US2194380A - Cathode ray tube - Google Patents

Cathode ray tube Download PDF

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Publication number
US2194380A
US2194380A US12214A US1221435A US2194380A US 2194380 A US2194380 A US 2194380A US 12214 A US12214 A US 12214A US 1221435 A US1221435 A US 1221435A US 2194380 A US2194380 A US 2194380A
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United States
Prior art keywords
cathode
electrode
screen
potential
modulating
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Expired - Lifetime
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US12214A
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English (en)
Inventor
Broadway Leonard Francis
Tedham William Francis
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EMI Ltd
Electrical and Musical Industries Ltd
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EMI Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
    • H01J29/52—Arrangements for controlling intensity of ray or beam, e.g. for modulation

Definitions

  • the present invention relates to improvements in circuit arrangements comprising cathode ray tubes.
  • Cathode ray tubes for television and like purt poses generally comprise a cathode, a modulating electrode and one or more anodes arranged within an evacuated envelope; means for deflecting the ray over va liuorescent screen associated with the tube may also be provided.
  • the anode or anodes are maintained, in operation, at positive potentials relative to the cathode; these electrodes cooperate with one another in accelerating electrons from the cathode and focusing them upon the fluorescent screen.
  • a circuit arrangement comprises a cathode ray tube of the '20 kind in which means, such as one or more modulating electrodes, are provided for modulating the intensity of the ray in accordance with an applied modulating potential associated with means for varying the mean slope oi the curve representing the relation between the modulating potential and the fluorescent screen current of the tube without altering the disposition of the electrodes thereof.
  • the mean slope of the modulating potentialfluorescent screen current characteristic may be dened as the ratio oi the change in screen current to the corresponding change in modulating potential, and .it will be seen that unless the characteristic is rectilinear, the value of the mean slope will depend upon the limiting values of the change in modulating potential considered. Thus when in this specification a change in mean slope is mentioned, it will be assumed that the change is measured for the same range of modulating L0 potential.- i
  • a circuit arrangement comprises acathode ray tube of the kind in which i'neansl such as one or more modulating electrodes, are provided for modu- 4? lating the intensity of the ray in accordance with an applied modulating potential associated with means for Varying the curvature of thecurve representing the relation between the modulating potential and the fluorescent screen current "o of the tube without altering the disposition of the electrodes thereof.
  • a cathode ray tube may comprise, in addition l to the electrodes mentioned above, a further electrode (which will hereinafter be referred to as.v ⁇
  • the accelerating electrode or accelerator arranged between the cathode and the modulating electrode.
  • a cathode shield or screening electrcde is also usually provided lclose to the cathode. near cathode potential and electrons pass outwards throughan aperture therein.
  • the -accelerator is maintained at a positive potential relative to the cathode, while the modulator is given a negative bias, and the arrangement is such that electrons from the cathode are rst accelerated by the accelerating electrode, then decelerated by the modulator, and then again accelerated by the anodes.
  • the potentials applied to the electrodes are suitably, chosen, it is found that as the potential'applied to the modulator is made more negative'the electron current flowing directly to the accelera- This electrode may be maintained at ont,
  • tor electrode increases, while the current flowing f to the fluorescent screen decreases.
  • the tube described is an example of one in which electrons from a cathode are rst accel. erated and then decelerated, before being finally accelerated and focused upon the screen, and in the present specification, such tubes will be referred to for convenience as being of the double acceleration type. All tubes of this type will be regarded as characterised in that an accelerating electrode is disposed between the cathode and the modulator electrode. It is to be understood that in a tube of the double acceleration type, the electrons may be subjected to more than two accelera-tions during their passage from the cathode to the screen; furthermore, it must be appreciated that, between the two accelerations in question, the electrons are subjected to a deceleration. v
  • the tube employed is of the double acceleration type and variations in mean slope are effected by varying the value of a resistance inserted between the accelerating electrode of the tube and the associated source of potential dif ⁇ ference; for effecting variations in the curvature of 'the characteristic, means are provided. for increasing the effective potential difference furnished by this source as the value of this resistance is increased.
  • a circuit arrangement comprises a cathode ray tube of the double acceleration type having a cathode, an accelerating electrode, a rmodulator electrode, one or more anodes, and a iiuorescent screen and means associated with the tube for supplying operating potentials for the electrodes thereof, a resistance being arranged in the connection between the accelerating electrode and 'the said means,
  • FIG. 1 illustrates one method of carrying the invention into eiect, and shows a cathode 'ray tube and part of the associated circuit thereof
  • Fig. 2 illustrates a modification of the invention
  • Fig. 3 is an explanatory figure.
  • a cathode ray tube comprises an evacuated, sealed glass envelope I consisting of a cylindrical portion flaring out into a frusto-conical portion. Disposed within the envelope I, and mounted therein in any known or suitable manner, are a cathode 2 of the indirectly heated type, a cathode shield 3, an accelerator electrode 4, a modulator electrode or grid 5, a rst anode E and a second anode 1.
  • the electrodes 3, 4, 5 and 6 are all of cylindrical shape and may be mounted in any convenient manner, for example, as sliding nts within a tubular member of glass (not shown) arranged within the cylindrical portion of the envelope I, while the electrode l may be mounted upon the wall of the envelope as shown, for example in the form of a silvering of the surface of the envelope; the cathode may be supported upon its own lead and the leads to its heater.
  • leads to the various electrodes are taken out through the side wall of the envelope, it is to be understood that ⁇ in practice some or all of these leads may be taken out through a foot t sealed into the end of the cylindrical portion of the envelope.
  • the second anode 'l is arranged slightly to overlap the rst anode 6, these two electrodes constituting an electron lens and serving to focus a beam of electrons upon a uorescent screen 9 disposed on the end wall of the frusto-conical portion of the envelope l.
