The 9001 miniature valve is a sharp cut-off UHF pentode. Essentially this is the 954 acorn valve on a B7G base.
The high frequency of operation is possible without a co-axial construction mainly due to the very small size of the electrode system.
The 9001 is a true pentode with three wire grids that pass flat across the cathode. The anode is a rectangular box with reduced height facing the electron stream. What appears at first sight to be the anode is in fact the electrostatic screen that surrounds the other electrodes.
The grid wires can be seen extending beyond the anode.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 36 mm tall.
References: Datasheet & 3002. Type 9001 was first introduced in 1943.