The AZ1 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. For the AZ1 the re-issue was be the AZ31 with identical electrical characteristics. Thanks to Kajetan Rozycki for confirming these facts.
It has a 4 Volt filament rated at 1.1 Amp. The maximum anode RMS voltage is 500 Volts. At this anode Voltage the DC current could be up to 60 mA. At 400 Volts on the anode the output could rise to 75 mA and with 300 Volts on the anodes the output current could be 100 mA. The maximum reservoir capacitor had to be no more than 60 µF.
The anode cavities are grey treated to radiate more heat and are made of Nickel. The single piece anode is bent to shape, stitched together and finally spot welded to the supports.
The filaments are oxide coated ribbons. Note that the ribbon is spot welded to its support. The fact it is welded and not clamped shows that the ribbon base is not tungsten. The latter metal has to be clamped in place.
The classic envelope is 45 mm in diameter and, excluding the Ct8 base pins, is 102 mm tall.
References: Datasheet & 1040. Type AZ1 was first introduced in 1938.