We have two UU6 exhibits complete with base and external paint. The UU6 from Mazda is grey and the rebadged UU6 from Bentley Acoustic Corporation is Red. This exhibit has UU6 etched into the envelope but over time has lost all of its paint making the internal structure visible. The overheating of these painted rectifiers caused the paint to flake off. Also the base has had the spigot broken off. This suggests that someone has used this valve as a replacement for an IO based valve where the spigot hole is slightly smaller.
Each anode is formed from sheet and is essentially a cylindrical space with a flange to assist heat loss.
From the side the profile of the twin anodes is clear. Note that the anodes are not bright but treated to make them better radiators. Strange to paint the envelope.
The UU6 full wave rectifier was produced from 1938 by Mazda. Essentially the UU6 is a UU4 on an MO base. The maximum reservoir capacitor has to be 16 µF.
The classic envelope is 32 mm in diameter, and excluding the MO base pins, is 80 mm tall.
References: Data-sheet, 1040 & 1043. Type UU6 was first introduced in 1938.