432,485

PATENT SPECIFICATION

Application Date: Dec. 29, 1933. No. 36653/33.

Complete Specification Left: Dec. 27, 1934.

Complete Specification Accepted: July 29, 1935.

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PROVISIONAL SPECIFICATION

Improvements in and relating to Television and the like Systems employing Cathode Ray Tubes

I, ALAN DOWER BLUMLEIN, a British Subject, of 7, Courtfield Gardens, Ealing, London, W.13, do hereby declare the nature of this invention to be as follows:-

The present invention relates to television and the like systems of the type in which a cathode ray tube is employed to reconstitute the transmitted image. The invention is particularly concerned with cathode ray tubes for use in such systems.

Television and the like systems have already been proposed in which, at the receiver, the transmitted image is reconstituted by means of a scanning device co-operating with a plurality of light sources which may be controlled by signals received upon a single channel. The signals applied to any one of these light sources are out of phase by a certain definite amount with respect to the signals applied to any of the remaining sources. The several light sources are arranged in space relation to each other with respect to the scanning means, and the phase differences between the signals applied thereto are made such that reproduced images due to the several light sources are superimposed one upon the other.

Such arrangements confer the very considerable advantage that, without increasing the number of channels of transmission, the intensity of the reconstituted image may be made several times greater than when it is formed by one similar light source alone. It will be at once appreciated that the use of, say, four modulated light sources instead of only one results, other things being equal, in a fourfold increase in the intensity of the reconstituted image, for the same degree of definition. A similar intensity using only one light source could be obtained either by reducing the scanning speed or by decreasing the number of elementary areas in the reconstituted image, or by decreasing both the scanning speed and the number of elementary areas, but in any case the definition in the reconstituted picture would be reduced correspondingly.

Television systems such as those under consideration are known as multiple spot scanning systems, and it is an object of the present invention to provide a cathode ray tube capable of being used in such a system.

It is a further object of the invention to provide a multiple spot scanning television system in which a cathode ray tube is employed to reconstitute the transmitted image.

According to the present invention, a cathode ray tube comprises a plurality of control electrodes, each adapted to be associated with a separate control circuit. By a control electrode in this context is meant an electrode so arranged that it may serve to control the intensity of a cathode ray beam.

According to a feature of the invention, the control electrodes are spaced from one another in a direction transverse of and preferably at right angles to the longitudinal axis of the tube, and means are provided for bringing the electrons from the cathode to a post focus upon a fluorescent screen associated with the tube, the arrangement being such that the position of the spot when the beam co-operates substantially entirely with one of the control electrodes is different from its position when the beam co-operates with another of the control electrodes.

According to a further feature of the invention, a receiver for a television or the like system comprises a cathode ray tube such as is referred to in either of the two preceding paragraphs, and means for applying controlling impulses such, for example, as picture signals representing the light and shade values of the transmitted image, to each of the control electrodes, the phase of the signals applied to any one control electrode being different from the phase of the signals applied to any of the remaining control electrodes. Such means may comprise one or more delay circuits to which the controlling impulses are applied.

In carrying the invention into effect, I may proceed as follows:-

A cathode ray tube comprises a glass or like envelope having a frusto-conical portion and a cylindrical portion, one end of the latter being sealed to the smaller end of the frusto-conical portion, and the other end thereof being closed by a suitable foot. The two portions are arranged with their longitudinal axes in substantially the same straight line, and the frusto-conical portion is closed at its larger end by a suitably shaped glass plate, on the inner surface of which is provide a screen of fluorescent material.

An electron emitting cathode is mounted upon the foot; the cathode preferably comprises a thin wire of tungsten or the like coated with electron emitting material, and so disposed as to lie in a plane containing the longitudinal axis of the tube and to be at right angles to that axis. The control electrodes of the tube are constituted by fine parallel wires arranged in an aperture in a screen, the screen and the control electrode wires being insulated from one another and lying in substantially the same plane, which is preferably at right angles to the longitudinal axis of the tube.

The control electrodes are arranged in front of the cathode, and are so disposed as to lie at right angles thereto. A suitable electron lens, comprising for example two cylindrical electrodes adapted to be maintained at different high positive potentials with respect to the cathode, are provided for the purpose of focusing the cathode ray beam upon the fluorescent screen, and magnetic or electrostatic deflecting means are provided, in any known or suitable manner, for causing the beam to sweep over the screen under the control of scanning impulses applied to the deflecting means.

