Type UU4 is a indirectly heated full wave rectifier. The cathode is strapped to one side of the heater and so the heater has to be connected to a separate winding on the mains transformer.
The identification lettering is on the top of the dome.
Each anode is a complex pressed plate, blackened to make a better radiator.
Another example with a clearer glass bulb. The heaters can be seen to be connected in parallel.
The complex anode pressing.
In this image the anode shape can be seen with each section having a central cyindrical cavity for the cathode and on each side two further cylinders both punched with four holes.
The classic envelope is 42 mm in diameter and, excluding the B4 base pins, is 100 mm tall.
References: Data-sheet, 1040 & 1043. Type UU4 was first introduced in 1936. See also1936 adverts.
