US2289906A

US2289906A - Cathode ray tube

Info

Publication number: US2289906A
Application number: US302217A
Authority: US
Inventors: David W Epstein
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1939-10-31
Filing date: 1939-10-31
Publication date: 1942-07-14
Anticipated expiration: 1959-07-14

Description

D. w. EPSTEIN 2,289,906

CATHODE RAY TUBE Filed Oct. 31, 1959 2 Sheets-Sheet 1 ZSnugntor 8 Ln C(ttorneg David at P NN July 14, 1942.

Patented July 14, 1942 CATHODE RAY TUBE David W. Epstein,

to Radio corpora of Delaware Merchantviiie, N. 1., assignor tion of America, a corporation Application October 31, 1939, Serial No. 302,217 10 Claims. (01. 250-141) My invention' relates to cathode ray tubes and particularly to cathode ray tubes of the high voltage type such as projection tubes.

One of the difficulties formerly encountered in projecting pictures with a cathode ray tube was that, at the high voltage used on the high volt age anode such as the second anode (50,000 volts, for example), there frequently was an insulation breakdown between the deflecting yoke and the second anode, the deflecting yoke being substantially at ground potential as compared with the second anode voltage.

It is, accordingly, an object of my invention to provide an improved cathode ray tube which may be operated without encountering the abovem-entioned difficulties.

A further object of my invention is to provide an improved cathode ray tube which has a long leakage path between the second anode and the lower voltage elements of the tube.

In the preferred embodiment of my invention, the foregoing objects are accomplished by providing the cathode ray tube envelope with a reentrant portion upon which there is formed a coating which functions as the second anode. Either in this manner or in some other suitable way, there is provided what may be referred to as a double-walled structure at the portion of the tube which is surrounded by the deflecting yoke, there being a vacuum between the yoke and the second anode. Because it is very dimcult to produce a voltage discharge through a high vacuum, the possibility of a breakdown between the deflecting yoke andsecond anode is substantially eliminated. I

The invention will be better understood from the following description taken in connection with the accompanying drawlngs in which Figure 1 is a view, partly in longitudinal section and drawn to full scale, of a cathode ray tube embodying my invention,

Figure 2 is a view showing schematically the tube of Figure 1 with operating voltages applied thereto, and

Figures 3 and 4 are views of other embodiments of my invention.

Referring to Figs. 1 and 2, the cathode ray tube may comprise a highly evacuated envelope I having a reentrant tubular section II. The envelope l0 contains an electron gun comprising an indirectly heated cathode l2, a control elec-- trode 13, a. screen grid or electrode I4 and a first anode I6. I

The screen grid II and the first anode Ii are supported from glass beads or rods H which themselves are supported from the control grid IS.

The speciflc gun structure illustrated, in which the skirted screen grid II is employed, is described and claimed in my copending application Serial No. 338,058, filed May 31, 1940, and assigned to the RCA. The present invention, however, does not require the use of this particular gun structure. For example, the gun may be of conventional construction with the screen grid omitted entirely.

In accordance with a preferred embodiment of my invention, the second anode consists of a conductive coating ll on the inner surface of the reentrant portion II. There preferably is provided a smooth metal ring I! mounted on the end of the reentrant portion facing the first anode I and in electrical contact with the coating. II. The ring I! is provided in order to make the end of the second anode smooth. At the high voltage employed, if it were omitted there might be electrical discharges between the ragged edge of the coating I0 and the first anode l6. Voltage is applied to the second anode It in the usual way through a terminal 2|.

The usual fluorescent screen is provided on the end of the cathode ray tube as indicated by the legend.

The deflecting yoke for causing the cathode ray to scan the fluorescent screen is indicated at 22. This yoke preferably is of the distributed coil type described and claimed in Tolson Patent No. 2,167,379, issued July 25, 1939. It comprises a pair of deflecting coils, one pair of them being represented at 23 in Fig. 2. As indicated in Fig. 2, at least one pair of windings in the deflecting yoke 22 is at approximately ground potential, as compared with the second anode voltage. example, one end of a coil may actually be grounded, or it may be two or three hundred volts above ground. In either case, there is a very high voltage between the yoke 22 and the second anode.

In a cathode ray tube embodying my invention, this high voltage diflerence will not cause a breakdown of the insulation because a substantial portion of the insulation is a vacuum between the reentrant section II and the outer wall of the envelope l0.

It will be seen, also, that there is a long leakage path between the second anode l0 and the other two electrodes whereby the possibility of leakage along the inner surface of the envelope "is greatly reduced.

Referring to Fig. 3, there is shown an embodiare indicated by the same reference numerals.

