The Z759 is an RF pentode with a high mutual conductance designed for video or other wideband RF amplification.
The remains of the Osram brand label. Off the same M-OV production line the valve could have been branded GEC or Marconi.
The coating was thin enough for the internal structure to be seen. The anode is formed from a single nickel sheet as two plates and a joining strap. The suppressor grid has rounded ends and a flat section as it passes across the anode. The screen grid can be seen as a series of flat wires. The control grid has copper supports but the winding is not easy to see.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 47 mm tall.
References: Data-sheet & 3002. Type Z759 was first introduced in 1955.