Cover band supreme BackTrax gets a serious case of Saturday Night Fever on June 29 for “Disco Inferno,” the 7th annual edition of the Bell Bottom Bash. The groove thing, a benefit for public broadcaster KSVY FM and TV, starts shaking at 6 p.m. at the Moose Lodge, 20580 Broadway. Bellbottombash.com. Tickets are $20 at the door. Don’t forget the costume contest!