In the late 1960s and early '70s, the Siegel-Schwall Band was one of the hottest tickets in town. Evolving from a curiosity--a white-fronted blues band that jammed on the south side--to a cult item to a concert attraction, Siegel-Schwall played with artists ranging from Howlin' Wolf to the Jefferson Airplane to the San Francisco Symphony. Their calling cards were Corky Siegel's gaspingly energetic harmonica and wry, sly singing, Jim Schwall's stinging solos on amplified acoustic guitar, the taut backing provided by bassist Rollo Radford and drummer Shelley Plotkin, and an infectious playfulness that ran through their witty originals and butt-busting covers of the classics. A one-night reunion concert two years ago, and the live album it produced, showed that time had deepened their playing without eroding the buoyancy that pleased audiences a generation earlier. This weekend's "re-reunion" shows--just around the corner from the old Quiet Knight (where Avalon is now), which was their home base--should prove the group to be still in sharp form: not a nostalgia act but a musical force to be joyfully reckoned with, especially with the presence of master drummer Sam Lay in Shelley Plotkin's old slot. Tonight and Saturday, 7:30 PM, the Vic, 3145 N. Sheffield; 472-0449 or 248-7277.