US2119119A - Cathode ray tube - Google Patents

Description

May`31, 1938. 1. sHoENBERG ET A1.

CATHODE RAY TUBE Filed Sept. 28, 1934' 2 SheeLs--Smscl 1 NSN G. i. comm/FFE BY AND mFRd/VCISTEDHAM ATTORNEY May 31, 1938. 1. sHoENBERG ET Al.

CATHODE RAY TUBE Filed Sept. 28, 1934 2 Sheets-Sheet 2 q S. QS n.. S. S. @.w N5 QJ @SNQQF SEQ wf) N I NV EN TORS L SHDFNBFRG, 6. E. CUNDUfFE AND #FRANC/5 TED/MM BY Mffw ATTORNEY Patented May 31, 193s UNITED STATES ori-lc CATHODE BAY TUBE Application September 28, 1934, Serial No. '145,838 In Great Britain October 3, 1933 9Clalms.

The present invention relates to improvements in cathode ray tubes.

A cathode ray tube is known which comprises a cathode, a modulating electrode or modulator", one or more focusing electrodes, an anode and a fluorescent screen. Tubes of this kind are used for purposes such as television reception,

received picture signals being applied between the l cathode and modulator so as to vary the intensity of the ray reaching the screen and thus produce a corresponding variation in intensity of the fluorescent light emanating from this screen.

There are two classes of known cathode ray tube. The older soft types are not highly evacuated and the concentrating effect exerted by the ions of a gas upon the electron stream serves to focus the ray in a small spot upon the screen. The newer hard types are highly evacuated and require electrostatic or electromagnetic focusing means. The present invention relates exclusively to the latter class of cathode ray tube.

It has been found, however, that the modulation characteristic curves of hard tubes, that is to say, the curves obtained by plotting modulator volts (relative to the cathode) as abscissae against iiuorescent screen current as ordinates, are excessively curved, changes in fluorescent screen current for large changes in modulator volts being disproportionately large compared with the changes in fluorescent screen current produced by smaller changes in modulator volts.

It has been found that the size of the spot varies with the modulator volts, generally increasing as the potential of the modulator approaches that of the cathode, thus giving rise` to loss of detail in the reconstituted picture.

It is an object of the present invention to provide means for at least partially eliminating the above mentioned disadvantages.

It is another object oi. the present invention to provide an electric circuit comprising a cathode ray tube of the hard type having arranged within its envelope, in the order mentioned, a cathode, a first accelerating electrode, a decelerating electrode having an apertured diaphragm and a second accelerating electrode and a screen, the accelerating and decelerating electrodes being in the form of electrodes, so disposed that the ray constituted by electrons from said cathode can pass through them to a screen associated with the tube, the tube being provided with electrostatic or electromagnetic means for focusing the ray in a. small spot on the screen and with means for defiecting the ray over the screen, and means for applying to said accelerating electrodes potentials positive with respect to the cathode potential and to the decelerating electrode a potential approximately equal to the cathode potential, the shape and disposition of the electrodes and the potentials applied thereto being such that, in operation, increases of potential of the decelerator, in the negative sense with respect to the cathode potential, produce increases of current to the iirst accelerator.

The aperture in the diaphragm of the decelerator is of the ordinary type, that is to say, it is not obstructed by grid wires or the like extending across it.

With this arrangement electrons emitted from the cathode are slowed up to a velocity not differing greatly from zero in a region lying in the neighbourhood of the decelerating electrode and are accelerated from this region towards said screen. Such a region will for convenience be referred to as a deceleration region.

