Abstract:
A CRT socket has a partition wall for partitioning a focus contact storing chamber and a base insertion hole which has sufficient strength, while maintaining a creepage distance between a focus contact and a signal contact sufficient to avoid arcing. The focus contact is formed in a leaf shape. A partition wall on a side of the base portion is interposed utilizing a gap in which a pin-type focus contact is interposed between a base and a focus pin in a cathode ray tube. The outside face of a projecting portion is covered with the partition wall. Increased strength is obtained in the partition wall for partitioning the focus contact storing chamber and the base insertion hole. The creepage distance between the focus contact and the signal contact is lengthened by forcing charges to travel, not only over the surfaces, but also along overlapping surfaces.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to the structure of a CRT (Cathode-Ray-Tube) socket for connecting a cathode ray tube used in a color television, etc., and particularly relates to a CRT socket for reliably insulating a focus contact and a signal contact from each other.  
           [0003]    2. Description of the Background Art  
           [0004]    Referring now to FIGS. 9 and 10, a base insertion hole  101 , in a conventional CRT socket  100 , is formed in an insulating housing  102 . A plurality of signal contacts  103 ,  103 , - - - and focus contacts  104 ,  104 , - - - are formed at predetermined intervals in the insulating housing  102 , around the outside of the base insertion hole  101 , on the same circular circumference concentric to the base insertion hole  101 .  
           [0005]    A columnar base  100   a  of a CRT tube is inserted into the base insertion hole  101  and connected from a front face side (an upper side in FIG. 10) of the CRT socket  100  to the base insertion hole  101 . A signal pin  100   b  and a focus pin  100   c,  arranged on the same circular circumference around the base  100   a,  respectively, are in physical and electrical contact with the signal contact  103  and the focus contact  104  facing the front face side.  
           [0006]    The signal contact  103  and the focus contact  104  both have a conductive metallic plate that has been press-worked and formed in a bottle type (sometimes known as a banana plug) in which a connecting portion has a cylindrical shape and a drawn intermediate portion. The columnar signal pin  100   b  and the focus pin  100   c  are inserted into the drawn portion and are secured in place by a predetermined contact pressure.  
           [0007]    A neck diameter of the cathode ray tube is reduced to make the cathode ray tube compact. As a result, the attaching positions of the contacts  103 ,  104  in the insulating housing  102  are closely spaced to each other. Accordingly, there is a concern that the focus contact  104  and the signal contact  103  are short-circuited along a surface of the insulating housing  102  since a high voltage of several thousands volts is applied to the focus pin  100   c.  To reduce the chance of such arc-over, the insulating housing  102  includes a ring-shaped portion  105  attached to the signal contact  103 , a cover portion  106  attached to the focus contact  104 , and a base portion  109  covering the rear of the cover portion  106 .  
           [0008]    Creepage is defined as the conduction of electricity across the surface of a dielectric. A creepage distance is the distance along a dielectric that such conduction must occur for an arc to be formed. The creepage distance in the prior-art device is the distance along the surface of the insulating housing  102  between the focus contacts  104  and the signal contacts  103 . The creepage distance is extended by interposing a slit  107  between the ring-shaped portion  105  and the cover portion  106 . The rear face of a focus contact storing chamber  108  for storing a contact portion of the focus contact  104  is covered with the base portion  109 . This construction reduces the chance of the above short circuit.  
           [0009]    Referring now also to FIG. 11, the gap (L) between the base  100   a  and the focus pin  100   c  is very narrow to reduce the neck diameter of the cathode ray tube. In the conventional CRT socket  100 , the focus contact  104  and a partition wall  106   a  of the cover portion  106  are interposed in this gap (L). Therefore, the thickness of the partition wall  106   a  is limited to a value that is less than desired. As a result, the strength of the partition wall  106   a  for partitioning the focus contact storing chamber  108  and the base insertion hole  101  is insufficient. Therefore, there is a chance that the partition wall  106   a  will be damaged when the cathode ray tube is forced into the socket at a slant when making the connection.  
           [0010]    The rear face of the focus contact storing chamber  108  is covered by the base portion  109 . A short-circuited electric current flows to an abutting portion of the cover portion  106  and the base portion  109 , i.e., a rear face side of the ring-shaped portion  105  via a rear face of the partition wall  106 . Accordingly, the distance between the focus contact  104  and the signal contact  103  cannot be made great enough to avoid arc-over.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0011]    To solve the above problems, an object of this invention is to provide a CRT socket in which a partition wall for partitioning a focus contact storing chamber and a base insertion hole has sufficient strength, and the creepage distance between a focus contact and a signal contact can be set to a sufficient length.  
