The N Marconi triode dates to 1914-15. The valve is described as soft with a 2 V 4 A filament. It has an asbestos pellet at the top as seen on the right of the picture.

The anode cylinder is brought out to a side connection and the grid is brought out nearer to the top. The grid is a close mesh wire cage as can be seen from the insert in the picture.

The wide glass tube envelope is 46 mm in diameter, and excluding the base pins is 170 mm tall.