Rick Wright (with the beard) plays keyboards and does co-lead vocals on this song. Waters plays bass here and doesn't sing though he wrote the lyrics to this one. In the early days Gilmour, Wright & Waters would all sing leads for different songs. For this particular concert recording, for example, they played 6 songs: 2 instrumentals "One Of These Day" & "Mademoiselle Nobs", "Saucerful of Secrets" with a small part sung by David, "Echoes Part 1 & 2" sung by David & Rick, & 2 songs sung by Waters: "Set The Controls for the Heart Of The Sun" & "Careful With That Axe Eugene"
This was still pretty early on for the band, before they became arguably the biggest band in the world with their Dark Side Of The Moon record. As time went on Rick sung less & less & the band would be co-fronted by Roger & David during the period where they were at the peak in terms of acclaim & success.