The SG210 was Cossor's 2.0 Volt answer to the M-OV S625 screened grid valve and was the first two volt SG valve. The SG210 was introduced in 1927, the same year as the S625. The Cossor valves were available in August 1927 and displayed at the National Radio Exhibition (Olympia) in the September.
The original M-OV S625 has a thoriated tungsten filament whereas the cossor SG210 and its 6 volt brother the SG610 had coated filaments. The early Cossor coated filaments were not very successful and the 'New Process' was not introduced until 1929. By 1929 the two double ended SG valves had been superseded by single ended types. In fact the SG210 was replaced by the SG220 early in 1928. The SG220 was later renamed to the 220SG.
The SG210 was specified for the first Cossor Melody Maker receiver. Later production used the single ended SG220.
The filament is a V between the grid winding. Only one side of the grid is acting as a control as the structure is essentially planar. The Cossor paper label carries the BVA logo on the reverse side.
Here is another example of this early screeded grid valve.
A close-up of the control grid with filament within and sreeening grid placed in the top of the lower cylinder.
The wide glass envelope is - mm in diameter, and excluding the base pins is - mm tall.
References: 1043 Type SG210 was first introduced in 1927.