GB2144574A

GB2144574A - Improvements in or relating to electron guns

Info

Publication number: GB2144574A
Application number: GB08318903A
Authority: GB
Inventors: Robert Douglas Barr
Original assignee: English Electric Valve Co Ltd
Current assignee: Teledyne UK Ltd
Priority date: 1983-07-13
Filing date: 1983-07-13
Publication date: 1985-03-06
Also published as: GB2144574B; GB8318903D0; JPS6047346A; NL8402210A

Abstract

To support the electrodes (8) etc of an electron gun, allowing recovery of components and minimising brittleness and deformation of the supports, ceramic spacers (16, 17, 18, 19) strung on a tensioned pliable wire separate support members (7, 8, 13) anchoring the components, insulated by sleeve (15). End pieces (20, 21) hold the wire in position. Several such wires may be used; the construction is shown applied to a camera tube. <IMAGE>

Description

SPECIFICATION Improvements in or relating to electron guns This invention relates to electron guns as used in electronic tubes, for example camera tubes.

Conventionally, in constructing an electron gun, components of the gun (e.g. one or more grids and a cathode), are first located on an axis and then pressed together. Three strips of molten glass are then applied across the components in a longitudinal direction and allowed to harden, holding them together. However, the glass is brittle and may fracture, and is also not rigid enough to prevent some deformation. In addition, components used in the gun cannot be reclaimed if it is found to be unsatisfactory, since the glass cannot be easily removed without the salvageable components becoming damaged, so as at least to prevent subsequent re-alignment.

these disadvantages are particularly acute for electron guns used in small camera tubes.

If three strips of glass are used they must be thin enough to fit in the tube, but they then are even less rigid, causing difficulties in keeping the grids and cathode accurately aligned and with a greater tendency to break.

Because of the tolerances which must be met in their manufacture, it is especially desirable for components used in small tubes to be reusable if the gun proves to be unsatisfactory upon test.

One way which has been suggested of reducing these disadvantages is to use two large pieces of glass almost completely surrounding the components to be positioned.

However, components still cannot be recovered, brittleness is still a problem and two pieces of glass give less stability than three. It also makes access, which may be required for further work within the tube, very difficult.

It is an object of the invention to reduce or overcome these difficulties.

According to a first aspect of the invention there is provided an electron gun wherein an element is positioned by means including an elongate member arranged to extend through an aperture in the element and retainers positioned on said member and arranged on each side of the element to hold it in position. Said element may comprise a component such as a grid or the support for a component such as a grid or cathode. The element, and thus the component that it comprises or supports, may be recovered simply by removing one of the retainers. The elongate member is preferably a pliable wire which is tensioned so that the elements are held in position with sufficient rigidity. Several elements may be positioned using a single member which passes through an aperture in each of them. Also, a plurality of members is used, distributed around the edges of the elements, to give stability.

It is preferred that said retainers comprise end pieces and at least one spacer, positioned between an end piece and the element, having apertures through which said member extends. The member, end pieces, element and spacer or spacers thus form a column.

The end pieces may be fixed to the member itself to hold the element in position.

Where the elongate member is a wire and the portion of said element through which said wire passes is electrically conductive, preferably said wire is surrounded by a tubular electrical insulator which extends through the aperture of the element and through the aperture of said at least one spacer. Thus, where a number of elements are included in the column they may be at different electrical potentials. The insulator may be ceramic, as may the spacer.

According to a feature of the invention, a camera tube includes an electron gun as described above.

According to a second aspect of the invention, a method of positioning an element of an electron gun includes passing an elongate member through an aperture in the element; slipping retainers having apertures on to the member on either side of the element; applying tension to the member and bringing the retainers and element into contact; and then fixing the retainers in that position.

The invention is now further described by way of example with reference to the accompanying drawings, in which: Figure 1 shows in part section the electron gun and one example of a small camera tube in accordance with the present invention; Figure 2 is a sectional view along line ll-ll on Fig. 1; and Figure 3 shows part of Fig. 1 in greater detail.

With reference to Fig. 1, an electron gun in a camera tube is surrounded by a glass envelope (not shown) and has a glass valve base 1 through which several pins 2 extend. The pins 2 provide electrical connections between various parts of the gun and power sources outside the envelope.

