The LF610 is an audio triode for battery operation. The envelope carries the filament voltage and the words 'General Purpose'.
The etched lettering is difficult to see but most of the information can be made out.
The reverse of the envelope carries the BVA logo.
The envelope has the mirror finish gettering on one side and here the oval anode , grid and M shaped filament can be seen. The filament is oxide coated as one would expect from the low heater power requirement.
A closer look at the lower end of the anode and associated components.
The balloon envelope is 44 mm in diameter, and excluding the B4 base pins is 96 mm tall.
Reference: 1043. Type LF610 was first introduced in 1928.