The 5U4 type of rectifier was made in several forms over its life time. This version has the modern glass base construction and a tubular envelope. It delivers 100 Watts of DC power, a reasonable size valve. It would be used for all types of medium power equipment.
The original 5UG dates to 1938 and these rectifiers were used in the 1940s and 1950s. They were not specified for new equipment by the 1960s.
The IEC brand on the glass and Japan on the base cap. The rectifier sections are held in mica discs.
The Servicemaster brand. IEC Servicemaster being a reseller.
The octagon on the glass with 5U4GB within is typical of RCA et al. At the base of the anodes can be seen the oxide coated ribbon filament.
The glass tubular envelope has a maximum diameter of 38 mm and length excluding IO base pins, is 89 mm.
Reference: Data-sheet & 1043. Type 5U4GB was first introduced in 1956. See also1956 adverts.
