial water glass) or potassium silicate may be used.

I claim:

LA cathode ray tube having a transparent face, a fluorescent screen extending over a pre- I'he'bindin'g material may be allowed to, overlap the mask without deleterious effect. After the bindingmaterial has been applied, the fluorescent material, e. g. zinc. sulphide or any .of the other mat'erials'well knownfinthe'cathode ray .tube art, is applied in kn'own manneron the binder, for exampleby the *air settling" method. The tube may then be placed faceuppermost and the inner surface of the face dried with a Jet of air. When the inside of the tube has completely dried no further adhesion between the mask and the face of the tube will be effected, and the mask will generally drop by the force of gravity alone, carrying with it the unwanted fluorescent material and leaving a fluorescent screen as shown in Figs. 1 and 2 having sharply defined .edges surrounded by the uncoated glass face.

The tube parts are then assembled.

In the operationof the cathode ray tube provided by the invention, the electron beam is preferably swept somewhat beyond the four edges of the fluorescent screen, but since the border around thescreen is transparent glass the observer sees no picture beyond the edge of the screen. The tube as shown has the further advantage that the surfaces in back a of the tube face are painted with a dull black graphite mixv ture (aquadag) so thatthere isno light visible within the tube, and hence the contrast is very great.

The drawing illustrates the use of a rectangular screen that is particularly advantageous for television program reception. Other purposes may require differentrshapes of the screen and it is to be understood that the invention is not intended to be limited to a rectangular screens cover any form of screen in round, rectangular,

or other shaped tube faces. Various modifica- 'inscribed in a circular tube, but is intended to determined portion only of said face, said screen corresponding in shape to the shape of the picture to be shown, the area of said screen being slightly less than the area to be scanned by the cathode ray, the portion of said face surroundin said screen being fully transparent to visibile light;

2, A cathode ray tube as claimed in 7 and at least a portion of the surrounding uncoa't ed face, being transparent and visible to an. ob-

server.

4. In a cathode ray tube having acircular glass face at one end, a rectangular fluorescent screenextending over a predetermined portion only of said face and corresponding with the shape of the picture to be shown, the remainder. of said face being uncoated and transparent.

v5. A cathode ray picture tube having a visible screen supporting surface, a fluorescent screen extending over a portion only of said visible surface, said screen corresponding in shape to the picture to be produced thereon, the area of said screen, being slightly less than the area tofxbe-scanned by the cathode ray, the portion of said surface surrounding said screen being .j

unmasked. v

JOHN S. 'VANSAN'I.

claim 1, characterized in that the visible surfaces of the

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