This magnificent example of the R Type was made in England and is branded Marconi's W T Co. The envelope is made of slightly smoked glass and the pin formation suggests that this dates from WW1. See alsoR Type.
The side view above shows the concentric formation of the electrodes and the single fine strand of tungsten that is the filament.
The fragile and brittle filament has been partly protected by the coil formation adjacent to the support. This gives a measure of tension to prevent sag when the filament is at operating temperatute. The grid support can also clearly be seen.
By processing the photograph to add false colours the lettering becomes visible.
The spherical envelope is 52 mm in diameter and, excluding the B4 base pins, is 95 mm tall.
References: Private communication, 1005 & 1003. Type R Type was first introduced in 1916.