AUDIO VALVES: U50, 5Y3G, 5Y3GT, CV1268, CV3754,

The U50 is a directly heated full wave rectifier.  Introduced in 1937 as the smaller brother of the U52 for less current hungry applications, it shares the same similar electrode cage construction characteristics with the U52 in having a pinch mounted cage, with top mica envelope security and a pinch situated bar getter.   The filament is a suspended inverted V tape filament. 
The maximum reservoir capacitance is 32 µF and minimum series resistance is 100 Ohms.