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 company logo on the metal base shell. The anode is held in a cage of four stout wires as this is a rugged design aimed at applications where high temperature and vibration is expected.
A closer view of the graphite anode. The helical filament is just visible.
The top of the anode showing the fixing arrangements.
The Wide glass tube envelope is 51 mm in diameter, and excluding the base pins is 163 mm tall.