JPS6216491B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a hot cathode structure, in which heat loss is small and the relative positional relationship between the cathode and other electrodes, such as an anode electrode, hardly changes when the cathode is heated to a high temperature. The purpose is to provide a cathode holding structure.

The requirement to maintain hot cathodes with as low heat loss as possible is particularly strong in image pickup tubes such as home video cameras that are powered by an independent power supply, and in particular impregnated cathodes, which suffer from increased heat loss due to high operating temperatures. Particularly strong in maintaining the tendency to

On the other hand, sufficient holding strength of the cathode is also strongly required to prevent the characteristics of the image pickup tube from being significantly degraded due to fluctuations in the position of the cathode due to vibrations or shocks applied from the outside.

In response to such requests, conventionally, for example, the first
The cathode holding structure shown in the figure was used.

In FIG. 1, 1 is an electron emitting surface, 2 is a cylindrical electron emitting surface support that supports the electron emitting surface,
Together with the electron emitting surface 1, it constitutes a cathode. 3 is a ceramic cylinder that supports the support 2; 4 is a metal thermal radiation shield that blocks heat radiation from the support 2; 5 is a G provided between the electron emission surface 1 and the anode 8; _One electrode has a hole 6 on the opposite side of the electron emitting surface 1. 7 is an aperture provided in the anode 8. 9 is a heater that heats the electron emission surface to the operating temperature; 10 and 11 are cathodes, respectively;
Cathode lead wire, making the electrical connection to the G ₁ electrode;
G is _{the 1} lead wire.

The outer diameter of the support 2 is 1.2 mmφ and the length is 3.5 mm, which are generally common dimensions for 2/3-inch image pickup tubes.
To obtain an operating temperature of 1000°C for the cathode, the heater power was required to be approximately 1.2W. This electric power depends on the dimensions and physical properties of the ceramic cylinder 3.
The above power value varies greatly, and the above power value is based on the case that the cylinder 3 has an outer diameter of 1.6 mmφ, a wall thickness of 0.17 mm, a length of 7 mm, and a thermal conductivity of 4×10 ^-4 [cal・mm/mm ² ℃sec] (20 ℃).

In order to further reduce the heater power in this conventional holding structure, it is conceivable to make the ceramic cylinder 3 thinner or longer to increase the heat conduction resistance of the cylinder 3. None of these methods are practical due to their limitations. Furthermore, it is extremely difficult to process ceramics such as cordierite, which have a conductivity even lower than the above-mentioned thermal conductivity, into the above-mentioned thin-walled cylindrical shape, and for this reason, the above-mentioned heater power value is Further reduction is
This is difficult with the above holding structure.

Furthermore, at the stage where the heater 9 is turned on and the support body 2 is heated to the cathode operating temperature, the support body 2 that is heated first undergoes thermal expansion using the junction point a with the ceramic cylinder 3 as a fulcrum. After the support 2 is heated, the temperature of the ceramic cylinder 3 gradually rises, and the thermal expansion that takes place with b as the fulcrum with a time delay overlaps with the electron emitting surface 1.
The distance D to the _G1 electrode varies in a complicated manner with time and settles to a steady value approximately 15 to 20 minutes after the heater is turned on. This distance variation is occurring. During the above 15 to 20 minutes, the amount of electrons emitted from the electron emitting surface 1, and therefore the signal current passing through the aperture 7, also decreases.
Naturally, it fluctuates, and various characteristics of the image pickup tube, such as modulation degree and shedding, are not sufficiently stable. On the other hand, regarding the usage status of imaging cameras at home, 15
In many cases, imaging is completed in ~20 minutes, and in the end, the above-mentioned conventional cameras are used with unstable characteristics.

The present invention eliminates the above two points and provides a cathode holding structure with less heat loss, and will be described below with reference to drawings of one embodiment.

FIG. 2 shows a hot cathode structure that was conceived prior to the present invention, and this will be explained first. The metal conductive flat plate 5 is a cathode abutting body having a contact portion 17 in which a protrusion 12 substantially integral with the support 2 of the electron emitting surface 1 abuts via a ceramic ring 18. ,
A hole 6 is provided at a portion opposite to the electron emitting surface 1 . The corresponding contact body 5 is substantially integrally provided with a metal cylindrical member 16 having a coil spring support 19 against which one end of a substantially cylindrical coil spring 15 abuts via a ceramic ring 14 . Further, the other end of the coil spring 15 is in contact with the support body 2 at a position indicated by 13.

The coil spring 15 is in a compressed state as shown in the figure, and presses the support body 2 into contact with the abutting body 5 via the ceramic ring 18. In this state, the distance between the electron emitting surface 1 and the flat plate 5 is approximately determined by the thickness of the ring 18.

The cathode structure configured in this manner is fixed to the anode electrode 8 via the electrical insulating material 20, and the flat contact body 5 functions as a _G1 electrode. Further, the metal cylindrical member 16 functions as a thermal radiation shield that blocks thermal radiation from the cathode.

Incidentally, if the _G1 electrode constituted by the contact body 5 is always used at the same potential as the cathode, the ceramic rings 18 and 14 are not necessary. At this time, protrusion 1
The distance between the tip of the electron emitting surface 1 and the electron emitting surface 1 can be easily reset as necessary using an appropriate jig. In the hot cathode assembly constructed as described above, effects regarding heat loss will be described first.

