US2788468A - Cathode ray tubes - Google Patents

Cathode ray tubes Download PDF

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Publication number
US2788468A
US2788468A US526395A US52639555A US2788468A US 2788468 A US2788468 A US 2788468A US 526395 A US526395 A US 526395A US 52639555 A US52639555 A US 52639555A US 2788468 A US2788468 A US 2788468A
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US
United States
Prior art keywords
coils
focussing
ray
cathode ray
tube
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US526395A
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English (en)
Inventor
Leng Geoffrey
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Marconis Wireless Telegraph Co Ltd
BAE Systems Electronics Ltd
Original Assignee
Marconi Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Marconi Co Ltd filed Critical Marconi Co Ltd
Application granted granted Critical
Publication of US2788468A publication Critical patent/US2788468A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • H01J29/58—Arrangements for focusing or reflecting ray or beam
    • H01J29/64—Magnetic lenses

Definitions

  • This invention relates to cathode ray tubes and though not limited to its application thereto is primarily intended for, and of particular advantage in connection with, relatively large cathode ray tubes wherein a relatively short neck portion merges into a tapered portion (usually, though not necessarily, conical) of wide angle and terminating in a relatively flat end wall.
  • This tube has a neck portion 1, a conical portion 2 and an end wall 3.
  • the deflection centre of the cathode ray in the tube is represented by a cross 4 and a typical ray position by a chain line 5. It will be seen that the end wall 3 is relatively flat and does not follow the spherical surface which it would have if it were arcuate with the deflection centre 4 as centre. This spherical surface is represented by the broken line 6.
  • a screen is deposited as in the usual way on the inside of the end wall 3. If the ray is correctly focussed on the screen when in the undeflected position, i. e. when it impinges centrally on the screen, it will become increasingly out of focus on the screen as deflection away from the central position increases for the locus of the points for which the beam will be correctly focussed lies on the spherical surface 6. Focussing error arising in this way is obviously most serious in wide angled tubes.
  • the Q value of the line deflector coil shall be as high as possible.
  • the focussing coil is bound to be near the deflecting coil assembly, particularly in a tube with a wide angle and a short neck, in order that the size of the spot on the screen shall be small and the resolution accordingly high. If, however, the above mentioned high Q value is to be obtained the focussing coil assembly must not, despite its closeness to the deflecting coil assembly, introduce substantial losses into or otherwise undesirably interfere with the said deflecting coil assembly, e. g.
  • a cathode ray tube is provided with a focussing system including two permanent magnets arranged adjacent one another and in magnetic opposition along the neck of the tube and two focus modulating coils also connected in magnetic opposition to each other, one of said coils being arranged when energised to oppose the field of one magnet and the other arranged when energised to oppose the field of the other magnet, said coils being in use energised in dependence upon ray deflection so that as the ray is deflected the combined focussing effect due to the magnets and the coils maintains substantially correct focussing in all positions of the ray.
  • the magnets are ring magnets arranged side by side along the neck of the tube and preferably also one of the coils is mounted in one ring magnet and the other inside the other.
  • the longitudinal spacing between the magnets is adjustable for the purpose of adjusting the unmodulated focussing component, i. e. the component which provides accurate focussing when the coils are not energised and the ray is central in the tube.
  • two permanent magnets 7, 8 preferably of the magnetic material known under the trade designation Magnadur. These magnets encircle the neck 1 of the tube and are mounted side by side in magnetic opposition. The spacing between them is arranged to be adjustable by any convenient means (not shown) to facilitate accurate focussing of the ray 5 by the magnets alone when the ray is in its undeflected position.
  • a focus modulating coil 9 or 10 Inside each of the two magnets is a focus modulating coil 9 or 10. These coils are connected in series and magnetic opposition, the field of the coil 9 when energised opposing that of the magnet 7 and the field of the coil 10 when energised opposing that of the magnet 8.
  • the series connected coils are energised in any convenient manner known per se in dependence upon deflection of the ray. Thus they may be energised through an amplitude control unit 11 from the normally provided ray deflection circuits 12. So as not to complicate the drawing the ray deflecting coil assembly is not represented but it is, of course, provided as in the usual way.
  • the illustrated arrangement has important practical advantages as compared to previously known proposals.
  • the permeability of magnetised Magnadurthe preferred magnetic material-4s near unity and consequently the use of this material in association with the focussing coils only slightly increases their inductance and therefore keeps the required reactive power low while in addition, because the magnets have near unity permeability, they do not appreciably distort the field of the deflecting coils.
  • the lens can be placed very close to the deflector coils without appreciable damping eifects due to eddy currents and the further the lens can be removed from the cathode and the nearer it can be brought to the screen, the smaller is the spot size, the less the image magnification and the smaller the lens power required for a given aperture.
  • the smaller the spot size the better the resolution and the smaller the lens power required the smaller the reactive power required in the coils and therefore the smaller and cheaper are the control circuits required.
  • the dual arrangement of focussing coil described gives very little external field and, in consequence, spiral distortion of the raster is very small.
  • Such distortion is apt to be very serious if a single coil lens system is placed very close to the deflector coils because the lens field leaks into the deflector'coil'region and when the beam is deflected by even a small amount inside the deflector coils and it passes through even a weak focussing field spiral distortion is produced.
  • the arrangement of the focussing coils close to the neck of the tube and inside the magnet rings means that the coil diameters are small and this too leads to l0w coil;inductance and consequent low reactive power required.
  • a cathoderay tube focussing system comprising two permanent magnets arranged adjacent one another and in magnetic-opposition along the neck of the tube and two-focus modulating coils also connected in magnetic opposition to each other, one of said coils being arranged-When energised .to oppose thefield of; one magnet and the other arranged when energised to oppose the ,field of the other magnet, gsaid ,coils being energised in dependence upon raydeflectionso that as the ray is deflected the combined'sfocussing effect due to the magnets and the coils maintains substantially correct focussing in all positions of the ray.
  • magnets are ring magnets arranged side by side along the neck of the tube with one coil mounted inside one ring magnet and the other coil mounted inside the other.

