Videocolor was a fabricant of Electronic components in Anagni (Italy). Was formed from an Italian CRT Fabricant called ERGON which was sold to Thomson in 1971 and the technology further called PIL (Precision In Line) was produced by a collaboration with RCA. In 2005 Videocolor was sold to Videocon An Indian conglomerate wich has converted it to Plasma Lcd (Crap) manufacturing, resulting in a total FAIL !! Now Videocolor has Stopped the production, it's gone (Forever) !!
In-line electron gun PRECISION IN LINE TECHNOLOGY p.i.l. VIDEOCOLOR (RCA TECHNOLOGY):
The three co-planar beams of an in-line gun are converged
near the screen of a cathode ray tube by means of two plate-like grids
transverse to the beam paths and having corresponding apertures for the
three beams. The three beam apertures of the first grid are aligned with
the three beam paths. The two outer beam apertures of the second grid
are offset outwardly relative to the beam paths to produce the desired
convergence. The three sets of apertures also provide separate focusing
fields for the three beams. The second plate-like grid is formed with a
barrel shape, concave toward the first grid, to minimize elliptical
distortion of beam spots on the screen due to crowding of the adjacent
focusing fields. Each of the two outer beams is partially shielded from
the magnetic flux of the deflecting yoke by means of a magnetic ring
surrounding the beam path in the deflection zone, to equalize the size
of the rasters scanned on the screen by the middle and outer beams.
Other magnetic pieces are positioned on opposite sides of the path of
the middle beam, to enhance one deflection field while reducing the
transverse deflection field for that beam. 
1. In a color picture tube including an evacuated envelope comprising a
faceplate and a neck connected by a funnel, a mosaic color phosphor
screen on the inner surface of said faceplate, a multiapertured color
selection electrode spaced from said screen, an in-line electron gun
mounted in said neck for generating and directing three electron beams
along co-planar paths through said electrode to said screen, and a
deflection zone, located in the vicinity of the junction between said
neck and said funnel, wherein said beams are subjected to vertical and
horizontal magnetic deflection fields during operation of said tube for
scanning said beams horizontally and vertically over said screen; said
electron gun comprising: 2. The structure of claim 1, wherein said
electron gun further comprises a pair of magnetic elements positioned in
said deflection zone on opposite sides of the middle beam path and in a
plane transverse to the common plane of said paths for enhancing the
magnetic deflection field in said middle beam path transverse to said
common plane and for reducing the magnetic deflection field in said
middle beam path along said common plane, thereby increasing the
dimension of the raster scanned by the middle beam in said common plane
while reducing the dimension of said raster in said transverse plane. 3.
In a color picture tube including an evacuated envelope comprising a
faceplate and a neck connected by a funnel, a mosaic color phosphor
screen on the inner surface of said faceplate, a multi-apertured color
selection electrode spaced from said screen, an in-line electron gun
mounted in said neck for generating and directing three electron beams
along co-planar paths through said electrode to said screen, and a
deflection zone, located in the vicinity of the junction between said
neck and said funnel, wherein said beams are subjected to vertical and
horizontal magnetic deflection fields during operation of said tube for
scanning said beams horizontally and vertically over said screen, and
wherein the eccentrity of the outer ones of said beams in the deflection
fields causes the sizes of the rasters scanned by the outer beams to
tend to be larger than the size of the raster scanned by a middle beam,
said electron gun comprising; 4. The tube as defined in claim 3,
including two small discs of magnetic material located at the fringe of
the deflection zone on opposite sides of the middle beam transverse to
the plane of the three beams, whereby the magnetic flux on the middle
beam transverse to the plane of the three beams is enhanced and the flux
in the plane of the three beams is decreased thereby increasing the
middle beam dimension in the plane of the three beams while reducing the
middle beam dimension in the plane of the three beams.
Description:
BACKGROUND OF THE INVENTION
The present invention relates to an improved in-line electron gun for a
cathode ray tube, particularly a shadow mask type color picture tube.
The new gun is primarily intended for use in a color tube having a line
type color phosphor screen, with or without light absorbing guard bands
between the color phosphor lines, and a mask having elongated apertures
or slits. However, the gun could be used in the well known dot-type
color tube having a screen of substantially circular color phosphor dots
and a mask with substantially circular apertures.
