This exhibit is a double beam tetrode on a B9D base. As there is no internal neutralising capacitors or anodes brought out to top caps this does not shout RF. It is only a guess but as this is on a B9D base that was used in TV receivers it could be a push-pull audio amplifier or push-pull frame output valve.
Each anode is folded into a flat U shape.
The two control grids are offset slightly one from the other.
The base with the centre tapped heater.
A photomicrograph of one control grid. The winding has been made in the notch and peen normal manner and then one side has been cut off. In this image the grid wire is present on the lower side of the support rod only.
The wide glass tube envelope is 28 mm in diameter, and excluding the B9D base pins is 68 mm tall.
