Device for fixing a pyrolytic graphite grid onto the base of an electron tube

A high frequency electron tube having at least one grid of pyrolytic graphite having a skirt portion which is fixed to the base of the electron tube comprising a first continuous metallic outer ring integral with the base of the electron tube, a plurality of separated metallic abutments for defining an inner segmented ring concentric with and spaced apart from the outer ring by a distance essentially equal to the thickness of the skirt portion of the grid, and means for fixing the inner ring to the outer ring, the skirt portion of the grid being fitted in the space between the inner and outer rings and being provided with recesses for passage therethrough of the means for fixing the inner ring to the outer ring, said fixing means and bolts passing between said inner ring and outer ring through recesses in the skirt portions, and in which the abutments forming the inner ring are spaced from the base of the electron tube.