The Mazda AC/SG is and AC heated Screen Grid or tetrode amplifier for RF use. Our other AC/SG has a different construction and shows how the box screen moved to a helical grid.
The heater is the then UK standard of 4.0 Volts at 1.0 Amp. The original valves in 1929 had a metal screw top cap as can be seen in the advert. The screw top cap style of this exhibit is difficult to determine as it is missing. The lack of adhesive residue is a possible indication that this originally had the metal screw top cap connection. However, the balloon envelope does not have the lower cylindrical section that appears in both the advert and AC/SG. It is possible that the bulb shape altered before the top cap was replaced with the Bakelite screw top version.
The construction has a bright anode either side of a rectangular screening cage. This view is looking directly at one anode. The thick wires either side are supports that are connected to the screen. The two anode plates are bridged together and connect to the top cap wire.
This image was taken looking at the corner of the screening box. The control grid is hard to see as the wires have a very similar pitch to the screen.
A closer view.
The balloon envelope is 45 mm in diameter, and excluding the B5 base pins is 104 mm tall.
References: 1040 & 1043. Type AC/SG was first introduced in 1929.