US2099749A - Electron tube - Google Patents

Description

Nov. 23, 1937. R. T. ORTH 2,

ELECTRON TUBE Filed May so, 1935 2 SheetsSheet' 1 70 /3 /0 \OPM /70 10 INVENTOR 7 RICHARD T. ORTH /z 12 BY ATTORNEY Nov. 23, 1937. Y R. 'r. ORTH 2,099,749

ELECTRON TUBE Filed May 30, 1933 2 Sheets-Sheet 2 INVENTOR ATTORNEY Patented Nov. 23, 1937 UNITED STATES PATENT OFFICE Corporation of America,

Delaware a. corporation of Application May 30, 1933, Serial No. 673,572

3 Claims.

This invention relates to electro-optical devices and systems and more particularly to the use of a cathode ray tube frequently referred to as a Braun tube in connection with such systems.

In the prior art the cathode ray tube used for television and oscilloscope purposes usually employs a translucent screen which has the property of fluorescing when subjected to the bombardment of an electronic beam. In cases where it is desired to producevariations in intensities of the resulting fluorescent effects, which variations might be in accordance with variations in photoelectric currents resulting at a point of transmission in accordance with the scanning of a subject of which the electrc-optical image was desired, the beam may be modulated by means of an electrostatic control electrode or grid which is disposed in the path of the electronic beam di rected toward the fluorescent viewing plane. The control electrode or grid is biased under the influence of the photoelectrically controlled signal eifects to vary the degree of fluorescence.

According to still other arrangements of the prior art, it has been proposed to control the intensities of the observable effects upon the fluorescent end wall of the cathode ray tube by deflecting the cathode ray pencil with respect to an aperture or opening in a screen plate or with respect to a limiting or beam defining edge of a screen plate which is opaque to the passage of the electrons. This type of prior art arrangement functions so as to control variably the number of electrons which pass through the opening or past the beam defining edge of the shield.

Still other arrangements of the prior art have provided for intensity control of the fluorescent efiects by a variation in the velocity of impact of the electron stream upon the fluorescent screen. Other arrangements operate to control the ob- 4 servable intensity of the fluorescent spot by varying the velocity of traversal of the cathode ray stream projected at constant instantaneous impact. velocity upon the fluorescent viewing plane so that the variations produced in the pc- 45 riods of actual impact of the cathode ray beam at any diilerential area upon the screen produce the efiects of varying lights and shadows from the resulting light spot, the intensity of fluorescence being a function of both velocity of impact and 50 time of impact.

All such arrangements of the prior art while, in general, satisfactory, particular reference being made to the grid control effect so universally used, nevertheless are somewhat unsatisfactory 55 for extremely accurate control for one reason or another. One of the more important reasons is that the intensity controls of the types above outlined frequently cause the effects of streaking or the like in the view-ed electro-optical effects produced from screen fluorescence. 5

While the grid control has, up to the present time, been practically universally adapted, it nevertheless has the inherent disadvantage that upon impressing various voltages or biasing potentials to produce the control action the effect 10 is that of changing the cross-sectional area of the electron beam, as will become more apparent from what follows.

Cathode ray tubes, as designed for television work, reference being made herein to the subject 15 of television merely in order to illustrate one suitable use for a type of cathode ray tube and control therefor, as herein disclosed, are usually characterized by a long tubular neck one end of which carries the base of the tube and the other a conical portion terminating in a section whose normal projection is perpendicular to the axis of the tube. This section is usually concave on the inside, although for small tubes especially it may be fiat or even convex, and is provided with screen structure of a fluorescent character upon which the cathode ray stream or pencil impinges. The pencil or beam of rapidly moving electrons has its origin in a heated cathode or, where desired, even a cold cathode located at the base end'oi' 0 the tube. From the point of origin of the oathode ray beam or pencil to the point where it strikes the fluorescent screen the beam is controlled by either electrostatic or electromagnetic fields or both so arranged as to accelerate, focus 35 and deflect the cathode ray pencil in the direction or directions desired.

