The VR99 is a triode hexode, and the VR denotes that it was designated for use with the RAF as a receiver device. The direct commercial equivalent is the X66 and when the CV register was built the VR99 became the CV1099. The X66 itself is a selected X65.
The triode was designed for local oscillator use and an injection voltage of 10 V peak to peak was produced. The hexode mixer took the signal into the top cap grid, thus maintaining the greatest separation between grid and anode circuits.
The internal coating obscures the details of the construction but the copper supports of the control grid that connects to the top cap can be seen as can the close spaced rods of the other grids.
Grids two and four are joined across the tops of the grid support rods.
The classic envelope is 38 mm in diameter and, excluding the IO base pins, is 98 mm tall.
References: Data-sheet & 1043. Type VR99 was first introduced in 1940.