This R5 is a rare example of a De Forest style triode. Thrower1003 discusses the R5 but illustrates with the NR5 which is cylindrical and on and IS/1 base like the ORA-B. Vyse1005 says the R5 was on an IS/1 base and the R5V was on a B4 base and had a V filament and was the last incarnation of the R Type. It is therefore, probably that this is an R2 rather than and R5 as it was labelled in the Collingwood Museum collection.
The Candelabra base connects to the single strand filament. The silk insulated wires connect to the anode and grid. The anode is a bright cylinder 17 mm long by 10 mm in diameter. The grid is an open weave of fine wire carried on a single thin rod between two end supports.
See also R2 and R4.
The balloon envelope is 48 mm in diameter and, excluding the Candelabra base is 85 mm tall.
References: Datasheet, 1003 & 1005.
Updated April 26, 2013.