The control electrode wires are insulated from one another, and each is associated with a separate input terminal. In operation, the screen and the control electrode wires are given a negative potential with respect to the cathode such that substantially none of the electrons from the cathode are able to escape through the mesh formed by the control electrodes. The modulating impulses, such for example as the picture signals, are then applied to the control electrodes in such a sense as to cause their potentials to become less negative with respect to the cathode. Let it be assumed that a picture signal impulse is applied to one of the control electrodes in such a sense as to make its potential less negative with respect to the cathode; electrons escape form the control electrode mesh in the neighbourhood of the control electrode under consideration, and are brought to a focus on the fluorescent screen, and it is arranged that the luminous spot so formed is approximately equal in area to one picture dot, or one elemental area of the transmitted image. If now the potential of another control electrode is reduced, electrons will escape in the neighbourhood of this electrode also, and will be brought to a focus on another point on the screen, also equal in area to substantially one picture dot.

It will be seen, therefore, that the fluorescent screen of the tube is scanned simultaneously by as many luminous points as there are control elements, and the arrangement is, accordingly, a multiple spot scanning system. The picture signals applied to the several control elements may, then, be given such phase relationships that the reproduced images are superimposed upon one another.

The control electrodes may be fed with the picture signals from tappings in a suitable delay network, the picture signals being applied to the input terminals thereof, and taken off from points in the network after suitable phase retardations. One form of delay network, which will be described by way of example, comprises two input terminals, of which one is connected to a source of bias potential and the other is connected to the input terminal of one control electrode, and four pairs of coils, all of the same inductance, and all connected in series with respect to the input terminals. The value of the inductance of these coils will be referred to as L. A condenser of capacity C3 is connected in shunt with the input terminals, and further shunt condensers, of a value which will be referred to as C1, are provided at the junction of the coils of each pair, while shunt condensers of a value C2 are provided at the junctions between neighbouring parts of coils. A lead is taken from the junction of each pair of coils with the adjacent pair to the input terminals of three further control electrodes respectively, and a lead is taken from the end of the eight inductance coil to the input terminal of the fifth control electrode. The network is terminated by a resistance of value R, such that R= EQUAT. HERE and a condensers of value C3 is connected in shunt with the terminating resistance. The capacity C2 is made smaller than C1 by an amount sufficient to compensate for stray capacity introduced by the control electrodes, and the capacity C3 is made half the capacity C1, less an allowance for stray capacity due to the first and last control electrodes. The delay introduced by one section (comprising a series inductance coil and a shunt condenser) of such a network is given by EQUAT. HERE , and the delay between two successive control electrodes is therefore twice this amount.

The control electrodes may be so spaced that the distance apart of the portions of the fluorescent screen illuminated by the electrons controlled by adjacent electrodes, is say, two thirds of the width of one elemental area. If, then, t is the dot time, that is to say the time of scanning one picture dot at the transmitter, the network is designed in accordance with the equation

EQUAT. HERE

 

The network is also preferably made such that its cut-off frequency is well above the highest frequency of the picture signals, so that the delay introduced is substantially the same for all picture frequencies.

It should be noted that the separation in time of the action of the control electrodes of two thirds of the dot time is only chosen by way of example, and any other time separation may be employed as desired. Similarly, more or less sections of the delay network may be connected between each control electrode, and the network may be of a type more complex than that described and capable of being worked nearer to its cut-off frequency without introducing appreciable differences in the delay for the various picture frequencies.

The electrode arrangement is the cathode ray tube above described is one of the simplest contemplated, and it will be appreciated that many other arrangements, constituting a plurality of electrode systems for producing a plurality of electrode systems for producing a plurality of scanning spots on the fluorescent screen, may be constructed in accordance with the invention. For example, the control electrodes may operate upon a comparatively wide electron beam, which may subsequently be narrowed by means of apertured diaphragms or the like.

In a cathode ray tube such as the described, it may be found that the application of a signal potential to one control electrode may affect the electron flow in the neighbourhood of adjacent control electrodes. This effect may be counteracted by applying to the adjacent electrodes signal impulses of opposite phase and smaller amplitude, and these reverse signals may be obtained from a delay network similar to that described, but fed with signals of the opposite phase. Alternatively, the wave form of the modulating signals may be so modified that a change in one sense in the amplitude of the signals is preceded and followed by a slight change in the opposite sense, and this may be accomplished by applying the signals to three suitable delay networks, and combining the outputs thereof in such magnitudes and senses as to produce the required waveform.