  • Either electrostatic or electromagnetic deflecting means (not shown) are provided for cleecting the beam and for causing it to scan the fluorescent screen.
  • the tube described is substantially the same as that described with reference to Fig. 1 of the drawings accompanying the specication of the above-mentioned application, and may have substantially the same dimensions as the tube there described.
  • the various electrodes of the tube all derive their operating potentials from a potential divider I0, Il which is fed with direct current from a rectifier I2 fed with alternating current from the mains throughl a step-up transformer I3. It is arranged that the potential at the terminal I0 of the potential divider, and hence the potential on the second anode l, relative to earth is about 3,600 volts.
  • the first anode 6 is connected to a tapping point I4 in the potential divider, and this tapping point may be made adjustable so as to provide for adjustment of the focus of the beam; the first anode potential may conveniently be made about 1000 volts.
  • the grid 5 is connected to earth through a suitable input circuit which is connected between the terminals I5; the input circuit may, for example, comprise a source of picture signals such as a wireless receiver.
  • the accelerator Il is connected through a variable resistance I5 to an adjustable tapping point Il in the potential divider, such that a potential of the order of 250 volts relative to earth is applied to the accelerator.
  • the cathode 2 and the cathode screen 3 are connected together and to a point IB in the potential divider such that a potential of about 20 volts positive relative to earth is applied to these electrodes.
  • Decoupling condensers I9, 20 and 2l are vconnected between the tapping points I4, Il and I8 respectively and earth.
  • Electrons passing through the aperture in the grid 5 are then acceleratedby electrodes 6 and 'l and focused thereby upon the screen 9.
  • the grid and the rst and second anodes L are kept constant at about O, 20, 1000 and 3300 respectively and the fluorescent screen current is measured for different values of accelerator voltage, it will be found that the fluorescent screen cunrent increases approximately parabolically with increasing values of accelerator voltage. Thus the fluorescent screen current may increase from zero at Zero accelerator voltage at an increasing rate.
  • the accelerator voltage is kept constant, for example at about 250 volts relatively to the cathode, and the grid voltage is increased from Zero in a negative sense relatively to the cathode, it will be found that the accelerator current increases substantially rectilinearly whilst the fluorescent screen current and the first anode current decrease substantially rectilinearly and at approximately the same rate.
  • the curve A in Fig. 3 shows the rectilinear relationship between the grid (or modulator) potential and the uorescent lscreen current; in Fig. 3, the modulatorcathode potential difference is plotted against fluorescent screen currents as ordinates.
  • the value of the accelerator current for zero grid voltage may be taken to represent thecurrent which ilows directly from the cathode to the accelerating electrode.
  • the rectilinear increase vof the'acceleratorcurrent with increasing negative grid. voltage may be interpreted as being due to the electrons which are returned to the accelerating electrode by the repulsive field of the grid.
  • a resistance of value R be arranged in series between the accelerating electrode and the source of current from which it is supplied, that is, referring to the drawings, between the electrode il and the tapping point Il, the voltage EA at the accelerating electrode will be given by where V is the voltage of the source and IA the current through the resistance R.
  • ince IA increases with increasing negative grid voltage. It followsthat EA decreases and therefore the total current drawn from the cathode by the accelerator voltage is decreased. This has the effect of making the mean slope of the fluorescent screen current-grid voltage characteristic curve of the tube greater than Where the resistance R is omitted and the accelerator voltage is kept constant. Hence if the value R be made adjustable, the mean slope of the grid volts-fluorescent screen current characteristic can be controlled without altering the dispositions of the electrodes of the tube.
  • the resistance i6 is made variable so as to provide a control of the mean slope of the characteristic in the manner set forth. It is to be noted that the control thus obtained has substantially no adverse effect on the focusing of the beam.
  • the tube described may have a substantially rectilinear grid volts-uorescent screen current characteristic curve as already explained; this may be of advantage for such purposes as television reception because modulating potentials of substantially all amplitudes applied between the cathode and grid are converted into light Values substantially Without any selective effect. If in addititon, control of the mean slope of the linear characteristic is provided, the modulation sensitivity of the tube may be controlled thus giving the equivalent of volume control (with no frequency selection) in audio receivers.
  • the grid volts-fluorescent screen current characteristic is not quite rectilinear but is slightly concave, as seen from the origin, the insertion of such a resistance of suitable value may have the eiect of straightening the characteristc, at least to a small extent. Further increase in the value of the resistance may cause the characteristic to depart from rectilinearity and to tend to become convex, as seen from the origin. Control of the resistance may therefore also be used in some cases to control the cunrvature of the characteristic.
  • nlm television control of the curvature of the tube characteristic may also be used to compensate for an unsuitable value of the relative contrast in the dark and light portions of the nlm being transmitted. It is at present common practice in the nlm industry to develop motion picture iilrns in such manner that detail is brought out in the light portions of the picture relative to the detail in the dark portions, lms developed in this way appearing quite natural to eye when projected upon a screen.
  • a cathode ray tube having a rectilinear characteristic may be regarded as having an intensity contrast of unity, while if the characteristic is parabolic, the intensity contrast is 2, and so on. Increasing the curvature of the characteristic so as to make it more convex, as seen from the origin, may thus loe regarded as increasing the intensity contrast of the tube.
  • the resistance in the accelerator lead also operates as a safety circuit, to some degree, if there occurs an insulation break-down within the tube.
  • Vals such as picture signals for example are derived 'from a tlierinionic valve E2 lie-ving an anode resistance the va ve 22 may Vform part oi a wireless receiver.
  • the anode of the valve 22 is connected through a condenser 2li a res'otance in series to an adjustable tapping pouit in a part 2l of the potential divider' i3.
  • adjustable tapping point 28 in resistance 25 is connected to the cathode shield 3 o the tube.
  • the anode of valve 22 is also connected through condenser and resistance 3G in series to a tapping point 3i in a potential divider 3:2 connected in shunt ith the part El'.
