At his best, Percy Sledge combines a keening, tear-swollen tenor and an unreconstructed backwoods drawl to express an abjection so deep it sounds almost sainted. That vulnerability is famously on display in his breakout 1966 hit, “When a Man Loves a Woman,” but it’s there in lesser-known gems too, like his 1967 take on the sublime Dan Penn-Spooner Oldham ballad “Out of Left Field” and an epic rendition of David Egan and Buddy Flett’s “First You Cry,” from his 1995 comeback album, Blue Night. But he’s often stumbled into bathos: his second-biggest hit, 1968’s “Take Time to Know Her,” with its tremulous gasps and watery intonation, sounds more like an exercise in self-pity than a cautionary sermon. Similarly, Sledge shouldn’t have been allowed anywhere near the schlocky “A Lonely Violin,” an unreleased Bee Gees tune he recorded for his latest album, last year’s Shining Through the Rain (Velvet Steamroller). He also sounds oddly detached from the faux-country lament “Change My Mind,” but elsewhere on the album he sounds poised and deeply engaged: he brings an emotional urgency to the redemptive message of the title track, sings “Love Come Rescue Me” with wracked-soul fervor, and on a cover of Steve Earle’s “My Old Friend the Blues” he attains a sodden honky-tonk desperation worthy of George Jones. The biggest kick is his cover of “Searching for My Love,” a 1966 hit for Bobby Moore & the Rhythm Aces: Sledge summons the teen-dream ebullience of the original while adding a bracing and utterly unexpected dose of bluesy toughness. The Chicago Blues Museum All Stars open. Fri 10/14, 7 and 10 PM, Old Town School of Folk Music, 4544 N. Lincoln, 773-728-6000 or 866-468-3401, $28, $24 seniors and kids. All ages.