The 25Z5 is an American TV rectifier. Within the envelope, sharing a common heater, are two independent rectifiers. The heater current of 0.3 Amps is one of the standard heater chain currents.
The independent rectifiers make three configurations possible: the pair as a full wave rectifier, the pair to produce 250 V from 117 V mains in voltage doubler configuration, and lastly in parallel as a half wave rectifier.
The maximum reservoir capacitor is quoted at 16 µF.