US3031580A

US3031580A - Cathode ray tube

Info

Publication number: US3031580A
Application number: US840616A
Authority: US
Inventors: Raymond H Kocot; Alexander L Bearman
Original assignee: Fairchild Camera and Instrument Corp
Current assignee: Fairchild Semiconductor Corp
Priority date: 1959-09-17
Filing date: 1959-09-17
Publication date: 1962-04-24
Anticipated expiration: 1979-04-24

Description

A ril 24, 1962 R. H. KOCOT ETAL CATHODE RAY TUBE Filed Sept. 1'7, 1959 Fig. 3

INVENTOR.

RAYMOND H. KOCOT ALEXANDER L. BEARMAN ATTORNEYS intensifier, impinging radiation, visible, or ultraviolet,

United States Patent This invention relates to a cathode ray tube, and more g zparticularly to a structure for use therein.

In the 'type ofizatlfodelray tube known as an image that corresponds to the pattern of impinging rays. To accomplish this, the weak or invisible incident rays fall upon a photocathode, which These are operated upon in such a manner that they bombard a film of phosphorescent material that glows to produce the visiblejmage. Two such tubes acting in cascade produce a brighter image than a single one; and

if the two image tubes are combined into a single evacuated envelope, this arrangement is even more efiicient than two separate tubes.

In the manufacture of image converters, there are two problems known as phosphor poisoning and cesium migration.

The first arises in the following way. In order to form the photocathode that emits electrons under the influence of impinging rays, cesium must be deposited upon a prepared surface. This deposition is achieved by heating cesium, or one of its compounds, to its vaporizing temperature. Cesium mist then fills the entire tube, and condenses upon the various surfaces. When the cesium mist condenses upon the phosphors, it poisons" them, with the result that the phosphor is blotched and its light emitting efiiciency is reduced. This poisoning is irreparable. vaporizing the cesium, which is necessary to form the photocathode, endangers the phosphor.

The second problem, cesium migration, arises because the sealed-off tube still contains microscopic traces of cesium vapor. This gradually condenses on the various surfaces, and coats insulators with a very thin conductive film thus reducing their insulative properties, and permitting leakage currents that show up as background noise.

It is therefore-the principal object of our invention is to provide an improved cathode ray tube.

It is another object of our invention to provide an image intensifier type of cathode ray tube wherein the phosphor screen is partially protected during evaporation.

It is an additional object of our invention to simultaneously form two photocathodes, which therefore tend to have matched characteristics.

It is a further object of our invention to provide a cathode ray tube wherein an additional cathode may be readily prepared, and then positioned.

The attainment of these objects and others will be realized from the following specification, taken in conjunction with the drawings, in which, 1

FIG. 1 shows an overall representation of an image intensifier tube;

FIG. 2 illustrates my invention; and

FIGS. 3 and 4 depict a locking arrangement therefor.

Broadly speaking, my invention contemplates a cathode ray tube internal structure for the condensation of cesium thereon, which simultaneously shields the phosphor, and may then be reversed to, properly position the cesium coated surface.

The background for my invention may be readily understood from a study of FIG. 1, which shows a cascaded image intensifieratube comprising an evacuated such as infrared. produces a bright visible image thereupon emits electrons.

It may thus be seen that ice- - Z envelope 12. Impinging rays, approaching as shown by the arrows, traverse the transparent faceplate of tube 10 and-impinge upon photocathode 14, which thereupon emits electrons. These electrons are accelerated and directed, by means which are not shown, but are well known, to strike fluorescent screen 16. This is mounted on a thin transparent supporting sheet 18, such as mica. The electron bombardment of screen 16 produces light that passes through mica sheet 18,- and strikes a second photocathode 20. This photocathode emits electrons that are directed toward the final fluorescent screen 22;

,thelight from which passes through the glass end surto the observefs eye. As previously explained,

photocathodes

14 and 20 must be coated withcesium' which, however, tends to poison

phosphor screens

16 and 22.

My invention comprises two separate but coacting ele ments, shown in'FIG. 2. The first is a support structure" 24 that comprises a supporting ring 26 and two extending arms 28. Arms 28 have keyhole shaped slots therein, the longitudinal. parallel sided slots 30 terminating in round holes 32.

The second element of my invention, structure 34, comprises an annulus 35 encircling a mica disk 18 that eventually has photocathode 20 on one surface, and

fluorescent screen 16 on its other surface as shown in FIG. 1. Annulus 35 has two diametrically opposite pivot pins 36, having cross-sections that are square, rectangular or oval shaped. These pins project through slots 30, and may have their ends flanged or flattened to prevent withdrawal. The width of slot 30 is slightly larger than the smaller dimension of the pivot pins, while the rounded end 32 of the slot has a diameter slightly larger than the larger dimension of the pivot pins. When assembled, the pivot pins can slide along slots 30 but cannot turn until they reach the end 32.

