The U625 is a half wave rectifier. It came in a U650 box. The input for the U650 was up to 300 V RMS and the maximum current was 40 mA. It is probable that the U625 has lower ratings and was superseded by the U650.
The etched dome identification clearly states U625.
The balloon envelope is 41 mm in diameter, and excluding the B4 base pins is 83 mm tall.
Reference: 1043. Type U625 was first introduced in 1930.
Absolute Maximum Operating Conditions¶
Updated April 15, 2013. shape:balloon construction:pinch type:rectifier.hw age:1920.1930 base:b4 heater:6.0v pins:4 pin:1.a pin:2.- pin:3.f pin:4.f