In this way there has been produced a cathode ray tube having a nearly straight characteristic, which is desirable for some purposes, and one in which there is reduced change of size of the iiuorescent spot with change in modulator voltage. It has, however, been found that with tubes of this kind there may be a halo of light around the fluorescent spot. It is thus a further object of the present invention to provide a cathode ray tube in which no such halo is formed around the iiuorescent spot. With this end in View an electric circuit comprises a cathode ray tube of the hard type having varranged Within its envelope in the order mentioned, a cathode, a first accelerator, a first decelerator having an apertured diaphragm, a, second accelerator, a second decelerator, a third accelerator and a screen, the accelerators and decelerators being in the form of electrodes so disposed that the ray constituted by electrons from said cathode can pass through them to said screen, the tube being provided with electrostatic or electromagnetic means for focusing the ray in a small spot on the screen and with means for deecting the ray over the screen, 'and means for applyingv to the accelerators potentials positive with respect to the potential of said cathode and to the decelerator potentials approximately equal to the potential of said cathode, the shape and disposition of the electrodes and the potentials applied thereto being such that, in operation, increases of potential of said rst decelerator in the negative sense with respect to the potential of said cathode, produce increases of current flowing to the first accelerator.

Tubes constructed in this way may have a characteristic which ls curved but to a less extent than the known tubes above referred to and the change of spot size with modulator potential is satisfactorily small whilst the halo is substantially absent. The relatively small but still definite curvature of the characteristic which is obtained is advantageous for some purposes where for example it is desired to increase the detail in the lighter parts of the reproduced picture in comparison with the detail in the darker parts.

Henceforth accelerating and delccerating electrodes will be called, for convenience, accelerators and decelerators respectively.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which Fig. 1 illustrates a tube having two accelerators and one decelerator arranged so that there is formed, during the operation of the tube, one deceleration region.

Fig. 2 shows a circuit arrangement for supplying appropriate potentials to the Various electrodes of a tube of the kind illustrated in Fig. 1.

Fig. 3 illustrates a tube having three accelerators and two decelerators arranged so that two deceleration regions are formed during the operation of the tube, and

Fig. 4 shows a circuit arrangement for supplying appropriate potentials to the various electrodes of a tube of the kind illustrated in Fig. 3.

In the embodiment illustrated in Fig. 1, a, cathode ray tube suitable for purposes of television reception, comprises an evacuated, sealed glass envelope consisting of a cylindrical portion I flaring out into a frusto-conical portion 2. The diameter and length of the cylindrical portion I are about 11/(2 inches and 8 inches respectively the diameter of the base 3 of the frusto-conical portion 2 is about 9 inches, whilst the overall length of the envelope is about 19 inches.

Sealed internally to the closed end of the cylindrical portion I is a glass tubular portion 4 which projects internally from and lies wholly within the cylindrical portion I. The tubular portion 4 is about 1/2 inch in internal diameter and 6%.; inches in length.

Disposed within the tubular portion 4 are a cathode heater 4A, a cathode 5, a cathode shield 6, a rst accelerator l, a decelerator 8 and a second accelerator 9, these electrodes being arranged within the glass tubular portion 4 in the order mentioned. The decelerator 8 is adapted to function as a modulator and the second accelerator 9 corresponds to what is sometimes known as the first anode of the tube. Leads to the electrodes disposed within the glass tube 4 may be passed through a pinch I0 sealed into the closed end of the tubular portion I, the leads to the cathode and its heater also serving as supports for these electrodes whilst the cathode shield, the two accelerators and the decelerator are mounted as sliding ts within the glass tubular portion 4. Leads to the three last mentioned electrodes pass from the pinch i0 through holes such as I I, I2 in the side walls of the glass tube 4 and back through holes such as I3, I4 on to the electrodes. The second accelerator 9, about 3 inches in length, is mounted within the tubular portion 4 in such manner that l inch or more of the electrode protrudes beyond the tubular portion. If desired a lead may be taken to this protruding portion through the side wall of the cylindrical portion I of the envelope instead of from the pinch IU. All of the electrodes mentioned, except the heater, are of cylindrical shape and are mounted co-axially within the envelope.

A second anode I5, in the form of a cylinder of 31/2 inches length, is also mounted as a sliding fit within the cylindrical portion I of the envelope in'such manner that the second anode overlaps the second accelerator or first anode by about A of an inch.