A cathode 3 is located within the gun and is heated by a cathode heater 4, generating a beam of electrons. The electrons are accelerated through a grid 5 and sent, via a cylindrical focussing assembly 6, to a target (not shown).

The cathode 3 and grid 5 are held in position by elements 7 and 8 respectively.

Element 7 consists of a cylinder which surrounds the cathode 3 and has a flange around its base. Element 8 is a metal plate on which the grid 5 is positioned, spaced from the element 8 by a ceramic ring 9.

Elements 7 and 8 have extensions at their edges which form part of three columns, 10, 11, 12, only two of which can be seen in Fig.

1. The three columns 10, 11 and 1 2 are spaced equidistant around the elements 7 and 8, as shown in Fig. 2, and hold them in position. Another element 1 3 forms part of the columns 10, 11 and 12.

Element 1 3 is a cylinder having a flange at its base and fits inside the base of the focussing assembly 6 to fix the columns 10, 11 and 12, and hence the other two elements 7 and 8, in the correct position.

One of the columns 10 is shown in Fig. 3.

A wire 14 forms the central core of the column 10 and is surrounded by a ceramic tube 1 5. The elements 7, 8 and 1 3 each have three apertures at their edges through which the ceramic tube 1 5 passes, the apertures being only slightly larger than the diameter of the ceramic tube 1 5 to give a good fit. They are separated from each other by ceramic spacers, 16, 1 7, 18 and 1 9. The elements 7, 8 and 13 and ceramic spacers 16, 17, 18 and 1 9 are held together by two metal end pieces 20 and 21 at each end of the column 10. The other columns 11 and 1 2 are similar structures.

The columns 10, 11 and 1 2 are assembled by fitting the ceramic tube 1 5 over the wire 14 and sliding the elements 7, 8 and 1 3 and ceramic spacers 16, 17, 18 and 1 9 into position over the tube 1 5. The end pieces 20 and 21 are then arranged at each end of the columns 10, 11 and 1 2. The wire is tensioned and the end pieces 20 and 21, spacers, 16, 17, 18 and 19 and elements 7, 8 and 1 3 brought into contact with each other.

When the columns 10, 11 and 12 are correctly aligned, the end pieces 20 and 21 are spot welded into position, forming a rigid structure.

The wire which forms the central core of the column 12 extends to form an electrical connection between part of the focussing assembly 6 and one of the pins 2 at the valve base 1. The wires of the other columns 10 and 11 extend from the base of the columns and are bent under the cathode assembly to form supports 22 and 23 for the cathode heater 4.

Claims

1. An electron gun wherein an element is positioned by means including an elongate member arranged to extend through an aperture in the element and retainers positioned on said member and arranged on each side of the element to hold it in position.

2. An electron gun as claimed in claim 1 and wherein said retainers comprise end pieces and at least one spacer, positioned between an end piece and the element, having apertures through which said member extends.

3. An electron gun as claimed in claim 2 and wherein said at least one spacer is an electrical insulator.

4. An electron gun as claimed in claim 1, 2 or 3 and wherein said elongate member is a pliable wire.

5. An electron gun as claimed in claim 4 and wherein, where the portion of said element through which said wire passes is electrically conductive, said wire is surrounded by a tubular electrical insulator which extends through the aperture of the element and through the aperture of said at least one spacer.

6. An electron gun as claimed in any preceding claim and wherein said element is positioned by means including three elongate members and their respective retainers spaced equidistant around the edge of the element.

7. An electron gun as claimed in claim 6 including a plurality of elements, each of which has three apertures through which respective elongate members extend.

8. A camera tube including an electron gun as claimed in any preceding claim.

9. A method of positioning an element of an electron gun including: passing an elongate member through an aperture in the element; slipping retainers having apertures on to the member on either side of the element:, applying tension to the member and bringing the retainers and element into contact; and then fixing the retainers in that position.

1 0. Apparatus substantially as illustrated in and described with reference to the accompanying drawings.

CLAIMS (24Apr1984)

1. An electron gun wherein an element is positioned by means including an elongate member arranged to extend through an aperture in the element, there being provided on said elongate member two retainers, one on either side of said element, which retainers are initially loose with respect to said elongate member but are fixedly located on said elongate member in contact with said element to hold the same in a desired position.