An in-line electron gun is one designed to generate or initiate at least
two, and preferably three, electron beams in a common plane, for
example, by at least two cathodes, and direct those beams along
convergent paths in that plane to a point or small area of convergence
near the tube screen. Various ways have been proposed for causing the
beams to converge near the screen. For example, the gun may be designed
to initially aim the beams, from the cathodes, towards convergence at
the
screen, as shown in FIG. 4 of Moodey U.S. Pat. No. 2,957,106,
wherein the beam apertures in the gun electrodes are aligned along
convergent paths.
In order to avoid wide spacings between the cathodes, which are
undesirable in a small neck tube designed for high deflection angles, it
is preferable to initiate the beams along substantially parallel (or
even divergent) paths and provide some means, either internally or
externally of the tube, for converging the beams near the screen. Magnet
poles and/or electrostatic deflecting plates for converging in-line
beams are disclosed in Francken U.S. Pat. No. 2,849,647, Gundert et al.
U.S. Pat. No. 2,859,378 and Benway U.S. Pat No. 2,887,598.
The Moodey patent referred to above also includes an embodiment, shown
in FIG. 2 and described in lines 4 to 23 of column 5, wherein an in-line
gun for two co-planar beams comprises two spaced cathodes, a control
grid plate and an accelerating grid plate each having two apertures
aligned respectively with the two cathodes (as in FIG. 2) to initiate
two parallel co-planar beam paths, and two spaced-apart beam focusing
and accelerating electrodes of cylindrical form. The focusing electrode
nearest to the first accelerating grid plate is described as having two
beam apertures that are offset toward the axis of the gun from the
corresponding apertures of the adjacent accelerating grid plate, to
provide an asymmetric electrostatic field in the path of each beam for
deflecting the beam from its initial path into a second beam path
directed toward the tube axis.
Netherlands U.S. Pat. application No. 6902025, published Aug. 11, 1970
teaches that astigmatic aberration resulting in elliptical distortion of
the focused screen spots of the two off-axis beams from an in-line gun,
caused by the eccentricity of the in-line beams in a common focusing
field between two hollow cylindrical focusing electrodes, can be
partially corrected by forming the adjacent edges of the cylindrical
electrodes with a sinusoidal contour including four sine waves. A
similar problem is solved in a different manner in applicant's in-line
gun. 
Another
problem that exists in a cathode ray tube having an in-line gun is a
coma distortion wherein the sizes of the rasters scanned on the screen
by a conventional external magnetic deflection yoke are different,
because of the eccentricity of the two outer beams with respect to the
center of the yoke. Messineo et al. U.S. Pat. No. 3,164,737 teaches that
a similar coma distortion caused by using different beam velocities can
be corrected by use of a magnetic shield around the path of one or more
beams in a delta type gun. Barkow U.S. Pat. No. 3,196,305 teaches the
use of magnetic enhancers adjacent to the path of one or more beams in a
delta gun, for the same purpose. Krackhardt et al. U.S. Pat. No.
3,534,208 teaches the use of a magnetic shield around the middle one of
three in-line beams for coma correction.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, at least two electron
beams are generated along co-planar paths toward the screen of a cathode
ray tube, e.g., a shadow mask type color picture tube, and the beams
are converged near the screen by asymmetric electric fields established
in the paths of two beams by two plate-like grids positioned between the
beam generating means and the screen and having corresponding apertures
suitably related to the beam paths. The apertures in the first grid
(nearest the cathodes) are aligned with the beam paths. Two apertures in
the second grid (nearest the screen) are offset outwardly with respect
to the beam paths to produce the desired asymmetric fields. In the case
of three in-line beams, the two outer apertures are offset, and the
middle apertures of the two grids are aligned with each other. The pairs
of corresponding apertures also provide separate focusing fields for
the beams. In order to minimize elliptical distortion of one or more of
the focused beam spots on the screen due to crowding of adjacent beam
focusing fields, at least a portion of the second grid may be
substantially cylindrically curved in a direction transverse to the
common plane of the beams, and concave to the first grid. Each of the
two outer beam paths of a three beam gun may be partially shielded from
the magnetic flux of the deflection yoke by means of a magnetic ring
surrounding each beam in the deflection zone of the tube, to minimize
differences in the size of the rasters scanned on the screen by the
middle and outer beams. Further correction for coma distortion may be
made by positioning magnetic pieces on opposite sides of the middle beam
path for enhancing one field and reducing the field transverse thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view, partly in axial section, of a shadow mask color
