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. In the hands of skilled operators the pellet could be heated to give just the right amount of gas in the valve to achieve good sensitivity. In unskilled hands performance was poor. The advent of the hard vacuum valves changed the perception of how a valve operated and the R could be operated by unskilled operators.
Thrower gives the filament current as 2.5 A and the anode potential as 40-80 Volts.
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.
References: 1003 & 1005. Type N was first introduced in 1915.
Updated January 08, 2013.