One suitable means for deflecting the cathode ray beam is by the use of electrostatic deflecting plates conveniently located in the neck of the 40 tube, or, where desired, externally of the tube. An electrostatic field produced between these plates upon the application of voltages of suitable frequency thereto produces an acceleration of the beam in line with the field between the plates. For television work two sets of deflecting plates may be used and, if so, the surfaces of each set are at right angles to each other. Such an arrangement permits deflection of the cathode ray pencil in two planes perpendicular to each other but both normal to the axis of the tube. Where desired, of course, it is possible to substitute electromagnetic deflection for the electrostatic deflection hereinabove suggested and it has been found in many instances desirable to combine electromagnetic and electrostatic deflection systems; 7

To controlthe intensity of the cathode ray thus deflected and positioned upon the tube screen, according to the prior art, the electrostatic or grid control consisted in an electrode member substantially surrounding the electron emitting area. in such manner that the issuin electrons were drawn through an aperture of predetermined size. Modulation of the cathode ray beam to vary the intensity of the resulting fluorescent effects was accomplished by varying the negative bias. With zero bias on the grid electrode the effective aperture has been found to be the same as the actual aperture. However, as the negative bias is increased the effective diameter of the aperture in the control grid member decreases with the result: that the size of the spot on the screen decreases in diameter. In television seanning this will result in a variation in the light spot diameter with each change in, modulation. This effect then becomes observable in the form of dark lines on the fluorescent screen because the line definition at all times throughout the scanning period remains constant. I

It is',. therefore; one of the primary objects of this invention to overcome this changing spot size defect and to producea scanned area on the flucrescent viewing screen which is devoid of all streaked eifects.

Still other objects of the invention are to provide more suitable means for controlling the density of a beam of electrons. I

Another object of the invention is to provide means by which a beam of electrons may be modulated and controlled by suitable controlling electrodes without in any wayafiecting the operation or changing the actual diameter of the resulting area of fluorescence upon the viewingscreen.

Other objects of the invention areto provide modulation or control arrangements for varying the intensity of a cathode ray pencil of electrons will become apparent and suggest themselves to those skilled in the art to which the invention relates from reading the following specification and claims in connection with the accompanying drawings, wherein: m V

Fig. 1 illustrates one type of cathode ray tube to which this invention is applicable}.

Fig. 2 illustrates one form of electrode struc- V ture which may be enclosed within the tube shown by Fig. 1; I

Fig. 2a represents a transversesection through the electron stream on the line A-A;

Fig. 3 shows various forms of modulating electrode whichmay be'incorporated as apart of the electrode structure within the tube of Fig. 1;'

-- Fig.'3a designates an electrode structure having a circular aperture across which the control element is provided;

Fig.f3b indicates an'electrode structure with a square aperture controlled similarly to the arrangement of Fig. 3a;

Figs. 3c and 3d respectively indicate longitudinal sections of the electrode structures shown by Figs. 3a and 3b;

Fig. 4 illustrates a modification of the invention in which a double helical heater and unipotential type cathode is provided with a hollow core and an electrode in position within the cathode member;

Fig. 5 illustrates a mandrel suitable for forming a unipotential cathode heater shown by Fig. 4; Fig. 6 illustrates conventionally a cathode ray tube assembly omitting the enclosing envelope and comprising the cathode of Fig. 4 and the helical heater assembly together with related electrodes adjacent thereto; and

Fig. 6a illustrates the cross section of the electron beam at the line B-B of Fig. 6.

The general type of cathode ray tube used for television purposes is similar to that shown by Fig. 1. This tube, as has been above stated, is characterized by a long tubular neck portion I upon one end of which is supported the base 2 and the other a'conical portion 3 terminating in a fluorescent screen 4. The cathode rays are generated within an electron gun structure designated as 5 and the rays or electron stream thus developed and projected toward the fluorescent screen member 4 may be suitably deflected by applying suitable controllingv voltages in'the electrostatic deflecting plates 5 and to a second set of plates (not shown) arranged transverse to the set of plates 6. Of course, magnetic deflection or a combination of electrostatic and electromag- V netic, provided the electrostatic deflecting members are formed from non-magnetic material so as not to be subjected to the influence of the magnetic deflecting materials; might be used.

According to the conventional type of cathode ray tube design a control grid member, such as the structure Ill shown by'Figs. 3a and 3c, is usually arranged to surround substantially the cathode emitting surface and the developed electrons are projected toward the fluorescent screen structure 4 through the aperture l I. Such structure as is used in the cathode ray tubes ,now

usually known varies the modulation of the beam or electron stream by varying the negative bias applied to the grid or control electrode 10. For

conditions of zero bias on this control element Ill the efiective aperture through which the cathode ray stream I5 is adapted to pass is the same as the actual aperture ll so that the oath-1 ode ray pencil emerging from the grid structure will have an actual electronic diameter equal to the diameter of the aperture H. However,, as the negative bias is increased to vary the intensity of the resulting electronic light spot on the fluorescent screen structure the effective diamt eter of the aperture 1 I decreases due, for example, to repulsion of theemerging electrons from the edges of the diaphragm member, so that the spot; size also decreases. This efiect produces, as has been above defined in the statement of invention, dark lines on the fluorescent screen because the line definition remains, always constant.

