Abstract: An evacuated envelope having a plurality of spaced, parallel support walls extending between and substantially perpendicular to flat substantially parallel front and back walls to provide a plurality of parallel channels extending along the front and back walls. The front and back walls and the support walls are of an electrically insulating material, typically glass. Compressed between each of the support walls and the front wall is a metal strip which serves as the tip of the support wall and which extends along the entire length of the support wall. Each tip is tapered in thickness from a thickness substantially equal to the thickness of the support wall at the support wall to a thinner thickness at the front wall. Means is provided between each metal tip and either the support wall or the front wall to prevent movement of the tip transversely of the channels. A shadow mask extends across each of the channels and extends between the metal tips and the support walls.