The DC2/SGVM is from the Mazda DC valve range. The SG stands for screened grid and the VM is variable μ
These valves were designed for series heater operation in areas where DC mains voltages were available. The heater chain would also work on AC mains but the transformer based AC sets would not operate on DC mains. The valve is a variable μ tetrode for RF or IF amplification in superhet receivers. The screw top cap places this valve in the early to mid 1930's.
The operating conditions listed are from a close relative in the AC series and should be seen as a guide only.
The silvering is on one side only and from the back the internal structure can be seen. The anode is connected to the top cap.
The anode and connection to the top cap. On the right is the screen grid.
The screen grid is fitted with a plate at the top for better screening. At the bottom the screen connects to the skirt over the pinch.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 111 mm tall.
References: Data-sheet, 4022 & 1043. Type DC2/SGVM was first introduced in 1932.