JPS6014728A - Method and device for heating electrode or electrostatic lens of electron gun of cathode ray tube during production - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for heating an electrode or lens of an electron gun of a cathode ray tube, particularly a cathode ray tube for color television, during manufacture.

A television picture tube, generally a cathode ray tube, includes one or more electron guns for generating one or more beams for the excitation of the luminescent material forming the screen.

The electron gun includes on the one hand an emitter cathode heated by a filament and on the other hand a set of electrodes, commonly referred to as a grid, and an electrostatic lens. The grids are composed of an electrode, namely a Bohnelt electrode G1, to which a generally negative variable voltage is applied to the cathode to control the excitation of electrons, in particular their quantity, and a second electrode G1 for accelerating the electron beam.
2, and two electrostatic lenses G3 and G4 for focusing the electron beam.

This electron gun is placed at the rear of the vacuum enclosure forming the cathode ray tube.

During the manufacture of cathode ray tubes, subsequent to mounting the electron gun within the enclosure and evacuating the enclosure, the cathode is heated to a temperature above normal operating temperature in order to stabilize the materials that make up the cathode. A voltage is then applied to the grid in order to purify the cathode ray tube, ie to remove undesirable gas particles absorbed by so-called gaseous substances. This type of purification operation consists, on the one hand, in a sparking operation, in which a high pressure of the order of 50 kilovolts is applied between grid G4 and the other grids or the grounded cathode, and, on the other hand, in a heating action on the different grids. These heating effects take place in several stages. In one of these stages, a low voltage, high current current flows between the cathode and the grid G2, which makes it possible to heat the grid G2 and serves to purge the gas from the cathode ray tube. In another step, a voltage is applied between the cathode and grid G3 to generate a current that heats this grid G3.

A voltage generator is utilized to provide a potential difference between the cathode and the grid for grid heating effects. The output of this voltage generator is often connected to the grid via a low value resistor, this low value having the purpose of limiting the current intensity absorbed in case of a short circuit. At the same time, the cathode heating filament is powered. Thus, an electric current flows between the cathode and the grid (forming the anode) and heats the anode for the purpose of performing a degassing or purification operation.

The inventor has found that satisfactory results are not always obtained with the known methods, ie purification or degassing operations do not always give the desired quality. In particular, in one and the same cathode ray tube manufacturing equipment line, the phenomenon known as "afterglow" is manifested by the emission of screen light for a considerable period of time after a television receiver equipped with a cathode ray tube is turned off. There are some drawbacks.

Research conducted by the inventors has demonstrated that the cause of this drawback is due to: That is, even for essentially the same type of cathode ray tube, the dimensions of the various cathodes and grids vary from cathode ray tube to tube due to unavoidable variations during mass production. Similarly, the distance between the cathode and the various grids is also not constant. As a result of this discovery, it was found that even if a voltage generator supplies a constant voltage, the current generated is not of constant strength. Therefore, the power applied to the cathode to be heated is not constant and is often The temperature applied is too low, resulting in lower power than would allow effective contaminant removal.

To eliminate this drawback, according to the invention, the parameters of the feeding circuit are such that the current intensity between the cathode and the anode has a practical influence on changes in the dimensions of the cathode and the grid, as well as on changes in the distance between the cathode and the grid. be chosen so as not to be

As a result, the anode heating power is virtually equal and constant. This power is chosen such that the temperature achieved by the grid is above a certain critical value.

When a resistor is placed in series with the generator to eliminate said variations, it is preferred to give a high value to the voltage of the generator and the series resistance. In fact, in this case a change in the value of the dynamic resistance between cathode and anode does not affect the intensity of the heating current of the anode only slightly. However, it is not essential that the series resistance has a high value compared to the dynamic resistance. In practice, if the series resistance is of the same order of magnitude as the average dynamic resistance between cathode and anode to heating power (and temperature) above a critical value at which the contaminant removal operation is insufficient. has been proven to be sufficient.

Next, the present invention will be explained with reference to the drawings.

Referring to FIG. 1, after the grid is attached to a glass enclosure (not shown) and the enclosure is placed under vacuum,
A voltage generator 11 is used to heat the grid (electrode or electrostatic lens) of the electron gun (not shown in detail) of a television picture tube. The highest voltage terminal 12 of this generator 11 is connected via a resistor 13 of value R to the grid 10 forming the anode, and the lowest potential terminal 14 of this generator 11 with common ground is connected to the cathode 15 and the current is supplied to the heating filament 16 of this cathode. This means that from cathode 15 to anode 10
A closed circuit is formed by the electrons emitted toward the

According to the invention, sufficiently high values are chosen for the voltage 1 and the resistance 13 so that changes in the value r of the dynamic resistance between the cathode 15 and the anode 10 have little effect on the current intensity in the circuit.

