US2534571A - Circuit for cathode-ray tubes and method of operating the same - Google Patents

Circuit for cathode-ray tubes and method of operating the same Download PDF

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Publication number
US2534571A
US2534571A US35038A US3503848A US2534571A US 2534571 A US2534571 A US 2534571A US 35038 A US35038 A US 35038A US 3503848 A US3503848 A US 3503848A US 2534571 A US2534571 A US 2534571A
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Prior art keywords
cathode
electrons
source
potential
circuit
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Expired - Lifetime
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US35038A
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English (en)
Inventor
Buchanan William Hudspith
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Cinema Television Ltd
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Cinema Television Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
    • H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
    • H04N3/16—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by deflecting electron beam in cathode-ray tube, e.g. scanning corrections
    • H04N3/24—Blanking circuits
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
    • H01J3/02—Electron guns
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
    • H01J3/02—Electron guns
    • H01J3/024—Electron guns using thermionic emission of cathode heated by electron or ion bombardment or by irradiation by other energetic beams, e.g. by laser

Definitions

  • This invention relates to improvements in circuits for cathode ra tubes and to methods of operating such tubes and is especially concerned with circuits for cathode ray tubes of the kind in which an electron beam of high intensity is produced by means of a thermionic cathode heated by bombardment with electrons.
  • Cathode ray tubes of this type comprise an anode, a cathode adapted to be heated by electron bombardment, a modulator electrode arranged to control the emission of electrons from said cathode towards said anode and a source of electrons for bombarding said cathode.
  • Cathode ray tubes of this type will hereinafter be referred to as being of the type defined. Tubes of this type may, of course, contain also other electrodes such as additional anodes for focusing and acceleration of the electron beam and plates for the deflection of the beam in one or more directions, but these additional electrodes form no part of the present invention and are therefore ignored in this specification.
  • cathodes of this type may therefore be constructed to operate at high temperatures, with consequent increased thermionic efiiciency and without the disadvantage of shortness of operating life which has hitherto accrued to high-temperature cathodes.
  • a further advantage of bombarded cathodes is that the shape of the cathode is not influenced by the necessity to provide a return path for the heating current and, moreover, as the heating current is supplied to the cathode at high voltage and consequent small current, the connection to the cathode may be of small diameter, thus reducing the heat loss from end cooling.
  • the present invention seeks to avoid the above-described disadvantages by arranging that such contaminating electrons are not present in the electron beam emitted from the cathode during operative periods of the cathode ray tube.
  • a circuit arrangement including a cathode ray tube of the type defined wherein a source of cyclically varying unidirectional potential is connected between said source of bombarding electrons and said cathode so that in operation said cathode is periodically rendered positive with respect to said source.
  • the said source of unidirectionally varying potential comprises a source of alternating potential and a unidirectionally conducting device connected in series.
  • source of alternating potential is not to be understood as limited to a source of substantially sinusoidal potential, but is intended to include any source of potential such that the polarity of its terminals is periodically reversed.
  • a method of operating a cathode ray tube of the type defined comprising applying between the cathode and the source of bombarding electrons, during part only of a cycle of operation to which said cathode ray tube is subjected, a potential such as to cause electrons emitted from said source to bombard said cathode.
  • said cycle is one cycle of a scanning operation performed by the electron beam of said cathode ray tube.
  • Fig. 1 is one embodiment of a circuit arrangement according to the invention.
  • Fig. 2 is another embodiment of a circuit arrangement according to the invention.
  • Fig. 1 there is shown part of a cathode ray tube l containing an anode 2, a cathode 3, which is arranged to be heated by bombardment with electrons from a helical filament 4 surrounding it, and a modulator electrode 5 surrounding one end of said cathode.
  • a source of high-tension potential (not shown) is connected between the anode and cathode so that electrons emitted from the latter are accelerated towards a part of the cathode ray tube in which the electron beam is utilized.
  • the purpose for which and means whereby the said beam is utilized form no part of the present invention.
  • the helical filament 4 which serves as the source of bombarding electrons is heated by the passage therethrough of an electric current of suitable magnitude supplied from any convenient source of alternating current by means of a transformer 5, and a potential sufficient to accelerate the emitted electrons on to the cathode 3 is produced between the filament and cathode 3 by the connection therebetween of the secondary Winding of a transformer H, to the primary of which is applied an alternating potential derived from a circuit controlling cycles of operation of the cathode ray tube, in series with a thermionic diode valve 8 which is so connected that it substantially prevents the passage of electrons within the cathode ray tube in the direction from the cathode 3 to the filament l, but freely allows their passage in the reverse direction.
  • the result of this arrangement is that the cathode 3 is bombarded by electrons from the filament l during such times as the potential derived from the transformer l is such as to maintain the cathode positive with respect to the filament, but that at all other times the cathode is not bombarded.
