The M8180 is a high reliability special quality RF pentode on a flying lead base and is for operation up to 400 MHz. The basic design is the 5654/6AK5W and on a B7G base it is the CV4010. The 5654 is equal to the Mullard M8100 special quality version of the EF95.
The hole in the anode in the direction of minimum electron flow provides for both radiation cooling and observation of the grids. The envelope also carries the identification CV4050 showing direct equivalence.
All thee grids are visible.
The thin glass tube envelope is 18 mm in diameter and, excluding the flying leads, is 35 mm tall.