Since the thermal connection between the support body 2 and the ceramic ring 18 is a point contact connection by the protrusion 12, it has an extremely large thermal conduction resistance. Further, the thermal connection between the support body 2 and the cylindrical member 16 is through the coil spring 15, but increasing the overall length of the wire of the coil spring 15 and increasing the thermal conduction resistance of this portion is the same as that of the coil spring. 15 designs, it can be easily done.

Specific figures are shown below. The material of the coil spring 15 is Hastelloy, which can be used at high temperatures.
The wire diameter is 0.15mmφ, the coil outer diameter is 2.5mmφ, the total number of turns is 7, the free length is approximately 5mm, and the winding pinch is approximately 0.7mm.
mm. The spring constant at this time is approximately 4.2gr/mm
A cathode with a total weight of 21 mg and a ceramic ring 18
It is used compressed to approximately 3.5mm so that it can be held firmly even in the event of a maximum impact of 100G.

Next, when calculating the thermal conduction resistance of this coil spring 15, the cross-sectional area S of the spring wire is S≒1.8×10 ^-2 mm ² ,
The total length L of the wire is L≒55mm, and the thermal conductivity λ of Hastelloy is λ≒4.2×10 ^-3 at around 500℃.
[cal·mm/mm ² sec°C], and therefore, the thermal conduction resistance R is R=1/λl/S≈6.6×10 ⁵ [sec°C/cal]. On the other hand, the heat conduction resistance of the ceramic cylinder in the conventional structure is similarly R=2.3×10 ⁴ [sec°C/cal], and as a result, the heat conduction resistance of the coil 15 is as follows: The amount of heat is approximately 29 times greater, and the amount of heat escaping through the coil 15 by thermal conduction is almost negligible.

Figure 3 A and B show the heater power and electron emitting surface 1 in the conventional holding structure and the holding structure shown in Fig. 2.
A comparison of the relationship between temperature and temperature is shown. In the hot cathode structure shown in FIG. 2, the power is reduced by about 0.16 W at a cathode operating temperature of around 1000°C.

In addition, due to thermal expansion of the support 2, the electron emitting surface 1
It is obvious from the structural point of view that the distance variation between the support body 2 and the support body 2 is significantly smaller than that in the conventional example, and can be completely ignored in practical terms. Further, the distance between the _G1 electrode 5 and the electron emission surface 1 can be easily and precisely adjusted by changing the thickness of the ring 18.

Next, an embodiment of the present invention is shown in FIG. The numerals in FIG. 2 and FIG. 4 correspond, and the same numerals represent the same thing.

In FIG. 4, the coil spring 15 is configured such that each winding is in close contact with the adjacent winding. As a result, (1) the wire length of the coil spring 15 increases significantly compared to that shown in FIG. Above, equal to zero.

(2) Since each winding of the coil spring 15 arranged to enclose the cathode is in close contact with each other, it can also function as a thermal radiation shield for the cathode. And this thermal radiation shield is
For the reason stated in (1) above, it functions as an ideal thermal radiation shield that virtually never loses the amount of heat obtained by absorbing a portion of the thermal radiation from the cathode through thermal conduction. Therefore, it is possible to obtain the effect that the thermal radiation loss of the cathode can be further reduced than in the hot cathode structure shown in FIG.

Regarding the embodiment shown in FIG. 4, the relationship between the heater power and the temperature of the electron emission surface 1 is shown in FIG. 3C.
Compared to the hot cathode structure shown in Figure 2, power is further reduced, and at a cathode operating temperature of 1000°C,
Compared to the conventional example, power consumption is reduced by approximately 0.25W.

As described above, the present invention solves the conventional drawbacks and exhibits excellent effects as a cathode holding structure.

FIG. 5 shows another embodiment of the invention. Figure 5 shows the case where the cathode and the _G1 electrode operate at the same potential.
5 is fixed by spot welding to the support body 2 and a spring support portion 19 that is substantially integral with the contact body 5;
Due to the tensile force of the coil spring 15, the cathode is moved against the contact body 5.
is under pressure.

Since the coil spring 15 is tightly wound to also serve as a heat radiation shield, a separate radiation shield for the cathode is not required. The coil spring 15 is fixed to the support body 2 and the contact body 5 by spot welding.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing a conventional hot cathode structure;
The figure is a sectional view of a hot cathode structure conceived prior to the present invention, FIG. 3 is a characteristic diagram of heat loss for explaining the present invention, and FIGS. FIG. 3 is a cross-sectional view of the cathode structure. DESCRIPTION OF SYMBOLS 1... Electron emission surface, 2... Support body, 5... Contact body, 1
5...Coil spring.

Claims (1)

[Scope of Claims] 1. A cathode having an electron emitting surface for thermoelectrons and an electron emitting surface supporter that supports the electron emitting surface and is substantially integral with the electron emitting surface, including a substantially cylindrical or substantially conical coil spring. and a cathode abutting body with which a part of the cathode abuts in a pressed state directly or indirectly through another member, one end of the coil spring abuts or fixed on the cathode, and the other end of the coil spring abuts or is fixed to the cathode, One end is in contact with or fixed to a coil spring support part that is substantially integral with the cathode contact body, and is connected to the cathode contact body directly or indirectly through another member by the spring force of the coil spring. The hot cathode assembly is configured to be pressed and supported, and each winding of the coil spring is in substantially close contact with an adjacent winding. 2. A hot cathode structure in which the cathode abutting body is a conductive flat plate, and a hole is provided in a portion of the flat plate opposite to the electron emitting surface, so that the flat plate operates as a _G1 electrode.