US2185133A

US2185133A - Control grid arrangement in cathode ray tubes

Info

Publication number: US2185133A
Application number: US120775A
Authority: US
Inventors: Schlesinger Kurt
Original assignee: LOEWE RADIO Inc
Current assignee: LOEWE RADIO Inc
Priority date: 1936-01-20
Filing date: 1937-01-15
Publication date: 1939-12-26
Anticipated expiration: 1956-12-26
Also published as: GB488948A; FR816443A

Description

K. SCHLESINGER 2,185,133

CONTROL'GRID ARRANGEMENT IN QATHODE RAY TUBES Filed Jan. 15, 1937 v 2 Sheets-Sheet 1 mas/m Dec. 26, 1939. 2,185,133

CONTROL GRID ARRANGEMENT IN CATHODE RAY TUBES K. SCHLESINGER 2 Sheets-Sheet 2 Filed Jan. 15, 1957 Ill/ll Ill Ill/Ar a I V Patented Dec. 26, 1939 1 UNITED STATES CONTROL GRID ARRANGEMENT IN CATHODE RAY TUBES Kart Schlesinger, Berlin, Germany, assignor, by mesne assignments, to Loewe Radio, 1110., a corporation of New York Application January 15, 1937, Serial No. 120,775 in Germany January 20, 1936 9 Claims.

The light intensity control of television cathode ray tubes is performed, as a rule, by an arrangement in which a circular cathode surface I is situated behind a perforated diaphragm 2, whilst a positively biassed perforated anode 3 is placed behind the grid 2. In some arrangements the anode 3 is employed at the same time as a diaphragm, the aperture of which is reproduced sharply on the luminous screen by a lens mounted in axial consecution thereto. The operation of such an arrangement is unsatisfactory in several respects. The sensitivities fluctuate within wide limits. The control sensitivity becomes, as a rule, poorer when the anode potential of 3 increased. It also deteriorates when the spacing between the grid and the anode is reduced. A decrease of the spacing between the grid and the cathode does not necessarily increase the steepness, and moreover. results in an extremely undesirable effect, viz., contraction of the image point in the case of modulation towards'black. If the aperture in the anode 3 is a diaphragm aperture to be electron-optically reproduced, it is desirable for the illumination with electrons of this aperture always to cover evenly the entire diaphragm aperture independently of the current intensity of the ray, so that the size of the image point will remain constant in respect of all conditions of intensity.

In the following explanation and description of, the present invention, reference will be made to the accompanying drawings each figure of which shows the system for exciting and con trolling electron emission in a cathode ray tube,

Figs. 1, 2a, and 21), being of a diagrammatic type, showing systems which are not in accordance with the invention, and in connection with which the drawbacks which the invention removes are explained, whereas Figs. 3, 4, and 6, likewise being of a diagrammatic type, and Fig. 5, being a more detailed sectional elevation, show systems which are in accordance with the invention.

In the arrangement according to Fig. 1, the desired inclependency from the beam intensity of the size of the image point is not obtainable, but the ray progressively contrasts in this arrangement as the intensity decreases, so that eventually the diaphragm is no more completely filled out by the rays and the size of the image point diminishes steadily as the intensity is further reduced. In consequence the scanning lines of the television image become visible to such an extent as to produce an unpleasant impression.

To explain the above remarks relative to sensitivity and steepness it is assumed that a hot cathode l having a spot of oxide of 1 mm. in diameter disposed behind the aperture in a grid diaphragm 2 of equal size, requires with a spacing of l between the anode 3 and the grid 2, more than 30 volts for complete modulation the characteristic having a varying steepness, via, one which decreases as the intensity decreases. Upon increasing the spacing between 2 and 3 to give it an amount of 3 mm. the sensitivity is raised to'about 10 volts required for complete modulation, the anode tocathode voltage being in these considerations assumed to amount to about 500 volts. if the anode to cathode voltage is 199. volts instead, the sensitivity is increased still further by a factor of about two or three. It is particularly this effect, viz. the apparent dependency of the steepness on the anode potential, which is quoted in the literature as a general law in support of the usefulness of a preliminary acceleration. v

The inventor has found that the last mentioned conclusion does not stand. In the following there will be set forth general observations with regard to the control operation and practical methods of obtaining a light control in televisiontubes, which 1. Result in a considerable sensitivity,

2. Ensure an even thickness of the ray without I tively biassed grid 2 and a positively biassed anode 3 is represented by two lines, of which the one labelled (1 represents the potentials of the metallic parts, whilst the other b indicates the potential in the axis of the ray, 1. e., within the apertures. The latter potential is less negative in the grid aperture than the grid itself, since, in accordance with the diagram of the equipotential surfaces given in Fig. 2b the equipotential surfaces are bent through the grid aperture. The more positively the anode ii is biassed and the wider the opening in the grid 2 is, the more strongly will the equipotential surfaces be bent through the grid aperture. occur that at the center-point of the grid aperture the potentialis zero, (1. e., cathode potential, curve 6 in Fig. 2a) although the grid is biassed to l0 volts (curve coin Fig. 2a). In consequence electrons are propagated at the central part of the arrangement, whilst at the marginal zones currentless control is already obtained.