On the inner side of the base 3 of the frustoconical portion 2 of the envelope is deposited a fluorescent screen I6 of any known or suitable material. Either electrostatic or electromagnetic means such as two pairs of coils Il, I8 may be utilized to deect the ray so as to scan the uorescent screen I6 and these means may be situated, either inside or outside the tube between the second anode I5 and the screen I6 and close to the second anode.

The cathode 5 may be of any suitable kind but preferably is in the form of a shallow open pill-box of 1A; inch diameter, electrons being emitted from the fiat circular base which is indirectly heated by means of the heater which lies within the box. The cathode may be coated with an electron emitting substance such as a mixture of strontium and barium oxides.

The shield 6 is also in the form of a pill-box, of about l inch length and diameter, having a central aperture I9 in its base and being disposed around the cathode 5 so that the cathode lies close to (but does not touch) the bottom of the shield B and emits electrons through the aperture I9 in the base of the shield.

The rst accelerator 'I is in the form of a very shallow open pill-box; about 2 millimetres in length and 1/ inch diameter. It has a central aperture 20 in its base which is disposed about 3 millimetres away from the base of the shield 8 and the skirt of the rst accelerator is turned toward the cathode 5.

The decelerator 8 is in the form of a short cylinder, about 1/2 inch length and 1/2 inch diameter, with a disc (having an aperture 2| disposed therein) disposed along its length somewhat nearer the rst accelerator 'I than the second accelerator 9. One end of the decelerator 8 is about le of an inch away from the rst accelerator 1.

The second accelerator or rst anode 9 bears two discs, the one disposed at the end of the electrode lying closer to the deceleratoi1 8 having an aperture 22, and the other being disposed about l inch from the opposite end and having an aperture 23.

The second anode I5 carries no apertured discs, 1 i

and a lead to this electrode may be taken through the wall of the frusto-conical portion 2 of the envelope.

The apertures I9, 20, 2| and 22 are all of 0.075 inch in diameter, whilst the second aperture 23 in the accelerator 9 is of 0.15 inch diameter.

The various electrodes are maintained at their appropriate potentials by means of the'circuit arrangement shown in Fig. 2.

An alternating potential difference of any convenient voltage, is stepped up by means of a transformer 34 to 5,000 volts and rect-ied in the device indicated generally at 35. This steady potential is maintained across a potentiometer resistance 36, 31.

A tapping 38 on the potentiometer is connected both to the cathode 5 and to the cathode shield 6, these electrodes being in this manner maintained at about 40 volts positive with respect to earth. Tappings 39, 40 and 4I on the potentiometer are connected to the first accelerator 1, the second accelerator 9 and the anode l5, respectively, in such 'manner that these electrodes are respectively maintained at about 200 volts, 1,000 volts and 3,600 volts positive with respect to the earth potential.

Where the arrangement is to be used as a television receiver, the received signals are detected and amplified in a device shown generally at 42. The output from the device d2 is applied across a resistance 43 one end of which is earthed and the other end of which is connected to the decelerator or modulator 8.

It will be seen that the modulator 8 derives a negative bias from the high tension supply to the tube and a positive bias from the ow of picture signal current through resistance 43. The resultant bias is such that the picture signals operate to vary the potential of the modulator 8, relative to the cathode, from zero down to about -30 volts, at which voltage the ray is extinguished.

The potentials above given have been so selected in relation to the shape and disposition of the electrodes that increases in potential of the decelerator 8 in the negative sense produce increases in current flowing to the rst accelerator 1.

It is believed that the operation of the tube is somewhat as followsz- Referring more particularly to Fig. 1, electrons emanate from the cathode 5 with random velocities and directions. The electrostatic accelerating eld existing between the positive ilrst accelerator 1 on the one hand and the earthed cathode 5 and shield 6 on the other hand has the effect of extracting a large number of electrons from the cathode and concentrating these electrons so as to pass through the aperture 2l in' the decelerator 8.

The decelerator is at a negative potential with respect to the first accelerator 1 so that between these two electrodes the electrons are decelerated and a deceleration region is formed close to the aperture 2l in the decelerator 8.

