The 610RC is a six volt directly heated triode. The original 610RC dates to 1927 and the 'New Process' to September 1929. It was designed for use in resistance-capacitance coupled amplifiers and has an oxide coated filament.
See also210RC with the 2 volt filament. The range also included the 410RC four volt version.
The silvering of the bulb makes viewing the electrodes difficult.
From one angle the construction is revealed. The box anode carries the C for Cossor and has a top mica support.
The four filament strands pass along the anode, their lower ends are held by folding over the support wires and clamping the fold over the tungsten wire. The grid is wound between two support rods and is held to the support in notches.
The balloon envelope is 41 mm in diameter, and excluding the B4 base pins is 83 mm tall.
References: Data-sheet, 1043 & 1040. Type 610RC was first introduced in 1927.