According to the present invention these above mentioned difficulties have been substantially overcome by changing the control electrode structure to some extent from the form now used in 7 tubes known in the art. In the new form of the control electrode herein disclosed the control electrode structure includes the disk or plate member in formed with the shielding structure 7 l2 attached theretoso that it resembles closely the usual grid structure 10 above discussed but is distinguishable therefrom both in formation and operation as will herein be pointed out. As shown by all of Figs. 3a through 301 inclusive, the aperture of the control electrode 10 may be round, as shown by the apertures ll of Figs. 3a and 30, or square, as shown by the apertures l3 of Figs. 3b and 3d, or may be of any other suitable formation. In addition, the aperture should be formed slightly larger than the aperture in the regularly used control elements wherein the light spot diameter depended upon the aperture diameteri Across the aperture H or l3 in such manner as to divide the area of the aperture into two substantially equal parts there is attached to either side thereof, by welding or by other suitable means, a wire M which is stretched and forms electrical contact with the disk surface 10.

The effect of this design, as can be seen more particularly from Fig. 2 of the drawings and also from Fig. 2a thereof, is to control the center of the electron pencil or beam l5, which is developed by drawing the electrons issuing from the electron emitting surface I! of the heated cathode member l8 by means of the application of suitable positive voltages upon an anode electrode [9 for example, rather than to change the beam diameter as is the case when modulation is produced by the usual type of control electrode. The apertures I! and I3, depending upon the shaping of the disk member as in Figs. 3a and 3c, are so large that little or no current will be cut off from the outside of the electron beam and the wire l4 stretched across the aperture will cut a diametric swath from the beam 15. As the bias on the control electrode comprising the disk member l and. the shielding portion I2 is increased negatively the apparent size of the wire l4 as regards the control of the electron beam will increase. This effective or apparent increase in the size of the wire l4 causes a reduction in the number of electrons forming the central portion of the electron beam or pencil l5 which passes through the aperture 20 of the disk member 2| forming a part of the anode structure I9. This effect, in turn, results in an electron stream which takes the general form of the aperture 20 of the electrode l9 except that the fluorescent spot produced upon the fluorescent screen structure 4 is divided by the wire member 14 into two parts as can be readily appreciated from an observation of Fig. 2a which represents a cross-section through the electron stream on the line A-A intermediate the aperture 20 and the screen structure 4. From what has been above stated, it will be appreciated that the wire l4 effectively casts its shadow upon the screen structure 4 but this shadow is not in any way detrimental to any detail of the area scanned provided that the electron beam is swept back and forth across the fluorescent screen structure in such manner that the resulting shadow or dark line produced is perpendicular to the direction of beam motion.

It is also possible in accordance with the teachings of this invention, disclosed especially by Figs. 2 and 3, to modulate the electrons emanating from the heated cathode in still another manner in accordance with this invention. In such form use is made of a double helically wound filament which is hollow along its axis. With such a construction a rod-like electrode is then supported within the hollow portion of the filament member. Such a construction is shown more particularly by Fig. 4 which represents the various companion parts of a filament assembly.

In Fig. 4 the filament 34 is formed so as to be hollow along its axis A-A. The electrode member 40 is so formed as to extend beyond the continuous end of the filament 34. To the end of the electrode 40 nearest to the terminal members 35 and 36 of the filament 34 there is attached a suitable tab or contact member 39 to which electrical connections may be established.

In manufacturing a filament of this general type the filament is wound upon a mandrel such as that shown by 42 in Fig. 5. This mandrel is formed preferably of molybdenum and provided with a double helical groove 43. A tip portion 44 is machined on the end of the mandrel to. prevent the wire which is wound thereon crossing the -axis of the coil. This suggested method of winding is merely illustrative since there are various suitable methods for performing this operation.

Following the winding of the filament it is covered with a layer of insulating material which is baked by suitable heat treatment. The electrode 40 which will constitute the control electrode and which can be seen in its assembled form from the showing in Fig. 6 is also coated with insulating material and baked whereupon it is inserted into the coil so that the contactor tab portion 39 lies at the same end as the lead wires of the filament 34. This assembly is suitably inserted into the cathode sleeve portion 31 which is provided with a conducting tab portion 4i electrically connected thereto by welding or other suitable means. The cathode sleeve portion 31 is provided with an aperture 38 of suitable diameter through which the electrode member 45 protrudes. The annular face 45 of the cathode sleeve 31 is coated with a thermionically active substance prior to the assembly operation so that upon heating the cathode member by the application of current to the terminals 35 and 36 of the filament 34 electrons are emitted from the activated surface of the annular face 45 to form an electron beam 46. This electron beam 46 is suitably controlled, limited and focused by the electrodes 49, 411, 48 and 33.

