Music technology (electric) remained so until the 1920s, when several recent radio-related developments in electronics converged to revolutionize the recording process. These included improved microphones and auxiliary devices such as electronic filters, all dependent on electronic amplification to be of practical use in recording. In 1906, Lee De Forest invented the "Audion" triode vacuum tube, an electronic valve that could amplify weak electrical signals. By 1915, it was in use in long-distance telephone circuits that made conversations between New York and San Francisco practical. Refined versions of this tube were the basis of all electronic sound systems until the commercial introduction of the
Bjork–Shiley valve and to pay for the costs of heart surgery to replace the valve. More recent models of the Björk–Shiley valve did away with the convexo-concave design and are reliable valves that do not require replacement. Bjork–Shiley valve The Björk–Shiley valve is a mechanical prosthetic heart valve. The valve was co-invented by American engineer Donald Shiley and Swedish heart surgeon Viking Björk. Beginning in 1971, it has been used to replace aortic valves and mitral valves. It was the first successful tilting-disc valve. It was manufactured first by Shiley Laboratories, then later by Pfizer after that company purchased Shiley. One model