It's a De Armond moving coil pickup mounted in the sound-hole for the Echoplex effects chain , and a Barcus Berry piezo-electric bug just below the bridge (stuck on with grey tape) for the acoustic clean feed.
The first of two tunes in the set he played on BBC 2's OGWT in January 1975 to publicise the newly released 'Sunday's Child' LP . (It's the opening track). He is tuned C.F.Bb.Eb.G.C same pattern as standard tuning but 4 semitones lower. It's why seems to be fingering in the key of A major, but ...
I was able to extract and slow down this audio track. There is a quick paste of the result uploaded in my account. It is John, he's using his meditative London accent.
It is indeed a still picture of Nick playing live. I first recall seeing it published in the late 1970s in a fringe UK music magazine called 'Dark Star'.
The mics are AKG C451 condensers with a CK5 capsule screwed onto the end of a VR1 extender tube. The BBC had acquired a large number of these kits from AKG in the early 1970s, and you often see them used on BBC2 music programs of this period.
It's a De Armond moving coil pickup mounted in the sound-hole for the Echoplex effects chain , and a Barcus Berry piezo-electric bug just below the bridge (stuck on with grey tape) for the acoustic clean feed.