US3641391A

US3641391A - Device for restoring cathode emission in cathode-ray tube guns

Info

Publication number: US3641391A
Authority: US
Inventors: Albert R Badewitz
Original assignee: BELTRON Inc
Current assignee: BELTRON Inc
Priority date: 1969-06-06
Filing date: 1969-06-06
Publication date: 1972-02-08
Anticipated expiration: 1989-02-08

Abstract

The heater filaments of the cathode-ray guns of a color television picture tube are connected across the low-voltage secondary winding of a transformer, the primary of which is connected across the terminals of a conventional household alternating current supply through a thermistor to effect gradual increase of potential across the secondary winding. As the filament voltage increases to normal operating potential, the degree of intensity of the lamps indicates the relative electron emission of the cathodes. As the filament voltage increases above normal operating potential, the temperature of the filament and cathode are increased above normal to effect progressive removal of contaminating materials from the cathodes. The cathodes are connected to one terminal of the alternating current supply and the control grids are connected to the other terminal of the alternating current supply each through a dropping resistance, circuit breaker and indicator lamp, to produce a pulsating direct current which effects progressive drawing of fresh electron emissive material to the surface of the cathodes. This automatic progressive restoration of the cathode is evidenced by progressive brightening of the lamps and when restoration of each cathode is completed, the associated circuit breaker opens automatically to terminate the treatment.

Description

United States Patent Badewitz Feb. 8, 1972 [54] DEVICE FOR RESTORING CATHODE EMISSION IN CATHODE-RAY TUBE GUNS [72] Inventor: Albert Badewitz, Vancouver, Wash.

[73] Assignee: Beltron, Inc., Vancouver, Wash.

[22] Filed: June 6, 1969 [211 Appl. No.: 842,073

Primary Examinerlohn F. Campbell Assistant ExaminerRichard Bernard Lazarus Attorney0liver D. Olson [57] ABSTRACT The heater filaments of the cathode-ray guns of a color television picture tube are connected across the low-voltage secondary winding of a transformer, the primary of which is connected across the tenninals of a conventional household alternating current supply through a thermistor to effect gradual increase of potential across the secondary winding. As the filament voltage increases to normal operating potential, the degree 'of intensity of the lamps indicates the relative electron emission of the cathodes. As the filament voltage increases above normal operating potential, the temperature of the filament and cathode are increased above normal to effect progressive removal of contaminating materials from the cathodes. The cathodes are connected to one terminal of the alternating current supply and the control grids are connected to the other terminal of the alternating current supply each through a dropping resistance, circuit breaker and indicator lamp, to produce a pulsating direct current which efiects progressive drawing of fresh electron emissive material to the surface of the cathodes. This automatic progressive restoration of the cathode is evidenced by progressive brightening of the lamps and when restoration of each cathode is completed, the associated circuit breaker opens automatically to terminate the treatment.

10 Claims, 1 Drawing Figure PATENTEDFEB 81872 ALBERT R. BADEWITZ INVENTOR.

AGENT.

BACKGROUND OF THE INVENTION Restoration of cathode emission of cathode-ray tubes, and 5 particularly television picture tubes, heretofore has involved the application of high-voltage direct current across the cathode and control grid for one or more short intervals of time. There are many disadvantages in such procedure: The application of high voltage direct current effects such a large rush of electrons from thecathode that an excessive amount of the barium oxide or other electron emissive cathode material is removed with the contaminants. The resulting improvement therefore is of short duration and the tube usually is destroyed after a single treatment.

The application of high-voltage direct current also is capable of producing an electrical short between the cathode and control grid. Accordingly, in those very frequent instances in which a short is produced during normal operation of the tube by expansion of the metallic elements during heating, the application of high-voltage direct current almost always insures the production of a permanent short by welding the elements together.

Additionally, costly equipment is required to provide such high-voltage direct current, and expert personnel is needed to operate such equipment since it requires the critical supervision of electrical quantities appropriate to the various types of cathode-ray tubes.

Further, such equipment is operable only upon one cathode-ray tube gun at a time. The restoration of cathodes of color television picture tubes thus involves the time required to process all three cathodes.

