This type the 45AX FST TUBE BY PHILIPS WAS WIDELY USED AROUND THE WORLD and fabricated form more than 22 YEARS.
CRT TUBE PHILIPS A59EAK(xx)X(xx) FLAT SQUARE Hi-Bri COLOUR PICTURE TUBE 45AX SYSTEM
• Flat and square screen
• 110° deflection
• In-line, hi-bi potential A RT* gun with quadrupole cathode lens
• 29, 1 mm neck diameter
• Mask with corner suspension
• Hi-Bri technology
• Pigmented phosphors
• Quick-heating low-power cathodes
• Soft flash
• Slotted shadow mask optimized for minimum moire at 625 lines systems
• Internal magnetic shield
• Internal multipole
• Reinforced envelope for push-through mounting
• Anti-crackle coating
GENERAL OPERATIONAL RECOMMENDATIONS
INTRODUCTION
Equipment
design should be based on the characteristics as stated in the data
sheets. Where deviations from these general recommendations are
permissible or necessary, statements to that effect will be made. If
applications are considered which are not referred to in the data sheets
of the relevant tube type, extra care should be taken with circuit
design to prevent the tube being overloaded due to unfavourable
operating conditions.
SPREAD IN TUBE CHARACTERISTICS
The
spread in tube characteristics is the difference between maximum and
minimum values. Values not qualified as maximum or minimum are nominal
ones. It is evident that average or nominal values, as well as spread
figures, may differ according to the number of tubes of a certain type
that are being checked. No guarantee is given for values of
characteristics in settings substantially differing from those specified
in the data sheets.
SPREAD AND VARIATION IN OPERATING CONDITIONS
The
operating conditions of a tube are subject to spread and/or variation.
Spread in an operating condition is a permanent deviation from an
average condition due to, e.g.. component value deviations. The average
condition is found from such a number individual cases taken at random
that an increase of the number will have a negligible influence.
Variation in an operating condition is non-permanent (occurs as a
function of time). e.g .. due to supply voltage fluctuations. The
average value is calculated over a period such that a prolongation of
that period will have negligible influence.
LIMITING VALUES
Limiting
values are in accordance with the applicable rating system as defined
by IEC publication 134. Reference may be made to one of the following 3
rating systems. Absolute maximum rating system. Absolute maximum ratings
are limiting values of operating and environmental conditions
applicable to any electronic device of a specified type as defined by
its published data, and should not be exceeded under the worst probable
conditions. These values are chosen by the device manufacturer to
provide acceptable serviceability of the device, taking no
responsibility for equipment variations, environmental variations, and
the effects of changes in operating conditions due to variations in the
characteristics of the device under consideration and of all other
electronic devices in the equipment. The equipment manufacturer should
design so that, initially and throughout life, no absolute maximum value
for the intended service is exceeded with any device under the worst
probable operating condit- ions with respect to
supply voltage
variation, equipment components spread and variation, equipment control
adjustment, load variations, signal variation, environmental
.conditions, and spread or variations in characteristics of the device
under considerations and of all other electronic devices in the
equipment.
Design-maximum rating system.
Design-maximum
ratings are limiting values of operating and environ- mental conditions
applicable to a bogey electronic device* of a specified type as defined
by its pub- lished data, and should not be exceeded under the worst
probable conditions. These values are chosen by the device manufacturer
to provide acceptable serviceability of the device, taking
responsibility for the effects of changes in operating conditions due to
variations in the charac- teristics of the electronic device under
consideration. The equipment manufacturer should design so that,
initially and thoughout life, no design-maximum value for the intended
service is exceeqed with a bogey device under the worst probable
operating conditions with respect to supply-voltage variation, equipment
component variation, variation in char- acteristics of all other
devices in the equipment, equipment control adjustment, load variation,
signal variation and environmental conditions.
Design-centre rating system.
Design-centre
ratings are limiting values of operating and environmental conditions
applicable to a bogey electronic device* of a specified type as defined
by its published data, and should not be exceeded under average
conditions. These values are chosen by the device manufacturer to
provide acceptable serviceability of the device in average applications,
taking responsibility for normal changes in operating conditions due to
rated supply-voltage variation, equipment component spread and
variation, equipment control adjustment, load variation, signal
variation, environmental conditions, and variations or spread in the
characteristics of all electronic devices. The equipment manufacturer
should design so that, initially, no design-centre value for the
intended service is exceeded with a bogey electronic device* in
equipment operating at the stated normal supply voltage.
