This valve has no identification apart from some code letters on the dome. Testing for the heater connections was followed by gradually increasing the voltage and current until the correct colour on the filament was reached. This was 1.74 A at 5.0 V. The museum advanced search was used to find possible matches for an IO based full wave rectifier. The 5W4 was the closest and had the same missing pins.
The 5W4GT is a directly heated full wave rectifier with an oxide coated filament. The reservoir capacitor is given as 4 μF.
The folded anode with side flange. The ribbon filament can be seen at the base.
The dome has 3E0 137 printed on it. Within can be seen the top mica with the coated ribbon filament.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 68 mm tall.
Reference: Data-sheet. Type 5W4GT was first introduced in 1940. See also1940 adverts.