There was once a time when blues, jazz, and gospel music poured out of the clubs that crowded Seventh Street in West Oakland, where longshoremen mingled with Navy men and soldiers from the Army base. Those days may be long gone, but one of their last vestiges remains in the form of a blues jam at JK Brickhouse, a longshore workers’ bar situated at the mouth of the Port of Oakland. While the hum of the Interstate 880 overpass mixed with the rattle of a passing semi or the regular wail of a BART train creates its own kind of symphony, the real music is inside. Every other Tuesday, singer Margie Turner hosts a house band with a rotating group of singers and musicians, who play blues, R&B, and soul standards. Drinks are cheap (though don’t expect speedy service), and there’s ample room to dance.