If the tube data specify limiting values according to more than one rating system the circuit has to be
designed so that none of these limiting values is exceeded under the relevant conditions.
In addition to the limiting values given in the individual data sheets the directives in the following
paragraphs should be observed.
HEATER SUPPLY
For
maximum cathode life and optimum performance it is recommended that the
heater supply be designed at the nominal heater voltage at zero beam
current. Any deviation from this heater voltage has a detrimental effect
on tube performance and life, and should therefore be kept to a
minimum. Jn any case the deviations of the heater voltage must not
exceed+ 5% and -10% from the nominal value at zero beam current. Such
deviations may be caused by:
• mains voltage fluctuations;
• spread in the characteristics of components such as transformers, resistors, capacitors, etc.;
• spread in circuit adjustments;
• operational variations.
•
A bogey tube is a tube whose characteristics have the published nominal
values for the type. A bogey tube for any particular application can be
obtained by considering only those characteristics which are directly
related to the application.
CATHODE TO HEATER VOLTAGE
The
voltage between cathode and heater should be as low as possible and
never exceed the limiting values given in the data sheets of the
individual tubes. The limiting values relate to that side of the heater
where the voltage between cathode and heater is greatest. The voltage
between cathode and heater may be d.c., a.c., or a combination of both.
Unless otherwise stated, the maximum values quoted indicate the maximum
permissible d.c. voltage. If a combination of d.c. and a.c. voltages is
applied, the peak value may be twice the rated Vkf; however, unless
otherwise stated, this peak value shall never exceed 315 V. Unless
otherwise stated, the Vkf max. holds for both polarities of the voltage;
however, a positive cathode is usually the most favourable in view of
insulation during life. A d.c. connection should always be present
betweeh heater and cathode. Unless otherwise specified the maximum
resistance should not exceed 1 M.Q; the maximum impedance at mains
frequency shou Id be less than 100 k.OHM.
INTERMEDIATE ELECTRODES (between cathode and anode)
In
no circumstances should the tube be operated without a d.c. connection
between each electrode and the cathode. The total effective impedance
between each electrode and the cathode shou Id never exceed the
published maximum value. However, no electrode should be connected
directly to a high energy source. When such a connection is required, it
should be made via a series resistor of not less
than 1 k.OHM.
CUT-OFF VOLTAGE
Curves
showing the limits of the cut-off voltage as a function of grid 2
voltage are generally included in the data. The brightness control
should be so dimensioned that it can handle any tube within the limits
shown, at the appropriate grid 2 voltage. The published limits are
determined at an ambient illumination level of 10 lux. Because the
brightness of a spot is in general greater than that of a raster of the
same current, the cut-off voltage determined with the aid of a focused
spot will be more negative by about 5 Vas compared with that of a
focused
raster.
LUMINESCENT SCREEN
To prevent permanent
screen damage, care should be taken: - not to operate the tube with a
stationary picture at high beam currents for extended periods; - not to
operate the tube with a stationary or slowly moving spot except at
extremely low beam currents; - if no e.h.t. bleeder is used, to choose
the time constants of the cathode, grid 1, grid 2, and deflection
circuits, such that sufficient beam current is maintained to discharge
the e.h.t. capacitance before deflection has ceased after equipment has
been switched off.
EXTERNAL CONDUCTIVE COATING
The external
conductive coating must be connected to the chassis. The capacitance of
this coating to the final accelerating electrode may be used to provide
smoothing for the e.h.t. supply. The coating is not a perfect conductor
and in order to reduce electromagnetic radiation caused by the line time
base and the picture content it may be necessary to make multiple
connections to the coating.
See also 'Flashover'.
METAL RIMBAND
An
appreciable capacitance exists between the metal rimband and the
internal conductive coating of the tube; its value is quoted in the
individual data sheets.To avoid electric shock, a d.c. connection should
be provided between the metal band and the external conductive coating.
In receivers where the chassis ,can be connected directly to the mains
there is a risk of electric shock if access is made to the metal band.
To reduce the shock to the safe limit, it is suggested that a 2 Mil
resistor capable of handling the peak voltages be inserted between the
metal band and the point of contact with the external con- ductive
coating. This safety arrangement will provide the necessary insulation
from the mains but in the event of flashover high voltages will be
induced on the metal band. It is therefore recommended that the 2 Mil
resistor be bypassed by a 4, 7 n F capacitor capable of withstanding the
peak voltage determined by the voltage divider formed by this capacitor
and the capacitance of the metal rimband
to the internal conductive
coating, and the anode voltage. The 4, 7 n F capacitor also serves to
improve e.h.t. smoothing by addingthe rimband capacitance to the
capacitance of the outer conductive coating.
