JPH05151884A - Electronic tube - Google Patents

Abstract

PURPOSE:To provide an electronic tube wherein even in the case of using an inverter power supply, a filament temperature can be relatively high set and unstability of oscillation can be avoided almost without generating deformation even when the temperature of a cathode filament is set to such as a high temperature of 1880 to 1920 deg.C. CONSTITUTION:In an electronic tube, its cathode filament 15 is composed of tungsten containing thorium oxide by a 0.5 to 2wt% range and potassium by a 20 to 100ppm range, and the above-mentioned end can be attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron tube such as a magnetron, and more particularly to an improvement of its cathode filament.

[0002]

2. Description of the Related Art Conventionally, thorium-tungsten (Th-W) has been used in a spirally heated cathode filament of an electron tube such as a magnetron. This thorium / tungsten has features such as high electron emission density and instantaneous operation.

By the way, as a recent tendency of the microwave oven,
A high frequency inverter system (hereinafter referred to as an inverter power source) has been widely used for a power source section. conventionally,
A magnetic resonance type power supply using a magnetic leakage type transformer and a capacitor has been used. However, in this method, the output control of the magnetron can be performed only at a substantially constant output power in the range of 400 to 600 W or intermittent output control. , It is not enough to handle complicated cooking menus. The operation of the inverter power supply has the following characteristics when viewed from the magnetron side. (1) The filament voltage is affected by the secondary high voltage of the transformer. That is, the filament voltage changes in conjunction with the magnetron anode voltage. (2) A wide range of output control is possible by controlling the anode current.

[0004]

When the conventional magnetron is used for the inverter power supply having the above-mentioned characteristics, the following problems may occur.

Generally, a ferrite magnet is used in a magnetron for a microwave oven. Since the thermal demagnetization is extremely large, the anode voltage greatly drops as the anode temperature rises. Along with this, the filament voltage drops,
The filament current (If) may decrease, and as illustrated in FIG. 3, the current may decrease by 2 to 3A. In addition, the magnetron has an electron reverse impact, and normally, when the anode current is large, the reverse impact increases and the filament temperature rises. In fact, if the anode current is reduced to a small value with the output control, the reverse impact will decrease,
As shown in FIG. 4, the filament temperature decreases. When the anode voltage is sufficiently reduced when the anode voltage is sufficiently reduced, the filament temperature is lowered too much and oscillation cannot be maintained (If reduction due to Po control in FIG. 3). In order to avoid this, the filament temperature (filament current) at the initial stage of operation is set high. However, thorium-tungsten has a very high temperature (generally 1880 ° C).
Above) and deformation will occur.

In short, when a magnetron is used in the inverter power supply, the change in filament current is larger than that in the conventional power supply system. Therefore, the upper limit of filament current is due to life (deformation), and the lower limit is due to insufficient thermoelectron emission. Oscillation instability must be taken into consideration (generally 1600 ° C or higher).

According to the present invention, the filament current (filament temperature) during operation can be set to a high value, oscillation instability due to current decrease can be avoided, and accelerated operation instability due to deformation of the cathode filament can be avoided. The purpose is to provide an electron tube that can be prevented.

[0008]

According to the present invention, a spirally heated direct-heating cathode filament contains thorium oxide in an amount of 0.5 to 2.0.
20% to 100 ppm of potassium in the range of weight%
It is an electron tube made of tungsten contained in the range of.

[0009]

According to the present invention, since the initial filament current can be set high, instability of oscillation due to a decrease in filament current after operation can be avoided, and accelerated malfunction due to deformation of the cathode filament can be avoided.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. An electron tube according to the present invention, such as a magnetron for a microwave oven, is constructed as shown in FIG.

That is, a plurality of vanes 12 are radially arranged inside the anode cylinder 11 made of copper, which is a part of the vacuum container, to form a cavity resonator. The upper and lower ends of each vane 12 have a pair of large and small strap rings 13, 14 respectively.
Are linked by every other. In the electron action space S surrounded by the free ends of the plurality of vanes 12, a spiral directly heated cathode filament 15 is arranged along the axis of the anode cylinder 11, and both ends thereof are end shields 16 and 17, respectively. Is stuck to. The end shields 16 and 17 are fixed to the cathode support rods 18 and 19, respectively. The cathode filament 15 is a feature of the present invention and will be described in detail later.

