The VS24 is a variable-μ screen grid or tetrode. The plastic top cap support with a screw tread indicates that this was one of the early batches as by the mid 1930s the top hat top cap was the norm.
The Type designation printed on the metal paint has been damaged but part of the S can just be made out.
The Marconi branding.
The classic envelope is 44 mm in diameter, and excluding the B4 base pins is 111 mm tall.
