The EC157 lighthouse planar triode was designed to provide RF power in broadband microwave circuits. The circuit topography the EC157 was designed for was grounded grid. The grid sits across the width of the valve and the grid connection is fitted with a screw thread for direct fixing into a cavity based enclosure.
The base also has a number stamped into it.
The working area of the valve is very small with the flat cathode mounted close the control grid disc on one side and the flat base of the anode mounted on the other.
The thin glass tube envelope is 18 mm in diameter, and excluding the base pins is 43 mm tall.
Reference: Datasheet. Type EC157 was first introduced in 1960.