           [0012]    To solve the above problems, a CRT socket of the invention comprises an insulating housing in which the insulating housing is constructed by a ring-shaped portion in which a cylindrical base insertion hole is bored and plurality of signal contact storing chambers are concavely arranged from a rear face side on an outside circular circumference of the base insertion hole; a cover portion for arranging a focus contact storing chamber on the same circular circumference as the signal contact storing chambers by projecting a projecting portion concavely having the focus contact storing chamber from the rear face side to a portion having no ring-shaped portion; and a base portion for covering the rear face side of the cover portion; and the cover portion and the base portion are integrated with each other by molding the ring-shaped portion integrally with the cover portion or the base portion, and engaging the cover portion and the base portion with each other; a signal contact stored in each signal contact storing chamber; and a focus contact stored in the focus contact storing chamber; wherein a pin insertion hole communicated with the signal contact storing chamber and the focus contact storing chamber from front face sides of the ring-shaped portion and the projecting portion is bored, and a signal pin and a focus pin of a cathode ray tube arranged on an outside circular circumference of a base are respectively electrically connected to the signal contact and the focus contact, the CRT socket includes the focus contact constructed by a conductive metallic plate of a band shape, and an intermediate portion of the conductive metallic plate is bent at an acute angle, a bent basic end side is set to a supporting portion, and a bent tip side is set to a leaf spring contact portion; the supporting portion rises and is supported along an inner wall face of the focus contact storing chamber facing a direction of the base insertion hole, and the leaf spring contact portion faces the pin insertion hole; and an outside face of the projecting portion is covered with a partition wall rising on the front face side from the base portion.  
           [0013]    The focus contact is formed in a leaf type in which an intermediate portion of the metallic plate of a band shape is bent at an acute angle. A supporting portion of the focus contact rises and is supported along an inner wall face facing the direction of the base insertion hole. Therefore, there is no focus contact interposed in a gap (L) between the base and the focus pin in the cathode ray tube. Accordingly, it is possible to increase the thickness of the partition wall to a thickness of the focus contact from the base portion, and cover the outside face of the projecting portion.  
           [0014]    Since the partition wall of the base portion overlaps the outside of a partition wall of the projecting portion, increased strength is obtained in the partition wall for partitioning the focus contact storing chamber and the base insertion hole.  
           [0015]    The distance between the focus contact and the signal contact is extended by the partition wall rising from the base portion sufficiently to achieve sufficient length for mutual insulation.  
           [0016]    The CRT socket of the invention includes the ring-shaped portion and the base portion being integrally molded. The cover portion is engaged with the base portion and is attached to the front face side of the base portion.  
           [0017]    The signal contact is stored in the signal contact storing chamber concavely arranged from the rear face side of the ring-shaped portion. The focus contact is stored in the focus contact storing chamber concavely arranged in the cover portion.  
           [0018]    Since the cover portion is engaged with the front face side of the base portion integrated with the ring-shaped portion, the focus contact is stored on the front face side and the signal contact is stored on the rear face side through the ring-shaped portion and the base portion. Accordingly, the distance between the focus contact and the signal contact can be easily lengthened.  
           [0019]    The CRT socket according to a further embodiment of the invention includes a base portion formed in a box shape in which the partition wall rises along a peripheral portion of the base portion, and the cover portion is formed in a contour shape internally fitted to the box shape.  
           [0020]    Since the base portion is formed in a box shape, the base portion is easily positioned with respect to the cover portion, and the base portion and the cover portion engage each other without rattling.  
           [0021]    The CRT socket of the invention is characterized in that a pair of projecting portions forked into two branches is formed in the cover portion, and the focus contact is stored in the focus contact storing chamber of each projecting portion.  
           [0022]    The outside face of the projecting portion is also covered with the partition wall rising from the base portion even in a double focus type having a pair of focus contacts. Accordingly, the distance between the respective focus contacts, or the distance between each focus contact and the signal contact can be set to a sufficient length to provide insulation.  
           [0023]    The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    [0024]FIG. 1 is a partially broken side view of a CRT socket according to an embodiment of the present invention.  
