The 5U4G directly heated rectifier delivers 100 Watts of DC power. It would be used for all types of medium power equipment and was used extensively in 1940's equipment.
The Type designation with an octagonal border on the glass and the RCA logo on the base cap.
The anode is folded to shape but does not have horizontal ribs for extra rigidity like some other makes. This valve was made in the USA.
The top mica showing the filament ribbon held in the hook of the tension spring.
The classic envelope is 51 mm in diameter and, excluding the IO base pins, is 116 mm tall.
References: Data-sheet, Data, 1040 & 1043. Type 5U4G was first introduced in 1938. See also1938 adverts.
