SHOWCASE 9. CELL 9-31

Up to late 1941, the vacuum tubes used in WR 1 receivers were Telefunken metal tubes DCH 11, DF 11 (2 pcs), DAF 11, DC 11 and DDD 11. Because the "11th Series" tubes were designed for civilian radio equipment, to be allowed to WR 1's they had to pass additional military acceptance test.