Sometime during 1976
Sweet & Blackmore   
People involved
Brian Connolly (vcl); Steve Priest (bss/vcl); Andy Scott (gtr); Mick Tucker (drm); plus Ritchie Blackmore (gtr).
During a Sweet gig in Santa Monica, California, Blackmore got up on stage and jammed together with Sweet during one of their encores, viz "All Right Now By Now". They dedicated the song to Paul Kossoff (from the band Free) who had died earlier.

Albums & singles
All Right Now [live cd] : Japan 1996