Electronic – What effect would a hydrogen bomb detonated at high enough altitude have on the power grid and solid state electronics

After reading several dozen reports on EMP effects of nuclear explosions and viewing archived government footage of nuclear weapons testing I have come up empty handed.

As for example let us assume 1-5 megaton hydrogen bomb at an altitude sufficient so that the line of sight would be the continental U.S. I use line of sight as straight lines extending from the fireball.

Some reports say only minor disturbance. And Other reports say all transformers and all electronics that does not belong to the military with the exception of some automobiles. With manufacturing electronics , communications electronics and networking equipment destroyed. In addition to all high voltage transformers, nuclear plant cooling transformers and electronic control. All aviation, train , trucking distribution centers electronics. Air and cooling equipment as well as gas distribution , water and sewage treatment electronics.

One source I found said the disturbance would actually be no different than a powerful lightning storm and pale in comparison to a Solar Coronal Event and that the danger has been overblown in the media. While other sources like National Geographic say it would be the end of civilization and no country on earth would have the manufacturing ability to replace even the transformers needed much less the electronics. They site South Africa's rolling blackouts as an example of how hard it is to get transformers let alone electronics.

Are there any reliable sources or is this one of those hush hush topics understood perhaps only by our military people?