Type 6KS6 is a late 1940s 'gated beam' valve for use as an FM discriminator. It is a dual control valve but unlike the dual control pentode the grids are shielded and the control range is small. Also if the grids are positive the current does not reach damaging levels.
The article above describes the discriminator function in detail.
The beam travel across the width of the valve and here can be seen the cathode side with the cathode within the shielding box.
The three sections. The central box is the accelerator. The box on the right contains the quadrature grid.
An attempt to image the winding across the face of the accelerator.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 59 mm tall.
Reference: Data-sheet. Type 6KS6 was first introduced in 1965.