The 577 is a high vacuum half wave rectifier and is a smaller version of the 371B.
The 577 is designed for service where high peak inverse voltages are incurred. The average rectified current is 300 mA but a peak of 1,500 mA is possible. The PIV is 25kV. The main application seems to be airborne radar.
The filament is thoriated tungsten and the anode is graphite.
The anode is supported by a cage along its length and fixed only to the top cap.
The thoriated tungsten helical filament and the central rod that connects to the top of the filament.
The anode cage and within the filament top .
The wide glass tube envelope is 51 mm in diameter, and excluding the base pins is 162 mm tall.