The VP4A is a variable μ screened pentode designed for mains radio receivers. The variable μ characteristic enables automatic gain control of RF and IF amplifiers in superhet receivers. The VP4A was made in both B5 and B7 base formats.
This exhibit, sadly without its black bakelite screw top cap, is of the earlier B5 based type.
The missing top cap and large skirt allows a view into the envelope. The anode is the cylinder of mesh and the visible grid is the suppressor.
The suppressor grid is clearly visible, less obvious is the screen grid. With a glass and looking into the envelope the oxide coated cathode is seen as is the control grid, neither structure is seen in the image.
The balloon envelope is 49 mm in diameter and, excluding the B7 base pins, is 118 mm tall.
References: 1040. Type VP4A was first introduced in 1934.