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 for universal valves from the 1930s. Universal meant valves for AC or DC supplies. The electrically identical AZ31 is fitted with an IO base cap.
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 probably made of Nickel.
The anodes are held between mica supports. The single carburised sheet is formed into the anode tube and side flange. The flange is stitched through and the whole anode is spot welded to the support rod.
The top mica showing the oxide coated ribbon filament and tension springs.
The classic envelope is 45 mm in diameter and, excluding the Ct8 base pins, is 100 mm tall.
References: Data-sheet & 1040. Type AZ1 was first introduced in 1936.