The “Yellow Tinker” is a tune in the G mixolydian mode. In other words the scale used is a C Scale but played in the key of G.
The tune is associated with the playing of Galway accordionist Joe Burke , and perhaps because of Burke, it is very popular and widely played.
The first and third parts of the tune are almost pure mixolydian, whilst the second part of the tune is almost pure G Major, although Tony didn’t alter the key signature for the second part, despite there being an argument for doing so. Overall he just felt it was more convenient to leave t
A distinguishing feature of the Mixolydian mode is that the chord progression typically consists of G chords and F chords.
With the small exception of the C chord in bar 20, the entire tune is a three-chord wonder, but the chords are G, D, and F (not G, D, and C).