The 5654/M8100 is the special quality version of the 6AK5. It is an wideband RF amplifier pentode for VHF and above. The rugged construction is to allow the valve to operate in situations of vibration and knocks.
The valve is labelled 5654 in this view but also as shown below as the M8100.
Now it is an M8100.
The working faces of the anode are parallel to the grids and at the ends metal is removed as no electron flow is required in this direction. The three wire grids can, therefore, be seen end on.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 37 mm tall.
References: Data-sheet & 1040. Type 5654 was first introduced in 1948.