NEW YORK — With the curtain soon to fall on David Letterman’s late-night television career, the end comes Friday for an odd and emotional holiday tradition that involves comic Jay Thomas, the Lone Ranger, a giant meatball and, most indelibly, singer Darlene Love. Love will sing “Christmas (Baby Please Come Home)” for the 21st and final time on Letterman’s annual holiday show. “I’m looking forward to it this year more than any other year, with mixed feelings, of course,” said Letterman’s longtime bandleader, Paul Shaffer. [...] as he’s done since 1998, Thomas tries to knock the meatball off the top of a Christmas tree with a football. “Christmas (Baby Please Come Home)” was the single from “A Christmas Gift for You,” an album by producer Phil Spector and the artists in his orbit. “The Phil Spector album has always been the one that has gotten me through the Christmas season, which can be depressing for people in show business, who are often working instead of being with their families,” he said. The song has been covered multiple times — by the likes of U2, Mariah Carey, Michael Bublé and Joey Ramone — since Love began making her Letterman appearances. In true Spector “Wall of Sound” tradition, Shaffer’s “CBS Orchestra” has greatly expanded to a stage filled with musicians.