I've often heard that because the Soviet Union lagged behind in integrated circuit development, they built their fighters to rely less on them compared to NATO and American platforms.
The Mig25 is often brought up as an aircraft that utilized a heavy number of vacuum tubes for the aforementioned reason, but also as a defense against EMP related issues when tasked with intercepting American bomber formations.
How much of the Mig25 utilized vacuum tubes, especially in comparison to semiconductor/transistor-based circuitry?