picture tube in which the present invention is incorporated;
FIG. 2 is a front end view of the tube of FIG. 1 showing the rectangular
shape;
FIG. 3 is an axial section view of the electron gun shown in dotted
lines in FIG. 1, taken along the line 3--3 of that figure;
FIG. 4 is an axial section view of the electron gun taken along the line
4--4 of FIG. 3;
FIG. 5 is a rear end view of the electron gun of FIG. 4, taken in the
direction of the arrows 5--5 thereof;
FIG. 6 is a transverse view, partly in section, taken along the line
6--6 of FIG. 4;
FIG. 7 is a front end view of the electron gun of FIGS. 1 and 4;
FIG. 8 is a similar end view with the final element (shield cup)
removed; and
FIGS. 9 and 10 are schematic views showing the focusing and converging
electric fields associated with two pairs of beam apertures in FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a plan view of a 17V-90° rectangular color picture tube, for
example, having a glass envelope 1 made up of a rectangular (FIG. 2)
faceplate panel or cap 3 and a tubular neck 5 connected by a rectangular
funnel 7. The panel 3 comprises a viewing faceplate 9 and a peripheral
flange or side wall 11 which is sealed to the funnel 7. A mosaic
three-color phosphor screen 13 is carried by the inner surface of the
faceplate 9. The screen is preferably a line screen with the phosphor
lines extending substantially parallel to the minor axis Y-Y of the tube
(normal to the plane of FIG. 1). A multi-apertured color selection
electrode or shadow mask 15 is removably mounted, by conventional means,
in predetermined spaced relation to the screen 13. An improved in-line
electron gun 19, shown schematically by dotted lines in FIG. 1, is
centrally mounted within the neck 5 to generate and direct three
electron beams 20 along co-planar convergent paths through the mask 15
to the screen 13. 
The
tube of FIG. 1 is designed to be used with an external magnetic
deflection yoke, such as the yoke 21 schematically shown, surrounding
the neck 5 and funnel 7, in the neighborhood of their junction, for
subjecting the three beams 20 to vertical and horizontal magnetic flux,
to scan the beams horizontally and vertically in a rectangular raster
over the screen 13. The initial plane of deflection (at zero deflection)
is shown by the line P--P in FIG. 1 at about the middle of the yoke 21.
Because of fringe fields, the zone of deflection of the tube extends
axially, from the yoke 21, into the region of the gun 19. For
simplicity, the actual curvature of the deflected beam paths 20 in the
deflection zone is not shown in FIG. 1.
The in-line gun 19 of the present invention is designed to generate and
direct three equally-spaced co-planar beams along initially-parallel
paths to a convergence plane C--C, and then along convergent paths
through the deflection plane to the screen 13. In order to use the tube
with a line-focus yoke 21 specially designed to maintain the three
in-line beams substantially converged at the screen without the
application of the usual dynamic convergence forces, which causes
degrouping misregister of the beam spots with the phosphor elements of
the screen, the gun is preferably designed with samll spacings between
the beam paths at the convergence plane C--C to produce a still smaller
spacing, usually called the S value, between the outer beam paths and
the central axis A--A of the tube, in the deflection plane P--P. The
convergence angle of the outer beams with the central axis is arc tan
e/c+d, where c is the axial distance between the convergence plane C--C
and the deflection plane P--P, d is the distance between the deflection
plane and the screen 13, and e is the spacing between the outer beam
paths and the central axis A--A in the convergence plane C--C. The
approximate dimensions in FIG. 1 are c = 2.7 inches, d = 9.8 inches, e =
0.200 inch (200 mils), and hence, the convergence angle is 55 minutes
and s = 157 mils. 
The
details of the improved gun 19 are shown in FIGS. 3 through 8. The gun
comprises two glass support rods 23 on which the various electrodes are
mounted. These electrodes include three equally-spaced co-planar
cathodes 25, one for each beam, a control grid electrode 27, a screen
grid electrode 29, a first accelerating and focusing electrode 31, a
second accelerating and focusing electrode 33, and a shield cup 35,
spaced along the glass rods 23 in the order named.
Each cathode 25 comprises a cathode sleeve 37, closed at the forward end
by a cap 39 having an end coating 41 of electron emissive material and a
cathode support tube 43. The tubes 43 are supported on the rods 23 by
four straps 45 and 47 (FIG. 6). Each cathode 25 is indirectly heated by a
heater coil 49 positioned within the sleeve 37 and having legs 51
welded to heater straps 53 and 55 mounted by studs 57 on the rods 23
(FIG. 5). The control and screen grid electrodes 27 and 29 are two
closely-spaced (about 9 mils) flat plates having three pairs of small
(about 25 mils) aligned apertures 59 centered with the cathode coatings
41 to initiate three equally-spaced coplanar beam paths 20 extending
toward the screen 13. Preferably, the initial paths 20a and 20b are
substantially parallel and about 200 mils apart, with the middle path
20a coincident with the central axis A--A. 
