The 6EH7 is a high gain amplifier pentode. It was used for RF amplification in television receivers.
The construction inside the mesh screen is of a flat cathode surrounded by flat grids, and is known as frame grid construction. On the sturdy support frame the grid wire is wound at about 50% of the wire's breaking strain. This gives a closely defined plane that the grid wire occupies. With such precision the grid to cathode separation can be extremely small and thus generate a high gm figure. The anode consists of two plates connected by straps on either side of the cathode and separated by 4 mm.
The Cathodeon name with EF183 printed below.
Through the outer screen the wide helix of thw suppressor grid can be seen and at the centre the inner grids close to the cathode.
A closer view.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 53 mm tall.
References: Datasheet & 1040. Type 6EH7 was first introduced in 1960.