Brad Zellar spent three decades amassing the grand slam of baseball collections, and now the writer and former used-book store owner is hoping that it’s also a hit with his fellow baseball fanatics.

“How I got all this stuff is truly beyond me at this point,” he admitted as he sorted through the contents of one of the 500 boxes of collectibles he has accumulated. “I went all over the country looking for books for my bookstore — I went to estate sales and farm auctions and secondhand stores — and anytime I found something dealing with baseball, I bought it.”

It all will be for sale Saturday and Sunday and April 13-14 in a storefront that he has rented near the intersection of Raymond and University Avenues in St. Paul.

With prices ranging from $3 to more than $1,000, the collection includes a bit of everything. There are obscure books written by authors no one had ever heard of before (or since, in most cases) to a 1911 first edition of the book “Base Ball” by Albert Spaulding. There’s a ball signed by Ted Williams and Mickey Mantle, mitts dating to the 19th century and a souvenir ashtray from the Kansas City A’s — that’s right, not the Royals, the A’s before their move to Oakland 45 years ago. He has kids’ books, board games and team giveaways, including a set of miniature bats.

He has so much stuff that even he won’t be sure what all he has until he finishes unpacking it.

“A lot of this stuff, I look at it and go, ‘Oh, yeah, I remember that,’ ” he said. “But some of it, I don’t remember where it came from.”

Most of the collection consists of things he intended to sell in his store but was reluctant to part with. It wasn’t so much that he wanted to keep them as it was that he wanted them to go to good homes where they would be appreciated.

“To me, this is all about the fans,” he said. “Dealers would come in, pick out the good stuff and then mark it up to sell to someone else. I didn’t want it just passing through the hands of someone who was looking to make money off wealthy collectors. I wanted it to go to people who would go crazy about finding it the same way I did when I found it.”

In storage for long enough

He sold his interest in the store, Rag & Bone Books, 10 years ago, and the collection has been sitting in storage since.

“I realized that I hadn’t looked at this stuff for 10 years,” he explained when asked why he had decided to sell it now. “Plus, I had to keep moving it from one storage spot to another. About the third or fourth time I was moving 500 boxes of books, I started thinking about getting rid of it.”

He has culled a couple of things that he wants to keep, but only a couple.

“I’m an obsessive collector,” he said. “My home is full of stuff; I don’t have room for more. I took some books that my dad and grandfather liked, and there’s a Harmon Killebrew glove from when he played with the Washington Senators [before the team became the Minnesota Twins] that I still might keep. But that’s about it.”

One of the things he thought about keeping was a signed baseball. Not the one autographed by Williams and Mantle — signatures Zellar got himself — but one signed by someone who will forever remain anonymous. It’s a Little League baseball on which someone has written: “This is the ball that Jerry hit for a home run to win the 1961 championship.”

“I realize that this has little if any [monetary] value,” he said, picking up the ball to examine the inscription. “But every time I look at it, I wonder: Why would anyone get rid of something like this? This was really special to someone.”