Electrode
31 comprises first and second cup-shaped members 61 and 63,
respectively, joined together at their open ends. The first cup-shaped
member 61 has three medium-sized (about 60 mils) apertures 75 close to
grid electrode 29 and aligned respectively with the three beam paths 20,
as shown in FIG. 4. The second cup-shaped member 63 has three large
(about 160 mils) apertures 65 also aligned with the three beam paths.
Electrode 33 is also cup-shaped and comprises a base plate portion 60
positioned close (about 60 mils) to electrode 31 and a side wall or
flange 71 extending forward toward the tube screen. The base portion 69
is formed with three apertures 73, which are preferably slightly larger
(about 172 mils) than the adjacent apertures 67 of electrode 31. The
middle aperture 73a is aligned with the adjacent middle aperture 67a
(and middle beam path 20a) to provide a substantially symmetrical beam
focusing electric field between apertures 67a and 73a when electrodes 31
and 33 are energized at different voltages. The two outer apertures 73b
are slightly offset outwardly with respect to the corresponding outer
apertures 67b, to provide an asymmetrical electric field between each
pair of outer apertures when electrodes 31 and 33 are energized, to
individually focus each outer beam 20b near the screen, and also to
deflect each beam, toward the middle beam, to a common point of
convergence with the middle beam near the screen. In the example shown,
the offset of each beam aperture 73b may be about 6 mils. 
The
approximate configuration of the electric fields associated with the
middle and outer apertures are shown in FIGS. 9 and 10, respectively,
which show the equipotential lines 74 rather than the lines of force.
Assuming an accelerating field, as shown by the + signs, the left half
75 (on the left side of the central mid-plane) of each field is
converging and the right half 77 is diverging. Since the electrons are
being accelerated, they spend more time in the converging field than in
the diverging field, and hence, the beam experiences a net converging or
focusing force in each of FIGS. 9 and 10. Since the middle beam 20a
passes centrally through a symmetrical field in FIG. 9, it continues in
the same direction without deflection. In FIG. 10, the outer beam 20b
traverses the left half 75 of the field centrally, but enters the right
half 77 off-axis. Since this is the diverging part of the field, and the
electrons are subjected to field forces perpendicular to the
equipotential lines or surfaces 74, the beam 20b is deflected toward the
central axis (downward in FIG. 10) as it traverses the right half 77,
in addition to being focused. The angle of deflection, or convergence,
of the beam 20b can be determined by the choice of the offset of the
apertures 73 b and the voltages applied to the two electrodes 31 and 33.
For the example given, with an offset of 6 mils, electrode 33 would be
connected to the ultor or screen voltage, about 25 K.V., and electrode
31 would be operated at about 17 to 20 percent of the ultor voltage,
adjusted for best focus. The object distance of each focus lens, that
is, the distance between the first cross-over of the beams near the
screen grid 29 and the lens, is about 0.500 inch; and the image distance
from the lens to the screen is about 12.5. inches.
The above-described outward offset of the beam apertures to produce beam
convergence is contrary to the teaching of FIG. 3 of the Moodey patent
described above, and hence, is not suggested by the Moodey patent.
The focusing apertures 67 and 73 are made as large as possible, to
minimize spherical aberration, and as close together as possible, to
obtain a desirable small spacing between beam paths. As a result, the
fringe portions of adjacent fields interact to produce some astigmatic
distortion of the focusing fields, which produces some ellipticity of
the normally-circular focused beam spots on the screen. In a three-beam
in-line gun, this distortion is greater for the middle beam than for the
two outer beams, because both sides of the middle beam field are
affected. In order to compensate for this effect, and minimize the
elliptical distortion of the beam spots, the wall 69, or at least the
surface thereof facing the electrode 31, is curved substantially
cylindrically, concave to electrode 31, in the direction normal or
transverse to the plane of the three beams, as shown at 79 in FIG. 3.
Preferably, this curvature is greater for the middle beam path than for
the outer beam paths, hence, the wall 69 may be made barrel-shaped. In
the example given, the barrel shape may have a stave radius of 8 inches
(FIG. 4) and a hoop radius of 2.28 inches (FIG. 3), with the curvature
79 terminating at the outer edges of the outer apertures 73b.
