90C1=CV2225=QS.1215 Voltage Regulator NOS (10 in stock) (similar to 5651)
3) 90C1 Mullard old logo NOS in white boxes 1960's
3) CV2225=90C1 Mullard NOS no logo in white boxes 1967
4) QS.1215=90C1 NOS branded English Electronic Valve Co, Chelmsford UK 1977
4) CV2225=90C1 NOS branded English Electronic Valve Co, Chelmsford UK 1978
The Mullard 90C1 is a voltage regulator discharge tube. The tube will strike at 115 Volts and will regulate to 90 Volts for currents of between 1 and 40 mA. The specifications show a regulation of 14 Volts for this range of currents. This would be a wide tolerance by any standard. It is probable that this was intended to supply something like an oscillator that required sensibly constant current.
Special quality versions were made and given the type designation M8206 on a B7G base and M8207 with flying leads.
The thin glass tube envelope is 17 mm in diameter, and excluding the B7G base pins is 45 mm tall.
Type 90C1 was first introduced in 1956