Historic recordings featuring three founding members of Fleetwood Mac performing together in the months before they started the band — and eight years before Lindsey Buckingham and Stevie Nicks joined — will be released on April 21st.

Titled John Mayall’s Bluesbreakers – Live in 1967 (Never Before Heard Live Performances), the album features a lineup that includes Mick Fleetwood, John McVie and guitarist Peter Green, along with bandleader John Mayall. That version of the Bluesbreakers lasted only three months, before the trio left to form the Mac. The recordings were made by a Dutch fan who secretly lugged a reel-to-reel tape machine to five London club shows and eventually sold them to Mayall, who’s restored the sound quality as well as current technology will allow.

Between 1965 and ’69, John Mayall’s Bluesbreakers also served as a launching pad for Cream‘s Eric Clapton and Jack Bruce, and The Rolling Stones Mick Taylor.