The function of the electrode 40 is similar to that of the wire I 4 of Fig. 2, in that, its purpose is to modulate the cathode beam or pencil 46. However, with the arrangement shown by Figs. 4 through 6, and more particularly by Fig. 6, it will be seen that the cathode ray beam or pencil 46 is similar to a hollow cylinder as shown by the section through the beam taken on the line BB, whereas the cathode ray pencil l5 of Fig. 2 has a crosssection which consists substantially of two areas bounded by semi-circles.

In the operation of the arrangement shown by Fig. 6 the electrode member 40 tends to spread the cathode ray beam 46 with any increase in negative potential. If the anode element 33 has a fixed aperture 3| provided at one end thereof and has a constant positive potential impressed thereupon the beam passing through this aperture will at all times be constant in cross-section regardless of the potential impressed upon the modulating electrode 4B. The electrode 33 will collect any of the electrons which may have been spread out to cover a larger area than that of the aperture 3|. Thus, modulation of the cathode ray beam may be accomplished without changing its diameter or boundaries. The luminescent spot produced upon the fluorescent screen structiu'e 4 will then be of uniform size, that is, the boundaries will at all times remain constant, regardless of the modulating voltages impressed thereon.

The cathode ray spot thus produced and con- Way of the metal cap 50 formingcontact theretrolled or modulated may be, focused 31)! the screen structure in such a way as to eliminate the dark spot which would naturally be expected from the hollow nature of the beam. This focusing Fig. 1', for example, the conical portion 33 of the tube member is formed of conducting material and suitable voltages may be applied thereto by with in any suitable manner, such as shown for example by my copending application, Serial No. 643,955, filed November 23, 1932. Other voltages for operating the tube are-applied to the tip members or contact points 5i formed as a part of the base member 2, except that it isusually preferable to make electrical contact to the deflecting mem bers such as the deflecting plates 6 at points substantially adjacent these members byway of lead wires connected to the deflecting elements and passing through the tube wall at points closely adjacent to the'deflecting members.

' Without departing from the spirit and scope of 7 this invention it will be apparent that other and various waysand means may be provided for controlling the intensity of the fluorescent spot resulting upon the, fluorescent screen of a cathode ray tube or other type of electronic device where in the effect of variation in the size or diameter of the resulting fluorescent spot is avoided, and I there-fore believe myself, in accordance with the modifications of this general scheme herein suggested, to be entitled tomake and use any and all of these modifications which fall fairly within the spirit and scope of the invention asset forth by theappended claims. I

Having thus described the invention, what I claim and desire to secure by Letters Patent is the following:

1. An electron device including an electrode serving as an electron source, means to cause the electrons emitted to be projected along a predetermined path, an observation screen in the path of the projected electrons adapted to become luminescent when the projected electrons impinge thereon, means for maintaining constant the. bounding area of instantaneous impact of electron stream upon the screen to maintain a constant outer boundary of the resultant luminous effect, and a control electrodelocated within the outer boundary of the electron source electrode for reducing the electron density of, the projected electron stream withina central portion of the boundary limits to produce an annular shaped electron stream with a constant outer diameter and a variable inner'diamet er so as to vary thereproduced.

2. An electron tube which comprises an emissive by the observable intensity of the luminous effect f of the tube end wall opposite the electron emissive surface, means for causing the electrons generated at the source to pass toward the fluorescent end wall of the tube as a pencil of electrons, means for maintaining the bounding area of the electron pencil developed constant, means for causing the electron pencil to traverse the fluorescent screen according to a predetermined pattern of traversal,

and a control element protruding beyond the central portion of the electron sourceandlocated within the outerboundaries of the emissive surface electrode, said element adapted to have yary- 7 ing voltage applied thereto tovary the electron density within, a central portion of the electronbeam to vary the intensity of luminescence pro- :duced over a substantially constant area of the fluorescent screen. 1

v3. A cathode ray tube comprising a surface for emitting a stream of electrons, a target positioned in the stream and adapted to luminesce under impactof the electrons, means to focus the emitted electron stream on the target ,means to limit and fix the boundary area of the instantaneouslyimpinging electrons and electrode means acting only within the emitted electron'stream to variably remove under the control of signals the electrons from the inner portion of the boundary area of:v

impact to vary the intensity of the luminescent effects produced. I

RICHARD T. ORTH.

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