Not sure i would be inclined to believe the soviet tube/EMP explanation.. it sounds great yes, like they were really on top of things, however, from subs sinking to chernobyl, to the ripped off plans and inferior execution of the concordsky as well as most sukhoi and migs, post 1965, looking quite similar to our designs from years before and last but not least , their VAST , VAST missile arsenal that i was told as a kid, they had, (which was just not true at all) all adds up to the fact they had no money and IMO, lacked the capacity to develop state of the art, like the free enterprise west was able to.... good example, broken down "poor" east germany versus the thriving west germany... ONLY my observation, i dont want to cause an argument....i think the emp resistance , which is true, is just an accidental bonus for their continued use of what technology they had that still seemed to work for them and didnt cost additional funds for a whole bunch of new R&D that they were not capable of acheiving given their "closed doors"...... my totally uneducated 2 cents...