Electron gun

Details Electron gun Electron gun

1999-05-03

2001-06-05

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

With support and/or spacing structure for electrode and/or...

For indirectly heated cathode

C313S337000, C313S3460DC

Reexamination Certificate

active

06242852

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an electron gun used for a CRT (cathode ray tube) or the like, and particularly to an electron gun in which an impregnated type cathode is provided in a heater built-in inner sleeve and the inner sleeve is connected to and supported by an outer sleeve by means of strap-like connecting members, called, tabs. In more particular, the present invention relates to an electron gun capable of leesening the diameter of the inner sleeve for reducing radiation heat propagating to grids and the like, thereby reducing power consumption in combination with prevention of inconveniences such as plane stray.
As shown in
FIGS. 1 and 2
, a CRT includes a tube main body T having a face panel portion F and a neck portion N, wherein an aperture grill AG and a fluorescent layer L are provided on the face panel portion F, and an electron gun E is provided on the neck portion N. The electron gun E, if it is of a Trinitron type, has prefocus lens system having three cathodes KB, KG and KR and, a first grid electrode G
1
and a second grid electrode G
2
; a main lens system having a third grid electrode G
3
, a fourth grid electrode system G
4
AB, G
4
C, G
4
DE, and a fifth grid electrode G
5
; and a deflection system having a convergence deflection plate CP and a shield CS. In
FIG. 2
, reference character DY designates a deflection yoke.
In recent years, to improve the controllability of electron beams, the electron gun E is configured such that the cathode (hereinafter, represented by reference character K) and the first and second grid electrodes G
1
and G
2
are integrally assembled into a cathode structure A.
The cathode structure A is, as shown in
FIGS. 3 and 4
, configured such that the cathode K is fixed at an end portion, on the grid electrodes G
1
and G
2
side, of a heater
11
built-in inner sleeve
10
; the inner sleeve
10
is inserted in an outer sleeve
20
and is fixed thereto by means of strap-like tabs (not shown); the outer sleeve
20
is mounted on a ceramic disk
22
via a holder
21
; and the first grid G
1
is directly provided on the ceramic disk
22
and the second grid electrode G
2
is provided on the ceramic disk
22
via a spacer
23
. In
FIG. 3
, reference numeral
30
designates a lead for making the grid electrode G
1
conductive, and in
FIG. 4
, reference numeral
17
designates a cap for mounting the cathode.
In recent years, an impregnated type cathode K in which a porous base such as a tungsten sintered body is filled with a cathode material has been developed and has come to be used for the electron gun E shown in
FIGS. 3 and 4
in place of a conventional oxide cathode.
As is known, the impregnated type cathode has an advantage that the electron emission density is higher than that for the oxide cathode, and therefore, the electron gun E using the impregnated type cathode K is advantageous in enhancing the performance of the CRT.
However, in the electron gun E using the above impregnated type cathode K it is essential to heat the impregnated type cathode K at a high temperature because the operational temperature of the impregnated type cathode K is higher than that of the oxide cathode. That is to say, the operational temperature of the oxide cathode is about 800° C., while the operational temperature of the impregnated type cathode K is about 1000° C.
As a result, there occur a first problem that a calorie transferred from the built-in heater
11
to the first and second electrodes G
1
and G
2
by way of the inner sleeve
10
, outer sleeve
20
and ceramic disk
22
is large, thereby to increase the power consumption of the heater
11
; a second problem that when the grid electrodes G
1
and G
2
are over-heated at high temperatures, Ba and BaO are evaporated and scattered from the cathode K and are deposited on the grid electrodes G
1
and G
2
to form emission sources ES (see FIG.
4
), and thermal electrons are emitted from these emission sources ES, to increase the stray emission intensity, thereby exerting adverse effect not only on an image quality but also on the focus characteristic, resulting in a phenomenon (so-called plane stray) in which the center of the screen becomes bright after completion of the deflecting operation; and a third problem that a leakage current from the grid electrodes G
1
and G
2
is increased, to cause a malfunction of the circuit.
It is known that the above problems can be somewhat solved by reducing the area of the inner sleeve
10
, that is, reducing the diameter of the inner sleeve
10
, thereby reducing the radiation heat from the inner sleeve
10
.
If the diameter of the inner sleeve
10
is reduced, however, a gap between the inner sleeve
10
and outer sleeve
20
becomes large, so that a calorie propagating by thermal transmission is increased, to make large the power consumption of the heater required to keep the temperature of the inner sleeve at about 1000° C., and it is required to ensure the supporting rigidity of the inner sleeve
10
fixed to the outer sleeve
20
by enlarging the dimension such as the thickness of each tab in accordance with the gap between the inner sleeve
10
and outer sleeve
20
, to increase a calorie propagating by thermal conduction.
To reduce radiation heat, it may be considered to reduce not only the diameter of the inner sleeve
10
but also the diameter of the outer sleeve
20
; however, if the diameter of the outer sleeve
20
is reduced, a work of connecting the outer sleeve
20
with the holder
21
upon assembly of the outer sleeve
20
in the ceramic disk
22
is complicated, and increases to increase the number of assembling steps, thereby increasing the manufacturing cost.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention has been made, and an object of the present invention is to provide an electron gun capable of reducing the caloric amount propagating to grid electrodes due to thermal conduction and thermal radiation, reducing the power consumption of a heater, preventing inconveniences such as plane stray, and simplifying the assembly of the electron gun.
To achieve the above object, according to the present invention, there is provided an electron gun including: a heater built-in inner sleeve at the leading end of which an impregnated type cathode is provided; an outer sleeve in which the inner sleeve is inserted; and strap-like connecting members for connecting the inner sleeve to the outer sleeve at a plurality of positions spaced at intervals in the peripheral direction such that the inner sleeve is disposed coaxially with the outer sleeve, the impregnated type cathode is positioned at the leading end of the outer sleeve, and the inner sleeve is separated from the outer sleeve with an annular space kept therebetween; wherein the outer sleeve has on the leading end side a small-diameter portion having a diameter smaller than that of the remaining portion of the outer sleeve on the base end side; the inner sleeve is positioned in the small-diameter portion; and the leading end of the small-diameter portion is connected to the base end of the inner sleeve by means of the strap-like connecting members.
Further, in the electron gun of the present invention, since the diameter of the inner sleeve is reduced (specificallly to a value ranging from about 1.0 mm to about 1.2 mm) and the small-diameter portion having a small diameter (specifically in a range of about 2.2 mm to about 2.6 mm) on the leading end side of the outer sleeve, a suitable gap can be formed between the inner sleeve and the small-diameter portion of the outer sleeve without reducing the diameter of the portion on the base end side of the outer sleeve (specifically while ensuring the outside diameter of the portion in a range of about 2.6 mm to about 3.0 mm).
Accordingly, it is possible to reduce a caloric amount propagating by thermal radiation and thermal transmission toward the grid electrodes, to avoid the enlargement of the tab thereby reducing the caloric amount propagating by thermal conduction, and to facilita

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