This projection tube comprises an evacuated envelope having an inner wall 28 and an outer wallll. The portion between the walls 28 and 21 is highly evacuated like the portion containing the tube electrodes. It will be apparent that the danger of voltage breakdown between the anode l8 and the deflecting yoke 22 is minimized by the presence of the evacuated space between them.

Referring to Fig. 4, there is shown an embodiment of the invention wherein magnetic focusin of the cathode ray is employed. The tube comprises an evacuated envelope 30 having a reentrant portion 3 I An electron beam is produced by means of an indirectly heated cathode 32, a control electrode 33 and an anode 34. The anode consists of a conducting coating on the inner surface of the reentrant portion 3| and may include a metallic ring portion 36. g

The means for focusing the cathode ray includes a magnetic focusing coil 31. Deflection of the cathode ray for scanning a fluorescent screen at the end of the tube preferably is accomplished by means of the deflecting yoke 22.

From an inspection of the drawings, it will be apparent that there is a vacuum between the high voltage anode 34 and the

coils

22 and 31, these coils being close to ground potential, whereby there is substantially no danger of insulation breakdown.

I claim as my invention:

1. A cathode ray tube of the high vacuum type comprising a highly evacuated envelope having a reentrant portion supported from one end of said envelope only, an electron gun supported in the located outside said envelope for directionally I controlling said cathode ray, said inner wall section being supported, at. least in part, from the screen end of said envelope and being spaced.

from said envelope to provide an evacuated space between said directional controlling means and said high voltage anode and thereby prevent voltflecting the cathode ray, said inner wall section being supported, at least in part, from the screen end of said envelope and being spaced from said envelope to provide. an evacuated space between said deflecting yoke and said high voltage anode and thereby prevent voltage breakdown thereother end of said envelope and comprising a first anode, and a second anode supported by said reentrant portion and facing said first anode for accelerating and focusing the cathode ray.

2. In combination, a cathode ray tube of the high vacuum type comprising a highly evacuated envelope having an'electron gun therein which includes a first anode, a reentrant section in said envelope extending from the end of the envelope opposite said gun which comprises a conductive portion facing said first anode and functioning as a second anode to accelerate and focus the cathode ray, and a deflecting yoke surrounding a portion of said reentrant section whereby there is a vacuum between said yoke and said second anode.

3. In combination, a cathode ray tube of the high vacuum type comprising a highly evacuated envelope having a reentrant portion supported from one end of said envelope only, an electron gun supported in the other end of said envelope and comprising a first anode, and a second anode supported by said reentrant portion and comprising a conductive coating on the inner surface thereof, and a deflecting yoke surrounding said envelope at a region opposite said coating whereby there is a vacuum between said yoke and said second anode.

4. A cathode ray tube comprising an envelope havinig therein a fluorescent screen and an electron gun structure for directing a cathode ray against said screen, said envelope having an inner wall section, said gun structure including a comparatively low voltage anode and a comparatively high voltage anode, said high voltage anode being between.

6. A cathode ray tube comprising an envelope having a reentrant innerwall portion supported from one end of said envelope only, said envelope having therein a screen structure and an electron gun structure for directing a cathode ray against said screen, said gun structure comprising a cathode supported from the other end of said envelope and further comprising an anode supported on said reentrant portion, and a deflecting yoke surrounding at least a portion of said reentrant inner wall.

"I. A cathode ray tube comprising an envelope having a reentrant inner wall portion supported from one end of said envelope only, said envelope having therein a screen structure and an electron gun structure for directing a cathode ray against said screen, said gun structure comprising a cathode and a first anode supported from the other end of said envelope and further comprising a second anode supported on said reentrant portion, and a deflecting yoke surrounding at least a portion of said reentrant inner wall.

8. A cathode ray tube comprising a highly the coating and anode at the same potential, said inner wall section and said conductive coating extending far enough into the screen end of said tube to prevent sufllcient electrostatic charges from building up on the tube envelope to disturb control of said beam of electrons, there being an evacuated space between said inner wall section and the wall of said envelope.

9. In combination, deflecting means, a cathode ray tube comprising a highly evacuated envelope having therein a screen structure at one end and an electron gun at the other end for producing a beam of electrons and directing them towards said screen, an anode which faces said gun and which is supported on said envelope at a point removed from the region of said deflecting means and in spaced relation to said envelope in the region of said deflecting means whereby there is supported on said inner wall section, and means 751 a highly evacuated space between the anode a d said envelope in said last region, said anode for at least a portion of its length being conical in shape and having its largest diameter facing said screen, said deflecting means being located outside said envelope for directionally controlling said beam of electrons, the conical portion of said anode extending a substantial distance beyond said deflecting means and toward said screen.

10. The invention according to claim 9 wherein the anode comprises a cylindrical portion facing the electron gun and a conical portion facing said screen.

DAVID W. EPSTEIN.