         [0025]    [0025]FIG. 2 is a longitudinal sectional view of a main portion of the CRT socket of FIG. 1.  
         [0026]    [0026]FIG. 3 is a perspective view of the CRT socket of FIG. 1.  
         [0027]    [0027]FIG. 4 is views showing respective portions of an insulating housing in which FIG. 4( a ) is a plan view of a ring-shaped portion and a base portion, and FIG. 4( b ) is a plan view of a cover portion.  
         [0028]    [0028]FIG. 5 is a bottom view of the CRT socket in which one portion of the base portion is broken away.  
         [0029]    [0029]FIG. 6 is an exploded perspective view of the cover portion.  
         [0030]    [0030]FIG. 7 is a longitudinal sectional view showing an attachment of the cover portion.  
         [0031]    FIGS.  8 ( a ),  8 ( b ) and  8 ( c ) are respectively front, side and bottom views of a focus contact.  
         [0032]    [0032]FIG. 9 is a plan view showing a conventional CRT socket.  
         [0033]    [0033]FIG. 10 is a longitudinal sectional view of the conventional CRT socket.  
         [0034]    [0034]FIG. 11 is a longitudinal sectional view of a main portion of the conventional CRT socket.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    Referring to FIGS. 1, 2,  3  and  4 ( a )- 4 ( b ), a CRT socket 1 has an injection molded insulating housing  2  of synthetic resin. A plurality of signal contacts  6  and a pair of focus contacts  7  are attached to the insulating housing  2 . The insulating housing  2  includes a ring-shaped portion  3 , a base portion  4  and a cover portion  5 . A base insertion hole  8  is formed at a center of the ring-shaped portion  3 . The base portion  4  is arranged backward (leftward in FIG. 4) from the ring-shaped portion  3 , and is integrally continuously connected to the ring-shaped portion  3 . A front face side of the base portion  4  is covered with the cover portion  5 .  
         [0036]    The base insertion hole  8  is cylindrical with an inside diameter slightly larger than the outside diameter of a base  100   a  of the cathode ray tube so as to permit insertion of the base  100   a  from a front face side of the ring-shaped portion  3 . In the ring-shaped portion  3 , a signal contact storing chamber  9  is concavely arranged from a rear face in each of nine positions on the same circular circumference outside the base insertion hole  8 . Each of nine signal contacts  6  is attached and stored in signal contact storing chamber  9  from the rear face side.  
         [0037]    As shown in FIG. 7, each signal contact  6  is formed by bending a band-shaped elongated conductive metallic plate. One end of a supporting portion  6   b  is bent at an acute angle to form a signal contact portion  6   a.  The other end of the supporting portion  6   b  is double bent into a crank shape, with the outer portion of the crank shape forming a guiding portion  6   c.  The signal contact portion  6   a  is further bent in its intermediate portion on a side of the supporting portion  6   b  and is formed in a leaf type having an L-shape in section.  
         [0038]    In this signal contact  6 , engaging claws on both edges of the supporting portion  6   b  engaged inner walls of the signal contact storing chamber  9  to fixedly position the signal contact  6  in the ring-shaped portion  3 . As best seen in FIG. 1, the supporting portion  6   b  passes upward within the signal contact storing chamber  9  with the signal contact  6  fixedly attached in the ring-shaped portion  3 . The signal contact portion  6   a  is a cantilever spring projecting in a central direction (toward the base insertion hole 8) of the ring-shaped portion  3  with a side of the supporting portion  6   b  as a basic end. The guiding portion  6   c  is bent in the rear direction to project radially beyond the rear face of the ring-shaped portion  3  (hereinafter, a rear face direction of the insulating housing 2 is called downward and a front face direction of the insulating housing 2 is called upward in FIG. 1). The guiding portion  6   c  is soldered to a pattern of a printed wiring board  110 .  
         [0039]    An upper side of the signal contact storing chamber  9  communicates with the front face side of the ring-shaped portion  3  by a pin insertion hole  10 . A signal pin  100   b  of the cathode ray tube is inserted into the pin insertion hole  10  and is guided downward by this pin insertion hole  10 . The signal pin  100   b  inserted into the pin insertion hole  10  comes in elastic contact with the signal contact portion  6   a  of the signal contact  6  in the signal contact storing chamber  9 .  
