The AZ1 directly heated full wave rectifier is fitted with an eight pin side contact base. These bases were used by Philips in Europe for universal valves from the 1930s. Universal meant valves for AC or DC supplies. In the UK Ct8 based valves were made by Mullard.
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.
The AZ1 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 cement between the base cap and the envelope has failed and the base is loose.
The top support in this exhibit is a ceramic disc rather than a mica sheet. The ceramic disc is strong but not flexible and so there are wires either side to press on the glass and hold the assembly rigid.
A closer view of the top ceramic disc, pressure wires and filament tension springs.
The classic envelope is 45 mm in diameter and, excluding the Ct8 base pins, is 98 mm tall.
References: Datasheet & 1040. Type AZ1 was first introduced in 1936.