US1973606A - Cathode ray apparatus - Google Patents

Description

p 1934- W. R. BULLXMORE Er AL 1,973,606

CATHODE RAY APPARATUS Filed Dec. 29, 1932 INVENTORS William R. Bullimore Patented Sept. 11, 1934 PATENT OFFICE CATHODE RAY APPARATUS William Richard Bullimore and Leslie Herbert Bedford, Highbury Grove, England, 'assignors to C. Cossor Limited, land,

Highbury Grove, Enga company of Great Britain Application December 29, 1932, Serial No. 649,400 In Great Britain January 29, 1932 4 Claims. (Cl. 250-275) This invention relates to electrical discharge apparatus and more particularly to cathode ray oscillographs, televising tubes, relays and like apparatus in which the electrical discharge is pro- 5 duced in the form of a beam capable of being deflected by an electrostatic or electro-magnetic control.

The object of the invention is to provide improvements in the construction and operation of apparatus of the kind referred to and more particularly to increase the sensitiveness of apparatus in which the cathode rays are deflected by the electrostatic influence of control electrodes located within the envelope, to facilitate the manufacture of the apparatus and to increase the working frequency limit.

One improvement according to the invention applicable to apparatus of the kind referred to and in which the cathode rays are deflected by the electrostatic influence of control electrodes enclosed within the envelope consists in the provision of a conductive shield or screen for screening or protecting the control electrodes from electrons reflected or emitted from the fluorescent screen or electrode upon which the cathode rays are focussed. The effect of this screen is to eliminate or minimize the discharge which would otherwise take place between the control. electrodes due to the action of secondary electrons.

The shield or screen therefore increases the sensitiveness of the apparatus by reducing the load on the input circuit.

A further improvement according to the invention applicable to apparatus of the kind referred to in which cathode rays are deflected by the electrostatic influence of control electrodes disposed within the envelope consists in mounting the electrodes upon a star-shaped foot or pinch formed at the end of a re-entrant tube to through which the lead-in conductors pass into the evacuated envelope. This construction en= ables the electrodes to be assembled as a unit carried by the re-entrant tube and also enables the conductor supports to be well separated so as as to improve the insulation thereof.

The invention consists also in an electrical discharge apparatus of the kind referred to in which the deflection of the cathode rays is effected either by electrostatic or electro-magnetic action '30 wherein a filling of a light gas such as helium is employed for bringing the cathode rays to a focus. It has been customary in cathode ray tubes to employ a small quantity of a heavy gas, such as argon, to effect focussing so as to secure 5 the greatest focussing efiect for a. given pressure.

but we have discovered that a light gas such as helium is effective for focussing and greatly increases the operating frequency limit of the apparatus as compared with apparatus in which aheavy gas is used.

In order that the invention may be more readily understood an example of an oscillograph or televising tube constructed inaccordance with the invention will now be particularly described with reference to the accompanying drawing in which:--

Figure 1 is an elevation, partly in section, of the electrode system,

Figure 2 is a fragmentary elevation partly in section taken at right angles to Figure 1,

Figure 3 is a sectional view on the line 3,3 of Figure 1 showing the star-shaped pinch and Figure 4 is a plan view in which all the electrodes with the exception of the control electrodes are omitted for the purpose of enabling the dis- '35 position of the control electrodes in relation to the star-shaped pinch to be seen.

The apparatus shown in the accompanying drawing is of the known type comprising an electron emitting hot cathode 1, a perforated anode 2, an insulated tubular iocussing shield 3 surrounding the cathode and two pairs of parallel rectangular control electrodes or deflector plates 4: and 5 set at right angles to one another and embracing the cathode stream which issues from the central aperture in the anode 2, at dilierent distances from the anode. The cathode stream is focussed upon asuitable fluorescent screen (not shown) and is controlled by the electrostatic action of the electrodes 4 and 5 in known manner so that the light spot produced from the fluorescent screen by the action of the cathode stream moves in accordance with the control potentials impressed on the electrodes 4 and 5.

In the operation of known discharge apparatus employing an electrode system of this type there is a tendency for electrons reflected or emitted from thefluorescent screen to be collected by the control electrodes with the result that current due to these electrons flows in the input circuits.

In accordance with the present invention a conductive shield or screen connected to the anode or otherwise held at a suitable positive potential isprovided for the purpose of protecting the control electrodes from these secondary electrons. As shown in the drawing, the conductive shield or screen takes the form of an openended metal cylinder 6 mounted directly on the anode 2 which is provided with a flange 2a for this purpose. This cylinder surrounds the control electrodes and extends from the anode 2 towards the fluorescent; screen as shown so as to be capable of collecting the secondary electrons before they can reach the control electrodes. The cylinder is preferably provided with atransverse partition 7 which acts as a barrier to intercept secondary electrons which might otherwise pass down through the cylinder 6 and reach the control electrodes. The partition 7 is provided with a central aperture 8 of sufllcient diameter to permit of the passage of the cathode stream. The cylinder 6 and partition 7 also act as an electrostatic screen for protecting the control electrodes from.the effects of glass charges.

In an alternative construction, the interior of the envelope is metalised by any suitable known process to form a conductive coating which is connected to the anode or otherwise held at a suitable positive potential so that secondary electrons reflected or emitted from the fluorescent screen are attracted to the coating and thereby prevented from reaching the control electrodes. This coating may take the place of the screen 6 shown in the drawing.

In order to facilitate the manufacture of the apparatus and to improve the insulation between the lead-in conductors to the several electrodes, in accordance with the present invention the electrode system is mounted upon a star-shaped foot or pinch 9 formed at the end of the re-entrant tube 10 through which the lead-in conductors pass into the envelope 11. This construction enables the electrode system to be assembled as a unit carried by the re-entrant tube and also enables the conductor supports to be well separated since the star-shape of the pinch is well adapted to enable the rectangularly arranged electrodes 4 and 5 to be carried on widely spaced conductor supports.

In the preferred construction according to the invention and as illustrated in the drawing the cathode 1 is supported on two conductor supports in sealed into two opposite arms of the starshaped pinch and connected each to a suitable lead-in conductor as shown, whilst the focussing shield 3 is carried on two conductor supports 3a which are sealed into the other two opposite arms of the star-shaped pinch and one of which is connected to a suitable leading-in conductor. The anode 2 carrying the cylinder 6 is supported directly on the focussing shield 3, a disc 12 of mica or other suitable insulating material, provided with a central aperture in register with the aperture in the anode, being interposed between the anode 2 and the focussing shield 3. The anode is fastened to the focussing shield by means of bolts and nuts or other suitable fastening devices 13 which pass through the anode 2 and disc 12. The bolts also pass through an annular disc 14 of mica or other suitable insulating material additional to the disc 12 and having its outer edge engaging within a flange 2a depending from the periphery of the anode and its inner edge clamped between a flange 3b formed on the end of the focussing shield and a flange 15a formed on the end of a tube 15 which is telescoped into the focussing tube, as shown in Figure 1 of the drawing, and secured by spot welding or otherwise. Current is led to the anode by means of a conductor 16 which is welded to the flange 2a and is sealed into the reentrant tube at a point below the pinch as shown at 17 in Figure 1.

Each of the control electrodes or deflector plates 4 and 5 is supported at one .end by a coning discs 12 and 14. Moreover they are conveniently situated for supporting the two pairs of parallel deflector plates 4 and 5 at right angles to one another as illustrated in Figure 4.

The cylinder 6 carried on the anode is preferably formed with pressed out ears or projections 20 which engage against the walls of the envelope, as illustrated in Figure 1 of the drawing, to hold the cylinder 6 and anode 2 against transverse movement.

The envelope 11 may be fllled with any suitable gas for the purpose of focussing the cathode stream. However, if a heavy gas such as argon is employed as is usual in cathode ray tubes of this character, difficulties will be experienced owing to the sluggishness of the focussing effect in reestablishing itself after a disturbance of the beam due to a rapid change of potential on the control electrodes, and the apparatus will be unable to respond fully to waves whose frequency is above a certain limit. We have discovered that adequate focussing of the cathode rays can be effected by filling the envelope with a light gas such as helium and that the rapidity of the re-establishment of the focussing effect is greatly increased when such a light gas is employed. In

accordance with our invention therefore, we prefer to provide a fllling of helium or other light inert gas instead of the heavy gas which has been employed heretofore for focussing purposes.

It will be understood that, although the invention has been described with reference to the accompanying drawing as applied to a cathode ray 'oscillograph or televising tube employing a fluorescent screen, the invention is not limited to this particular application but can be applied to any apparatus in which cathode rays focussed by the action of a gaseous filling are deflected by electrostatic or electromagnetic control.

,We claim:

1. A cathode ray tube comprising a sealed envelope having a reentrant tube; a substantially star shaped pinch formed on the end of said reentrant tube and having a plurality of radiating arms; a pair of conductor supports sealed into two different arms of said pinch; a cathode connected to and supported by said conductor supports, a

second pair of conductor supports sealed into two different arms of said pinch; a tubular focussing shield connected to and carried by said second pair of conductor supports and surrounding said cathode, said focussing shield having an open end; a plate shaped perforated anode secured to the open end of said focussing shield; an insulator interposed between said anode and said shield, said anode and insulator having at least one pair of openings, at least one pair of conductor supports sealed into two different arms of said pinch and projecting through said openings, and a plurality of control electrodes connected to and carried by said last mentioned conductor supports, said insulator engaging and locating said last mentioned conductor supports relatively to said anode.

2. A cathode ray tube comprising a sealed envelope having a reentrant tube provided on its end with a pinch of substantially a star-shape, a plurality of conductor supports sealed into said pinch, an electron emitting cathode carried by a pair of said conductor supports, a focusing shield surrounding said cathode and carried by a second pair of said conductor supports, a plate shaped anode supported by said focusing shield, said anode having an opening for the passage of electrons emitted by said cathode and a plurality of apertures spaced from said opening, a disc of insulating material between said focusing shield and said anode and having a plurality of apertures aligned with but of smaller area than those of said anode, and a plurality of control electrodes supported by a third series of said conductor supports, said third series of conductor supports extending through the apertures of said anode and insulating disc and mechanically supported by said disc.

3. A cathode ray tube comprising a sealed envelope having a reentrant tube; a substantially cross-shaped pinch formed on the end of said reentrant tube and having pairs of arms in crossed relation; a pair of conductor supports sealed into one pair of said arms of said pinch, a cathode connected to and supported by said conductor supports, a second pair of conductor supports sealed into another pair of the arms of said pinch;

an open-ended tubular focusing shield surrounding said cathode and connected to and carried by said second pair of conductor supports; a plate shaped anode secured to the open end of said focusing shield, said anode having an opening for the passage of electrons emitted by said cathode and a pair of apertures spaced from said opening, an insulator between said anode and said shield and having a pair of apertures aligned with but of smaller area than those of said anode, a third pair of conductor supports sealed into a pair of the arms. of said pinch and extending through the apertures of said anode and insulator, a plurality of control electrodes connected to and carried by said last mentioned conductor supports, said insulator engaging and locating said last mentioned conductor supports relatively to said anode, and a metallic shield electrically connected to said anode and surrounding said control electrodes.

4. A cathode ray tube according to claim 3, wherein the focusing screen comprises a pair of metallic cylinders fitted one within the other, each of said cylinders having at its end adjacent the anode a flange provided with a pair of apertures aligned with but of larger area than those of the insulating disc.

WILLIAM RICHARD BULLIMORE. LESLIE HERBERT BEDFORD.

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