JPS6241374B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic focusing cathode ray tube incorporating a permanent magnet.

Electrostatic focusing and electromagnetic focusing are often used in cathode ray tube electron guns to focus the electron stream into a narrow beam, but electromagnetic focusing provides better results in terms of resolution. This is an electromagnetic lens system,
In the lens space that focuses the electron beam,
There is less risk of dielectric breakdown than with the electrostatic method,
Therefore, since a high anode voltage can be applied, the first thing to do is to suppress the effects of repulsion between the electrons that make up the electron beam and prevent the beam from spreading.
It is the cause of The second reason is that the distance in the beam traveling direction of the working space that acts as a lens can be made longer in the case of electromagnetic focusing than in the case of electrostatic focusing, so that aberrations can be reduced. However, although the electromagnetic focusing method has the above-mentioned advantages, it has disadvantages such as requiring a focusing coil and a power source for the current flowing through the focusing coil, making it expensive, and increasing the size and weight. ,
Generally not used much.

In order to eliminate such drawbacks, instead of generating the tube axial magnetic field along the electron flow path required for electromagnetic focusing by a focusing coil placed outside the vacuum envelope, the magnetic field shown in Figs. As shown in the figure, a pair of yokes made of soft ferromagnetic material and having holes for electron flow on the end faces are placed inside the tube, isolated and facing each other in the direction of the tube axis. A structure was proposed in which a permanent magnet magnetized in the same direction is inserted and a pair of yokes are closely attached to the magnetic pole faces at both ends of the permanent magnet. Figures 1 and 2 show an example of the electromagnetic focusing type in-line color picture tube with a built-in permanent magnet according to this proposal, and Figure 1a
is a side cross-sectional view of the electron gun part in a plane including the inline 3 electron gun, Fig. 1b is a front view of the yoke seen from the tube axis direction, and Fig. 2 is a yoke including the tube axis and perpendicular to the plane of the inline 3 electron gun. FIG. 3 is a side cross-sectional view of the electron gun section; In the figure, 1 is a vacuum envelope (valve neck tube),
2 is a cathode, 3 is a first grid, 4 is a second grid, 5 is a third grid bottom, 6 is a yoke, 7 is an anode spring, 8 is an internal conductive film at an anode potential, 9 is a permanent magnet, 10 is glass, etc. This is an electrode support rod made of. In order to generate a sufficient focusing magnetic field with such a structure, after completing the sealing and evacuation process as a picture tube, surround the outer periphery of the valve neck tube and attach it as close as possible to the cylindrical portions of the pair of yokes, facing each other. With the magnetic poles of the magnetic device arranged, a large current is applied to the conductor of the magnetizing device interlinked with the magnetic path to magnetize the permanent magnet. In this case, since it is desirable that the magnetic resistance (reluctance) of the magnetic path be small, the length of the cylindrical portion of the yoke 6 in the tube axis direction needs to be considerably long as shown in the figure. However, in such a structure, when the electrodes of the electron gun, especially the first and second grids, are inductively heated during the exhaust process, the magnetic flux generated by the induction heating coil of the induction heating device (bombarder) is coupled with the third grid bottom 5. Yoke 6 forming part of the third grid
In particular, the cylindrical wall portion of the yoke 6, which is quite long in the tube axis direction and forms a closed loop with low resistance as described above, surrounds a large area and has a large number of interlinked magnetic fluxes. A large current flows through the part and heats it to a high temperature, and the permanent magnet 9 is not only heated as its cross section is interlinked with the magnetic flux, but also heat conduction from the yoke 6 is added, and the permanent magnet 9 is heated to a high temperature, e.g.
It is heated to about 550℃. As a result, the material of the permanent magnet (e.g. alnico) changes and its magnetic properties deteriorate, enough to generate the magnetic field needed to focus the electron stream into a narrow beam during the magnetization process after the evacuation. There was a problem that the permanent magnet 9 could not be magnetized to such an extent. As shown in FIG. 3, when induction heating the grid, it is possible to prevent the induced magnetic flux 13 from reaching the yoke 6 or the permanent magnet 9 by placing a shot ring 12 on the yoke side of the induction heating coil 11. , in this way, the magnetic flux 13 for heating the first and second grids
This causes a problem in that the first and second grids cannot be heated or exhausted sufficiently.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electromagnetic focusing cathode ray tube with a built-in permanent magnet that is free from the above-mentioned problems.

