The AZ2 directly heated full wave rectifier is fitted with an eight pin side contact base. These bases were used originally by Philips in Europe and Mullard in the UK for universal valves from the 1930s. Universal meant valves for AC or DC supplies. When the Ct8 base proved unpopular in the UK some of the valves were re-issued on a standard International Octal base.
The AZ2 follows the pattern of the AZ1 but has more than double the current rating at 500 Volts.
The filament is oxide coated ribbon.
The Ct8 base contact construction.
Thanks to Mark Mallison for sending the images.
The classic envelope is 43 mm in diameter and, excluding the Ct8 base pins, is 101 mm tall.
References: Datasheet & 1043. Type AZ2 was first introduced in 1936.