Dated this 29th day of December, 1933.

REDDIE & GROSE,

Agents for the Applicant,

6, Breamís Buildings, London, E.C.4.

COMPLETE SPECIFICATION

Improvements in and relating to Television and the like Systems employing Cathode Ray Tubes

I, ALAN DOWER BLUMLEIN, a British Subject, of 7, Courtfield Gardens, Ealing, London, W.13, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:-

The present invention relates to television and the like systems of the type in which a cathode ray tube is employed to reconstitute the transmitted image. The invention is particularly concerned with cathode ray tubes for use in such systems.

Television and the like systems have already been proposed in which, at the receiver, the transmitted image is reconstituted by means of a scanning device co-operating with a plurality of light sources which may be controlled by signals received upon a single channel. The signals applied to any one of these light sources are out of phase by a certain definite amount with respect to the signals applied to any of the remaining sources. The several light sources are arranged in spaced relation to each other with respect to the scanning means, and the phase differences between the signals applied thereto are made such that reproduced images due to the several light sources are superimposed one upon the other.

Such arrangements confer the very considerable advantage that, without increasing the number of channels of transmission, the intensity of the reconstituted image may be made several times greater that when it is formed by one similar light source along. It will be at once appreciated that the use of, say, four modulated light sources instead of only one results, other things being equal, in a fourfold increase in the intensity of the reconstituted image, for the same degree of definition. A similar intensity using only one light source could be obtained either by reducing the scanning speed or by decreasing the number of elementary areas in the reconstituted image, or by decreasing the number of elementary areas in the reconstituted image, or by decreasing both the scanning speed and the number of elementary areas, but in any case the definition in the reconstituted picture would be reduced correspondingly.

Television systems such as those under consideration are known as multiple spot scanning systems, and it is an object of the present invention to provide a television system of this kind in which a cathode ray tube is employed to reconstituted the transmitted image. The invention also provides a cathode ray tube suitable for use in such a system.

According to the present invention, in a cathode ray tube comprising means for producing a plurality of electron beams, controlling means for separately modulating the intensity of each of said beams, and as screen, there are provided means for concentrating the electrons in each of said beams upon a small spot on said screen, the spots so produced lying close to one another in substantially a straight line on the surface of said screen, and means whereby said spots can be caused to scan said screen in a plurality of strips substantially parallel to said straight line. The spots formed upon the screen are arranged to be displaced from one another in a direction along the line in which they lie by not more than a few times the width of the spots.

According to a feature of the invention, in a cathode ray tube comprising a source of electrons and a plurality of control electrodes each adapted to be associated with a separate control circuit, in which the control electrodes are spaced from one another in a direction transverse of the longitudinal axis of the tube, and in which said control electrodes are adapted to subdivide electrons emitted from said source among a plurality of beams, means are provided for focusing said beams upon a screen associated with the tube, and the arrangement is made such that the position of the focus on the surface of said screen of electrons co-operating substantially entirely with one of the control electrodes is different from the position of the focus on the surface of said screen of electrons co-operating substantially entirely with one of the control electrodes is different from the position of the focus on the surface of said screen of electrons co-operating with another of the control electrodes, the several foci all lying in substantially the same straight line upon said screen.

According to yet another feature of the invention, a receiver for a television or the like system comprises a cathode ray tube of the kind specified in either of the two preceding paragraphs, having controlling means in the form of a plurality of control electrodes, and means for applying controlling signals such, for example, as picture signals representing the light and shade values of the transmitted image, to each of said control electrodes, the phase of the signals applied to any one control electrode being different from the phase of the signals applied to any of the remaining control electrodes. Such means may comprise one or more delay circuits to which the controlling impulses are applied.

Reference will now be made by way of example to the accompanying drawings, in which Fig. 1 shows in cross-section one form of cathode ray tube according to the invention, Fig. 2 shows a form of delay network suitable for use with the tube of Fig. 1, and Fig. 3 is a cross-section of a further form of cathode ray tube according to the invention.

Referring to Fig.1, a cathode ray tube comprises a glass or like envelope 1 having a frusto-conical portion 2 and a cylindrical portion 3, one end of the latter being sealed to the smaller end of the frusto-conical portion 2, and the other end thereof being closed by a suitable foot 6. The two portions are arranged with their longitudinal axes in substantially the same straight line, and the frusto-conical portion 2 is closed at its larger end by a suitably shaped glass plate 4, on the inner surface of which is provided a screen of fluorescent material.