Further, substantially funnel-shaped iron pole pieces 20 and 21 made of iron are fixed to both open ends of the anode cylinder 11, and one of the pole pieces 20 is also a vacuum vessel. A cylindrical metal container 23, which serves as a part, is covered, and the other pole piece 21 is similarly covered with a cylindrical metal container 24. Each metal container 23, 24 is made of an iron material, has nickel plating adhered to the surface, and is also hermetically welded to the anode cylinder 11. Further, reference numeral 22 in the figure is derived from one of the vanes 12 and penetrates through the pole piece 20 to form a metal container 23.
It is an antenna lead extending inside.

Generally, a cathode filament of a magnetron for a microwave oven is made of thorium-tungsten having a diameter of 0.4 to 0.6 mm, and a carburized layer is further formed on the surface thereof.
In No. 5, potassium is further added. That is, it is composed of tungsten (W) containing thorium oxide (ThO ₂ ) in the range of 0.5 to 2 wt% and potassium (K) in the range of 20 to 100 ppm.

In such a cathode filament 15, the dope effect (dope tungsten) due to bubbles is positively utilized, and the longitudinal (L) / lateral (W) ratio L / of the crystal after operation is L /
W is capped to improve heat distortion resistance. FIG. 2 is a model view showing the L / W ratio of the crystal in the axial cross section of the cathode filament 15.

In the cathode filament of the conventional electron tube, the thorium oxide particles keep the L / W ratio,
It was found that it is not sufficient in the high temperature range exceeding 1900 ° C, and the heat distortion resistance is improved in the high temperature range by the synergistic effect with the doping effect of the bubble of potassium.

As an example, a trial wire, which is used in a magnetron for a microwave oven, having a diameter of 0.5 mm and containing 1 wt% of thorium oxide and having 60 ppm of potassium added thereto, was subjected to a JIS heating test (V-shape). : 80%
When evaluated by the 90% FC method, which is further strengthened than the FC method), the sag value was improved to 20 to 25 of the conventional material and 10 to 12 in the embodiment of the present invention.

Further, as a result of experiments, it was found that even when the cathode filament temperature was set to 1880 to 1920 ° C. by mounting it on an actual magnetron, no deformation occurred. As a result, even when used as an inverter power source, the cathode filament temperature could be set relatively high and oscillation instability could be avoided.

When the amount of thorium oxide is less than 0.5% by weight, the supply of thorium monatoms to the electron-emissive portion of the surface is reduced at an early stage, the life is shortened, or tungsten crystal growth is caused. Thermal deformation is likely to occur. On the contrary, when the amount of thorium oxide is more than 2.0% by weight, forging and drawing after sintering become difficult.
If the potassium content is less than 20 ppm, thermal deformation tends to occur. On the contrary, if the potassium content is more than 100 ppm, the resistivity increases, drawing is difficult, and the electron tube is easily contaminated due to the evaporation of thorium.

In this embodiment, the magnetron for a microwave oven has been described, but the same reliability can be expected when used in an electron tube having a cathode filament used in other high temperature regions, such as a transmitter tube or an X-ray tube. ..

[0020]

As described above, according to the present invention,
Spiral direct heating type cathode filament contains thorium oxide 0.5
To 2.0% by weight, and potassium 20 to 1
Since it is made of tungsten contained in the range of 00 ppm, the temperature of the cathode filament should be 1880 to 192.
Even if the temperature is set to a high temperature of 0 ° C, there is almost no deformation. As a result, even when using the inverter power supply,
The filament temperature can be set relatively high, and oscillation instability can be avoided.

[Brief description of drawings]

FIG. 1 is a sectional view showing a main part of an electron tube (magnetron for microwave oven) according to an embodiment of the present invention.

FIG. 2 shows the crystal L / W in the axial cross section of the cathode filament.
The model figure which shows a ratio.

FIG. 3 is a characteristic curve diagram showing the relationship between operating time and filament current (If) and filament temperature (Tf) in a microwave oven using an inverter power supply.

FIG. 4 is a characteristic curve diagram showing a relationship between a filament current (If) and a filament temperature (Tf) in an output of a microwave oven using an inverter power supply.

[Explanation of symbols]

 15 ... Cathode filament.

Claims (1)

[Claims] 1. An electron tube provided with a spiral directly heated cathode filament, wherein the cathode filament contains thorium oxide in an amount of 0.5 to 2.
0 wt% range and potassium 20 to 100 pp
An electron tube comprising tungsten contained in the range of m.