[rangibaby]

From wiki for the MiG-25:

The majority of the on-board avionics were based on vacuum-tube technology, not solid-state electronics. Although they represented aging technology, vacuum tubes were more tolerant of temperature extremes, thereby removing the need for environmental controls in the avionics bays. With the use of vacuum tubes, the MiG-25P's original Smerch-A (Tornado, NATO reporting name "Foxfire") radar had enormous power – about 600 kilowatts. As with most Soviet aircraft, the MiG-25 was designed to be as robust as possible. The use of vacuum tubes also made the aircraft's systems resistant to an electromagnetic pulse, for example after a nuclear blast

[hef19898]

Well, at least in that case it seems like a conscious design decision. Not sure how much of the state of the art design and tech was driven by "I like the colour" or "the supplier is in my state".

[Kadin]

The Soviet design bureaus certainly had their irrationalities. They behaved like big, vertically-integrated companies, and preferred 'their' stuff over the other design bureaus' stuff.

Soviet gear was robust because robustness and repairability was priorities as a design criterion. It's not an automatic product of how they doled out work, or of their defense industry generally.