US2222197A - Braun tube - Google Patents

Description

B. ENGELS BRAUN TUBE Nov. 19, 1940.

Filed April 22, 1938 @m/mf @fm v @Kw Patented Nov. .19, 1940 BRAUN TUBE Bernhard Engels, Waldenburg-Altwasser, Schlesien, Germany Application April 22, 1938, Serial No. 203,549 In Germany November 5, 1935 2 Claims.

ln television practice there are used for the reception of the image cathode ray oscillographs in the form of the so-called Braun tube. This consists of a Vdischarge tube which is suitably evacuated until almost absolute vacuum, with a cathode connected on to negative potential as the source of the rays, an anode usually earthed, a diaphragm also earthed, allowing the passage of a narrow beam of rays, one or more deflecting condensers or deecting coils and a luminous screen perpendicular to the path of the cathode rays, which is arranged directly in front of or on the inner surface of the end of the tube oppositethe cathode.

Such Braun tubes were at first made com pletely of glass and this in the usual Way by blowing in a mould. In this way, however, such tubes could only be made up to limited dimensions determined by the working conditions applying with this method of shaping, and it was hardly possible to go beyond 20 cm. in the diameterof the reception end of the tube having the form if an Erlenmeyer bulb. This limitation, however, carries with it a limitation of the images received on the surface given in this way, with respect to their size, vwhich limitation is very undesirable.

A further disadvantage of the blown tubes lies in the fact that in the production by blowing the glass is never plane-parallel but shows uctuations in thickness and certain distortions.

It has already been proposed if even without recognition of the possibilities thereby given for the enlargement of the reception surface, to make such Braun tubes in several parts instead of blowing them in one part out of glass, that is, to subdivide them into the jacket and the end surface when the jacket for the purpose of avoiding surface charges and for the electric screening of the cathode rays consists preferably of a metal `tube of suitable shape, as a rule earthed, and which is joined vacuum-tight with the end consisting of glass upon which is applied the receiving luminous screen.

It is known to avoid the distortions of the image resulting from the coating of the end itself with the luminous substance in the case of blown and thus more or less curved ends, by forming the end by a plane-parallel mirror glass plate.

While with tubes constructed in this Way independence is attained of limitations in size caused by the peculiarities of the process of shaping the vglass by blowing, yet there arises the other difficulty that the flat plate closing the tube may not be suiiiciently resistant even with (Cl. Z50-164) the usual diameter of the end in the order of size of about 20 cm., in view of the high pressure stresses occurring and which in practice may amount on account of the almost complete vacuum in the interior of the tube, to l kg. per square 5 cm. Consequently with the known tubes either a plurality of plane-parallel plates have been superposed or a plate has been supported by a metal grid. This has naturally as a result a less sharpness or definition of the image to be 10 reproduced, in consequence of the great thickness of the multiple plate or of the arrangement of the grid.

In order to obviate this difficulty to some extent at least with tubes of the `hitherto usual 15 end dimensions, it has been proposed to close the tube by a simply curved cylindrical glass disc the axis of which is perpendicular to the axis of the tube. Whilst this arrangement presents a certain increase of the resistance to pressure, yet 20 in this the pressure stresses are still directed comparatively unfavourably; there is furthermore given in this arrangement a diftlcult construction of the joining of the disc with the metal tube on a curved surface, which can only be 25 made absolutely vacuum-tight with difficulty.

According to the invention, it is proposed to use for closing the tube, which may consist of glass or metal, a spherical cap-shaped mirror glass plate of flat curvature, ground and pol- 30 ished plane-parallel, which rests tightly along a flat and/or circularly curved-and thus in both cases easily worked-surface on a corre sponding surface of the tube jacket and is thus joined thereto. An absolutely secure vacuum- 35 tight closing can here be'attained either by cementing or by fusing, according to recent processes, with the tube wall. Such a closing of the tube by a spherically curved mirror glass plate represents the best form of construction for taking the pressure stresses, it being possible according to the diameter of the end of the tube to select the curvature of the mirror glass plate bearing in mind the pressure stresses to be taken thereby, i. e., to make the curvature so great as 45 is necessary for taking these stresses.

