This is an Osram Type R. The other side of the envelope carries the Osram name, GEC and Made in England.
The horizontal anode with helical grid and single strand filament.
In this image can be seen the end of the filament wound to form a spring to take-up the slack when hot.
The anode support is a folded sheet.
The grid support is formed by two wires twisted together and then opened out to hold the support wire attached to the grid helix.
Using the microscope, the fold holding the tungsten filament is clear as is the spring end of the filament that prevents sag when hot. The support holding the grid helix rigid is attached by a thin wire wrapped round each loop.
The broken end of the filament.
Here the wire securing the helix loops to the main support is clearly seen.
The balloon envelope is 55 mm in diameter, and excluding the B4 base pins, is 92 mm tall.
References: 1005, 1003 & 1004. Type R Type was first introduced in 1916. See also1916 adverts.