In a more specific method, {circle around (2)} and R are chosen sufficiently high to allow for variations in the value of the dynamic resistance r, but so that the heating power always remains at a value sufficient to effect a proper degassing operation. That is, the values ■ and R are such that even for the highest possible value of r, the current intensity I is sufficient for contaminant removal. These different values are such that, as mentioned above, the heating power supplied to the anode 10 is also independent of changes in the dimensions of the cathode 15 and the anode 10 and changes in the distance between the cathode 15 and the anode 10. It is. The same device can be used consisting of cathode ray tubes of different types, ie cathode ray tubes with different dimensions of the cathode 15 and anode 10 and different cathode-anode spacings.

Experiments have demonstrated that it is sufficient for resistor 13 to have a magnitude comparable to the average value rffl of the dynamic resistance between cathode 15 and anode 10 in order to eliminate said variations.

In order to demonstrate the advantages of the invention, comparative experiments between the known method and the method of the invention are described below.

A first example is the so-called low voltage "extraction" process.

In the hitherto known method, this method consists of applying a voltage of between 300 and 400 volts to the grid G2 of the electron gun, with a resistance in series with the generator of 2.5 and 5
It had a value between kiloohms.

In this case, changing the process from one cathode ray tube to another did not always produce satisfactory results.

In the method of the invention, a generator 1 generating a voltage of the order of 800 to 900 volts (i.e. 850 volts) is used.
1 is used, and the value R of the resistor 13 is, for example, 31 and 3
between 9 kilohms, or between 30 and 40 kilohms. The results obtained are in this case even more satisfactory and the heating power is more constant.

A second embodiment will be described with reference to FIG.

This second embodiment relates to heating grid G3 to prevent contamination of grid G3 and to prevent the aforementioned "afterglow" effect.

In the same known method, a generator is used which produces a voltage of the order of 800 to 1000 volts;
It is connected to grid G3 via a 9 kilohm resistor. Another generator generating +450 volts is connected to grid G2 through a 5 kilohm resistor, while grid G1 and the cathode are grounded. Again, the process is extremely sensitive to dimensional changes.

For this process, the present invention provides +1840 volts (1
It is proposed to use a single voltage generator supplying a positive voltage of the order of 800 volts), and the output terminal of the voltage generator 20. and is connected to grid G3. The terminal 22 of the resistor 21 on the opposite side from the terminal 20 is 47
It is connected via a resistor 23 with a value of 0 kilohms to a terminal 24 which is directly connected to the grid G2. This terminal 24
is grounded via a resistor 25 with a value of 350 kilohms. In this arrangement (forming a voltage divider consisting of resistors 21, 23 and 25), the cathode K and the grid G1
is grounded as in known methods. grid G
The power to heat 3 is more constant in this arrangement than in known method arrangements. Stability of the voltage of grid G2 contributes to stability of power consumed by grid G3.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the method of the invention. FIG. 2 is a diagram of the circuit utilized to heat grids G3 and G2 of a color television picture tube. (Main reference numbers) 10 grid, 11 generator, 15 cathode,
16 heating filament, 13 resistance, 21.23.
25 Resistance Patent Applicant Video Color Varnish, Ar. Representative Patent Attorney Masahiko Arai

Claims (6)

[Claims] (1) During the manufacture of a vacuum cathode ray tube, the cathode and the grid are heated to generate a current to heat the grid, in a method for heating the grid electrode or electrostatic lens of an electron gun placed inside the vacuum cathode ray tube. In between, apply a certain voltage by a voltage generator and select the parameters of the supplied current so that the current intensity is not particularly affected by changes in the dimensions of the cathode and the grid and by changes in the distance between the cathode and the grid. A method characterized in that the temperature reached is higher than a certain critical value. (2) A resistor is arranged in series with the generator to eliminate said variation, and the voltage and resistance of the generator are chosen to have sufficiently high values. Method described. 3. A method as claimed in claim 2, characterized in that the resistor in series with the voltage generator has a value of the same magnitude as the average dynamic resistance between the cathode and the grid. (4) The voltage of the generator is of the order of 850 volts and the value of the series resistor is between 30 and 40 kilohms so that a low voltage of the order of 400 volts is applied to the grid. The method described in Section 3. (5) A patent claim characterized in that the voltage of the generator is of the order of 1,800 volts and the value of the series resistance is of the order of 40 kilohms, so that a voltage of the order of 800 to 1,000 volts is applied to grid G3. The method described in Clause 3 of the scope. (6) During the manufacture of a vacuum cathode ray tube, in a device that heats grids G2 and G3 of the electron gun placed inside the vacuum cathode ray tube, there is a gap between the cathode and grids G2 and G3 so as to generate a current that heats these grids. consisting of a single voltage generator that applies a specific voltage to the grid, a resistor in series with the generator whose resistance is 140 kilohms, the same magnitude as the average dynamic resistance between the cathode and the grid; and grids G3 and G2 are connected to separate taps of a voltage divider, the resistor arrangement comprising a voltage divider such that the stability of the voltage of grid G2 contributes to the stability of the current intensity of grid G3, The voltage of the device is about 1800 volts, and the grid G
A device characterized in that the voltage applied to grid G2 is about 400 volts, and the voltage applied to grid G2 is about 800 volts.