FLASHOVER
High
electric field strengths are present between the gun electrodes of
picture tubes. Voltages between gun electrodes may reach values of 20 kV
over approx. 1 mm. Although the utmost precautions are taken in the
design and manufacture of the tubes, there is always a chance that
flashover will occur. The resulting transient currents and voltages may
be of sufficient magnitude to cause damage to the tube itself and to
various components on the chassis. Arcing terminates when the e.h.t.
capacitor is discharged. Therefore it is of vital importance to provide
protective circuits with spark gaps and series resistors, which should
be connected according to Fig. 1. No other connections between the outer
conductive coating and the chassis are permissible. As our picture
tubes are manufactured in Soft-Flash technology, the peak discharge
currents are limited to approx. 60 A, offering higher set reliability,
optimum circuit protection and component savings (see also Technical
Note 039). However this limited value of
60 A is still too high for
the circuitry which is directly connected to the tube socket. Therefore
Soft-Flash picture tubes should also be provided with spark gaps.
IMPLOSION PROTECTION
All
picture tubes employ integral implosion protection and must be replaced
with a tube of the same type number or recommended replacement to
assure continued safety.
HANDLING
Although all picture tubes
are provided with integral implosion protection, which meets the
intrinsic protection requirements stipulated in the relevant part of IEC
65, care should be taken not to scratch or knock any part of the tube.
The tube assembly should never be handled by the neck, deflection unit
or other neck components. A picture tube assembly can be lifted from the
edge-down position by using the two upper mounting lugs. An alternative
lifting method is firmly to press the hands against the vertical sides
of the rimband. When placing a tube assembly face downwards ensure that
the screen rests on a soft pad of suitable material, kept free from
abrasive substances. When lifting from the face-down position the hand
should be placed under the areas of the faceplate close to the mounting
lugs at diagonally opposite corners of the faceplate.
When lifting from the face-up position the hands should be placed under the areas of the cone close
to the mounting lugs at diagonally opposite corners of the cone.
In
all handling procedures prior to insertion in the receiver cabinet
there is a risk of personal injury as a result of severe accidental
damage to the tube. It is therefore recommended that protective clothing
shou Id be worn, particularly eye shielding. When suspending the tube
assembly from the mounting lugs ensure that a minimum of 2 are used;
UNDER NO Cl RCUMSTANCES HANG THE TUBE ASSEMBLY FROM ONE LUG. If provided
the slots in the rimband of colour picture tubes are used in the
mounting of the degaussing coils. it is not recommended to suspend the
tube assembly from one or more of these slots as permanent deformation
to the rimband can occur. Remember when replacing or servicing the tube
assembly that a residual electrical charge may be carried by the anode
contact and also the external coating if not earthed. Before removing
the tube assembly from the equipment, earth the external coating and
short the anode contact to the coating.
PACKING
The packing
provides protection against tube damage under normal conditions of
shipment or handling. Observe any instructions given on the packing and
handle accordingly. The tube should under no circumstances be subjected
to accelerations greater than 350 m/s2.
MOUNTING
Unless
otherwise specified on the data sheets for individual tubes there are no
restrictions on the position of mounting. The tube socket should not be
rigidly mounted but should have flexible leads and be allowed to move
freely. It is very desirable that tubes should not be exposed to strong
electrostatic and magnetic fields.
DIMENSIONS
In designing the
equipment the tolerances given on the dimensional drawings should be
considered. Under no circumstances should the equipment be designed
around dimensions taken from individual tubes.
Picture display system including a deflection unit with a double saddle coil system
PHILIPS 45AX SYSTEM
1. A picture display system including a colour display tube having a neck accommodating an electron gun assembly for generating three electron beams, and an electromagnetic deflection unit surrounding the paths of the electron beams which have left the electron assembly, said deflection unit comprising
a field deflection coil of the saddle type having a front and a rear end for deflecting electron beams generated in the display tube in a vertical direction;
a line deflection coil of the saddle type likewise having a front and a rear end for deflecting electron beams generated in the display tube in a horizontal direction, and a yoke ring of ferromagnetic material surrounding the two deflection coils and having front and rear end faces extending transversely to the tube axis, the electron beam traversing the coils in the direction from the rear to the front ends when the deflection unit is arranged on a display tube, characterized in that the deflection unit also has first and second magnetically permeable portions arranged symmetrically with respect to the plane of symmetry of the field deflection coil on either side of the tube axis, each magnetically permeble portion having a first end located opposite the rear end face of the yoke ring and a second end located at the neck of the display tube in the proximity of the location where the electron beams leave the electron gun assembly, the length of the first and second magnetically permeable portions and their distance to the yoke ring being dimensioned for providing a self-convergent picture display system.