         [0040]    A ring-shaped ground fitting  11  is exposed in a slight discharge gap outside the signal contact  6  with in the signal contact storing chamber  9 . When an abnormal voltage is applied to the signal contact  6 , an electric current is discharged to the ground fitting  11 .  
         [0041]    As can be clearly seen by comparing FIGS.  4 ( a ) and  4 ( b ), the base portion  4  continuously arranged backward from the ring-shaped portion  3  is formed in a shape in which the cover portion  5  is fitted to a plane contour from an outer side to cover an entire rear face of the cover portion  5 . The base portion  4  is box shaped in which a partition wall  13  rises along this contour.  
         [0042]    A front portion of the base portion  4  is divided by three slits  12 ,  12 ,  12  into a pair of fan-shaped concave portions  4   a,    4   a  with the base insertion hole  8  as a center. The fan-shaped concave portions  4   a,    4   a  are continuous on the same circle as the ring-shaped portion  3 . The partition wall  13   a  covering a peripheral portion of each of the fan-shaped concave portions  4   a,    4   a  constitutes one portion of an inner wall of the base insertion hole  8 .  
         [0043]    An engaging frame portion  4   b  extends upward on both sides of the base portion  4 . The engaging frame portion  4   b  is integrally engaged with an engaging projection  5   a  of the cover portion  5 , covering the rear face side of the cover portion  5 . An insulating projection  14  is formed on an inner side of the base portion  4  surrounded by the partition wall  13 . The insulating projection  14  projects into the cover portion  5  when the insulating projection  14  is installed in the cover portion  5 . The insulating projection  14  prevents discharge between conductive portions such as the focus contact  7  located in the cover portion  5 , etc.  
         [0044]    As shown in FIG. 6, a pair of focus contacts  7 A,  7 B, a pair of discharge electrode plates  15 A,  15 B, a resistance element  16  and a terminal  17  are disposed in the cover portion  5 .  
         [0045]    Focus contact storing chambers  18 ,  18  for storing the focus contacts  7 A,  7 B, a joint connecting chamber  26  connected to the focus contact  7  and the discharge electrode plate  15 , a discharge chamber  19  oppositely arranged between the discharge electrode plates  15 A and  15 B, and lead connecting chambers  20 ,  27  in two places for inserting lead wires are respectively formed in concave portions spaced from the other chambers by an insulating projecting wall  21  formed vertically from an inner top face (an inner bottom face in FIG. 6) of the cover portion  5 . When the base portion  4  and the cover portion  5  are engaged, a notched portion of this insulating projecting wall  21  is covered with the above insulating projection  14  of the cover portion  5  to prevent electrical discharge between the respective chambers.  
         [0046]    Portions of the cover portion  5  fitted to the fan-shaped concave portions  4   a,    4   a  of the base portion  4  on their inner sides are set to a pair of fan-shaped projecting portions  22 ,  22 . The focus contact storing chambers  18 ,  18  are respectively concavely formed upward from a bottom side to this pair of projecting portions  22 ,  22 . As shown in FIG. 2, an upper portion of the focus contact storing chamber  18  communicates with the front face side of the cover portion  5  through a focus pin insertion hole  23  into which the focus pin  100   c  is inserted. When the base portion  4  and the cover portion  5  are engaged with each other during assembly, the focus pin insertion hole  23  is located in a position on the same circular circumference as the signal contact storing chamber  9  for storing the signal contact  6 , and is communicated with an upper portion of a front wall face  18   a  of the focus contact storing chamber  18 . The focus pin insertion hole  23  guides the focus pin  100   c  of the cathode ray tube downward along the front wall face  18   a  of the focus contact storing chamber  18 . A positioning groove  18   c  (see FIG. 6) for fixedly positioning the focus contact  7  in a vertical direction is concavely formed on both rear side faces in the focus contact storing chamber  18 .  
         [0047]    The focus contact  7  is formed by bending a band-shaped elongated electrically conductive metallic plate. As shown in FIGS.  8 ( a )- 8 ( c ), a high voltage contact portion  24  and a spring contact portion  25  respectively extend upward on the sides of a connecting portion  7   a  in its longitudinal direction. The high voltage contact portion  24  is continuously arranged on a front side of the connecting portion  7   a,  and is constructed of a rising supporting portion  24   a  and a leaf contact portion  24   b.  An upper end of the supporting portion  24   a  is bent at an acute angle to form the leaf contact portion  24   b  on its free end. An intermediate portion of the leaf spring contact portion  24   b  is bent on a side of the supporting portion  24   a  so that the leaf spring contact portion  24   b  is formed in a leaf type of an L-shape in section.  
