The 220SG was the new name for the SG220 of 1928.
The Cossor answer to the original screened grid valve from M-OV, the S625, was the SG210, another double ended valve. The single ended replacement for the SG210 was the SG220 that also had issues with its coated filament.
This valve dates to after 1929 when the Cossor New Process was introduced but is essentially the same electrically as the SG220.
The bright anode uses the C and the ridges to add rigidity to the thin Nickel sheet. Inside the anode can be seen the close wound screening grid. This also extends above the top mica. A close look reveals the coated filament strands.
A better view of the filament.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 1114 mm tall.
References: Datasheet & 1043. Type 220SG was first introduced in 1928.