2. A picture display system as claimed in claim 1 characterized in that regions of the rear end of the yoke ring located on either side of the plane of symmetry of the line deflection coil are left free by the rear end of the field deflection coil and in that the first ends of the magnetically permeable portions are located opposite said regions.
3. A picture display system as claimed in claim 1 characterized in that the field deflection coil and the line deflection coil are directly wound on a support.
4. Apparatus for adapting a self-convergent deflection unit of the type mountable on the neck of a display tube and including a saddle type field deflection coil screen end and a gun end extending away from said tube in a plane disposed at an angle to a tube axis, and a yoke ring having a screen end and a gun end, for use with display tubes having different screen formats comprising:
format adjustment means disposed adjacent to the gun end of the yoke ring for coupling flux from the yoke ring to the neck of the tube to supplement the field produced by the vertical deflection coil to uniformly increase the vertical deflection field to produce a raster having a different format from the raster produced by said deflection unit alone.
6. The apparatus of claim 5 wherein each of said first and second magnetically permeablel members comprises a first end located opposite a gun end face of the yoke ring, and a second end located at the neck of the display tube adjacent the location where the electron beams leave the electron gun assembly.
7. The apparatus of claim 6 wherein said first end comprises a portion of said permeable member disposed parallel to the neck of the displaya tube and said second end comprises a portion of said magnetically permeable member located perpepndicular to the neck of the display tube.
8. The apparatus of claim 7 wherein said second endsn of said magnetically permeable members have inwardly extending arms subending a first angle.
9. The appaaratus of claim 8 wherein said angle is large so that the supplemental field has a positive sixpole component.
11. Apparatus for adapting a self-convergent deflection unit of the type used on the neck of a display tube having an electron gun disposed in a neck of said tube, said deflection unit including a field deflection coil of the saddle type having a rear end portion disposed at an angle to the axis of said tube, comprising means disposed adjacent to said neck between said electron gun and said deflection unit, and coupled to said deflection unit for changing the distance between the line and field deflection points for causing said deflection unit to produce a different screen format.
1. A method of manufacturing a color display tube in which magnetic poles are provided in or around the neck of said tube and around the paths of the electron beams, which poles generate a permanent static multipole magnetic field for the correction of errors in convergence, color purity and frame of the display tube, which magnetic poles are formed by the magnetisation of a configuration of magnetisable material provided around the paths of the electron beams, the method comprising energizing a magnetisation device with a combination of direct currents with which a static multipole magnetic field is generated, and superimposing a decaying alternating magnetic field over said static multipole magnetic field which initially drives said magnetisable material into saturation on either side of the hysteresis curve thereof, said decaying alternating magnetic field being generated by a decaying alternating current. 2. The method as claimed in claim 1, 6 or 7, wherein the decaying alternating magnetic field is generated by means of a separate system of coils in the magnetisation device. 3. The method as claimed in claim 2, wherein the decaying alternating magnetic field varies its direction continuously. 4. The method as claimed in claim 3 wherein the frequency of the decaying alternating current is approximately the standard line frequency. 5. A colour display tube manufactured by means of the method as claimed in claim 4. 6. The method as claimed in claim 1 which further comprises erasing any residual magnetism in said configuration, prior to said magnetisation, with an alternating magnetic field. 7. The method as claimed in claim 6 which further comprises correcting the errors in convergence, color purity and frame of the display picture with a combination of direct currents applied to said magnetisation device and then reversing said direct currents while increasing the magnitudes thereof and applying these adjusted direct currents to said magnetisation device for the magnetisation of said configuration.
The invention relates to a method of manufacturing a color display tube in which magnetic poles are provided in or around the neck of the envelope and around the paths of the electron beams, which poles generate a permanent multipole magnetic field for the correction of the occurring errors in convergence, color purity and frame of the color display tube, which magnetic poles are formed by the magnetisation of a configuration of magnetisable material provided around the paths of the electron beams, which configuration is magnetized by energising a magnetising device with a combination of currents with which a static multipole magnetic field is generated.
