“Field density is very hard to project and there is no reliable data to support the article.”
You do know that one reason we don’t have some data on atmospheric tests back in the day is that the EMP blew out the data collection equipment.
Once the EMP effect was understood, it was immediately classified.
Does EMP effect tubes?
I was told that it does not which is why people are encouraged to have tube Ham Radios.
However, I do not know if that is just “knowledge” based on a scfi book from the early ‘60s, where the USSR ‘dropped/exploded’ EMP bombs over the US/world and their computers were unaffected as they were all tubes.