Many Deep Purple fans are certainly aware of this, a unique occasion in which guitarist Randy California, founding member of the band Spirit, took the place on stage of Purple's lead guitar player.
According to most sources, Ritchie Blackmore was ill and Randy California stepped in.
It took place at the Colisée de Québec in Quebec City, Canada, on April 6, 1972, just some days after the release of Machine Head, one of the top rock classic albums of all time.
Unfortunately the only copy I found of this has many noise glitches probably from CD ripping errors.