Cossor designed and made EHT rectifiers such as the SU2150A for use in CRT power supplies. Because the Cossor works tended to employ skilled glass-blowers rather than just factory girls, and because they were designing for a very limited market, the Cossor EHT rectifiers were designed to be hand made. Although naive looking they were electrically robust and entirely successful in their intended application.
A C Cossor & Co. were originally scientific instrument makers specialising in glass devices such as discharge tubes, CRTs and the like. During the 1930s they did much pioneering work in designing oscilloscopes and the CRTs for them.
Cossor’s supplied almost all the service oscilloscopes supplied to the British Services (especially the Navy) before WWII. During the war the increased demand for service oscilloscopes exceeded Cossor’s manufacturing capacity so some of the work was farmed out. Both Mullard and M-OV manufactured supposed equivalents to the SU2150A but in each case the valves were redesigned to suit factory production methods. The results were not excellent, having relatively short lives and being easily damaged when EHT faults occurred. The Navy insisted on the ‘real thing’ and since they went on using Cossor oscilloscopes into the 1970s, long after Cossor ceased to make its own valves, the Naval Stores organisation purchased and hoarded very large numbers of spare valves, including SU2150As. Our exhibit is an example of the ‘real thing’ manufactured during the 1950s (brown base cap) and probably kept in Naval Stores until the 1980s.
The saddle anode is connected to the top cap and is supported on glass pillars. The cathode assembly is always at least 6 mm distant from the anode, and is a horizontal rod. The maximum reservoir capacitor is 0.25 µF, and the minimum series resistance is 10 k Ohms.
The balloon envelope is 47 mm in diameter and, excluding the B4 base pins, is 108 mm tall.