SUMMARY OF THE INVENTION In its basic concept the cathode emission restorer device of this invention applies to the filament of a cathode-ray tube gun a voltage sufficient to heat it above normal operating temperature, to effect release of contaminants from the cathode. The restorer device then utilizes the cathode and control grid of the cathode-ray tube being restored to rectify conventional household alternating current to low-voltage pulsating direct current which is applied across said cathode and control grid to increase electron flow from the cathode and effect consequent exposure of more barium oxide or other electron emissive material at the surface of the cathode.

It is by virtue of the foregoing basic concept that the principal objective of this invention is achieved, namely to overcome the many disadvantages of prior restoring devices, as enumerated hereinbefore.

Another object of this invention is to provide a device of the class described which functions to restore cathode emission with minimum loss of electron emissive material, whereby restoration may be repeated many times and the useful life of the cathode-ray tube thus correspondingly extended.

Another object of this invention is to provide a device of the class described which is operable during the restoring operation automatically to repair electrical shorts which may exist between the cathode and control grid.

Still another object of this invention is the provision of a device of the class described which is usable with cathode-ray tubes having one or a plurality of cathodes.

A further object of this invention is the provision of a device of the class described which is operable with color television picture tubes to restore the emission quality of all three cathodes simultaneously.

A further objective of this invention is the provision of a device of the class described which is of simplified and inexpensive construction and is automatic in operation, whereby it is available for purchase at reasonable cost and is usable effectively by home television owners for repeated periodic restoration of television picture tubes.

The foregoing and other objects and advantages of this invention will appear from the following detailed description,

taken in connection with the accompanying drawing of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the drawing is a schematic diagram of an electric circuit of a cathode emission restoring device embodying the features of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT For purposes of illustration the drawing shows a portion of a color television picture tube 10 which includes three color cathode-ray tube guns. Thus, there is shown the filament I2, cathode l4 and control grid 16 of the green color.cathode-ray tube gun, the filament l8, cathode 20 and control grid 22 of the red cathode-ray tube gun, and the filament 24, cathode 26 and control grid 28 of the blue cathode-ray tube gun. These elements connect to corresponding pins (not shown) projecting from the base of the tube. Normally these pins are connected electrically to appropriate components of a television receiver through a complementary female connector. However, for purposes of this invention the conventional female connector is removed and a substitute female connector 30 associated with the device of this invention is attached to the prns.

The electrical conductors leading from the female connector 30 are carried in an elongated flexible cable of conventional construction. The cable may be of any desired length to permit placement of the instrument case 32 of the device at a convenient location for use.

On the front panel of the case therc'are mounted three

indicator lamps

34, 36 and 38, preferably colored to correspond to the associated color guns of the picture tube 10. A neon or other glow discharge tube 40 also is mounted on the case. Projecting from the case are flexible electrical conductors providing the

terminals

42 and 44 for connection to a conventional household supply of 1 lO-volt alternating current.

Within the case is mounted an alternating current stepdown transformer 46. The opposite ends of the primary winding 48 of the transformer are connected to the

terminals

42 and 44, one through a thermistor S0. The opposite ends of the secondary winding 52 of the transformer are connected through

conductors

54 and 56 to the opposite ends of the filaments of the cathode-ray tube. Although the filaments are shown connected together in series, it will be understood that they may be connected in parallel.

The function of the thermistor is to increase the voltage to the filaments slowly to a value greater than normal operating potential, so as to prevent damage to the filament. In this regard, the thermistor may be replaced by a surgister, or by a rheostat or similar device, placed either in the primary or secondary circuit. Alternatively, the secondary winding may be provided with multiple taps selectable by a conventional multiple position switch.

The cathodes are connected in parallel through conductor 58 to terminal 44 of the alternating current supply. The control grids are connected in parallel to the other terminal 42, each through a series arrangement of one of the indicator lamps, a circuit breaker 60 and a voltage dropping resistor 62. The cathode and control grid of each gun thus is connected across the

terminals

42, 44 of the alternating current supply selectively through its associated circuit breaker. When all of the circuit breakers are in their normally closed position, the cathode and control grid of all three guns are connected simultaneously across the supply terminals.

The circuit breakers 60 function to open each cathode and control grid circuit when current flow reaches a predetermined value, as explained hereinafter. The dropping resistors 62 serve to lower the voltage in each cathode and control grid circuit to a desired level, for example about 50 volts.