  • An adjustable tapping point 33 in resistance Sil is connected to the modulator E of the tube.
  • the ratio of the modulating potential applied to the cathode screen to that applied to the modulator may be varied, adjustment of t e intensity contrast introduced by he tube be obtained.
  • Such changes may be compensated by Varying the biasing potentials applied to he modulator and to the cathode screen by adjusting the position of either or both of the tapping points 45 and 3l.
  • the arrangement may be rnade such that as the modulating potential applied tc the modulator is uw., and that applied to the cathode screen is decreased, the biasing potential applied to the tor is made more negative, while that appl to the cathode screen is made less negative, and vice versa.
  • a circuit arrangement comprising a cathode ray tube having a cathode for emitting a beam of electrons, a screen for receiving said beam and, arranged between said cathode and said screen in the order named, an accelerator electrode, a modulator electrode and at least one anode, means for biasing said modulator electrode to a negative potential relative to said cathode, means for applying modulating potentials to said modulator electrode, a Source of current having a negative terminal and a tapping point adjustable to any of a number of positions at positive potentials relative to said negative terminal, a con* nection between said negative terminal and said cathode, and a connection including a variable resistance between said tapping point and said accelerator electrode for varying the potential supplied to the accelerator electrode so as to vary the curvature of the curve relating said modulating potentials and the number of electrons received at the screen.
  • a circuit arrangement comprising cathode ray tube having a cathode for emitting a beam of electrons, a screen for receiving said beam and, arranged between said cathode and said screen in the order named, a screen electrode, an accelerator electrode, a modulator electrode and at least one anode, means for maintaining said second electrode and said modulator electrode at negative potentiak relative to said cathode, means for maintaining said accelerator electrode at a positive potential relative to said cathode, means for applying modulating potentials to said modulator electrode and to said screen electrode and means for varying the ratio of the modulating potential applied to said modulator' to the modulating potential applied to said screen electrode.
  • a circuit arrangement comprising a cathode ray tube having a cathode for emitting a beam of electrons, a fluorescent screen for receiving said beam and, arranged between said cathode and said screen in the order named, a scree electrode, an accelerator electrode, a modulator electrode and at least one anode, means for applying modulating poten ls to said modulator electrode and to said screen electrode, means for applying to said modulator and to said screen electrode bias potentials relative to said cathode, means lor varying the ratio of the modulating potential applied to said modulator to the modulating potential applied to said second electrode and means for varying the magnitudes of said bias potentials.
  • a circuit arrangement comprising :athode ray tube having a cathode for eniitt' a beam of electrons, a fluorescent screen for receiving said beam and, arranged between cathode and said screen in the order a screen ⁇ electrode, an accelerator electrode, a modulator electrode and at least one anode, means for applying modulating potentials to said modulator electrode and to said screen electrode, means for applying to said modulator and to screen electrode bias potentials relative to said cathode and a control member for varying simultaneously the ratio of the modulating otential applied to said modulator to the modulating potential i plied to said screen electrode and the mai, tudes of said bias potentials.
  • a circuit arrangement compri ray tube having a cathode for emi of electrons, a screen for transmit arranged between said cathode and said so: the order named, a shield electrode, au accelerator electrode, a. modulator electrode, and ⁇ at l one anode, means for biasing said s d electrode to a negative potential relative to said cathode,
  • a circuit arrangement comprising a cathode ray tube having a cathode for emitting a beam of electrons, a screen for receiving said beam and, arranged between said cathode and said screen in the order named, a shield electrode, an accelera* tor electrode, a modulator electrode, and at least one anode, means for biasing said shield electrode to a negative potential relative to said cathode, means for biasing said modulator electrode to a negative potential relative to said cathode, means for biasing said accelerator electrode to a positive potential relative to said cathode, means for applying modulating potentials to said modulating electrode, and variable resistance means for varying the accelerator electrode potential so as to vary the curvature of the curve relating said modulating potentials and the number of electrons received at the screen.
  • a circuit arrangement comprising a cathode ray tube having a cathode for emitting a beam of electrons, a screen for receiving said beam and, arranged between said cathode and said screen in the order named, an accelerator electrode, a modulator electrode and at least one anode, means for biasing said modulator electrode to a negative potential relative to said cathode, means for biasing said accelerator electrode to a positive potential relative to said cathode, means for applying modulating potentials to said modulator electrode, means for varying the accelerator electrode potential so as to vary the curvature of the curve relating said modulating potentials and the number of electrons received at the screen and means for varying the biasing potential applied to said accelerator electrode.
  • a circuit arrangement comprising a cathode ray tube having a cathode for emitting a beam of electrons, a screen for receiving said beam and, arranged between said cathode and said screen in the order named, an accelerator electrode, a modulator electrode and at least one anode, means for biasing said modulator electrode to a negative potential relative to said cathode, means for biasing said accelerator electrode to a positive potential relative to said cathode, means for apl plying modulating potentials to said modulator electrode, means for varying the accelerator electrode potential so as to vary the curvature of the curve relating said modulating potentials and the number of electrons received at the screen and potentiometer means for varying the biasing potential applied to said accelerator electrode.
  • the method of controlling the modulation sensitivity of a cathode ray tube wherein is provided a source of electrons comprising the steps of providing a preliminary acceleration eld of substantially constant order for said electrons from said source, developing signalling energy, modulating the electrons in the region intermediate the source and said preliminary acceleration eld by the developed signalling energy, subsequently reducing the acceleration of said modulated electrons by an amount proportional to the magnitude of said developed signalling energy, and subjecting said decelerated electrons to a constant accelerating fieldl LEONARD FRANCIS BROADWAY. WILLIAM FRANCIS TEDl-IAM.

