The EF731 is a miniature variable-mu RF pentode with flying lead connections for direct wiring into a circuit. The 5899 is a special quality version of the EF731.
The three grids are wire wound and the anode is a cylinder around the centre of the grid length with two full height sections that are face on to the grids.
The support micas and the wide helix of g3 can be clearly seen.
Looking directly at the plane of the grids.
one side of the anode with side strap. All blackened to radiate heat away.
Looking along the line of the grids. All three can be seen, the control grid is easiest to see at the top.
The thin glass tube envelope is 9 mm in diameter, and excluding the base wires is 33 mm tall.
References: Data-sheet & 1040 Type EF731 was first introduced in 1958. See also1958 adverts.