Means also is provided for indicating conveniently the existence of a short between the heater filament and cathode of each gun. This is provided by the neon or other glow discharge tube 40 which is connected across the

common conductors

56 and 58 leading from the filaments and cathodes. The dropping resistor 64 connects the tube across the

supply terminals

42, 44.

The operation of the device described hereinabove is as follows:

Assuming it is desired to restore electron emission of the cathodes of a color television picture tube, the female connector normally associated with the tube is removed and replaced by the adapter 30 associated with the restoring device. In this regard it will be understood that the device will be provided with a number of adapters to accommodate connection to the various types of picture tubes in use.

With the primary winding 48 of the transformer connected to the alternating current supply, through the

terminals

42 and 44, the voltage across the primary winding 50, and hence the secondary winding 52, gradually is increased by operation of the thermistor 50. As the low voltage applied to the filaments increases to normal filament operating potential, and with the circuit breakers 60 in their normally closed position, the absence of, or only faint illumination from, the indicator lamps gives automatic indication that electron emission from the cathodes is below normal. This would confirm the lack of proper brightness and contrast on the screen of the picture tube.

The thermistor 50 operates to increase the voltage to the filaments slowly to a value greater than normal operating potential. Usually this potential is not substantially greater than twice the normal operating potential. in any event it is not sufficient to burn out or otherwise damage the filaments. However, this higher than normal filament potential causes the filaments to be heated to a temperature higher than normal, to effect automatic removal of contaminants from the cathode.

Simultaneously with the application of filament potential, alternating current from the

supply terminals

42, 44 is applied across the cathode and control grid of each of the color guns. Each cathode and control grid functions to rectify this alternating current, to produce a pulsating direct current at the frequency of the alternating current supply. The pulsating direct current flowing from the cathode to the control grid has the effect of automatically drawing to the surface of the cathode molecules of barium oxide or other electron emissive substance of which the cathode is made.

The foregoing restoration process progresses over a period of time, depending upon the degree of contamination of the cathodes and the magnitude of potentials applied to the filaments and across the cathodes and control grids of the color guns. In any event, visual evidence of this progress is provided automatically by the indicator lamps which increase progressively in brightness. Color balance between all guns of the picture tube thus is afforded by visual comparison of brightness of the lamps. If desired, the lamps may be replaced by indicating meters.

Automatic termination of the restoration process is provided by the circuit breakers 60. These are chosen to open when current flow reaches a magnitude corresponding to the desired degree of electron flow from the cathodes being restored.

In the event restoration of electron emission of one gun is completed before another, the circuit breaker associated with the completed gun will open, allowing the restoration process to proceed automatically on the other guns.

It will be apparent that the circuit breakers may be omitted and that any desired circuit may be opened manually simply by unscrewing the associated indicator lamp. Alternatively, the circuit breakers may be replaced by on-off switches for manual operation.

Simultaneously with the restoration process the pulsating direct current flowing from the cathode to the control grid of a gun has the effect of automatically repairing any electrical short that might exist between the cathode and the control grid. Such shorts generally occur upon heating of the elements, which heating tends to expand the elements into physical contact. However, as the elements approach mutual contact the pulsating direct current arcs across the elements and automatically burns away sufficient material to eliminate the short. The effect of this pulsating direct current is different from the effect of a steady direct current which, under the same circumstances, effects welding together of the elements.

The operation of the pulsating direct current to effect repair of electrical shorts between the cathode and control grid is automatic, as will be apparent, and will occur without the knowledge of the operator of the device.

lf an electrical short between the cathode and control grid exists at the time the device is applied, the associated circuit breaker will open to indicate it. If the circuit breaker is not employed, the indicator lamp will burnout, since it acts as a current limiting device or fuse.

Simultaneously with the testing and restoring procedure, visual indication is given automatically of the existence of an electrical short between a filament and cathode,.by extinguishing of the neon lamp 40. Correction of this problem generally is made by use of an isolation transformer to separate the filament supply of the picture tube from the filament supply of the other tube components in the television receiver.

The restoring device described hereinbefore also may be used to restore electron emission of the single cathode of a black and white television picture tube. In such instance the device is connected to the picture tube by the use of an appropriate adapter 30 which connects the filament to the secondary winding of the transformer, the cathode to one terminal of the alternating current supply and the control grid to the other terminal of the supply through one of the series arrangements of indicator lamp, circuit breaker and dropping resistance. The procedure for checking and restoring electron emission is the same as described hereinbefore.