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  • Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)
  • Image-Pickup Tubes, Image-Amplification Tubes, And Storage Tubes (AREA)
US12214A 1934-03-26 1935-03-21 Cathode ray tube Expired - Lifetime US2194380A (en)

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GB9473/34A GB435623A (en) 1934-03-26 1934-03-26 Improvements in or relating to cathode ray tubes

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US2194380A true US2194380A (en) 1940-03-19

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FR (1) FR787744A (fr)
GB (1) GB435623A (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2521255A (en) * 1946-08-23 1950-09-05 Patelhold Patentverwertung Cathode-ray tube with secondary intensity control of cathode rays
US2852716A (en) * 1954-07-14 1958-09-16 Gen Electric Cathode ray tube and electron gun therefor
US3004186A (en) * 1958-09-17 1961-10-10 Zenith Radio Corp Cathode-ray tube arrangement
US3015752A (en) * 1959-03-09 1962-01-02 Admiral Corp Flash-over suppression in cathode ray tubes

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2521255A (en) * 1946-08-23 1950-09-05 Patelhold Patentverwertung Cathode-ray tube with secondary intensity control of cathode rays
US2852716A (en) * 1954-07-14 1958-09-16 Gen Electric Cathode ray tube and electron gun therefor
US3004186A (en) * 1958-09-17 1961-10-10 Zenith Radio Corp Cathode-ray tube arrangement
US3015752A (en) * 1959-03-09 1962-01-02 Admiral Corp Flash-over suppression in cathode ray tubes

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Publication number Publication date
FR787744A (fr) 1935-09-27
GB435623A (en) 1935-09-25

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