Seasoned musicians drift into Dan Electro's on Thursdays and jam with whoever happens to be around. Frequently these impromptu groupings kick ass. On a recent night, veterans Andy Williams and Diunna Greenleaf took the stage with three others and unleashed a feverish set of blues. Williams made his guitar moan, while Greenleaf hammed it up diva-style, showcasing her rich, booming voice. Another group included two dudes named Jeremiah -- front man Jeremiah Johnson, fresh in from rural Missouri, and bassist Jeremiah Hamilton, who had just returned from doing sound for a Tower of Power tour. They played a set of full-throttle rockabilly and electric blues. Dan Electro's weekly blues jam has drawn the likes of Gregg Allman and Chris Duarte in its 12-year history. But it's the lesser-known players who give the event its gritty flair. "There's a lot of good local players you don't see till they come around and jam," says owner Jim Medenhall.