The U25 is a dedicated television EHT rectifier for picture tube supplies. The valve is rated at 19 kV peak inverse volts, and this suggests an output voltage suitable for a 12 inch black and white tube of say 16 kV.
Our other Mazda U25 has a different logo to this exhibit.
The valve is also rated for sine wave use, and in this case an input voltage of 9,500 volts would be the maximum. The reservoir capacitor would need a value of 0.001 µF or less. In practice the capacitor would be formed between the internal and external graphite coatings on the picture tube itself.
Mazda had great difficulty producing rectifier valves around the early 1950s. They all had flaking cathodes and usually ended in a firework display.
The lower strut connects and holds the cathode and one side of the heater at the top within the bell anode, the lower end of the heater connects to the bent lead on the pinch.
The thin glass tube envelope is 18 mm in diameter and excluding the base wires is 56 mm tall.
References: Datasheet & 1040.