The shield cup 35 comprises a base portion 81, attached to the open end
of the flange 71 of electrode 33, and a tubular wall 83 surrounding the
three beam paths 20. The base portion 81 is formed with a large middle
beam aperture 85 (about 172 mils) and two smaller outer beam apertures
87 (about 100 mils) aligned, respectively, with the three initial beam
paths 20a and 20b.
In order to compensate for the coma distortion wherein the sizes of the
rasters scanned on the screen by the external magnetic deflection yoke
are different for the middle and outer beams of the three-beam gun, due
to the eccentricity of the outer beams in the yoke field, the electron
gun is provided with two shield rings 89 of high magnetic permeability,
e.g., an alloy of 52 percent nickel and 48 percent iron, known as 52
metal, are attached to the base 81, with each ring concentrically
surrounding one of the outer apertures 87, as shown in FIGS. 4 and 7.
These magnetic shields 89 by-pass a small portion of the fringe
deflection fields in the path of the outer beams, thereby making a
slight reduction in the rasters scanned by the outer beams on the
screen. The shield rings 89 may have an outer diameter of 150 mils, an
inner diameter of 100 mils, and a thickness of 10 mils.
A further correction for this coma distortion is made by mounting two
small discs 91 of magnetic material, e.g., that referred to above, on
each side of the middle beam path 20a. These discs 91 enhance the
magnetic flux on the middle beam transverse to the plane of the three
beams and decrease the flux in that plane, in the manner described in
the Barkow patent referred to above. The discs 91 may be rings having an
outer diameter of 80 mils, an inner diameter of 30 mils, and a
thickness of 10 mils.
Each of the electrodes 27, 29, 31 and 33 are mounted on the two glass
rods 23 by edge portions embedded in the glass. The two rods 23 extend
forwardly beyond the mounting portion of electrode 33, as shown in FIG.
3. In order to shield the exposed ends 93 of the glass rods 23 from the
electron beams, the shield cup 35 is formed with inwardly-extending
recess portions 95 into which the rod ends 93 extend. The electron gun
19 is mounted in the neck 5 at one end by the leads (not shown) from the
various electrodes to the stem terminals 97, and at the other end by
conventional metal bulb spacers (not shown) which also connect the final
electrode 33 to the usual conducting coating on the inner wall of the
funnel 7.
screen, as shown in FIG. 4 of Moodey U.S. Pat. No. 2,957,106,
wherein the beam apertures in the gun electrodes are aligned along
convergent paths.
In order to avoid wide spacings between the cathodes, which are
undesirable in a small neck tube designed for high deflection angles, it
is preferable to initiate the beams along substantially parallel (or
even divergent) paths and provide some means, either internally or
externally of the tube, for converging the beams near the screen. Magnet
poles and/or electrostatic deflecting plates for converging in-line
beams are disclosed in Francken U.S. Pat. No. 2,849,647, Gundert et al.
U.S. Pat. No. 2,859,378 and Benway U.S. Pat No. 2,887,598.
The Moodey patent referred to above also includes an embodiment, shown
in FIG. 2 and described in lines 4 to 23 of column 5, wherein an in-line
gun for two co-planar beams comprises two spaced cathodes, a control
grid plate and an accelerating grid plate each having two apertures
aligned respectively with the two cathodes (as in FIG. 2) to initiate
two parallel co-planar beam paths, and two spaced-apart beam focusing
and accelerating electrodes of cylindrical form. The focusing electrode
nearest to the first accelerating grid plate is described as having two
beam apertures that are offset toward the axis of the gun from the
corresponding apertures of the adjacent accelerating grid plate, to
provide an asymmetric electrostatic field in the path of each beam for
deflecting the beam from its initial path into a second beam path
directed toward the tube axis.
Netherlands U.S. Pat. application No. 6902025, published Aug. 11, 1970
teaches that astigmatic aberration resulting in elliptical distortion of
the focused screen spots of the two off-axis beams from an in-line gun,
caused by the eccentricity of the in-line beams in a common focusing
field between two hollow cylindrical focusing electrodes, can be
partially corrected by forming the adjacent edges of the cylindrical
electrodes with a sinusoidal contour including four sine waves. A
similar problem is solved in a different manner in applicant's in-line
gun. Another
problem that exists in a cathode ray tube having an in-line gun is a
coma distortion wherein the sizes of the rasters scanned on the screen
by a conventional external magnetic deflection yoke are different,
because of the eccentricity of the two outer beams with respect to the
center of the yoke. Messineo et al. U.S. Pat. No. 3,164,737 teaches that
a similar coma distortion caused by using different beam velocities can
be corrected by use of a magnetic shield around the path of one or more
beams in a delta type gun. Barkow U.S. Pat. No. 3,196,305 teaches the
use of magnetic enhancers adjacent to the path of one or more beams in a
delta gun, for the same purpose. Krackhardt et al. U.S. Pat. No.
