The SS230SP from Six Sixty is in fact a Mullard PM252 and is a battery audio output triode. As the SS230SP dates to 1929 it would be the first improved version of the PM252. The SS240SP introduced by Six Sixty in 1931 would have been the second improved version of the PM252.
The paper label had become detached and thus could be easily scanned. Note the white of the paper on the right where it had been under the left end for many years when attached to the base. With bright emitter valves made obsolete only a few years earlier and thoriated tungsten filament running a bright orange and draining the accumulator quite fast, the label proudly proclaims the 'glowless' virtue of the Azide process oxide filament.
The etched lettering can be seen showing the 230 the makers logo and the BVA logo. Inside the horizontal box anode can be seen. The grid is just visible on the right.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 89 mm tall.
References: Datasheet & 1043. Type SS230SP was first introduced in 1929.