  • the potential applied to the primary winding of the transformer "i may be derived, for example from the time-base generator which controls one component of the scanning operation, the sense of connection being such that the cathode is bombarded only during the fiyback intervals of the scanning process.
  • This arrangement insures that only electrons emitted thermionically from the cathode can be utilized in the formation of the scanning electron beam, which is thus composed substantially wholly of electrons of nearly uniform velocity and of limited source of origin, whereby the focus of the electron beam is improved.
  • This arrangement may of course be adapted to other uses of the cathode ray tube, for example, in a radar receiving equipment the cathode may be arranged to be bombarded only dur-- ing the interval between the end of one stroke of the ranging time base and the commencement of the next stroke; the application of the invention to oscillographic uses of the cathode ray tube follows upon the same lines.
  • transformer I it may be found convenient to replace the transformer I by a source of cyclically varying unidirectional potential, the polarity of which is such that electrons are accelerated from the filament 4 to the cathode 3 during part of the cycle of variation of the said potential.
  • the circuit shown in Fig. 1 includes an arrangement which is found convenient in cases where modulation of the electron beam is effected during part of the operating cycle by means of signals applied to the modulator electrode 5 of the tube.
  • the modulator electrode is shown connected by way of a high resistance 9 and a source of potential, represented by a battery It shunted by a potentiometer l l, to the cathode.
  • Signals to be applied to the modulating electrode are applied to the terminal i2, whence they pass by way of condenser I3 to the modulating electrode 5, the resistance 9 being of sufliciently high value to have substantially no shunting effect thereon; this arrangement is, of course, well known.
  • the modulator electrode shall, during those portions of the operating cycle in which bombardment of the cathode is carried on, be held negative with respect .to the cathode in order to suppress emission therefrom and at the same time shall not acquire a potential so negative that bombarding electrons are repelled from that part of the cathode which is adjacent to the modulator electrode.
  • the modulating signal applied to the terminal i2 is preferably zero during heating portions of the operating cycle while during operating portions of the cycle it is such as to drive the modulator electrode 5 in the positive direction sufliciently to obtain the desired emission from the cathode 3.
  • An alternative method of suppressing emission from the cathode towards the anode during heating portions of the cycle is to modulate the potential applied to the anode, reducing this potential substantially, preferably to zero, during those times when the cathode is being heated.
  • Fig. 2 shows part of a cathode ray tube similar to that illustrated in Fig. l and in which similar parts have like numbers.
  • the modulator electrode 5 is connected to the cathode through resistors 9 and E8 in series for a purpose hereinafter to be described. 7
  • the electron beam produced by the system comprising cathode 3, modulator electrode 5 and anode 2 is focused by a magnetic field produced by a coil ll energized from a suitable source of current which is not illustrated.
  • the beam is then deflected as required by the magnetic field of a pair of coils l5 and it which are supplied with an appropriately varying current from a time base I4 of any suitable type.
  • the output of the time base is also applied to the primary winding of transformer I, so that the potential applied through diode 8 to the filament 4 to cause bombardment of the cathode 3 by electrons therefrom is always in synchronism with the deflection of the beam.
  • the connections of the transformer windings are so chosen that the cathode of the diode 8 is positive with respect to its anode; hence, the cathode of the tube is positive with respect to the source of bombarding electrons only during the flyback intervals of the scanning process performed by time base 14.
  • the cathode 3 is bombarded so that it is heated only during those times when the electron beam is not used to form the image on the screen of the cathode ray tube.
  • the shape of the cathode 3 may be varied from that shown so that the emissive portion is a sharp point, thus making use of the enhanced emission obtainable from such a cathode owing to the high field gradient obtaining in its neighborhood.
  • a further advantage which may be obtained is that the cathode of a cathode ray tube operated in accordance with the invention may more readily be made of a form which is conveniently removed from the tube and replaced when its emission falls oil.
  • a circuit comprising a cathode ray tube havin an anode, a cathode, a source of electrons for bombarding said cathode and a modulator electrode for controlling the emission of electrons from the cathode to the anode, and a source of cyclically varying unidirectional potential connected between said source of bombarding electrons and said cathode, whereby said cathode is periodically made positive with respect to said source of bombarding electrons.
  • said source of cyclically varying unidirectional potential comprises a source of alternating current and a substantially unidirectional conducting device connected in series.
  • the method of operating a cathode ray tube comprising the following steps: feeding to deflection means of the tube cyclical sweeping voltages, and bombarding the cathode with electrons in synchronism to the sweep voltages during predetermined portions of cycles thereof to heat the cathode.
  • the method of operating a cathode ray tube of the type defined comprising the following steps: feeding to deflection means of the tube cyclical sweeping voltages, bombarding the oathode with electrons in synchronism to the sweep voltages during the flyback portions thereof, and cyclically varying the potential between the modulator electrode and the cathode so as to prevent electron emission from the cathode towards the anode during bombardment of the cathode.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)
  • Electron Sources, Ion Sources (AREA)
US35038A 1947-07-10 1948-06-24 Circuit for cathode-ray tubes and method of operating the same Expired - Lifetime US2534571A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB18362/47A GB624832A (en) 1947-07-10 1947-07-10 Improvements in or relating to circuits for cathode ray tubes and methods of operating the same