3,534,208 teaches the use of a magnetic shield around the middle one of
three in-line beams for coma correction.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, at least two electron
beams are generated along co-planar paths toward the screen of a cathode
ray tube, e.g., a shadow mask type color picture tube, and the beams
are converged near the screen by asymmetric electric fields established
in the paths of two beams by two plate-like grids positioned between the
beam generating means and the screen and having corresponding apertures
suitably related to the beam paths. The apertures in the first grid
(nearest the cathodes) are aligned with the beam paths. Two apertures in
the second grid (nearest the screen) are offset outwardly with respect
to the beam paths to produce the desired asymmetric fields. In the case
of three in-line beams, the two outer apertures are offset, and the
middle apertures of the two grids are aligned with each other. The pairs
of corresponding apertures also provide separate focusing fields for
the beams. In order to minimize elliptical distortion of one or more of
the focused beam spots on the screen due to crowding of adjacent beam
focusing fields, at least a portion of the second grid may be
substantially cylindrically curved in a direction transverse to the
common plane of the beams, and concave to the first grid. Each of the
two outer beam paths of a three beam gun may be partially shielded from
the magnetic flux of the deflection yoke by means of a magnetic ring
surrounding each beam in the deflection zone of the tube, to minimize
differences in the size of the rasters scanned on the screen by the
middle and outer beams. Further correction for coma distortion may be
made by positioning magnetic pieces on opposite sides of the middle beam
path for enhancing one field and reducing the field transverse thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view, partly in axial section, of a shadow mask color
picture tube in which the present invention is incorporated;
FIG. 2 is a front end view of the tube of FIG. 1 showing the rectangular
shape;
FIG. 3 is an axial section view of the electron gun shown in dotted
lines in FIG. 1, taken along the line 3--3 of that figure;
FIG. 4 is an axial section view of the electron gun taken along the line
4--4 of FIG. 3;
FIG. 5 is a rear end view of the electron gun of FIG. 4, taken in the
direction of the arrows 5--5 thereof;
FIG. 6 is a transverse view, partly in section, taken along the line
6--6 of FIG. 4;
FIG. 7 is a front end view of the electron gun of FIGS. 1 and 4;
FIG. 8 is a similar end view with the final element (shield cup)
removed; and
FIGS. 9 and 10 are schematic views showing the focusing and converging
electric fields associated with two pairs of beam apertures in FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a plan view of a 17V-90° rectangular color picture tube, for
example, having a glass envelope 1 made up of a rectangular (FIG. 2)
faceplate panel or cap 3 and a tubular neck 5 connected by a rectangular
funnel 7. The panel 3 comprises a viewing faceplate 9 and a peripheral
flange or side wall 11 which is sealed to the funnel 7. A mosaic
three-color phosphor screen 13 is carried by the inner surface of the
faceplate 9. The screen is preferably a line screen with the phosphor
lines extending substantially parallel to the minor axis Y-Y of the tube
(normal to the plane of FIG. 1). A multi-apertured color selection
electrode or shadow mask 15 is removably mounted, by conventional means,
in predetermined spaced relation to the screen 13. An improved in-line
electron gun 19, shown schematically by dotted lines in FIG. 1, is
centrally mounted within the neck 5 to generate and direct three
electron beams 20 along co-planar convergent paths through the mask 15
to the screen 13. 
The
tube of FIG. 1 is designed to be used with an external magnetic
deflection yoke, such as the yoke 21 schematically shown, surrounding
the neck 5 and funnel 7, in the neighborhood of their junction, for
subjecting the three beams 20 to vertical and horizontal magnetic flux,
to scan the beams horizontally and vertically in a rectangular raster
over the screen 13. The initial plane of deflection (at zero deflection)
is shown by the line P--P in FIG. 1 at about the middle of the yoke 21.
Because of fringe fields, the zone of deflection of the tube extends
axially, from the yoke 21, into the region of the gun 19. For
simplicity, the actual curvature of the deflected beam paths 20 in the
deflection zone is not shown in FIG. 1.
