The 6197 is a special quality power pentode that was designed for operation for long periods either full on or at cut-off. The applications were within digital computers of the 1950s. Also on the data-sheet is a specification for operation as a Class A amplifier.
It is a true pentode with three wire grids.
The grids are shaped to pass flat across the cathode.
The thin glass tube envelope is 21 mm in diameter, and excluding the B9A base pins is 60 mm tall.
Reference: Datasheet. Type 6197 was first introduced in 1954.