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  • Details Of Television Scanning (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
US526395A 1954-08-04 1955-08-04 Cathode ray tubes Expired - Lifetime US2788468A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB22578/54A GB777846A (en) 1954-08-04 1954-08-04 Improvements in or relating to cathode ray tubes

Publications (1)

Publication Number Publication Date
US2788468A true US2788468A (en) 1957-04-09

Family

ID=10181680

Family Applications (1)

Application Number Title Priority Date Filing Date
US526395A Expired - Lifetime US2788468A (en) 1954-08-04 1955-08-04 Cathode ray tubes

Country Status (4)

Country Link
US (1) US2788468A (en, 2012)
FR (1) FR1125877A (en, 2012)
GB (1) GB777846A (en, 2012)
NL (1) NL199308A (en, 2012)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2539492A (en) * 1939-06-06 1951-01-30 Int Standard Electric Corp Focusing and deflecting means for cathode-ray tubes
US2656486A (en) * 1950-09-28 1953-10-20 Du Mont Allen B Lab Inc Stabilized television circuit
US2724075A (en) * 1951-04-23 1955-11-15 Hartford Nat Bank & Trust Co Device comprising a ferromagnetic circuit
US2730642A (en) * 1951-04-23 1956-01-10 Hartford Nat Bank & Trust Co Device comprising a cathode-ray tube
US2740064A (en) * 1952-08-26 1956-03-27 Hartford Nat Bank & Trust Co Permanent magnet focussing device for cathode ray tubes

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2539492A (en) * 1939-06-06 1951-01-30 Int Standard Electric Corp Focusing and deflecting means for cathode-ray tubes
US2656486A (en) * 1950-09-28 1953-10-20 Du Mont Allen B Lab Inc Stabilized television circuit
US2724075A (en) * 1951-04-23 1955-11-15 Hartford Nat Bank & Trust Co Device comprising a ferromagnetic circuit
US2730642A (en) * 1951-04-23 1956-01-10 Hartford Nat Bank & Trust Co Device comprising a cathode-ray tube
US2740064A (en) * 1952-08-26 1956-03-27 Hartford Nat Bank & Trust Co Permanent magnet focussing device for cathode ray tubes

Also Published As

Publication number Publication date
GB777846A (en) 1957-06-26
FR1125877A (fr) 1956-11-09
NL199308A (en, 2012)

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