The NR77 is an audio output pentode with an 18 Watt anode dissipation. The prototype was the Mullard EL35. The CV register renamed this valve the CV1286.
The cathode tube has a reduced diameter at the top to locate in the top mica. It is a true pentode with three wire grids. The inner or control grid is wound on copper supports. The anode is a carbonised mesh.
Face view of the top mica. It can be seen that there is a heat sink attached to the tops of the control grid supports.
The classic envelope is 44 mm in diameter, and excluding the IO base pins is 110 mm tall.
