The Catkin valve was developed in 1931-2 and introduced to the market in 1933. The revolutionary construction reduced inter electrode capacitances.
Beneath the screening shell is a small diameter copper/glass envelope. The actual Type designation was not visible.
This valve is probably an MS4B.
The thin metal tube envelope is 32 mm in diameter and, excluding the B5 base pins, is 104 mm tall.
Reference: Observation. Type Catkin was first introduced in 1931. See also 1931 adverts.
Updated November 20, 2018.