The invention also relates to a color display tube manufactured according to said method.
In a color display tube of the "delta" type, three electron guns are accommodated in the neck of the tube in a triangular arrangement. The points of intersection of the axes of the guns with a plane perpendicular to the tube axis constitute the corner points of an equilateral triangle.
In a color display tube of the "in-line" type three electron guns are arranged in the tube neck in such manner that the axes of the three guns are situated mainly in one plane while the axis of the central electron gun coincides substantially with the axis of the display tube. The two outermost electron guns are situated symmetrically with respect to the central gun. As long as the electron beams generated by the electron guns are not deflected, the three electron beams, both in tubes of the "delta" type and of the "in-line" type, must coincide in the center of the display screen (static convergence). Because, however, as a result of defects in the manufacture of the display tube, for example, the electron guns are not sealed quite symmetrically with respect to the tube axis, deviations of the frame shape, the color purity and the static convergence occur. It should be possible to correct said deviations.
Such a color display tube of the "in-line" type in which this correction is possible, is disclosed in Netherlands Pat. application No. 7,503,830 laid open to public inspection. Said application describes a color display tube in which the deviations are corrected by the magnetisation of a ring of magnetisable material, as a result of which a static magnetic multipole is formed around the paths of the electron beams. Said ring is provided in or around the tube neck. In the method described in said patent application, the color display tube is actuated after which data, regarding the value and the direction of the convergence errors of the electron guns, are established, with reference to which the polarity and strength of the magnetic multipole necessary to correct the frame, color purity and convergence errors are determined. The magnetisation of the configuration, which may consist of a ring, a ribbon or a number of rods or blocks grouped around the electron paths, may be carried out in a number of manners. It is possible, for example, first to magnetise the configuration to full saturation, after which demagnetisation to the desired value is carried out with an opposite field. A disadvantage of this method is that, with a combination of, for example, a 2, 4, and 6-pole field, the polarity and strength of the demagnetisation vary greatly and frequently, dependent on the place on the ring, and hence also the polarity and strength of the full magnetisation used in this method. Moreover it appears that the required demagnetising field has no linear relationship with the required correction field. Due to this non-linearity it is not possible to use a combined 2, 4 and 6-pole field for the demagnetisation. It is impossible to successively carry out the 2, 4 and 6-pole magnetisation since, for each magnetisation, the ring has to be magnetised fully, which results in the preceding magnetisation being erased again. The possibility of successively magnetising various places on the ring is very complicated and is not readily possible if the ring is situated in the tube neck since the stray field of the field necessary for the magnetisation again demagnetizes, at least partly, the already magnetised places.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a method with which a combined multipole can be obtained by one total magnetisation.
According to the invention, a method, of the kind described in the first paragraph with which this is possible, is characterized in that the magnetisation is effected by means of a decaying alternating magnetic field which initially drives the magnetisable material on either side of the hysteresis curve into saturation. After the decay of the alternating magnetic field, a hard magnetisation remains in the material of the configuration which neutralizes the externally applied magnetic field and is, hence, directed oppositely thereto. After switching off the externally applied magnetic field, a magnetic multipole field remains as a result of the configuration magnetized as a multipole. The desired magnetisation may be determined in a number of manners. By observing and/or measuring the deviations in the frame shape, color purity and convergence, the desired multipole can be determined experimentally and the correction may be carried out by magnetisation of the configuration. If small deviations are then still found, the method is repeated once or several times with corrected currents. In this manner, by repeating the method according to the invention, it is possible to produce a complete correction of the errors in frame, color purity and convergence. Preceding the magnetisation, residual magnetism, if any, in the configuration is preferably erased by means of a magnetic field.
The method is preferably carried out by determining the required correction field prior to the magnetisation and, after the erasing of the residual magnetism, by correcting the errors in the convergence, the color purity and the frame of the displayed picture by means of a combination of currents through the magnetising device, after which the magnetisation is produced by reversing the direction of the combination of currents, increasing the current strength and simultaneously producing the said decaying alternating magnetic field.
The correction field, obtained with the magnetizing device and measured along the axis of the electron beams, is generally longer than the multipole correction field generated by the configuration. So the correction of the deviations will have to be carried out over a shorter distance along the axis of the tube, which is possible only with a stronger field. During the magnetisation, a combination of currents, which in strength and direction is in the proportion of m:1 to the combination of currents which is necessary to generate a correction multipole field with the device, where m is, for example, -3, should flow through the magnetisation device. The value of m depends on the ratio between the length of the correction multipole field, generated by the magnetizing device, to the effective field length of the magnetized configuration. This depends upon a number of factors, for example, the diameter of the neck, the kind of material, the shape and the place of the configuration, etc., and can be established experimentally. If it proves, upon checking, that the corrections with the magnetized configuration are too large or too small, the magnetisation process can be repeated with varied magnetisation currents.
