JPH0782805B2 - Heater for indirectly heated cathode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to improvement of a heater for indirectly heated cathodes, and more particularly to improvement of coil winding specifications suitable for improving emission characteristics and heater life.

[Conventional technology]

A conventional indirectly heated cathode heater is disclosed in, for example, Japanese Patent Laid-Open No. 59-12536.
As seen in Japanese Patent Publication, a heater head shaped into a helical coil by a mandrel having a circular cross section, and a heater foot portion bent and shaped by a circular through hole portion are formed. The heater foot portion is a head portion. It cannot be smaller than the outer diameter of the coil. In general, the outer diameter of the foot is larger than that of the heater head due to the distance between the jig and the heater when shaping the foot and the springback of the heater foot. In the indirectly heated cathode, when the helical coil shaped shaping portion is disposed inside the cathode sleeve, heat loss due to conduction increases, resulting in a cathode system with large power consumption, and side effects such as stray emission occur due to temperature rise of the electrode. Further, when the heater foot is also arranged in the cathode sleeve, the inner diameter of the cathode sleeve is determined based on the outer diameter of the foot to prevent alumina cracks due to mechanical stress. As a result, the head of the heater becomes relatively small with respect to the cathode sleeve, the thermal efficiency between the heater and the cathode deteriorates, and the emission speed becomes slow.

[Problems to be solved by the invention]

The prior art described above does not consider the heat efficiency between the heater and the cathode, and the head of the heater becomes smaller in a coiled coil heater in which a primary coil is wound around a molybdenum wire or the like and then shaped into a spiral coil. However, there is a problem in that the insulation coating (alumina) cracks due to the temperature gradient inside the heater when the heater is ignited (the temperature at the contact point between the heat generation lines is low) and the insulation characteristics deteriorate. It was.

It is an object of the present invention to maximize the heater outer diameter within the allowable range within the cathode sleeve to improve the thermal efficiency and reduce the contact between the heating wires of the heater head to improve the reliability. Especially.

[Means for solving problems]

To improve the thermal efficiency between the heater and the cathode among the above purposes, the mandrel for shaping the spiral coil should have an elliptical section or a shape similar to this, and the heater foot should be arranged in the minor axis direction of this section. Is achieved by In addition, insulation failure caused by contact between the heating wires of the coiled coil heater is caused by making the direction of the direct current part of the heater zenith shaped into the elliptical spiral coil coincide with the minor axis direction of the elliptical shape, and bending radius of curvature. It is achieved by increasing.

[Action]

FIG. 2 is a sectional view showing the overall structure of an indirectly heated cathode using the heater according to the present invention. The temperature of the thermionic emission material 11 provided on the cathode base metal 12 is raised by the heat of the heater 15,
Emits thermoelectrons. The heater 15 is provided in the sleeve 13 held by the disk 14. The time until thermions are emitted from the thermionic emission material 11 is shortened, and the heater
In order to improve the thermal efficiency between the cathodes, the outer diameter of the spiral coil portion 15a of the heater 15 must be maximized inside the cathode sleeve 13. An example of a conventional heater structure is shown in FIG. This corresponds to the view from the zenith of the heater in FIG. As shown in FIG. 3, since the helical coil portion of the conventional heater is shaped by using a mandrel having a circular cross section, in order to secure an insertion space for this mandrel, the distance L between the heater legs 15b is set to the helical coil portion. Diameter d ₀
I have to be bigger than that.

That is, since the distance L between the heater legs 15b is large,
The outer diameter d ₀ of the helical coil portion 15a has to be relatively small in the cathode sleeve 13. According to the invention,
As shown in FIG. 4, the shaping mandrel of the helical coil portion 15a has an oval cross section, and the helical coil portion diameter (minor diameter) d in the direction of the heater foot portion 15b is small, but the helical coil portion diameter in the direction perpendicular to that is small. By shaping the (major axis) D relatively large, the helical coil portion can be enlarged as a whole, the post-heat rate can be improved, and a heater with a high emission speed can be manufactured.

