The UU8 is full wave rectifier, probably dating from the late 1930s.
Quite why they decided to metallise these rectifiers remains a mystery but the only obvious consequence was that they tended to overheat until the metallising corrected the problem by flaking off! This series of rectifiers was not as robust as the stalwart UU5, at least until the 1950s when Mazda seem to have realised that domestic HT rectifiers do not need metallisation See UU7
The maximum reservoir capacitor is 16 µF and no minimum series resistance is quoted.
The classic envelope is 52 mm in diameter and, excluding the MO base pins, is 98 mm tall.
References: Datasheet, 1040 & 1043. Type UU8 was first introduced in 1939.
Absolute Maximum Operating Conditions¶
Updated February 07, 2013. shape:classic construction:pinch type:rectifier.fw age:1930.1940 base:mo heater:4.0v pins:8 pin:1.h.k pin:2.- pin:3.a(2) pin:4.- pin:5.a(1) pin:6.m pin:7.- pin:8.h