I heard Archie Fisher in about 1980 ? and happened to record him in a pub in Aylesbury. He played in DADGAD and open G mainly. It changed my whole way of playing for ever, and once you master a set repertoire you can hear how to set other songs and tunes ,and work out which tunings are most appropriate. You also begin to realise how musicians like Joni Mitchell can create extraordinary songs using open chords.