It may accordingly ode l.

The more strongly the equipotential surfaces are bent, the greater will be the difference between the grid potential and the aperture potential, and the greater will be the contraction of the beam cross section, and accordingly the smaller the steepness of the modulation characteristic.

According to the invention remedy is obtained by extending the grid in the direction of the ray, as shown in Fig. 3. This figure shows a cathode I mounted behind a control grid 2, the diameter of the opening in which is equal to or greater than the diameter of the imissive layer la on the cath- A second grid 2 is maintained, together with the first one, at a constant potential. The two grids may also be formed from one solid piece of material having an axial boring. While now the anode 3 is able to produce a bend of the equipotential surfaces through the grid aperture 2', as indicated by the curve i, the corresponding curvature of the equipotential surface 4 through the aperture in the rear grid 2 is in any case much slighter. In consequence the emission of the cathode l is evenly controlled by the grid 2 over its entire cross-section, and the ray leaves the cathode with a constant cross-section.

In many cases the illumination of the diaphragm aperture of the anode 3 with electrons is desired to be as intense as possible in order to obtain as strong a current as possible. For this purpose preliminary concentration is required, which should be independent of the ray current intensity.

Fig. 4 shows an arrangement having a double grid, as illustrated in Fig. 3, and in which the grid on the anode side is made to be conical and thus produces a lens efiect. The anode 3 is a diaphragm having, for example, a square aperture. The inclination of the grid 2 is preferably made greater than calculated from geometric considerations by assuming that the electrons leave the surface 2 at right angles, i. e., the shape of the grid is so chosen as to result per se in an over-concentration. By varying the bias of the anode 3 an excessive concentration' may be electrically weakened, and thus regulated.

With arrangements according to Figs. 3 and 4, the emission of the cathode l, irrespective of the amount of the potential of the anode 3, can be completely modulated with 1-3 volts control voltage, if the length of the grid, i. e., the distance between the front and'rear grid surfaces, amounts to 2-4 mm. The sizes of the grid apertures have but a very small effect on the sensitivity of the grid. These apertures are preferably made larger than the emissive surface, viz., preferably of twice the diameter. Use was made in practice of cathodes of 1 mm. in diameter and grid apertures of 2 mm. in diameter. The distance of the cathode from the first grid has but little effect on the sensitivity. This distance amounts preferably to 1 mm. which value, however, does not require to be exactly adhered to.

In practice the provision of a cylinder 5 offers structural advantages, serving for aligning the cathode and the first grid. For preferred structural details see Fig. 5. According to this figure the cathode is mounted, with the interposition of an insulating tube 6, on the base member I. A tap incorporating the grid 2 is slipped onto the same base member. The cylinder 5 is supported by means of two sheet metal collars 8 and 9, of which the upper one is at the same time provided with a conical depression'i, which acts as the front grid, having condensing lens properties.

With the aid of the two collars 8 and 9 this control element is located in position by means of insulators mon with the anode 3. In this way it is ensured that the preliminarily concentrated ray is directed one to the aperture of the diaphragm 3 of about mm. diameter exactly centrally. It has been found in practice that an electron lens comprising a conical element 2 according to Fig. 5 possesses in itself a good lens eifect even in respect of rays remote from the axis. It is, however, further posible in accordance with the invention to employ the cylindrical lens systems which, in themselves, have already been proposed before, for example in an arrangement according to Fig. 6.

In Fig. 6 there is employed a long

double grid

2, 2, the two grid faces of which, taken each for themselves, are flat faces. The front grid face 2', however, is sunk into the interior of the mount- IU (preferably glass rods), in coming cylinder 5, so that the edge of this cylinder diaphragm 2 is sunk into the interior of 5 in.

conjunction with a given potential 3, or vice versa by selection of the potential 3 in the case of a given depth to which 2 is sunk into 5.