The in-line gun 19 of the present invention is designed to generate and
direct three equally-spaced co-planar beams along initially-parallel
paths to a convergence plane C--C, and then along convergent paths
through the deflection plane to the screen 13. In order to use the tube
with a line-focus yoke 21 specially designed to maintain the three
in-line beams substantially converged at the screen without the
application of the usual dynamic convergence forces, which causes
degrouping misregister of the beam spots with the phosphor elements of
the screen, the gun is preferably designed with samll spacings between
the beam paths at the convergence plane C--C to produce a still smaller
spacing, usually called the S value, between the outer beam paths and
the central axis A--A of the tube, in the deflection plane P--P. The
convergence angle of the outer beams with the central axis is arc tan
e/c+d, where c is the axial distance between the convergence plane C--C
and the deflection plane P--P, d is the distance between the deflection
plane and the screen 13, and e is the spacing between the outer beam
paths and the central axis A--A in the convergence plane C--C. The
approximate dimensions in FIG. 1 are c = 2.7 inches, d = 9.8 inches, e =
0.200 inch (200 mils), and hence, the convergence angle is 55 minutes
and s = 157 mils. 
The
details of the improved gun 19 are shown in FIGS. 3 through 8. The gun
comprises two glass support rods 23 on which the various electrodes are
mounted. These electrodes include three equally-spaced co-planar
cathodes 25, one for each beam, a control grid electrode 27, a screen
grid electrode 29, a first accelerating and focusing electrode 31, a
second accelerating and focusing electrode 33, and a shield cup 35,
spaced along the glass rods 23 in the order named.
Each cathode 25 comprises a cathode sleeve 37, closed at the forward end
by a cap 39 having an end coating 41 of electron emissive material and a
cathode support tube 43. The tubes 43 are supported on the rods 23 by
four straps 45 and 47 (FIG. 6). Each cathode 25 is indirectly heated by a
heater coil 49 positioned within the sleeve 37 and having legs 51
welded to heater straps 53 and 55 mounted by studs 57 on the rods 23
(FIG. 5). The control and screen grid electrodes 27 and 29 are two
closely-spaced (about 9 mils) flat plates having three pairs of small
(about 25 mils) aligned apertures 59 centered with the cathode coatings
41 to initiate three equally-spaced coplanar beam paths 20 extending
toward the screen 13. Preferably, the initial paths 20a and 20b are
substantially parallel and about 200 mils apart, with the middle path
20a coincident with the central axis A--A. 
Electrode
31 comprises first and second cup-shaped members 61 and 63,
respectively, joined together at their open ends. The first cup-shaped
member 61 has three medium-sized (about 60 mils) apertures 75 close to
grid electrode 29 and aligned respectively with the three beam paths 20,
as shown in FIG. 4. The second cup-shaped member 63 has three large
(about 160 mils) apertures 65 also aligned with the three beam paths.
Electrode 33 is also cup-shaped and comprises a base plate portion 60
positioned close (about 60 mils) to electrode 31 and a side wall or
flange 71 extending forward toward the tube screen. The base portion 69
is formed with three apertures 73, which are preferably slightly larger
(about 172 mils) than the adjacent apertures 67 of electrode 31. The
middle aperture 73a is aligned with the adjacent middle aperture 67a
(and middle beam path 20a) to provide a substantially symmetrical beam
focusing electric field between apertures 67a and 73a when electrodes 31
and 33 are energized at different voltages. The two outer apertures 73b
are slightly offset outwardly with respect to the corresponding outer
apertures 67b, to provide an asymmetrical electric field between each
pair of outer apertures when electrodes 31 and 33 are energized, to
individually focus each outer beam 20b near the screen, and also to
deflect each beam, toward the middle beam, to a common point of
convergence with the middle beam near the screen. In the example shown,
the offset of each beam aperture 73b may be about 6 mils. 
The
approximate configuration of the electric fields associated with the
middle and outer apertures are shown in FIGS. 9 and 10, respectively,
which show the equipotential lines 74 rather than the lines of force.
Assuming an accelerating field, as shown by the + signs, the left half
75 (on the left side of the central mid-plane) of each field is
converging and the right half 77 is diverging. Since the electrons are
being accelerated, they spend more time in the converging field than in
the diverging field, and hence, the beam experiences a net converging or
focusing force in each of FIGS. 9 and 10. Since the middle beam 20a
passes centrally through a symmetrical field in FIG. 9, it continues in
the same direction without deflection. In FIG. 10, the outer beam 20b
traverses the left half 75 of the field centrally, but enters the right
half 77 off-axis. Since this is the diverging part of the field, and the
electrons are subjected to field forces perpendicular to the
equipotential lines or surfaces 74, the beam 20b is deflected toward the
central axis (downward in FIG. 10) as it traverses the right half 77,
in addition to being focused. The angle of deflection, or convergence,
of the beam 20b can be determined by the choice of the offset of the
apertures 73 b and the voltages applied to the two electrodes 31 and 33.
