[arethuza]

Using vacuum tubes did have some advantages - notably being more EMP resistant than normal electronics. Given one of the MiG-25's roles was to intercept incoming nuclear bombers this was presumably an important requirement.

https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-25#Wester...

[yetihehe]

Not using vacuum tubes here would be kind of motivating, in a "intercept that bomber or fall off the sky" way.