US2058482A - Electron tube - Google Patents

Description

Patented Oct. 27, 1936 UNITE ELECTRON TUBE Fritz Michelssen, Berlin, Germany, assgnor to Telefunken Gesellschaft fr Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany Application April 6, 1934, Serial No. "719,275

In Germany August 22, *419(32 2 anims. (c1. 25o- 21tr The present invention relates to a method and means to focus and control an electron ray pencil or beam within an electron tube of the cathode ray type.

In the prior art means adapted to concentrate or focus electron pencils in discharge tubes have been disclosed, and at the same time a rule has been indicated in reference to the depth (position) of the electron source or issuing point inside a Wehnelt cylinder if optimum dosage (or regulation) of the volumes of electrons accessible to the anode potential is to be preserved, even in the presence of changes of the cylinder biasing voltage. Now, for a number of practical purposes it is desirable that the control or focusing cylinder should be given a shape other than circular, say, the shape of an ellipse or of a polygon. If the shape of the Wehnelt electrode enclosing the cathode is altered as stated, the condition regarding intervening distance of the electron source or issue point must be chosen in such a way that the vertical distance of the emissive point in the cathode figured in reference to the opening surface or plane of the Wehnelt electrode turned towards the anode should not exceed the maximum radius of this electrode.

In an arrangement of the kind here concerned, one pre-supposition is that the anode should be so shaped that the electrical fields thereof have a chance to engage or act inside the cylinder. The said condition, for a rule respecting the intervening distance as stated, can be readily fulfilled if the opening of the anode through which the electrons are to ily is smaller than the opening of the Wehnelt electrode. If, however, the aperture of the anode is made increasingly greater, then `the source of the electrons must be located at greater proximity to the plane laid through the anterior edge of the. Wehnelt electrode, in such a way that the distance between the electron issue point and the said surface or plane will not be more than one-third of the maximum diameter of the Wehnelt electrode if the anode aperture has become larger than the width of the Wehnelt electrode.

To accomplish this focusing or concentrating of the electron pencil in discharge tubes arrangements in which a planar or a curved surface electrode is used for the purpose of focusing electron ray beams in discharge tubes, most particularly Braun tubes used for television work have also been proposed.

In a number of cases and purposes it is of advantage that the opening of the surface electrode through which the anode potential is to act should not be circularly bounded, indeed, that instead of the latter` form, say, an elliptical or polygonal shape be chosen. By the aid of an elliptical form the pencil could be made for instance elongated rather than a punctiforxn cross-section. In an arrangement of this nature, the condition laid down with reference to the intervening distance or space between the cathode and the focusing electrode as indicated in the present patent specication should be fulfilled in this manner that the perpendicular distance between the emissive body and the plane laid through the opening of the focusing electrode should not exceed one half of the maximum longitudinal dimension of the said opening.

While as a general rule the aperture in the anode facilitating the flight therethrough of the electrons is chosen less than the opening of the focusing electrode, it is in some problems and cases a prerequisite and necessity that the anode under u no conditions should be struck by the pencil of electron stream, while yet permitting of an efficient control action upon this pencil. Hence, the width of the anode opening could be also so enlarged that the same is equal to, or larger than, the aperture of the focusing electrode. In order that also under these circumstances the force lines issuing `from the anode may act as far as the cathode, it is imperative that the source or issue point of the electrons be placed at a greater proximity to the control electrode. Hence, the basic condition is that the vertical distance between the electron source and a plane laid thro-ugh the aperture of the focusing electrode should not be over one-third of the maximum opening.

For the purpose of illustrating the invention an embodiment thereof is shown in the accompanying drawing.

Referring to Figures 1 and 2, the numeral l designates a suitable glass tube forming part of a cathode ray tube, provided at its one end with the leads 3 for the heating current, sealed at 2 into the glass tube. The electrons emitted by the cathode lament 4 are accelerated in the direction to the anode 6. In accordance with the present invention the numerals 5, 5 respectively, designate different types of focusing and controlling electrodes with a shape other than circular and accomplishing the above mentioned conditions referring to dimensions.

With reference to Figure 1, a focusing and controlling electrode 5 of the shape of a polygon is illustrated. In this case the distance a of the electron source 4 in reference to the opening plane of the Wehnelt electrode 5 turned towards the anode 6, does not exceed one half of the maximum longitudinal dimension d of the said opening.

Another embodiment of the invention is shown in Figure 2 wherein the numeral 5 designates a focusing and controlling electrode provided with an elliptical opening 'l with the maximum diameter d and the minimum diameter b. Corresponding to the case illustrated in Figure 1, the' distance a of the electron source 4 in reference to the opening place of the electrode 5' turned towards the anode 6 does not exceed one-half of the maximum diameter of the opening 1.-

Having thus described the invention,-I claim:

1. An electron concentrating means for a cathode ray tube comprising a cross-section electro'n source, an anode, a tubular non-cylindricalelectron beam focusing electrode surrounding the cathode and extending beyond the same toward the anode, said focusing electrode being so positioned relative to the electron source that where a represents the perpendicular distance between the source of the electrons and the end plane of the focusing electrode adjacent the anode and d represents the maximum diameter of the said tubular non-cylindrical focusing electrode 2. A cathode ray tube comprising an electron source, an anode electrode arranged in cooperative relationship with respect to the source so as to. cause electrons to be drawn from the source and to flow in an electron beam longitudinally of the tube, and a tubular non-cylindrical focusing electrode at least partially surrounding the electron source and extending therefrom toward the anode, the focusing electrode being so ark ranged. relative to the source that d equals at least 2a, where d represents the maximum diameter of the non-cylindrical tubular focusing electrode and a represents the distance from the electron source to the end plane of the focusing electrode adjacent the anode.

FRITZ lWICHELSSEN.

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