         [0048]    The high voltage contact portion  24  of the focus contact  7  is installed in the focus contact storing chamber  18 . As shown in FIG. 2, engaging claws on both sides of the supporting portion  24   a  engage respective positioning groove  18   c  to position and retain focus contact  7  in the focus contact storing chamber  18 . In this stored state, the supporting portion  24   a  rises along a rear side face within the focus contact storing chamber  18 , i.e., a rear wall face  18   b  facing a side of the base insertion hole  8 . The leaf spring contact portion  24   b  acts as a cantilever spring facing a lower portion of the focus pin insertion hole  23  with an upper end of the supporting portion  24   a  as a basic end.  
         [0049]    The spring contact portion  25  extends upward on a rear side of the connecting portion  7   a.  An upper end of the spring contact portion  25  forms a spring contact piece  25   a  bent at an acute angle on a rear side. As shown in FIGS. 5 and 6, the pair of focus contacts  7 A,  7 B are respectively attached to the cover portion  5  extending radially with the base insertion hole  8  as a center. The spring contact portion  25  of one focus contact  7 A is inserted and positioned within the joint connecting chamber  26 . A tip of the spring contact piece  25   a  comes in elastic contact with a connecting plate portion  15   a  of the discharge electrode plate  15 A crossing and exposed within the joint connecting chamber  26 . The spring contact portion  25  of the other focus contact  7 B is inserted and positioned in a lead connecting chamber  20  opened on a front face side, and nips and electrically connects an unillustrated first external lead wire inserted from the front face side between the spring contact piece  25   a  and an inside face of the lead connecting chamber  20 . The pair of focus contacts  7 A,  7 B connected to the discharge electrode plate  15  and the lead wire are formed in the same shape so that the same parts are commonly used and the number of parts is reduced and no error in connection is caused even when the focus contacts  7 A,  7 B are respectively attached on the other side.  
         [0050]    Further, a press contact slit  28  is formed on a side of the focus contact  7 A from a center of the connecting portion  7   a  to the spring contact portion  25  so permit electrical connection to an inside lead portion  16   a  of the resistance element  16 . The width of the groove in the press contact slit  28  is slightly narrower than an outside diameter of the inside lead portion  10   b  of the resistance element  16 . The inside lead portion  10   b,  inserted from the front face side to the press contact slit  28 , comes into press contact with the press contact slit  28  and is connected to this press contact slit  28 .  
         [0051]    A discharge portion  15   b  of a semispherical shape is formed at the center of a rectangular plate in each of the pair of discharge electrode plates  15 A,  15 B. The discharge portions  15   b,    15   b  are attached to the cover portion  5  along the insulating projecting wall  21  around the discharge chamber  19  such that the discharge portions  15   b,    15   b  face each across the discharge chamber  19 .  
         [0052]    The connecting plate portion  15   a  of an L-shape crossing within the joint connecting chamber  26  is integrally formed on a side of the rectangular plate of the one discharge electrode plate  15 A. The rectangular plate is connected to the spring contact portion  25  of the focus contact  7 A as mentioned above. A leg portion  15   c  is vertically arranged integrally from the rectangular plate in the other discharge electrode plate  15 B. The leg portion  15   c  is inserted into the base portion  4  where it is soldered to a ground pattern of the printed wiring board  110 .  
         [0053]    Thus, the focus contact  7 A is connected to the discharge electrode plate  15 A, and the ground pattern is connected to the discharge electrode plate  15 B. The discharge portions  15   b,    15   b  oppose each other across a discharge gap.  
         [0054]    When spark energy generated within the cathode ray tube is applied to the focus contact  7 A, a discharge between the discharge portions  15   b  and  15   b  discharges electric current to the ground pattern.  
         [0055]    Each lead connecting chamber  27  extends through front and rear sides of the cover portion  5  in a position of the cover portion  5  on an extension line of the focus contact  7 A. As shown in FIG. 7, an intermediate inside diameter of the lead connecting chamber  27  is reduced so that an unillustrated second external lead wire inserted from the front face side is guided by the lead connecting chamber  27  to a terminal  17  extending from an intermediate portion to a downward portion (rear face side).  
