The UU8 is a full wave rectifier on the short lived Mazda Octal base. The literature shows the valve with external metalisation and our other exhibit UU8 has the metal paint, this valve is clear. This exhibit is probably of late manufacture for use as a replacement part.
The maximum load current of 250 mA is substantial for a device of this sort. The maximum reservoir capacitor value of 16μF is typical.
The top mica shows that there are four rectifier segments in the envelope. Each anode fin has a support rod, cavity containing the cathode and a round heat sink fin on the outer end of the anode. The white hairpins are the tops of the heaters.
The right of the picture shows the anode design with the heater in the middle and the round heat sink on the far right.
Seen from below the heaters can be seen entering the cathode tubes.
The fixings of the electrodes to the mica support consist of smull lugs that would be bent outwards to provide a secure fixing during the final hand assembly of the valve prior to pumping.
The classic envelope is 55 mm in diameter, and excluding the MO base pins is 97 mm tall.
References: Datasheet, 1040 & 1043. Type UU8 was first introduced in 1939.