The second accelerator 9 is at a high positive eld existing between the various electrodes, and

electrons which emerge from the cathode with comparatively large transverse velocities (say up to 0.2 volt) are to a very large extent filtered out by the decelerator 8 so that the electrons drawn from the deceleration region toward the second accelerator 9 have almost the same axial and radial velocities and hence can be brought to a very sharp focus on the iiuorescent screen I6. The focusing is eiected in the following manner.

Between the deceleration region and the distant end of the second accelerator or first anode 9 the electrons tend to diverge owing to the shape of the electrostatic iields produced between the electrodes. On reaching the comparatively strong electrostatic eld maintained between the adjacent ends Iof the rst and second anodes, however, the diverging electrons are concentrated or focused back on to the axis of the tube and at the same time accelerated towards and through the second anode l5. The eld between these two electrodes acts upon the diverging cone of electrons in much the same way as a lens acts upon a diverging beam of light, and for this reason the arrangement of rst and second anodes may be called an electron lens. In the present case the cone of electrons which is diverging on entering the electron lens emerges as a converging cone and is brought to a focus upon the fluorescent' screen I6.

It has been found that with this arrangement a spot of very small size can be obtained upon the screen and that changes in size of the spot, with changes in modulator volts, are less than the corresponding changes which have been observed in tubes of known kind.

In a second embodiment of the invention the shield B, shown in broken lines in'Fig. l, may be omitted and the catho'de 5, together with its heater, moved up towards the first accelerator 1 I so that there is about 1A; inch between the base of the first accelerator and the base of the cathode 5.

The irst accelerator 1 is in this case maintained at about 10 volts positive with respect to the cathode whilst all other electrodes are maintained at the' potentials specified for the last described embodiment.

An accelerating field exists between the cathode and first accelerator 1 so that electrons are accelerated towards the first accelerator, some electrons passing through the aperture in this electrode.

Between the rst accelerator and decelerator the electrons are decelerated as they approach the deceleration region which, as before, lies in the neighbourhood of the aperture in the decelerator.

The rst and second anodes operate, as in the last described case, to accelerate and focus the electrons upon the fluorescent screen.

In the second embodiment described above the rst accelerator 1 is at a positive potential with respect to the cathode 5, so that many electrons which in the embodiment rst described pass through the aperture I9 in the shield 6, are in the second embodiment attracted towards and collected upon the first accelerator 1 so that a uorescent spot of comparatively weak intensity is formed upon the screen I6. Because of this the first embodiment is to be preferred.

It has been found that although with the two embodiments described above the change of spot size with modulator (or decelerator) volts is less than that obtained with known tubes, the spot possesses a halo of light. In the embodiment illustrated in Figs. 3 and 4, however, this disadvantage is almost entirely eliminated.

The tube illustrated in Fig. 3 is of the same general form as that illustrated in Fig. 1 but includes an extra decelerator and an extra accelerator. Thus within the glass tube 24, which corresponds to the tube d of Fig. 1, there are disposed,

'in the order mentioned, a cathode heater 24A, a

cathode 25, a shield 26, a iirst accelerator 21, a rst decelerator 28, a second accelerator 29, a second decelerator 30 and a third accelerator or rst anode 3l. A second anode 32 is mounted as a sliding t in the cylindrical portion of the envelope.

The cathode, shield and rst and second anodes are of the same form as those illustrated in Fig. 1. The rst accelerator 21 is in the form of an open pill box of 0.04 or 0.08 inch height, its base, which has a central aperture, being turned away from,

and being disposed about 0.08 or 0.12 inch from, the base of the shield 25. The first decelerator 23. which may be utilized as a. modulator, is also in the form of an apertured open pill box of about 0.08 or 0.12 inch height, its hase being turned away from and being disposed about 0.12 or 0.16 inch from the base of the lirst accelerator 21. 'Ihe second accelerator 29 is of exactly the same size and shape as the rst accelerator 21; its base is turned away from and is`disposed about `0.08 or 0.12 inch from, the base of the first decelerator 28. 'I'he second decelerator 30 is in the form of a short cylindrical tube having a centrally apertured disc disposed within it at a point somewhat nearer the end which is adjacent (about 0.04 inch from) the second accelerator 29 than the other end which is disposed about 0.04 inch from the third accelerator or first anode 3i- The apertures in the shield, accelerators and decelerators are all equal to about 0.08 inch diameter and the diameters of these electrodes themselves are all equal to the diameter of the first anode.