An electron emitting cathode 5 is mounted upon the foot 6; the cathode preferably comprises a thin wire of tungsten or the like coated with electron emitting material, and so disposed as to lie in a plane containing the longitudinal axis of the tube an to be at right angles to that axis. The cathode 5 is provided with leads 7 which pass through the foot. The control electrodes of the tube are constituted by fine parallel wires 11 to 15 arranged in a rectangular aperture in a screen 16, the screen and the control electrode wires being insulated from one another and lying in substantially the same plane, which is preferably at right angles to the longitudinal axis of the tube as shown. The wires 11 to 15 may be replaced by rods which are preferably flattened in a plane parallel to the longitudinal axis of the tube.

The control electrodes 11 to 15 are arranged in front of the cathode 5, and are so disposed as to lie at right angles thereto. A suitable electron lens, comprising two cylindrical electrodes 17 and 18 adapted to be maintained at different high positive potentials with respect to the cathode, is provided for the purpose of focussing electrons from the cathode upon the fluorescent screen. The electron lens 17, 18 is arranged to focus on to the screen an image of parts of the electron stream from the cathode lying behind, but usually very close to the control electrodes 11 to 15. Magnetic or electrostatic deflecting means are provided for causing the beam to sweep over the screen under the control of electric scanning oscillations applied to the deflecting means.

The deflecting means may take the form of two pairs of substantially solenoidal coils; the coils 8, or one pair re arranged one on either side of the tube 1 with their axes lying in the line 19, which passes through the longitudinal axis of the tube, while the coils of the other pair (of which only one, numbered 10, appears in the Figure) are similarly arranged with their axes lying in a line at right angles to the line 19. In operation, currents of saw-tooth wave form are caused to flow in the deflecting coils, the current in one pair being of the line scanning frequency, and that in the other pair being of the picture scanning frequency.

For the sake of clearness, the leads from the control electrodes, the screen 16 and the electrodes 17 and 18 to the exterior of the tube are omitted from the drawing.

The control electrode wires 11 to 15 are insulated from one another, and each is associated with a separate input terminal (not shown). In operation, the screen 16 and the control electrode wires 11 to 15 are given a negative potential with respect to the cathode 5 such that substantially none of the electrodes from the cathode are able to escape through the mesh formed by the control electrodes. The modulating impulses, such for example as the picture signals, are then applied to the control electrodes 11 to 15 in such a sense as to cause their potentials to become less negative with respect to that of the cathode 5. Let it be assumed that a picture signal impulse is applied to the control electrode 11 in such a sense as to make its potential less negative with respect to that of the cathode; electrons escape from the control electrode mesh in the neighbourhood of the control electrode 11, and are brought to a focus on the fluorescent screen, and it is arranged that the luminous spot so formed is approximately equal in area to one picture dot, or one elemental area of the transmitted image. The envelope of the cathode ray in these circumstances is indicated approximately by 20. If now the potential of another of the control electrodes 12 to 15 is reduced, electrons will escape in the neighbourhood of this electrode also, and will be brought to a focus on another point on the screen, also equal in area to substantially one picture dot.

It will be seen, therefore, that the fluorescent screen of the tube is scanned simultaneously by as many luminous points as there are control elements, and the arrangement is, accordingly, multiple spot scanning system. The picture signals applied to the several control elements may, then, be given such phase relationships that the reproduced images are superimposed upon one another.