Thus it is possible as long` as the diameter of the end of the tube is not too great, to curve the mirror glass plate forming the end only so slightly that the rise of the curvature in the 50 unloaded condition amounts to only a few millimetres, and is consequently so small that after the insertion of the plate and the evacuation of the tube, the plate, under the influence of the external pressure flexes so much inwardly that 55 in the nnal condition it has a level surface. The

increase in the circumference of the plate thereby occurring is so slight that it is practically immaterial and can be easily taken up by the 5 material of the jacket.

An embodiment in principle of the invention is shown on the annexed drawing in which, with the omission of the electrical parts, Fig. 1 represents a longitudinal section through the end l part of the improved tube, at the same time illustrating on the left-hand andon the righthand halves, different possibilities for the tight uniting of the closing plate with the tube, and Fig. 2 is a fragmentary sectional view of a tube l5 showing the end plate in its initial andl nal positions.

In Fig.` 1, a represents the jacket of the tube, which Vfor example consists of metal, whilst b indicates the end piece, consisting of a cap or 20 dome-shaped mirror glass disc, uniformly curved all over and ground and polished plane-parallel, the radius of curvature of which is approximately equal to the greatest diameter of the cap or dome and over which is applied in known 25 manner the luminous screen if this is not arranged independently thereof in front of the end of the tube.

The tight connection of the mirror glass plate with the jacket takes place according to the 30 embodiment of the invention represented on the right-hand side of Fig. 1 by the edge of the plate being ground circularly so that there is given a surface c directed substantially radially to the curvature of the plate and which with the interposing of a suitable jointing material d rests on a correspondingly curved counter-surface e of the end f of the jacket made in flange form.

This counter-surface can preferably also be provided with grooves g and such grooves can also 40 be ground into the edge surface of the mirror glass plate in order in this way to still further ensure the vacuum-tight connection. In addition, there can also be arranged jolnting material in the space h between the end of the 45 widened-out flange f and the outer surface of the mirror glass plate. A ring i is fitted round the flange, preferably under tension.

The embodiment shown on the left-hand side of the ngure diers from that previously described only by the form of the Joint surface; here the edge of the mirror glass disc is resolved into two surfaces at right angles to each other, v o1' which the one c1, which is vertical in the 5 gure, is radially curved, whilst the other, shown horizontally in the iigure and indicated by c2,

is fiat, so that the corresponding counter-surfaces g1 and a2 can be simultaneously produced on the flange f by a very simple working procl0 ess. Here, again, there are preferably provided additional grooves e in the supporting surfaces of the flange and/or of the disc and possibly also amount, not shown in the figure, partially overlapping the plate, although this in itself is not necessary on account of the pressure acting on the plate in the direction from the outside towards the interior.

Fig. 2 represents in exaggerated form an end plate b having an initially spherical curvature mounted over the end of the tube body a. Subsequent evacuation of the body of the tube causes the end plate b to assume its final level position which may be that indicated in dotted lines. While in the form shown the flnal position of the end plate is planar, it will be appreciated that any desired final curvature may be attained, so long as it is caused by distortion of a plate having initially spherical curvature.

What I claim is:

l. A Braun tube, including a jacket containing gas under sub-atmospheric pressure, an end member seated in said jacket having plane parallel surfaces, one of which is coated, and sealing means surrounding said end member, said end member being formed as a spherically formed plate and being suiliciently flexible to be bent by the diilerential pressure between the interior and exterior of the jacket into a plane position and being held in its plane position by the pressure diierence between the exterior and the interior of said jacket.

2. A Braun tube in accordance with claim 1 in which the peripheral surface of said end member is parallel to its-seat in said jacket and is maintained in parallelism by the pressure of the atmosphere.

BERNHARD ENGELS.

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