The POVT193 is a variable μ RF amplifier beam tetrode, and was first introduced in 1939.
Originally as can be seen on the envelope the GPO called this specification VT No. 193 but to avoid confusion with other VT series the accepted Type designation is now POVT193
The ellipse contains the M-OV Type designation of KTW61 and the GPO specification obviously matched the commercial product.
Near the top of the image can be seen the rectangular cathode and the inner wire grids and the beam plates.
The top view with the control grid connected to the top cap. The side mica pieces hold the electrodes firmly to the inside of the shoulder of the envelope.
The classic envelope is 38 mm in diameter and, excluding the IO base pins, is 104 mm tall.
References: Data-sheet, 1040 & 1043. Type POVT193 was first introduced in 1939. See also1939 adverts.
