 Bowen then started looking for a suitable receiver system , and immediately had a stroke of good luck ; EMI had recently constructed a prototype receiver for the experimental BBC television broadcasts on 6 @.@ 7 m wavelength ( 45 MHz ) . The receiver used seven or eight vacuum tubes ( valves ) on a chassis only 3 inches ( 7 @.@ 6 cm ) in height and about 18 inches ( 46 cm ) long . Combined with a CRT display , the entire system weighed only 20 pounds ( 9 @.@ 1 kg ) . Bowen later described it as " far and away better than anything which [ had ] been achieved in Britain up to that time . " 
