At 1980s levels of integration, then I'd agree that for many sorts of signal processing it's easier to do it in analog than digital. Especially if all your engineers are trained for analog. In 2014 the situation is the other way round.
Robustness of power electronics is another consideration: tubes are mechanically fragile but not vulnerable to ESD, whereas FETs are, especially during assembly. If their factory process control was poor it would have been easier to stick with the tubes.
Robustness of power electronics is another consideration: tubes are mechanically fragile but not vulnerable to ESD, whereas FETs are, especially during assembly. If their factory process control was poor it would have been easier to stick with the tubes.