Vocalist Johnny Christian has been a Chicago mainstay since the 1950s--first in gospel, later in blues and R & B--and for a while in the 70s he was appearing at clubs and show lounges throughout the northern midwest as well as in Chicago. These days he stays closer to home, where his expressive vocals and personable stage presence have made him a favorite on the south- and west-side club circuits. Christian's style--polished, with a gritty edge that some of his more famous contemporaries, like Tyrone Davis, lost on their way to stardom--is both soothing and emotionally charged; his repertoire includes a wide spectrum of material ranging from funky R & B standards to aching ballads like McKinley Mitchell's lovely "End of the Rainbow." Christian is sometimes criticized for the quality of his sidemen, but last time I saw him he'd put together a first-rate band capable of steamy excursions into James Brown-style funk as well as smooth renditions of contemporary pop blues. Friday and Saturday, Checkerboard Lounge, 423 E. 43rd St.; 624-3240.