The decaying alternating magnetic field can be generated by superimposing a decaying alternating current on the combination of currents through the magnetisation device (for example, a device as disclosed in Netherlands Pat. application No. 7,503,830 laid open to public inspection). The decaying alternating magnetic field is preferably generated in the magnetisation device by means of a separate system of coils. In order to obtain a substantially equal influence of all parts of the configuration by the decaying alternating field, it is recommendable not only to cause the alternating field to decay but also to cause it to vary its direction continuously. The system of coils therefore consists preferably of at least two coils and the decaying alternating currents through the coils are shifted in phase with respect to each other. Standard line frequency (50 or 60 Hz) has proven to give good results. The phase shift, when using coils or coil pairs, the axes of which enclose angles of 120° with each other, can simply be obtained from a three-phase line.
DESCRIPTION OF THE DRAWINGS
The invention will now be described in greater detail with reference to a drawing, in which
FIG. 1 is a diagrammatic sectional view of a known color display tube of the "in-line" type having an external static convergence unit,
FIG. 2 shows the pinion transmission used therein,
FIGS. 3 and 4 are two diagrammatic perpendicular cross-sectional views of the color display tube with a ring, which has not yet been magnetized, and in which the outermost electron beams do not converge satisfactorily,
FIGS. 5 and 6 are two diagrammatic perpendicular sectional views of a color display tube in which convergence by means of the magnetisation device has been obtained,
FIGS. 7 and 8 show the magnetisation of a ring arranged in the system of electron guns,
FIGS. 9 and 10 show two diagrammatic perpendicular sectional views of a color display tube with a magnetized ring with which the convergence error, as shown in FIG. 4, is removed,
FIGS. 11 and 12 show two types of devices suitable for magnetisation according to the invention, and
FIGS. 13 to 18 show parts of another type of magnetisation unit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a diagrammatic sectional view of a known color display tube of the "in-line" type. Three electron guns 5, 6 and 7, generating the electron beams 8, 9 and 10, respectively, are accommodated in the neck 4 of a glass envelope 1 which is composed of a display window 2, a funnel-shaped part 3 and a neck 4. The axes of the electron guns 5, 6 and 7 are situated in one plane, the plane of the drawing. The axis of the central electron gun 6 coincides substantially with the tube axis 11. The three electron guns are seated in a sleeve 16 which is situated coaxially in the neck 4. The display window 2 has on the inner surface thereof a large number of triplets of phosphor lines. Each triplet comprises a line of a phosphor luminescing green, a line of a phosphor luminescing blue, and a line of a phosphor luminescing red. All of the triplets together constitute a display screen 12. The phosphor lines are normal to the plane of the drawing. A shadow mask 12, in which a very large number of elongate apertures 14 are provided through which the electron beams 8, 9 and 10 pass, is arranged in front of the display screen 12. The electron beams 8, 9 and 10 are deflected in the horizontal direction (in the plane of the drawing) and in the vertical direction (at right angles thereto) by a system 15 of deflection coils. The three electron guns 5, 6 and 7 are assembled so that the axes thereof enclose a small angle with respect to each other. As a result of this, the generated electron beams 8, 9 and 10 pass through each of the apertures 14 at said angle, the so-called color selection angle, and each impinge only upon phosphor lines of one color.
A display tube has a good static convergence if the three electron beams, when they are not being deflected, intersect each other substantially in the center of the display screen. It has been found, however, that the static convergence often is not good, no more than the frame shape and the color purity, which may be the result of an insufficiently accurate assembly of the guns, and/or sealing of the electron guns, in the tube neck. In order to produce the static convergence, so far, externally adjustable correction units have been added to the tube. They consist of a number of pairs of multipoles consisting of magnetic rings, for example four two-poles (two horizontal and two vertical), two four-poles and two six-poles. The rings of each pair are coupled together by means of a pinion transmission (see FIG. 2), with which the rings are rotatable with respect to each other to an equal extent. By rotating the rings with respect to each other and/or together, the strength and/or direction of the two-, four- or six-pole field is adjusted. It will be obvious that the control of a display tube with such a device is complicated and time-consuming. Moreover, such a correction unit is material-consuming since, for a combination of multipoles, at least eight rings are necessary which have to be provided around the neck so as to be rotatable with respect to each other.
