You need WWII-era tech to do it. We've discussed this ad nauseum in the post-1900 forum.
The chemistry, the physics, the economy all have to be at 1930s+ level, so if you have A bombs by 1900 then you have cars by 1850, basically.
You have to speed up the entire tech-tree to get there.
So you're essentially saying, WI tech happened 50 (100 etc) years early.
Without totally huge changes to history, you can move the Abomb forward from '45 to '44. Maybe 43. That's just about it. If you want to posit a surviving Alexander the Great TL that lands on the moon in 1500, then you could have an A bomb ~1500. If dinosaurs weren't wiped out in 65 million BC, you could have an a bomb in 64 million bc....
The question as posed is so vague as to be almost meaningless, I'm afraid.