In order to achieve the above object, in the present invention,
When performing magnetization work to magnetize a permanent magnet, the area around the yoke, which faces the magnetic pole of the magnetizing device and the vacuum envelope (valve neck wall), is placed in a tube so that the reluctance is small as part of the radial magnetic path. Although it is necessary that the length (or thickness) in the axial direction be large,
Focusing on the fact that it does not need to be continuous in the circumferential direction, we created a slit around the yoke so that the yoke periphery does not form a closed loop for the magnetic flux for induction heating.
This prevents induced current from flowing around the yoke.

4 and 5 are diagrams showing an in-line color picture tube embodying the present invention, in which FIG. 4a is a side sectional view of the electron gun section including the inline 3 electron gun, and FIG. 4b is a tube axis. FIG. 5 is a side sectional view of the electron gun section along a plane including the tube axis and perpendicular to the plane of the in-line 3 electron gun. The difference from the conventional electromagnetic focusing type in-line color picture tube with built-in permanent magnet shown in FIGS. 1 and 2 is that the yoke 6a used in this embodiment is different from the conventional yoke 6, and
As can be seen from the cross-section of the cylindrical wall of the yoke 6a shown in FIG. 6 with diagonal lines drawn, there are four
The slits 14 are provided at different locations. With this slit, in the conventional yoke 6, the cylindrical wall surface, which forms a large-area closed loop for the high-frequency alternating magnetic flux for induction heating and generates a large amount of heat, can be clearly seen from FIG. In the yoke 6a according to the present invention, the induced current does not flow because it is divided.
This part is hardly heated, and a heat load is applied to the bottom of the cylinder, contrary to the conventional case. Therefore, the permanent magnet 9 is not heated by heat conduction from the yoke 6a, and the temperature of the permanent magnet 9 does not rise to a high temperature of, for example, 550°C, unlike in the conventional case, and there is no risk of material deterioration. , the permanent magnet 9 can be sufficiently magnetized to generate the magnetic field necessary for electromagnetic focusing.

As described above, according to the present invention, an electromagnetic focusing cathode ray tube with a built-in permanent magnet that is small, lightweight, and has excellent resolution can be obtained at a high yield.

[Brief explanation of the drawing]

Figure 1a is a side sectional view of the electron gun section of a conventional electromagnetic focusing inline color picture tube with a built-in permanent magnet, taken from a plane including the inline 3 electron gun, and Figure 1b is a view of the picture tube's yoke viewed from the tube axis direction. 2 is a side sectional view of the electron gun section taken along a plane including the tube axis of the picture tube and perpendicular to the plane of the in-line 3 electron gun; FIG. 3 is an explanatory diagram of the induction heating state of the picture tube electrode during exhaust; FIG. 4a is a side sectional view of the electron gun section of the inline color picture tube according to the present invention, taken from a plane including the inline 3 electron gun, and FIG. 4b is a front view of the yoke of the same embodiment as seen from the tube axis direction. Fig. 5 is a side cross-sectional view of the electron gun part of the same embodiment, taken along a plane perpendicular to the plane of the inline 3 electron gun, including the tube axis, and Fig. 6 is a front view showing the cylindrical wall section of the yoke of the same embodiment with diagonal lines drawn. It is a diagram. 3...First grid, 4...Second grid, 5...Third grid bottom, 6a...Yoke, 9...Permanent magnet, 11...Induction heating coil, 12...Shot ring, 13...Induced magnetic flux, 14...Slit.

Claims (1)

[Claims] 1. A plurality of electrodes that control the electron flow emitted from the cathode, and a 1.
In an electromagnetic focusing cathode ray tube comprising a pair of yokes and a permanent magnet inserted between the pair of yokes to generate a magnetic field in the tube axis direction along an electron flow path, a slit is provided at the periphery of the yoke. An electromagnetic focusing cathode ray tube characterized by being provided with.