The Jerni Collection, a homage to the Golden Age of toy making, has been amassed by Jerry Greene, 67, a Pennsylvania music executive whose company Collectables Records specialises in the reissue of golden oldies.
Greene, whose father was a toy-train dealer, began collecting at the age of 18 by putting a sign in the window of his record store in Philadelphia.
The pieces date from roughly 1850-1940 and, although half are by Märklin, together they form an encyclopaedic collection of toys and trains from every major European and American manufacturer. Greene is understood to own every one of the 150 or so hand-decorated tinplate stations Märklin ever made.
"Assembling this collection has been a 50-year journey for me," said Mr Greene. "I put it together piece by piece, and my quest for the highest quality trains and toys took me to thousands of toy fairs and shows.
"The collection has been my abiding passion… I collected everything I could." He added that he hoped the collection will remain intact.
"The fun is in the search. I want to sell it, so that I have a clean basement. After this, I will collect something else."
American toy specialists have waxed lyrically over the quality, condition and range on offer (it is the first time any portion of the collection has been on public display).
"Of all the collections I have seen in over 40 years in business, the Jerni Collection is by far the largest and most extensive, with hundreds of rare examples I've never seen before," noted Joe Freeman, renowned toy expert and restorer.
Sotheby's are tight-lipped on the price tag for this remarkable archive, but it hasn't stopped a number of educated guesses. Pennsylvania toy auctioneer Noel Barrett said: "I think $40m to $50m is a very comfortable number. It's beyond anything I've ever seen."