The 6K4P (6К4П Cyrillic) is a high frequency pentode from the Soviet era. Vibration resistance is given in the data-sheet and this suggests a special quality valve.
The opening in the anode reveals the three wire grids. The mica supports are quite thick and this will help in vibration resistance.
The anode face view with the grid supports visible above the top mica.
The thin glass tube envelope is 17 mm in diameter, and excluding the B7G base pins is 51 mm tall.
Reference: Data-sheet. Type 6K4P was first introduced in 1954. See also1954 adverts.
