The VX3517 shown here is an experimental valve from M-OV. It has ceramic insulators, indicating high voltage use, and the top cap connects to the anode. The Type VX3517 also refers to a B9A based pulse modulator also known as the CV2231 (See attached .PDF). It is possible that the two are related but no evidence has as yet been found.
The anode looking along the axis of the grids. The control grid has heat sink fins and the screen grid is wound on copper supports. The beam forming plates are fixed with tabs to the mica supports.
The anode working face.
The wide glass tube envelope is 28 mm in diameter, and excluding the base IO pins is 81 mm tall.
Reference: Observation & datasheet. Type VX3517 was first introduced in 1959.
Updated May 19, 2014.