The Russian 5C4M (5ц4М) is an example of a typical high current rectifier for small equipment use. It is indirectly heated but the cathode is tied to one side of the heater. The OTK mark indicates that it was made for military use. The data-sheet indicates that the 5Y3GB is equivalent.
The construction uses a glass foot base rather than a pinch and only four base pins are fitted.
The Cyrillic lettering and note that the cathode tube has a closed top.
Face view of one anode.
The OTK lettering.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 65 mm tall.