After the recent introduction of the ELROG ER5Z3, I thought it is a good idea to pick the 5Z3 as tube of the month.
The 5Z3 is a directly heated full wave rectifier. It is electrically identical to the 5U4 but has a different base.RCA data sheet for all technical details. The 5Z3 is a member of a small family of 3 tubes which share the same electrical characteristics and only differ in the base. The third one is the 5X4 which has the same base as the 5U4 but a different pinout. While the 5U4 has seen a widespread use and still is used a lot in current production amplifiers, the 5Z3 and 5X4 were less popular and are rarely used nowadays. Let's have a look at some 5Z3 rectifiers from different manufacturers, starting with RCA:
Another RCA 5Z3 made for the military: