The 572B is a replacement valve for the 811 transmitting tube. The valve is a hi μ power triode, used in many RF linear amplifiers. Examples are the KW1000 and Yaesu FL2100.
Typical operating conditions in amateur service are a Va of 2,400 V and an output power from a pair of 400 Watts.
Visually it conforms to the pattern of a medium power high voltage transmitting triode. The graphite anode is connected to the top cap, the insulation is ceramic and the grid supporting rods are visible.
The maker's name Cetron on the base cap together with the company logo. The locating pin for the bayonet base can be seen on the left.
The pinch and above. The getter holder is on the left of the pinch. The control grid connection is protected above the pinch by a glass tube.
The glass distorts the view of the graphite anode. The ceramic support has the two tension springs above it, these hold the top loops of the oxide coated filament.
The glass tube for the grid connection is lower left. The grid itself can be seen to be close wound. The anode is about 1 mm thick.
The wide glass tube envelope is 51 mm in diameter and, excluding the UX4 base pins, is 150 mm tall.
Reference: Datasheet. Type 572B was first introduced in 1961.