The control electrodes may be fed with the picture signals from tappings in a suitable delay network, the picture signals being applied to the input terminals thereof, and taken off from points in the network after suitable phase retardations. One form of delay network, which will be described by way of example, is shown diagrammatically in Fig. 2 and comprises two input terminals 21 and 22 to which the picture signals are applied from a suitable source such for example as a wireless receiver; the terminal 22 is connected to a point 23 in a source of bias potential (not shown), while the terminal 21 is connected to a terminal 111, which is connected in operation to the input terminal of the control electrode 1 of the tube. Four pairs of coils, all of the same inductance, and all connected in series with one another, are connected between the input terminals 21 and 22. These coils are all inducted by the reference L, and the inductance of each coil will also be referred to as L. A condenser 24 of a capacity which will be referred to as C3 is connected in shunt with the input terminals 21 and 22, and further shunt condensers 25, 26, 27 and 28, of a value which will be referred to as C1, are provided at the junction of the coils of each pair, while shunt condensers 29, 30 and 21, of a value which will be referred to as C2 are provided at the junctions between neighbouring pairs of coils. A lead is taken from the junction of each pair of coils with the adjacent pair to terminals 121, 131 and 141 respectively, and these terminals are connected in operation to the input terminals of the control electrodes 12, 13 and 14 respectively; a lead is taken from the end of the eighth inductance coil to a terminal 151 which is connected in operation to the input terminal of a control electrode 15. The network is terminated by a resistance 32 of a value which will be referred to as R, such that R = EQUAT. HERE, and a condenser 33 of the value C3 is connected in shunt with the terminating resistance 32. The capacity C2 is made smaller than C1 by an amount sufficient to compensate for stray capacity introduced by the control electrodes 12, 13 and 14, and the capacity C3 is made half the capacity C1, less an allowance for stray capacity due to the control electrodes 11 and 15. The delay introduced by one section (comprising a series inductance coil and the shunt capacity) of such a network is given by EQUAT. HERE and the delay between two successive control electrodes is therefore twice this amount.

The control electrodes 11 to 15 of the tube of Fig. 1 may be so spaced that the relative displacement of the portions of the fluorescent screen illuminated by the electrons controlled by adjacent electrodes is, say, two thirds of the width of one elemental area. If then, t is the dot time, that is to say the time of scanning one picture dot at the transmitter, the network is designed in accordance with the equation.

EQUAT. HERE

 

The network is also preferably made such that its cut-off frequency is well above the highest frequency of the picture signals, so that the delay introduced is substantially the same for all picture frequencies.

It should be noted that the separation in time of the action of the control electrodes of two thirds of the dot time is only chosen by way of example, and any other time separation may be employed as desired. Similarly, more or less sections of the delay network than the two shown and described may be connected between each control electrode, and the network may be of a type more complex than that described and capable of being worked nearer to its cut-off frequency without introducing appreciable differences in the delay for the various picture frequencies. Many suitable networks will readily suggest themselves to those versed in the art.

The electrode arrangement in the cathode ray tube described with reference to Fig. 1 is one of the simplest contemplated, and it will be apparent to those versed in the art that many other arrangements, constituting a plurality of electrode systems for producing a plurality of scanning spots on the fluorescent screen, may be constructed. It will be clear that in a tube comprising a plurality of separate electrode systems each producing its own scanning spot, certain electrodes of the several systems, such as the first anodes, may be united to form a single common structure, provided that the modulating electrodes are kept separate from one another so that the effect of each is confined to its own electron beam. Other modifications are also possible; for example, the control electrodes may operate upon a comparatively wide electron beam, which may subsequently be narrowed by means of apertured diaphragms or the like.

A further form of cathode ray tube according to this invention is of the double-acceleration type, and is shown in Fig. 3. Referring to Fig. 3, a cathode ray tube comprises an indirectly heated cathode 5 of the rectilinear form, a cathode screen 39, and accelerator electrode 40, three separate control or modulator electrodes 11, 12, 13, a first anode 17 and second anode 18. The modulators 11, 12, 13 have apertured diaphragms 111, 121, 131 and the cathode shield 39, the accelerator 40 and a diaphragm 38 at the cathode end of the first anode 17 all have apertures which are aligned with one another and with the apertures in the modulator diaphragms. The apertures in electrodes 39 and 40, and if desired the apertures in the electrodes 11, 12 and 13 also, may be in form of slits, the direction of the slits being transverse of the direction of the cathode 5. Screens 37 are provided to screen the modulators electrostatically from one another, and the second anode 18 is constituted by a silvering on the wall of the envelope. The apertures in the diaphragm 38 are preferably made wider in the direction in which the cathode ray beam moves in scanning a line than in the transverse direction.

In the operation of such a tube, the accelerator 40, the first anode 17 and the second anode 18 are biased so as to accelerate the electrons from the cathode, the modulators are arranged to serve as decelerators and the cathode shield 39 is given a potential equal to or not widely differing from the cathode potential. The screens 37 are held at a low potential relative to the cathode. Referring to the figure, the anodes 17 and 18 are connected to points at suitable positive potentials relative to the cathode in the current source 41, the accelerator 40 is also given a positive potential, less than the potential of the first anode, the cathode 5 and the cathode shield are connected together and to a point at a positive potential less than that of the accelerator, and the modulators may be earthed through suitable input circuits.

