The SP610/RR is an audio output valve from the Cosmos 1926-8 six volt range.
The etched identification on the dome includes the Cosmos brand, the type designation, BVA and the MetroVick logo. On the envelope are three lines: 6 V 0.1 A, r = 3200 and m = 8 for the basic operating parameters.
The anode is bright and has ridges pressed into the nickel to add rigidity. Only one filament support spring can be seen as the other half of the filament has failed.
The grid is wound between notched rods.
The balloon envelope is 50 mm in diameter, and excluding the B4 base pins is 102 mm tall.
Reference: 1043. Type SP610/RR was first introduced in 1928.