Several years ago, I read about Americans capturing Soviet-era jet fighters. They were analyzing it and finding all sorts of deficiencies compared to their own fighters, but noted its vacuum tube electronics were resistant to EMPs. > Perhaps the most stunning discovery was the fact that most of the MiG-25’s avionics were based on vacuum tubes—not solid state electronics. This was considered woefully outdated for a to…
I've deal with old soviet tubes. They where extremely specific, You even couldn't just place new tube into device, but need to make some manipulations with it before turn on (run it in special device on low currents).
And unfortunately, soviet tubes unreliable, many (not all), work very few hours. So MiG-25’s where for soviets, like SR-71 for US - very expensive in making and in support.
For example, known fact, MiG-25’s could for tiny time make more than 2.5Machs, but after this 100% engines go to landfill.