Further, the contact phenomenon between the heating wires in the coiled coil heater occurs at the portion P in FIG. 3, which means that the radius of curvature of the heater wire becomes small at the boundary between the heater zenith portion 15c and the spiral coil shaping portion 15a. Caused by. By forming the substantially straight portion of the heater zenith portion 15c to be short, the contact amount between the heating lines can be reduced to some extent, but in such a case, the heating portion of the heater closest to the thermionic emission material 11 is reduced. Therefore, the emission speed becomes slower. In order to increase the radius of curvature at the boundary between the heater zenith portion 15c and the helical coil shaping portion 15a, the minor axis direction of the helical coil shaping portion 15a and the direction of the heater zenith portion 15c can be made substantially coincident with each other as shown in FIG. desirable. As a result, the radius of curvature is increased, and a heater with less contact between heating lines can be obtained. When the contact amount between the heating wires is small, the temperature gradient inside the heater is small when the heater is ignited, so that the insulation coating (alumina) of the heater is not cracked and insulation failure can be prevented.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. First
In the heater shown in the figure, a molybdenum wire core wire (φ0.125 mm) (not shown) is wound with a tungsten wire (φ0.032 mm) at an equal pitch of 18 turns / mm to form a primary coil 15d, and then the fifth coil As shown in the figure, the spiral coil shaping is performed using a mandrel having an oval cross section in which both sides of the circular cross section C are shaved off. In addition, in FIG. 5, 16a is a slit portion for forming the zenith portion 15c of the heater. After that, coating alumina and sintering,
The molybdenum core wire is dissolved and removed. The shape of the helical coil portion 15a of the heater seen from the heater head is the first
As shown in FIG. 5A, the shape is roughly oval, and the diameter D in the major axis direction is the maximum diameter allowed in the cathode sleeve.
As a result, the thermal efficiency between the heater and the cathode is remarkably improved as compared with the conventional heater shown in FIG. Also, the heater zenith 15
Since the radius of curvature of the boundary (R part) between c and the helical coil shaping part 15a can be made larger than that of the conventional heater (when the inner diameter of the cathode sleeve 13 is φ1.5 mm, the radius of curvature can be increased from the conventional 0.08 mm to 0.13 mm). It is possible to reduce the amount of contact between the heating wires between the tungsten wires of the primary coil winding.

FIG. 6 shows another embodiment of the present invention. The heater shown in FIG. 6 is formed by directly shaping a tungsten wire (φ0.05 mm) into a spiral coil, and unlike the heater shown in FIG. 1, no contact between heating wires occurs on the heater head. Therefore, lengthening the tungsten wire of the heater zenith portion 15c closest to the thermionic emission material is effective in improving the thermal efficiency between the heater and the cathode. In this case, the mandrel used for shaping the spiral coil may be the mandrel shown in FIG. 5 in which the slit 16a is cut in a direction perpendicular to the case shown in the drawing (that is, in the long diameter direction of the mandrel).

〔The invention's effect〕

According to the present invention, since the thermal efficiency between the heater and the cathode can be improved, the emission speed (image output time in the case of a color cathode ray tube) can be increased by 0.3 to 0.5 seconds.

Further, in the coiled coil heater, the contact between the tungsten wire at the boundary between the heater zenith and the spiral coil shaping portion is reduced, and the temperature gradient inside the heater when the heater is ignited is reduced. As a result, damage such as cracks does not occur in the heater alumina and insulation failure does not occur. Heater voltage
According to the result of the accelerated test 3000Hr in which the rate was increased by 20% and the on / off was repeated at a cycle of 5 minutes, the conventional product showed about 5% insulation failure, whereas the present invention did not cause any insulation failure.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, in which FIG. 1 (a) is a front view, (b) and (c) are side views, and FIG. 2 is the overall constitution of a cathode using the heater of the present invention. 3 is a schematic sectional view showing
FIG. 4 is a front view corresponding to FIG. 2 when a heater having a conventional structure is viewed from the zenith, FIG. 4 is a front view similar to FIG. 3 showing a heater structure according to the present invention, and FIG. FIG. 6 is a perspective view showing an example of a mandrel used, FIG. 6 shows another embodiment of the present invention, FIG. 6 (a) is a front view, and FIG. 6 (b) is a side view. 15a …… Rasen coil part, 15b …… Heater foot part, 15c ……
Heater zenith part, 15d …… Primary coil part.

Claims (2)

[Claims] 1. A coil winding section shaped into a double helix, a zenith section formed at one end of the coil winding section, and two foot sections arranged at the other end of the coil winding section. In the indirectly heated cathode heater, the outer diameter of the coil winding portion viewed from the zenith portion is larger in the direction orthogonal to the direction connecting the two foot portions. Heater for hot cathode. 2. A heating portion located at the zenith portion formed at one end of the coil winding portion has a substantially linear shape, and the direction of the substantially linear portion is the double helix shaped coil winding portion. The heater for an indirectly heated cathode according to claim 1, wherein the heater substantially coincides with the minor axis direction when viewed from the zenith.