The 5Y3 is a full wave vacuum rectifier. Originally these rectifiers were built on a pinch but this modern version uses a glass foot construction. In essence an all glass valve with lead-out wires soldered to an International Octal base cap.
Face view of one anode with ridges for dimensional stability from the thin sheet nickel.
The twin rectifier sections with the folded edges on the inside.
The glass foot is just visible in the full size image. The electrodes are mounted close to the bottom of envelope.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 70 mm tall.