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US2534571A true US2534571A (en) 1950-12-19

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US35038A Expired - Lifetime US2534571A (en) 1947-07-10 1948-06-24 Circuit for cathode-ray tubes and method of operating the same

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US (1) US2534571A (de)
DE (1) DE857554C (de)
FR (1) FR968160A (de)
GB (1) GB624832A (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3193722A (en) * 1960-04-14 1965-07-06 United Aircraft Corp Method and means for control of a pulsed beam of charge carriers

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1864591A (en) * 1925-01-08 1932-06-28 Rca Corp Thermionic device
US2197033A (en) * 1937-06-10 1940-04-16 Telefunken Gmbh Electron device
US2207276A (en) * 1937-03-30 1940-07-09 Edison Inc Thomas A Electric discharge system
US2239416A (en) * 1939-01-25 1941-04-22 Emi Ltd Cathode for electron discharge devices
US2355795A (en) * 1942-08-17 1944-08-15 Bell Telephone Labor Inc Electrode system
US2398829A (en) * 1941-05-28 1946-04-23 Rca Corp Electron discharge device

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1864591A (en) * 1925-01-08 1932-06-28 Rca Corp Thermionic device
US2207276A (en) * 1937-03-30 1940-07-09 Edison Inc Thomas A Electric discharge system
US2197033A (en) * 1937-06-10 1940-04-16 Telefunken Gmbh Electron device
US2239416A (en) * 1939-01-25 1941-04-22 Emi Ltd Cathode for electron discharge devices
US2398829A (en) * 1941-05-28 1946-04-23 Rca Corp Electron discharge device
US2355795A (en) * 1942-08-17 1944-08-15 Bell Telephone Labor Inc Electrode system

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3193722A (en) * 1960-04-14 1965-07-06 United Aircraft Corp Method and means for control of a pulsed beam of charge carriers

Also Published As

Publication number Publication date
GB624832A (en) 1949-06-16
FR968160A (fr) 1950-11-21
DE857554C (de) 1952-12-01

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