The 12AF6 released in 1955 is an amplifier pentode for use in car radios operating with the anode at battery potential. The design use was as an IF amplifier.
The notch in the anode reveals the three wire grids.
The construction above the base foot. The grid support rods are made of Copper for good heat transfer. The suppressor grid is an open spiral. The screen grid is a tighter wind and the control grid is very close to the cathode. The electrode assembly has been spot welded to the shaped extensions to the base pins.
The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 48 mm tall.
Reference: Data-sheet. Type 12AF6 was first introduced in 1955.