Reply to "The question of B units (from AB, ABA, or ABBA sets) in O gauge trains and why they DON'T SMOKE... Did the prototypes not smoke too? Or is this a cost saving / amp draw UL approval issue?"

"Hot Water - I am learning. I don't have the incredible pool of knowledge about trains yet that you do. This is the whole reason I made a post ... to ask. To learn something. No, I was not kidding. Thank you."

You don't have to beg - and then say Thank You for the privilege. Manners are often in short supply around here. 

Yes, except for slugs and other specialty cars made from B units, they do have an engine and they do smoke. Yes, perfectly healthy diesels can smoke a bit - but not like most models. I don't care for all that smoke, either.

But, since you didn't know all that, off with your head!