In the Netherlands Pat. application No. 7,503,830, laid open to public inspection, the complicated correction unit has, therefore, been replaced by one or more magnetized rings, which rings are situated in or around the tube neck or in or around the electron guns.
However, it has proved difficult with the magnetising methods known so far to provide a combination of multipoles in the ring by magnetisation.
The method according to the invention provides a solution.
For clarity, identical components in the following figures will be referred to by the same reference numerals as in FIG. 1.
FIG. 3 is a diagrammatic sectional view of a display tube in which the electron beams do not converge in the horizontal direction. As is known, the outermost electron beams can be deflected more or less in the opposite direction by means of a four-pole, for example, towards the central beam or away therefrom. It is also possible to move the beams upwards and downwards. By means of a six-pole the beams can be deflected more or less in the same direction. For simplicity, the invention will be described with reference to a display tube which requires only a four-pole correction. The convergence errors in the horizontal direction of the electron beams 8 and 10 are in this case equally large but opposite.
FIG. 4 is a sectional view of FIG. 3. On the bottom of sleeve 16, a ring 18 is provided of an alloy of Fe, Co, V and Cr (known as Vicalloy) which can be readily magnetized. It will be obvious that the ring may alternatively be provided in other places around the guns or in or around the tube neck. Instead of a ring it is alternatively possible to use a ribbon or a configuration of rods or blocks of magnetisable material.
In FIG. 5 a device 19 for generating a controllable multipole magnetic field is provided around the neck 4 and the ring 18 according to the method of the invention. 2-, 4- or 6-poles and combinations thereof can be generated by means of the device 19. For the tube shown in FIG. 3, only a four-pole correction is necessary. The coils of the device 19, which device will be described in detail hereinafter, are in this case energized as four-poles until the point of intersection S of the three electron beams 8, 9 and 10, which in FIG. 3 was situated outside the tube 1, lies on the display screen 12. The current I through the coils of the device originates from a direct current source B which supplies a current -mI 1 (m being an experimentally determined constant >1) to the coils via a current divider and commutator A. The current can be adjusted per coil so as to generate the desired multipole. In this phase of the method, an alternating current source C does not yet supply current (i=0).
FIG. 6 is a perpendicular sectional view of FIG. 5. The current I 1 is a measure of the strength of the required correction field. The correction field of the multipole of the device 19 extends over a larger length of the electron paths than the magnetic field generated later by the magnetized ring. Therefore the field of the ring is to be m-times stronger.
FIG. 7 shows the step of the method in which the ring 18 is magnetized as a four-pole. As follows from the above, in this preferred embodiment of the method, the current through the coils of the device must be -mI 1 during the magnetisation, so must traverse in the reverse direction and be m-times as large as the current through the coils during the correction. Moreover, the alternating current source C supplies a decaying alternating current (i=i 1 >0) to the device 19, with which current the decaying alternating field is generated. When the alternating current is switched on, it must be so large that the ring 18 is fully magnetized on either side of the hysteresis curve. When the alternating field has decayed, the ring 18 is magnetized, in this case as a four-pole. It is, of course, alternatively possible to magnetise the ring 18 as a six-pole or as a two-pole or to provide combinations of said multipoles in the ring 18 and to correct therewith other convergence errors or color purity and frame errors. It is also possible to use said corrections in color display tubes of the "delta" type.
FIG. 9 shows the display tube 1 shown in FIG. 3, but in this case provided with a ring 18 magnetized according to the method of the invention as shown in FIGS. 5 and 7. The convergence correction takes place only by the magnetized ring 18 present in sleeve 16. The provision of the required multipole takes place at the display tube 1 factory and complicated adjustments and adjustable convergence units (FIG. 2) may be omitted.
FIG. 10 is a cross-sectional view perpendicular to FIG. 9. FIG. 11 shows a magnetisation device 19 comprising eight coils 20 with which the convergence (see FIG. 5) and the magnetisation (see FIG. 7) are carried out. For generating the decaying alternating magnetic field, two pairs of coils 21 and 22, extending in this case at right angles to each other, are incorporated in the device 19. The current i a through the pair of coils 21 is shifted in phase through 90° with respect to the current i b through the other pair of coils 22, so that the decaying alternating magnetic field changes its direction during the decay and is a field circulating through the ring 18. FIG. 12 shows a magnetisation device known from Netherlands Pat. application No. 7,503,830 laid open to public inspection. In this case, the decaying alternating current may be superimposed on the direct current through the coils 23 so that extra coils are not necessary in the device. The coils 23 are wound around a yoke 24.
