This valve is clearly a power valve as it has a blackened anode and cooling fins on the control grid supports. It is also unmistakably a tetrode with two wire grids. A literature search draws a blank on an audio output tetrode of this type - with good reason as the kink introduces too much distortion. Look at the lower end of the right hand screen grid support - it is connected to the anode. This is a triode.
On test the heater takes 1.1 Amps at 4 Volts.
The end view of the box anode.
The pinch end. The control grid is wound on copper supports, the heater passes through the cathode four times, the second grid is close wound and the support is connected to the anode.
The oxide coating on the cathode tube is easily seen.
The top mica showing the box radiator on the control grid.
The classic envelope is 56 mm in diameter, and excluding the B5 base pins is 120 mm tall.