An electron beam tube of the type having a fine conductive mesh adjacent a target is described, the fine mesh being clamped around its periphery between two annular members. An annular damping washer of flexible material is also clamped between the two members and extends inwards towards the picture area of the fine mesh. The two members are in addition dished away from one another and from the fine mesh in a region inwards of the clamping region so that the annular damping washer exhibits corrugations in the space between the fine mesh and the dished portion of the Clamping member which contacts the washer, the washer thereby contacting the fine mesh at a number of different places and restricting the degree to which the washer may lift away from the conductive mesh.