As before, appropriate potentials are applied to the electrodes from a common potentiometer resistance 44, 45 across which is maintained a steady potential difference of 5,000 volts. Relative to earth potential the cathode 25, cathode shield 26 and second decelerator 30 are all maintained at about 40 volts positive, the first and second accelerators 21 and 29 respectively at about 250 volts positive, the third accelerator 3i at about 1,000 volts positive and the second anode at 3,900'volts positive. Received picture signals are used to modulate the intensity of the ray in a manner similar to that described in connection with Figs. 1 and 2, bias for the tube being derived partly from the high tension supply and partly from the iiow of picture signals through a resistance 46 inserted in the output circuit of a radio receiver 41. The arrangement is such that the picture signals are effective in varying the potential of the first decelerator or modulator 28, relative to the cathode, from zero down to about -30 volts at which voltage the ray is extinguished. Over this range of modulator volts no halo and only a small change of spot size is observable.

As before, the potentials applied to the electrodes are such that an increase in the potential of the decelerator 28 in the negative sense produces an increase in the current flowing to the first accelerator 21.

During the operation of the tube shown in Figs. 3 and 4, two deceleration regions are formed. Electrons are extracted from the cathode 25 by the relatively positively charged first accelerator 21 and are focused upon the aperture in the modulator or first decelerator 28. The potential of the modulator varies from zero to 30 volts relative to the cathode, so that the electrons are slowed up as they approach a. deceleration region near the aperture in the rst decelerator 28. From this point the electrons are accelerated towards the second accelerator 29 and are focused upon the aperture in the second decelerator 30. This decelerator has the effect of again slowing up the electrons as they approach a, second deceleration region which lies in the neighbourhood of the second decelerator 30. The rst and second anodes 3| and 32 co-operate together in accelerating electrons from the second deceleration region and focusing them upon a fluorescent screen 33. The satisfactory operation of the tube described is dependent upon the relative potentials of the various electrodes, their separation, the sizes of the apertures in them and the density of the current flowing through the tube and the improvement in the constancy and definition of the fluorescent spot is believed to be due to the fact that the second decelerator 3l is not at a negative potential with respectio the ca thode 25.

In the tube illustrated in Figs- 3 and 4 modulation of the ray may be effected by varying the potential relative to the cathode, of the shield 2l or of either of the decelerators 2l and 3l, the potentials of those two of these electrodes not used for modulation being held at approximately cathode potential.

It is not essential that the rst and second accelerators 2l and 29 should be maintained at the same potentials relative to the cathode. It may. for instance, be convenient to keep either or both of.' them at the same potential as the first anode 3 The number of deceleration regions formed in the tube may be greater than two, the formation of each such region being achieved by the introduction of an extra pair of electrodes, one serving to accelerate the electrons and the other serving to decelerate them.

A magnetic electron lens may be used to assist in forming a focused spot upon the fluorescent described above. Moreover a magnetic electron lens may be used to assist in concentrating the electrons in the neighbourhood of the deceleration region, the final focusing on the fluorescent screen being then achieved by means of another electron lens.

Ii sharp focusing of the ray is not essential the second anode of either of the tubes illustrated (shown in broken lines in the iigures) may be omitted.

The characteristic curve of a cathode ray tube can generally be represented by the equation IAZKEQI, Where K represents a constant, In represents the uorescent screen current and E represents modulator voltage. For the tube just described :z: is equal to about 1.8, whilst for most known tubes :r has a value of 2 or more and for the tube illustrated in Fig. 1 :n is equal approximately to unity.