It will be apparent that various changes may be made in the size, number, type and arrangement of parts described hereinbefore without departing from the spirit of this invention.

Having now described my invention and the manner in which it may be used, I claim:

1. A device for restoring electron emission of the cathode of a cathode ray tube gun having a filament, a cathode and a control grid, the device comprising a. a low-voltage electric circuit arranged for connecting across the filament of the cathode-ray tube a voltage greater than normal filament operating potential, the lowvoltage circuit including voltage control means for increasing the voltage to the filament from normal operating potential to said greater than normal potential,

b. an alternating current circuit arranged for connecting a source of alternating current not exceeding about llO volts across the cathode and control grid of the cathoderay tube, and

. electrical indicator means removably connected in said alternating current circuit for indicating and interrupting the flow of electrons from the cathode to the control grid of the cathode-ray tube.

2. The device of claim 1 wherein the indicator means is an electric lamp.

3. The device of claim 1 including circuit breaker means in said alternating current circuit for opening the latter automatically upon attainment of a predetermined current flow through said circuit.

4. The device of claim 1 including means operatively associated with the low-voltage electric circuit for connecting across the filament of the cathode-ray tube normal filament operating potential for testing the magnitude of electron flow from the cathode to the control grid prior to applying said greater filament voltage.

5. The device of claim 1 wherein the low-voltage electric circuit comprises the secondary winding of a transformer, the primary winding of which is connected to said source of alternating current.

6. The device of claim 1 including electric indicator means interconnecting the low-voltage and alternating current circuits for connection across the filament and cathode of a cathode-ray tube for indicating an electrical short therebetween.

7. The device of claim 1 for restoring simultaneously electron emission of the cathodes of a plurality of cathode-ray guns of a color television picture tube, wherein the alternating current circuit includes means for connecting the cathodes and control grids of the plurality of guns simultaneously across the alternating current supply, and the indicator means comprises an electric lamp for each gun.

8. The device of claim 7 wherein each lamp corresponds in color to the color provided by its associated gun.

9. The device of claim 8 including circuit breaker means in the circuit of each cathode and control grid for opening said circuit automatically upon attainment of a predetermined current flow through said circuit.

10. A device for restoring electron emission of the cathodes of a plurality of cathode-ray tube guns of a color television picture tube wherein each gun has a filament, a cathode and a control grid, the device comprising:

a. a filament voltage circuit arranged for connecting across the filaments of the guns a voltage greater than normal filament operating potential, and including voltage control means for increasing the voltage to the filaments from normal operating potential to the greater than normal potential,

b. an electric circuit arranged for connecting a source of electric potential not exceeding about volts across the cathode and control grid of each gun, and

c. electrical indicator means removably connected in the cathode and control grid circuit of each gun for indicating and interrupting the flow of electrons therebetween.

Claims

1. A device for restoring electron emission of the cathode of a cathode ray tube gun having a filament, a cathode and a control grid, the device comprising a. a low-voltage electric circuit arranged for connecting across the filament of the cathode-ray tube a voltage greater than normal filament operating potential, the low-voltage circuit including voltage control means for increasing the voltage to the filament from normal operating potential to said greater than normal potential, b. an alternating current circuit arranged for connecting a source of alternating current not exceeding about 110 volts across the cathode and control grid of the cathode-ray tube, and c. electrical indicator means removably connected in said alternating current circuit for indicating and interrupting the flow of electrons from the cathode to the control grid of the cathode-ray tube.

2. The device of claim 1 wherein the indicator means is an electric lamp.

10. A device for restoring electron emission of the cathodes of a plurality of cathode-ray tube guns of a color television picture tube wherein each gun has a filament, a cathode and a control grid, the device comprising: a. a filament voltage circuit arranged for connecting across the filaments of the guns a voltage greater than normal filament operating potential, and including voltage control means for increasing the voltage to the filaments from normal operating potential to the greater than normal potential, b. an electric circuit arranged for connecting a source of electric potential not exceeding about 110 volts across the cathode and control grid of each gun, and c. electrical indicator means removably connected in the cathode and control grid circuit of each gun for indicating and interrupting the flow of electrons therebetween.