Electron gun and cathode ray tube using the same

Details Electron gun and cathode ray tube using the same Electron gun and cathode ray tube using the same

2000-03-10

2003-04-29

O'Shea, Sandra (Department: 2875)

Electric lamp and discharge devices

Cathode ray tube

Plural beam generating or control

C313S447000

Reexamination Certificate

active

06555952

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection color television tube, and more particularly to an electron gun for such tube having improved high voltage performance.
2. Description of the Related Art
A projection color TV uses three monochrome CRTs to produce the primary colors, i.e., red, blue and green, which are superimposed on a large projection screen to produce a full color display image. Because the images on the tube screens are not viewed directly, but are magnified and projected by a system of projection lenses, the individual cathode ray tubes are driven at higher voltages and beam currents than would be encountered for direct view tubes, in order to produce a full color display of acceptable brightness. U.S. Pat. No. 4,904,898, issued to Penird et al. discloses an electron gun assembly where a focusing electrode is coaxially surrounded by an accelerating electrode. A figure of U.S. Pat. No. 4,904,898 is reproduced here as FIG.
1
. It shows an electron gun having a cathode
21
to emit electrons, a control electrode
22
, and a screen electrode
23
. The electron gun further includes a first focus electrode
24
and a second focus electrode
25
. The end portion of the electron gun is coaxially surrounded by an accelerating electrode
26
. More particularly, the second focus electrode
25
has a cup-shaped portion, which is comprised of a short cylindrical portion
25
b
and a tapered portion
25
c,
integrally connected to a cylindrical base portion
25
a.
Tapering the wall of the second focus electrode
25
helps to reduce a surface comprising the high voltage gap between the second focus electrode
25
and the accelerating electrode
26
. It further increases the distance between the interior surface of the accelerating electrode
26
and the outer surface of the second focus electrode
25
. The disclosed electrode structure is stated to have good high-voltage performance. However, because the second focus electrode
25
still has a cylindrical portion
25
b
at one end thereof, there remains a possibility of a particle or projection becoming a field emitting site. There has been no attempt to taper the focusing electrode all the way to the end thereof presumably because it was believed that it is necessary to the main electronic lens.
SUMMARY OF THE INVENTION
To solve the above problem, an object of the present invention is to further improve the high voltage performance of an electron gun for a monochrome cathode ray tube without degrading its lensing performance.
Another object of the present invention is to provide an electron gun for a monochrome cathode ray tube which can be effectively high voltage conditioned.
In accordance with the invention, it has been discovered that the high voltage performance of the monochrome cathode ray still can be achieved by modifying the shape of the focusing electrode such that the end of the focusing electrode is also tapered.
In accordance with the invention, the side walls of the focusing electrode is tapered inwardly from the end.


REFERENCES:
patent: 5814930 (1998-09-01), Watanabe et al.
patent: 6031326 (2000-02-01), Suzuki et al.

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