For the example given, with an offset of 6 mils, electrode 33 would be
connected to the ultor or screen voltage, about 25 K.V., and electrode
31 would be operated at about 17 to 20 percent of the ultor voltage,
adjusted for best focus. The object distance of each focus lens, that
is, the distance between the first cross-over of the beams near the
screen grid 29 and the lens, is about 0.500 inch; and the image distance
from the lens to the screen is about 12.5. inches.
The above-described outward offset of the beam apertures to produce beam
convergence is contrary to the teaching of FIG. 3 of the Moodey patent
described above, and hence, is not suggested by the Moodey patent.
The focusing apertures 67 and 73 are made as large as possible, to
minimize spherical aberration, and as close together as possible, to
obtain a desirable small spacing between beam paths. As a result, the
fringe portions of adjacent fields interact to produce some astigmatic
distortion of the focusing fields, which produces some ellipticity of
the normally-circular focused beam spots on the screen. In a three-beam
in-line gun, this distortion is greater for the middle beam than for the
two outer beams, because both sides of the middle beam field are
affected. In order to compensate for this effect, and minimize the
elliptical distortion of the beam spots, the wall 69, or at least the
surface thereof facing the electrode 31, is curved substantially
cylindrically, concave to electrode 31, in the direction normal or
transverse to the plane of the three beams, as shown at 79 in FIG. 3.
Preferably, this curvature is greater for the middle beam path than for
the outer beam paths, hence, the wall 69 may be made barrel-shaped. In
the example given, the barrel shape may have a stave radius of 8 inches
(FIG. 4) and a hoop radius of 2.28 inches (FIG. 3), with the curvature
79 terminating at the outer edges of the outer apertures 73b.
The shield cup 35 comprises a base portion 81, attached to the open end
of the flange 71 of electrode 33, and a tubular wall 83 surrounding the
three beam paths 20. The base portion 81 is formed with a large middle
beam aperture 85 (about 172 mils) and two smaller outer beam apertures
87 (about 100 mils) aligned, respectively, with the three initial beam
paths 20a and 20b.
In order to compensate for the coma distortion wherein the sizes of the
rasters scanned on the screen by the external magnetic deflection yoke
are different for the middle and outer beams of the three-beam gun, due
to the eccentricity of the outer beams in the yoke field, the electron
gun is provided with two shield rings 89 of high magnetic permeability,
e.g., an alloy of 52 percent nickel and 48 percent iron, known as 52
metal, are attached to the base 81, with each ring concentrically
surrounding one of the outer apertures 87, as shown in FIGS. 4 and 7.
These magnetic shields 89 by-pass a small portion of the fringe
deflection fields in the path of the outer beams, thereby making a
slight reduction in the rasters scanned by the outer beams on the
screen. The shield rings 89 may have an outer diameter of 150 mils, an
inner diameter of 100 mils, and a thickness of 10 mils.
A further correction for this coma distortion is made by mounting two
small discs 91 of magnetic material, e.g., that referred to above, on
each side of the middle beam path 20a. These discs 91 enhance the
magnetic flux on the middle beam transverse to the plane of the three
beams and decrease the flux in that plane, in the manner described in
the Barkow patent referred to above. The discs 91 may be rings having an
outer diameter of 80 mils, an inner diameter of 30 mils, and a
thickness of 10 mils.
Each of the electrodes 27, 29, 31 and 33 are mounted on the two glass
rods 23 by edge portions embedded in the glass. The two rods 23 extend
forwardly beyond the mounting portion of electrode 33, as shown in FIG.
3. In order to shield the exposed ends 93 of the glass rods 23 from the
electron beams, the shield cup 35 is formed with inwardly-extending
recess portions 95 into which the rod ends 93 extend. The electron gun
19 is mounted in the neck 5 at one end by the leads (not shown) from the
various electrodes to the stem terminals 97, and at the other end by
conventional metal bulb spacers (not shown) which also connect the final
electrode 33 to the usual conducting coating on the inner wall of the
funnel 7.
Here below the images of the rest of the completely abandoned Anagni VIDECOLOR Production Factory
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