The SG220S is a screened version of the SG220 and is a directly heated battery tetrode that dates to 1935. In 1936 the SG220SW was being advertised for Short Wave work. The difference was in the base cap used. Frequentite was the trade name of the ceramic.
The screen grid is a full length woven mesh. The top cap connects to one of the control grid support wires.
The top structure is held in the envelope by the top mica.
The classic envelope is 39 mm in diameter, and excluding the B4 base pins is 119 mm tall.
Reference: 1043. Type SG220S was first introduced in 1935.