         [0056]    As shown in FIGS. 6 and 7, the terminal  17  is formed by bending a band-shaped conductive metallic plate to form a lead connecting piece  17   a  and a press contact connecting portion  17   b.  The lead connecting piece  17   a  is formed by bending this metallic plate at an acute angle on a rear side. A press contact slit is formed at a folding center of the press contact connecting portion  17   b.  An engaging claw projecting from a side face of the terminal  17  engages an inside face of the lead connecting chamber  27  so that the terminal  17  is retained in the lead connecting chamber  27 . The upper lead connecting piece  17   a  faces an intermediate downward portion of the drawn lead connecting chamber  27 , and nips and electrically connects the second external lead wire inserted from the front face side. When an outside lead portion  16   b  of the resistance element  16  comes in press contact with a press contact slit of the lower press contact connecting portion  17   b,  the resistance element  16  is positioned in a straight line collinear with the focus contact  7 A, and the focus contact  7 A to electrically connect the second external lead wire through the resistance element  16  and the terminal  17 .  
         [0057]    These parts in the cover portion  5  are respectively attached from above when an open face of the cover portion  5  on its rear face side is turned upward. Next, the cover portion  5  containing the respective parts therein is installed on a front face side of the base portion  4  with the cover portion  5  fitted into the partition wall  13  of the base portion  4 . Then, an engaging projection  5   a  (see FIG. 1) of the cover portion  5  and an engaging frame portion  4   b  of the base portion  4  are engaged and integrated with each other. At this time, the partition wall  13   a  of the base portion  4  covers a peripheral portion of the projecting portion  22  forming the focus contact storing chamber  18  therein from the rear face side. Accordingly, the distance between each of the focus contacts  7 A,  7 B and the signal contact  6 , or the distance between the focus contacts  7 A and  7 B is sufficient to provide mutual insulation. Further, since the focus contact storing chamber  18  is doubly covered with the projecting portion  22  and the partition wall  13   a,  sufficient strength is obtained.  
         [0058]    The present invention is not limited to the above embodiment mode, but can be variously modified. For example, the present invention may also have a structure in which the cover portion  5  and the ring-shaped portion  3  are integrally molded and the base portion  4  covering the rear face side of the cover portion  5  is separately molded and engaged with the cover portion  5 .  
         [0059]    In the embodiment shown and described, the CRT socket 1 is of a double focus contact type having two focus contacts  7 A,  7 B. However, the present invention can be also applied to a CRT socket having only one focus contact. The two focus contacts  7 A,  7 B have the same shape, but the shapes of the focus contacts  7 A,  7 B are not limited to the above example if the high voltage contact portion  24  coming in contact with the focus pin  100   c  is a leaf type.  
         [0060]    In the above example, the base portion  4  is formed in a box shape in which the partition wall  13  rises along a peripheral portion of the base portion  4 . However, if at least the partition wall  13   a  on a front face of the base portion  4  rises and is interposed between the projecting portion  22  and the base insertion hole  8 , this base portion  4  is sufficiently used in the present invention.  
         [0061]    In accordance with the invention, since the focus contact is a leaf type, no focus contact is interposed in a gap between the base and the focus pin in the cathode ray tube, and the partition wall  13   a  on a side of the base portion  4  can be interposed between the base and the focus pin. Accordingly, the partition wall for partitioning the focus contact storing chamber and the base insertion hole has sufficient strength, and the distance between the focus contact and the signal contact has a sufficient length.  
         [0062]    Further, since the focus contact is a leaf type in which a conductive metallic plate of a band shape is bent and molded, the focus contact is easily manufactured in comparison with a bottle type.  
         [0063]    In accordance with the invention, in addition to the foregoing invention, the ring-shaped portion and the base portion are further integrated with each other, and the focus contact is disposed on the front face side of the base portion, and the signal contact is disposed on the rear face side of the ring-shaped portion. Accordingly, the creepage distance between the focus contact and the signal contact is further lengthened.  
         [0064]    In accordance with the invention, the base portion is formed in a box shape in addition to the invention in the foregoing paragraphs so that the base portion can be easily positioned with respect to the cover portion, and the base portion and the cover portion can be integrated with each other without rattling.  
         [0065]    In accordance with the invention, each of outside faces of a pair of projecting portions is covered with the partition wall rising from the base portion. Accordingly, the distance between the respective focus contacts, or the distance between each focus contact and the signal contact is sufficient to provide adequate insulation.  
         [0066]    Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.