JPS6138574B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cathode ray tube electron gun,
In particular, the present invention relates to an electromagnetic field focusing type cathode ray tube electron gun that is small, lightweight, and easy to focus.

FIG. 1 is a schematic diagram of a conventional magnetic field focusing type negative magnetic ray tube electron gun. Electrons emitted from the cathode electrode 3 heated by the heater 2 are focused by a triode lens and a prefocus lens formed by the first grid electrode 4 and the second grid electrode 5, and are thus form a crossover. Thereafter, the electrons are accelerated by the third grid electrode 6 at a constant divergence angle, and the electromagnetic focusing coil is located approximately in the center of the third grid electrode 6 and is attached to the outside of the vacuum envelope 1. 7a, and the crossover is imaged onto a fluorescent surface (not shown). In this case, the crossover is just focused on the fluorescent surface by increasing or decreasing the current flowing through the electromagnetic focusing coil 7a and setting the strength of the magnetic field lens to an appropriate value. Note that 9 is a contact spring that conductively connects the internal conductive film 10 and the third grid electrode 6. However, if an attempt is made to generate the magnetic field necessary for focusing using only the electromagnetic focusing coil 7a, the weight and volume of the coil will increase, and the cost will also be high. At present, the magnetic field focusing method is only applied to products that require it. Moreover, when the electromagnetic focusing coil 7a is provided, the strength of the focusing magnetic field fluctuates significantly due to heat generated by the coil current, etc., so a temperature correction circuit is required, which increases the cost of the circuit. .

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a new cathode ray tube using an electromagnetic field focusing method, which eliminates the above-mentioned drawbacks of the prior art, has a focusing device that is small in weight and volume, is low in cost, and allows easy focus adjustment. It is in.

The present invention achieves the above object by using a conductive permanent magnet as a means for generating a focusing magnetic field, incorporating the permanent magnet in a vacuum envelope, and applying a focus adjustment voltage to the permanent magnet as desired. This is what I am trying to do.

Examples of the present invention will be described in detail below.

FIG. 2 is a sectional view of one embodiment of the present invention, and the same reference numerals as in FIG. 1 represent the same parts. 7b is a cylindrical permanent magnet made of a conductive material such as an alnico magnet, and 8 is a fourth grid electrode.
In the figure, the electron crossover formed near the opening of the second grid electrode 5 is accelerated by the third grid electrode 6 with a certain divergence angle, and then is formed by a magnetic field lens formed by the permanent magnet 7b. It is focused and focuses near the fluorescent surface. At this time, by applying an appropriate voltage _E2 to the permanent magnet 7b from the outside, a pair of electric field lenses are installed in the gap between the third grid electrode 6 and the fourth grid electrode 8 before and after the permanent magnet 7b. is formed, and the combined focusing action of these three lenses allows the electrons to be completely focused on the phosphorescent surface.
For example, in a 20-inch 110° deflection cathode ray tube, the anode voltage E ₁ = 5.0 KV and the axial focusing magnetic field of the permanent magnet.
In the case of 400 Gauss, the voltage applied to permanent magnet 7b is
When I set the voltage to around 4.3KV, I was able to focus exactly on the fluorescent surface.

In the above example, one conductive cylindrical permanent magnet is used in the electron gun electrode system, but multiple permanent magnets may be used, or only a part of a particular grid electrode is used as a permanent magnet. It is clear that a structure in which magnets are substituted may also be used. FIG. 3 shows an example of the latter, in which a part of the third grid 6 can be seen as being replaced by a conductive cylindrical permanent magnet 7c having the same inner diameter as that of the third grid 6, and its operation is similar to that in FIG. The same is true.

As described above, in the present invention, a conductive permanent magnet is built in the vacuum envelope, and if desired, by applying a focus adjustment voltage to the permanent magnet, an electric field lens and a magnetic field lens can be formed. Since a composite electron lens can be configured and spherical aberration can be corrected, it is possible to easily focus correctly on a phosphorescent surface with little aberration and form a high-resolution image. Therefore, the weight, volume and cost can be significantly improved compared to the conventional vacuum envelope which uses an electromagnetic focusing coil outside the vacuum envelope, and furthermore, the conventional focusing coil circuit can be omitted. Furthermore, it is clear that the conductive permanent magnet referred to in this specification is not limited to those whose material itself is conductive as described above, but also includes those whose surfaces are made conductive.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional magnetic field focusing type cathode ray tube electron gun, and FIGS. 2 and 3 are schematic diagrams of the present invention. 1... Vacuum envelope, 3... Cathode electrode, 4...
...first grid electrode, 5...second grid electrode,
6... Third grid electrode, 7b, 7c... Permanent magnet, 8... Fourth grid electrode.

Claims (1)

[Claims] 1. A cathode electrode disposed within a vacuum envelope;
In a cathode ray tube electron gun having a plurality of grid electrodes for focusing an electron beam emitted from a cathode electrode, at least a part of at least one grid electrode is composed of a conductive cylindrical permanent magnet, and the inside thereof is 1. A cathode ray tube electron gun characterized in that a magnetic field lens is formed in the gap between adjacent grid electrodes, and an electric field lens is formed in the gap between adjacent grid electrodes by applying a predetermined voltage to the magnetic field lens. 2. Claim 1, characterized in that a focus adjustment voltage is applied to the conductive permanent magnet.
The cathode ray tube electron gun described in Section 1.