I claim:

1. In and for a cathode ray tube comprising a cathode having an electron emissive spot and an anode mounted in operative relationship thereto for causing a substantially unidirectional electron emission from said cathode: a controlling electrode structure mounted between said cathode and said anode for modulating the emission from said cathode, said controlling electrode structure having an electron entrance aperture and an electron exit aperture both axially aligned with said cathode and said anode, said apertures being displaced from each other by a few millimetres in the direction from said cathode to said anode, the diameters of said apertures being substantially equal to the diameter of said emissive spot.

2. In and for a cathode ray tube comprising a cathode having an electron emissivespot and anode mounted in operative relationship thereto for causing a substantially unidirectional electron emission from said cathode: a controlling electrode structure mounted between said cathode and said anode for modulating the emission from said cathode, said controlling electrode structure havingv an electron entrance aperture and an electron exit aperture both axially aligned with said cathode and said anode, said apertures being displaced from each other by a few millimetres in the direction from said cathode to said anode, the diameters of said apertures being equal to about twice the diameter of said emissive spot.

3. In and. for a cathode ray tube comprising a cathode and an anode mounted in operative relationship thereto for causing a substantially unidirectional electron emission from said cathode: a controlling electrode structure mounted between said cathode and said anode for modulating the emission from said cathode, said controlling electrode structure having an electron entrance aperture and an electron exit aperture both axially aligned with said cathode and said anode, said apertures being displaced from each other to a,

distance, approximately equal to the diameters of said apertures, in the direction from said cathode to said anode.

4;. In and for a cathode ray tube comprising a cathode and an anode mounted in operative relationship thereto for causing a substantially unidirectional electron emission from said cathode: a cylinder surrounding said cathode and projecting beyond said cathode in the direction towards said anode, an apertured diaphragm mounted in said cylinder transverse to the direction from said cathode to said anode, and a further apertured diaphragm of hollow frusto-conical shape terminating said cylinder atlthe side thereof facing said anode, the hollow side of said further diaphragm facing said anode to cause a preliminary concentration of the electrons emitted from said cathode, said cylinder and diaphragms being adapted to have modulating voltages relatively to said cathode impressed thereon for modulating the emission from'said cathode, the apertures in said two diaphragms being axially aligned with said cathode and said anode and displaced from each other in the direction from said cathode to said anode.

5. In and for a cathode ray tube comprising a cathode and an anode mounted in operative relationship thereto for causing a substantially unidirectional electron emission irom said cathode: a cylinder surrounding said cathode and projecting beyond said cathode in the direction towards said anode, and two apertured diaphragms mounted in said cylinder transverse to the direction from said cathode to said anode with their apertures axially aligned with said cathode and said anode and displaced from each other in the direction from said cathode to said anode, said cylinder projecting in the direction towards said anode beyond that one of said two diaphragms disposed nearer to said anode to cause a preliminary concentration of the electrons emitted from said cathode, said cylinder and diaphragms being adapted to have modulating voltages rela-; tively to said cathode impressed thereon for modulating the'emission from said cathode.

6. In and for a cathode ray tube comprising a cathoe and an anode for causing a substantially unidirectional electron emission from cathode; a cylinder shaped base having said cathode co-axially secured thereto to support said said i cathode from the side of said cathode remote from said anode, a hollow cylinder fitted over said base to project beyond said cathode in the direction towards said anode, an apertured diaphragm terminating said hollow cylinder at the side thereof facing said anode, a further hollow cylinder fitted over the first said hollow cylinder to project beyond the first said hollow cylinder in the direction towards said anode, a further diaphragm having a central opening and being secured to said further hollow cylinder with the mentioned central opening disposed between the first said diaphragm and the end cross-section of said further hollow cylinder facing said anode, and means for locating said further hollow cylinder in position relatively to said anode.

7. The invention set forth in claim 6, and wherein said further diaphragm, is secured to the edge of said further hollow. cylinder facing said anode and is of hollow frusto-conical shape, the hollow side of said further diaphragm facing saidanode to cause a preliminary concentration of the electrons emitted from said cathode.

8. The invention set forth in claim 6, and wherein said further diaphragm is fiat and secured to said further hollow cylinder at a distance from the edge thereof facing said anode so that said further hollow cylinder projects beyond said further diaphragm in thedirection towards said anode to cause a preliminary concentration of the electrons emitted from said cathodev 9. In and for a cathode ray tube comprising a cathode and an anode mounted in operative relationship thereto for causing a substantially uniaxially aligned with said cathode and said anode,

said apertures heing displaced from each other by a few-millimetres in the direction from said cathode tosaid anode, said sheets being disposed substantially transverse to the direction from said cathode to said anode and, taken in the mentioned direction, one behind the, other.

KURT SCHLESINGER.