Over the greater part of the useful current range of the tubes described above the intensity of fluorescence is substantially proportional to the intensity of the current owing to the iiuorescent screen, so that in the equations given above IA may be taken as representing the intensity of fluorescence as well as the fluorescent screen current.

The index, or I figure in the above equations therefore determines what may be called the intensity-contrast of the tube. An appreciation of what is meant by the expression intensity-contrast" may be gathered from the following considerations:

It has long been recognized in the cinema art, that if the brightnesses of all points of an image viewed on a fiat projection screen are proportional to the brightnesses on the object from which the images are derived, the screen image appears flat and lminteresting to the eye. This effect is believed to be due to the fact that the images are projected in black and white and the additional effect of detail which would be given to the lighter parts of the picture by the natural colour is absent. It is therefore common prac-v tice in the cinema industry to develop picture films in such manner that detail in the lighter or less opaque portions of the positive nlm picf screen in place of the electrostatic electron lens tures is brought out, or amplied as it were, relatively to the detail in the darker or more opaque portions of the pictures. A lm developed in this way, and the images projected from it, are said to possess intensity contrasts" of value greater than unity and the images derived from the film are more pleasing and appear more full of detail than images projected from a lm of intensity contrast equal to unity, that is to say, a film in which the light transmitted through all points is exactly proportional to the brightnesses of the corresponding object points.

It is found in fact that a lm developed to an intensity contrast of from about 1.8 to 2.0 is most satisfactory in this respect.

Similarly a tube having an intensity contrast greater than unity is onewhich amplifles signals of large amplitude to a greater extent than it does signals of small amplitude and a tube having-an intensity contrast of unity is one which produces no amplitude distortion.

1f now the signals received at a cathode ray tube receiver are truly representative of the tone valueof 'the object, that is to say, are transmitted with an effective intensity-contrast of unity, then, since the reproduced images' are to be viewed upon a screen, the receiver tube should have an intensity-contrast higher than unity and usually in the neighbourhood of 1.8, because this is usually found to be the intensity-contrast which appears most pleasing to the eye. On the other hand if the signals are transmitted with an effective intensity contrast greater than unity (say, for example, are derived from a motion picture lm developed in the usual way so as to have an intensity-contrast of about 1.8, then the tube at the receiver should vhave an intensity contrast of about unity.

A tube having an intensity-contrast of 2.0 or

higher is rarely of use, however.

In the embodiments of. the present invention which have been described above it is found that if the potential on the modulator be increased negatively with respect to the cathode, the current owing to the rst accelerator increases in such a way that on plotting rst accelerator current vas ordinates and modulator volts as abscissae a roughly straight line of negative slope is obtained over the working range (0 to 30) of modulator volts.

The values given for the various members of the circuits illustrated in Figs. 2 and 4 are by way of example and should not be regarded as strictly limiting values.

We claim:

1. An electric circuit comprising a cathode ray tube, comprising a cathode, an apertured shield electrode, an apertured accelerator electrode, an

apertured decelerator electrode, a second apertured accelerator electrode, an anode and a screen, means for supporting said electrodes progressively in register with said cathode, means for applying potentials positive with respect to the cathode to both of said accelerator electrodes, means including a resistance to maintain the decelerator electrode negative with respect to the cathode, and means for supplying signalling potential across the resistance.

2. An electric circuit comprising a cathode ray tube, comprising a cathode, an apertured shield electrode, an apertured accelerator electrode, an apertured decelerator electrode, a second apertured accelerator electrode, an anode and a screen, means for supporting said electrodes progressively in register with said cathode, a power supply, means for supplying positive potentials relative to the cathode to the second accelerator electrode, a resistance connected in series with the power supply and the iirst accelerator electrode, means including a resistance to maintain the decelerator electrode at a potential negative with respect to the cathode, and means to supply signalling potentials across the resistance.

