Shake Shack’s sizzling stock has other burger joint operators looking to flip.

Jack’s, originally called Jack’s Hamburgers, is on the block, sources said. The 120-store chain started 50 years ago in Birmingham, Ala., and gained a following with 15-cent burgers and fries.

A Jack’s franchisee, Benny LaRussa, bought it from founder Jack Caddell in 1989.

Today, closely held Jack’s Family Restaurants generates $100 million a year in revenue. LaRussa, who did not return calls for comment, wants a buyer to keep the Jack’s name and the business concept, sources said.

Shake Shack’s stock has more than tripled since its IPO at $21 a share.