US2499957A - Beam forming electron discharge tube - Google Patents

Description

March 7, 1950 J. 1.. H. JONKER 2,499,957

BEAM FORMING ELECTRON DISCHARGE TIBE Filed May 10, 1946 \H o /ja JO/MN LODHi YJKIWHIKJOAKER I N VEN TOR.

A T TOR/VH1 Patented Mar. 7, 1950 BEAM FORMING ELECTRON DISCHARGE TUBE Johan Lodewijk Hendrik Jonker, Eindhoven, Netherlands, assignor, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn, as trustee Application May 10, 1946, Serial No. 668,827 In the Netherlands August 5, 1941 Section 1, Public Law 690, August 8, 194.6 Patent expires August 5, 1961 2 Claims. 1

This invention relates to a device having an electric discharge tube whose electrode system comprises a control grid which is located between two electrodes, one electrode being at a potential higher than that of this grid such as is the case, for instance, in mixing tubes, in which a control grid may be located between two screen grids.

Several means have already come to be known to obtain with these tubes a mutual conductance as high as possible between the control-grid voltage/anode current characteristic.

Thus, for instance, it has already been proposed to increase the mutual conductance b forming the electrons emitted by the cathode into a beam which is entirely or partly given a definite deflection. the various electrodes and more particularly the control grid being so proportioned that the component of velocity of the various electrons, whose paths extend in difierent directions, is the same normally to the surface of the control grid.

The present invention is based on the principle that the electrons are not subjected to a lateral deflection, but are formed into a beam in which the electrons follow parallel paths. A device according to the invention comprises an electric discharge tube having at least two grids whose active parts, viewed in a direction normal to the oathode, are located one behind the other and in which the voltages and configuration of the electrodes are so chosen that a beam emerges from these electrodes in which the electrons travel in substantially parallel paths, this beam striking the control grid at right angles in such manner that the grid plane is struck by the various beams about midway between two active parts.

By means of this device a high mutual conductance can be obtained; it is not only necessary that the control grid surface is struck at right angles by the electrons travelling in parallel paths, but also that the parts of the control grid immediately surround ng the control grid wires should be substantially free of impingement by the beam. This may be accomplished by the potential variation in the plane of the control grid, whose form is shown in Fig. 3 and which will be further explained in the description of this figure.

The passage the beam should strike the plane of the controlgrid about midway between two active parts is to be understood to mean that about half the space between two grid elements is struck by electrons so that about a quarter of the distance between these elements is left clear on either side of the beam.

In one form of construction which has proved to yield excellent results a discharge tube according to the invention has an electrode system consisting of a cathode, two grids having a positive potential and whose turns are located one behind the other, a control'grid whose turns are also located behind those of the preceding grids. this control grid being followed by an anode, if required with the interposition of one Or more grids. In this form of construction the first grid next to the cathode has a voltage H, the second grid having a voltage 25; the distance between the cathode and the first grid amounts to 1.5 mm., the distance between the first grid and the second grid amounting to 1 mm. and the distance between the second grid and the control grid amounting to 2 mm. Furthermore, the pitch of the first and the second grid amounts to 1 mm. and the thickness of the wire of these grids to 0.25 mm. Finally the distances and voltages of the elctrode(s) next to the control grid is so chosen that the average voltage of this grid is To this form of construction several variations can easily be added; upon examination of a mode of such a tube, for instance by means of a sheet of rubber so that the electrical properties of the tube and the movement of the electrons can be represented mechanically, the conditions under which the desired effect occurs, i. e. the passage of a beam of parallel electrons through the centre of the control grid can be found in a simple manner. Thus, for instance, the control grid may be preceded by three grids whose turns together with those of this grid are located one behind the other.

The invention will now be more fully explained by reference to one form of construction shown in Figures 1 and 2, where the position of the electrodes of a tube to be used in a device according to the present invention is schematically represented; Fig. 3 shows the curve of the mutual conductance of a tube in a device according to the present invention and of a tube in which the elec tron beam does not exclusively strike the centre of the control grid, but also reaches the regions directly surrounding the control grid elements; the improvement in mutual conductance is clearly visible.

In Figures 1 and 2 the electrode system is arranged concentrically; of the represented electrodes i is the cathode surrounded by a grid 2, a grid 3 and a grid 4 acting as a control grid. The active parts of all grids are located one behind the other as shown in Fig. 2. The control grid is surrounded by an anode ill, with or without the interposition of one or more grids.

Fig. 3 shows one adjacent each other the space between two grid elements 5 and the anodecurrent grid-voltage characteristic curve 6 in case the electrons are distributed throughout the space between the elements 5 and the characteristic curve I in case a beam containing the same current gains access to the grid plane exclusively midway between the elements 5. The reference number 8 designates the potential variation in the plane of the control-grid. From these figures it appears that all electrons are allowed to pass through the control-grid only after a considerable change of the grid voltage if the beam fills the whole space between the elements 5, whereas this voltage range is much smaller if the beam has only the width indicated by 9. The diiference in mutual conductance will be readily appreciated upon comparison of the curves 6 and 1.

What I claim is:

1. An electric discharge tube having an electron emissive cathode, a first grid surrounding said cathode, a second grid surrounding said first grid, a third grid surrounding said second grid, and an anode surrounding said third grid, said grids having elements arranged substantially in radial alignment from said cathode to the said anode, means for applying a direct biasing voltage to said first grid positive with respect to said cathode, means for applying a direct biasing voltage to said second grid positive with respect to said first grid, means for applying a voltage to said third grid negative with respect to said cathode, means for applying a signal voltage to said third grid, and means for applying a voltage to said anode positive with respect to said second grid, whereby electrons leaving said cathode and travelling towards said anode are bundled in beams directed centrally between the elements of said third grid, said beams having a width less than about half the spacing between said elements of said third grid at their point of passage therethrough.

2. An electric discharge tube having an electron emissive cathode, a helically wound first grid surrounding said cathode, a helically wound second grid surrounding said first grid, a helically wound third grid surrounding said second grid, and a cylindrical anode surrounding said third grid, said grids comprising grid wires arranged substantially in radial alignment from said cathode to said anode, means for applying a direct biasing voltage to said first grid positive with respect to said cathode, means for applying a direct biasing voltage to said second grid positive with respect to said first grid and about two and one-half times greater in magnitude than the voltage applied to said first grid, means for applying a voltage to said third grid negative with respect to said cathode and having a magnitude about one-third as great as that of said voltage applied to said first grid, the radially measured distance between said cathode and said first grid being about one and one-half times the radially measured distance between said first grid and said second grid, and the radially measured distance between said second and said third grid being about twice the radially measured distance between said first grid and said second grid, means for applying a signal voltage to said third grid, and means for applying a voltage to said anode positive with respect to said second grid, whereby electrons leaving said cathode and travelling towards said anode are bundled in beams directed centrally between the adjacent turns of the helix of said third grid, said beams having a width less than about half the space between said turns at their point of passage therebetween.

J OI-IAN LODEWIJK HENDRIK J ONKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,217,417 Peterson Oct. 8, 1940 2,404,919 Overbeck July 30, 1946 FOREIGN PATENTS Number Country Date 838,835 France Dec. 16, 1938

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