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 By 1929 the two double ended SG valves had been superseded by single ended types.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 BVA logo.
The basic operating conditions are written on the paper label.
The grid is wound as an ellipse across the two supports but only one side is active in the electron path. The filament is in the centre of the control grid. The screening grid fills the width of the tube. The anode plate is hidden behind the silver gettering.
The screening grid has an outer metal dish with wide spaced wires drawn across the rectangular aperture in the screening dish.
A closer view. The filament is a single v of oxide coated wire. On the right can be seen the central hook support and tension spring.
Another view of the filament.
Looking down on the main electrodes.
The filament and control grid base cap. The size is B4 but the anode pin is omitted.
The anode end of the valve. The pin arrangement is B4 but only pins one and two are fitted.
In this image the support for the filament tension spring is clearly seen.
The wide glass envelope is 31 mm in diameter, and excluding the B4 base pins is 99 mm tall.
References: 1043 Type SG210 was first introduced in 1927. See also1927 adverts.