In cathode ray tubes such as those described, it may be found that the application of a signal potential to one control electrode may affect the electron flow in the neighbourhood of adjacent control electrodes. This effect is probably due in part to electrostatic coupling between the control electrodes, and may be counteracted by superimposing on the signals fed to the adjacent electrodes signal impulses the phase and amplitude of which are such that they tend to counteract the influence of the first-mentioned electrode; these reverse signals may be obtained from a delay network similar to that described with reference to Fig. 2, but fed with signals of the opposite phase. Alternatively, the wave form of the modulating signals may be so modified that change in one sense in the amplitude of the signals is preceded and followed by a slight change in the opposite sense, and this may be accomplished by applying the signals to three suitable delay networks, and combining the outputs thereof in such magnitudes and senses as to produce the required wave form.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:-

  1. A cathode ray tube comprising means for producing a plurality of electron beams, controlling means for separately modulating the intensity of each of said beams, and a screen, wherein there are also provided means for concentrating the electrons in each of said beams upon a small spot on said screen, the spots so produced lying close to one another in substantially a straight line on the surface of said screen, and means whereby said spots can be cause to scan said screen in a plurality of strips substantially parallel to said straight line.
  2. A cathode ray tube according to claim 1, comprising a single source of electrons and controlling means, constituted by a plurality of control electrodes, adapted to subdivide electrons from said source to produce said plurality of electron beams, each control electrode being adapted to be associated with a different control circuit.
  3. A cathode ray tube comprising a source of electrons and a plurality of control electrodes each adapted to be associated with a separate control circuit, in which the control electrodes are spaced from one another in a direction transverse of the longitudinal axis of the tube, and in which said control electrodes are adapted to subdivide electrons emitted from said source among a plurality of beams, wherein means are provided for focusing said beams upon a screen associated with the tube, and wherein the position of the focus on the surface of said screen of electrons co-operating substantially entirely with one of the control electrodes is different from the position of the focus on the surface of said screen of electrons co-operating with another of the control electrodes, the several foci all lying in substantially the same straight line upon said screen.
  4. A cathode ray tube according to claim 2 or 3, wherein said source comprises a cathode of substantially rectilinear form, and said control electrodes are constituted by substantially parallel wires or rods arranged to lie in a direction transverse of said cathode and at right angles to the longitudinal axis of the tube.
  5. A cathode ray tube according to claim 4, wherein said wires or rods are arranged in an aperture in a diaphragm disposed in the electron path between said cathode and said screen, the rods of wires being insulated from one another and from said diaphragm.
  6. A cathode ray tube according to any of the preceding claims, comprising one or more focusing electrodes adapted to operate as an electron lens in focusing electrons from said cathode upon said screen.
  7. A cathode ray tube according to any of the preceding claims, comprising defecting means adapted to deflect the electron beam in two mutually perpendicular directions.
  8. A television or like receiver comprising a cathode ray tube according to any of the preceding claims, wherein means are provided for causing each of said beams to be modulated with like controlling signals, the arrangement being such that the phase of the signals by which one of said beams is modulated is different from the phase of the signals by which another of said beams is modulated.
  9. A television or like receiver comprising a cathode ray tube according to any of claims 2 to 7, wherein one or more sections of a delay network is arranged between any two of said control electrodes with respect to a source of controlling signals.
  10. A receiver according to claim 9, wherein said delay network comprises inductance elements arranged in series between said control electrodes, and condensers arranged in shunt in said network with respect to said source of controlling signals.
  11. A receiver according to claim 9 or 10, wherein said delay network is terminated by a resistance.
  12. A receiver according to any of claims 9 to 11, wherein the cut-off frequency of said network is substantially above the highest frequency which the remainder of the receiver is designed to handle.
  13. A television or like receiver comprising a cathode ray tube according to any of claims 2 to 7, wherein the potential of said control electrodes relative to said source of electrons is maintained at such a negative value that in the absence of controlling signals substantially no electrons from said source reach said screen.
  14. A cathode ray tube substantially as described or as shown in Fig. 1 of the accompanying drawing.
  15. A television or like receiver substantially as described.

Dated this 27th day of December, 1934.

REDDIE & GROSE,

Agents for the Applicant,

6, Breamís Buildings, London, E.C.4.

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Leamington Spa: Printed for His Majestyís Stationery Office, by the Courier Press. Ė 1935.