3. An electric circuit comprising a cathode ray tube, comprising a cathode, an apertured shield electrode, an apertured accelerator electrode, an apertured decelerator electrode, a second apertured accelerator electrode, an anode and a screen, means for supporting said electrodes progressively in register with said cathode, a power supply, means for supplying positive potentials relative to the cathode to the second accelerator electrode, means including a resistance for maintaining the decelerator electrode at a potential negative with respect to the cathode, means to supply signalling voltages across the resistance, and means to vary the potential of the first accelerator electrode with respect to the cathode in accordance with the signalling voltages supplied to the resistance.

4. An electric circuit comprising a cathode ray tube having arranged within its envelope a cathode, a iirst accelerator apertured electrode, a rst decelerator apertured electrode, a second accelerator apertured electrode, a second de.-

celerator apertured. electrode, and a third ac-` celerator apertured electrode, an anode and a screen, means to support progressively all of the electrodes in register with the cathode, means to maintain the three accelerator electrodes at a potential positive with respect to the cathode, means including a resistance for maintaining the first decelerator electrode at a potential negative with respect to the cathode, means to maintain the second decelerator electrode at a predetermined potential with respect to the cathode', and means to supply signalling voltages to the resistance.

5. An Aelectric circuit comprising a cathode ray tube having arranged within its envelope a cathode, a first accelerator apertured electrode, a rst decelerator apertured electrode, a second accelerator apertured electrode, a second decelerator apertured electrode, and a third accelerator apertured electrode, an anode and a screen, means to support progressively all of the electrodes in register with the cathode, means for maintaining the three accelerator electrodes at a potential positive with respect to the cathode, means including a resistance for maintaining the rst decelerator electrode at a potential negative with respect to the cathode, means for supplying signalling voltages to the resistance, and means for varying the potentials supplied to the iirst and second accelerator electrodes in accordance with the signalling voltage supplied to the resistance.

6. An electric circuit comprising a cathode ray tube having arranged within its envelope a cathode, a first accelerator apertured electrode, a first decelerator apertured electrode, a second accelerator apertured electrode, a second decelerator apertured electrode, and a third accelerator apertured electrode, an anode and a screen, means to support progressively all of the electrodes in register with the cathode, means -for maintaining the three accelerator eiectrodes at a potential positive with respect to the cathode, means including a resistance for maintaining the first decelerator electrode at a potential negative with respect to the cathode, means for supplying signalling voltages to the resistance. and resistance means for varying the potentials supplied to the rst and second accelerator electrodes in accordance with the signalling voltage supplied to the resistance.

'7. An electric circuit comprising a cathode ray tube having arranged within its envelope a cathode, a first accelerator apertured electrode, a rst decelerator apertured electrode, a second accelerator apertured electrode, a second decelerator apertured electrode, and a third doubly apertured cylindrical accelerating electrode, an anode and a screen, means to support progressively all ol the electrodes in register with the cathode, means to maintain the three accelerator electrodes at a potential positive with respect to the cathode, means including a resistance for maintaining the rst decelerator electrode at a potential negative with respect to the cathode, means to maintain the second decelerator electrode at a predetermined potential with respect to the cathode, and means to supply signalling voltages to the resistance.

8. 'I'he method of overcoming the halo eiect in cathode ray tubes, wherein is provided a.- source of electrons, comprising the steps of accelerating the electrons from said source, developing signalling energy, decelerating the electrons in accordance with the developedsignalling energy, reaccelerating the electrons, and varying the rate of reacceleration in accordance with the signalling energy.

9. The method of overcoming the halo eiect in cathode ray tubes wherein is provided a source of electrons, accelerating the electrons from said source, developing signalling energy, decelerating the electrons in accordance with the developed signalling energy, reaccelerating the electrons, simultaneously varying the rate of acceleration and reacceleration of the electrons in accordance with the signalling energy, subsequently decelerating the electrons, and accelerating the electrons, and directing said electrons upon a viewing surface.

ISAAC SHOENBERG. GEORGE EDWARD CONDLIFFE. W'ILLIAM FRANCIS TEDHAM.

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