The magnetisation device 19 may alternatively be composed of a combination of electrical conductors and coils, as is shown diagrammatically in FIGS. 13 to 18.
FIG. 13 is a sectional view of the neck 4 of a display tube 1 at the area of a ring 18 to be magnetised. A two-pole field for corrections in the horizontal direction is generated in this case by causing currents to flow through the conductors 25, 26, 27 and 28 in the direction as shown in the figure. Said conductors may be single wires or wire bundles forming part of one or more coils or turns, and extending parallel to the tube axis at the area of the ring 18.
FIG. 14 shows how, in an analogous manner, a four-pole field for corrections of the outermost beams 8 and 10 in the horizontal direction can be generated by electrical conductors 29, 30, 31 and 32. A four-pole field for corrections of the outermost beams 8 and 10 in the vertical direction is substantially the same. However, the system of conductors 29, 30, 31 and 32 is rotated through 45° with respect to the neck 4 and the axis of the tube 1.
FIG. 15 shows, in an analogous manner, a six-pole for corrections in the horizontal direction with conductors 33 to 38. By means of a combination of conductors (wires or wire bundles) with which 2-, 4- and 6-poles can be generated, all combinations of two-, four- and six-pole fields with the desired strength can be obtained by variations of the currents through said conductors 33 to 38.
The decaying alternating magnetic field in a magnetisation unit with conductors as shown in FIGS. 13, 14 and 15 can be obtained by means of coils positioned symmetrically around the neck 4 and the conductors as shown in FIGS. 16 and 17 or 18. By energizing the coils 39 and 40, shown in FIG. 16, with a decaying alternating current, a decaying alternating magnetic field is generated. A better influencing of the ring 18 by the decaying alternating field is obtained when a system of coils having coils 41 and 42 in FIG. 17 is provided which is rotated 90° with respect to the coils 39. In this case, 40 and the decaying alternating current through the coils 41 and 42 should then preferably be shifted 90° in phase with respect to the decaying alternating current through the coils 39 and 40.
It is alternatively possible to generate the decaying alternating magnetic field with one or more systems of coils as shown in FIG. 18. The coils 43, 44 and 45 are situated symmetrically around the tube axis and are energized with decaying alternating currents which are shifted 120° in phase with respect to each other (for example from a three-phase line).
CRT TUBE PHILIPS 45AX TECHNOLOGY Method of manufacturing a static convergence unit, and a color display tube comprising a convergence unit manufactured according to the method, PHILIPS 45AX INTERNAL STATIC CONVERGENCE SYSTEM Application technology:
IMACO RING (Integrated Magnetic Auto Converging )
The method according to the invention consists in the determination of data of the convergence errors of a color display tube, data being derived from the said determinations for determining the polarity and the intensity of magnetic poles of a structure. The structure thus obtained generates a static, permanent, multipole magnetic field adapted to the convergence errors occurring, so that the errors are connected.
Color television display tube with coma correction ELECTRON GUN STRUCTURE PHILIPS CRT TUBE 45AX
A color television display tube including an electron gun system (5) in an evacuated envelope for generating three electron beams whose axes are co-planar. The beams converge on a display screen (10) provided on a wall of the envelope and are deflected in the operative display tube across the display screen into two orthogonal directions. The electron gun system (5) has correction elements for causing the rasters scanned on the display screen by the electron beams to coincide as much as possible. The correction elements include annular elements (34) of a material having a high magnetic permeability which are positioned around the two outer beams. In addition a further correction element (38, 38", 38"') of a material having a high magnetic permeability is provided around the central beam in a position located further from the screen in order to correct field coma errors at the ends of the vertical axis and in the corners to an equal extent. The further element is preferably positioned in, or on the screen side of, the area of the focusing gap of the electron gun.
1. A color display tube comprising an envelope containing a display screen, and an electron gun system for producing a central electron beam and first and second outer electron beams having respective axes which lie in a single plane and converge toward a point on the screen, the electron gun system including an end from which the electron beams exit into a deflection field region of the envelope where a field deflection field effects deflection of the beams in a direction perpendicular to said plane and a line deflection field effects deflection of the beams in a direction parallel to said plane, said line deflection field producing a positive lens action;
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