In use, my invention operates as follows. Supporting ring 26 is fastened to the inside of tube 12 by means of cement, pins, flanges, or any other desired structure ment 34 slides down to the end of the slots without turning. Tube 12 is then quickly rotated, end for end, so that the positions of its ends are interchanged. During this upending, element 34 remains stationary due to its inertia. Tube 12 is now slowly reinverted, whereupon element 34 slides back along slots 30 Now though, the surfaces of element 34 face in opposite directions than previously. In this way, element 34 may be flipped, so that the desired side is uppermost.

When combined with tube 10, my invention solves the aforementioned problems as follows. Element 34 is originally positioned so that the prepared surfaces that are to become

photocathodes

14 and 20 face each other. Cesium is evaporated, by means not shown, in the upper portion of the tube. Due to the fact that supporting ring 26 fits close to the inner surface of the tube, very little of the cesium mist finds its way into the lower portion of the tube. The

phosphor surfaces

16 and 22, which are now facing each other in the lower end of tube 10, are thus shielded to prevent poisoning. Structure 34 is then flipped as explained above, and the photocathode and phosphor surfaces take the position shown in FIG. 1.

' Once structure 34 has been flipped, the cesium vapor 3 26, and are engaged in recess 38 of spring 40, the pressure of the spring holdingit lightly in this position. When it is desired to flip structure 34, a sharp jar or tap releases the pin from recess 38, whereupon structure 34 may be flipped as described. Once the flipped structure is in its desired orientation, it drops back to ring 26 but, as shown in FIG. 4, pins 36 are now closer to ring 26 than previously. The pivot pins are therefore held by the recess in the end of spring 40, which prevents them from jarring loose.

Alternatively, annulus 35 may be stepped, to seat end wall being transparent to impinging radiation, and

the second said end wall being transparent to visible radiation; a surface positioned on said first end wall, said surface being suitably prepared to receive cesium and form a photocathode; a fluorescent screen on said second end surface; a supporting ring positioned substantially parallel to said end surfaces and substantially halfway between them; a pair of arms aifixed to said ring, said arms being substantially parallel to each other and perpendicular to said ring, each said arm having a keyhole-shaped slot therein, said slot having longitudinal portions that extend parallel to said arms, said slot further having round end portions; an annulus having diametrically oppositely positioned pivot pins, said pins having a minor dimension slightly smaller than the width of said longitudinal portion of said slot, and having a major dimension greater than the width of said longitudinal portion of said slot but smaller than the diameter of said end portion of said slot; a mica disk positioned in said annulus; a fluorescent screen positioned on one surface of said mica disk, the other surface of said mica disk being suitably prepared to receive cesium and form a photocathode; whereby said mica disk can be positioned so that said prepared surface of said mica disk can be positioned to face said prepared surface on said'iirst end wall, and said fluorescent screen on said mica disk can be positioned to face said second end wail; means whereby cesium may be simultaneously deposited on both said prepared surfaces, and whereby after deposit of cesium said disk may be caused to slide to the round end of said slot and rotated through 180 by first slowly inverting the tube through 180 end for end and then rapidly rotating the tube through 180, and

aosnuso means for detenting said ring and disk in an original position with the surfaces of said disk parallel to the end surfaces of said tube, said means also serving to lock said ring and disk in rotated position with the surfaces of said disk again parallel to the end surfaces of said tube.

2. A cascaded image converter tube comprising: an evacuated envelope having two end walls, the first said allel to said end surfaces and substantially halfway between them; a pair of arms aflixed to said ring, said arms being substantially parallel to each other and perpendicular to said ring, each said arm having a keyholeshaped slot therein, said slot having longitudinal portions that extend parallel to said arms, said slot further having round endportions; an annulus having diametrically oppositely positioned pivot pins, said pins having a minor dimension slightly smaller than the width of said longitudinal portion of said slot, and having a major dimension greater than the 'width of said longitudinal portion of said slot but smaller than the diameter of said end portion of said slot, said'pins being offset from the central plane of said annulus; a mica disk positioned in said annulus; a fluorescent screen positioned on one surface of said mica disk, the other surface of said mica disk being suitably prepared to receive cesium and form a photocathode; whereby said mica disk can be positioned so that said prepared surface of said mica disk can be positioned to face said prepared surface on said first end wall, and said fluorescent screen on said mica disk can be positioned to face said second end wall means whereby cesium may be simultaneously deposited on both said prepared surfaces; means flipping said annulus so that the positions of said surfaces are interchanged, and spring means fixed to at least one of said supporting arms to maintain said ring in its original position prior to deposit of cesium, said spring means permitting sliding of said annulus in said slots when the tube is inverted, said spring means serving also to lock said ring at the end of said slot after rotation has been efiected.

References Cited in the file of this patent UNITED STATES PATENTS 575,696 Bums Ian. 26,, 1897 1,354,095 Evans Sept. 28, 1920 2,283,413 Cashman May 19, 1942 2,508,856 Cassman May 23, 1950