[In answer to question of how Brian had modified his pickups over the years- see LETTERS]
All I did originally to the Burns pickups was fill them up with Araldite – to stop them whistling – screaming – feeding back by themselves.
Feeding back via the string is, of course, nice, and what I wanted. I actually think my guitar was the first one to be designed to feed back in this way. All the Gibson Les Pauls and Fenders were designed with solid bodies so that they would NOT feed back. It’s just that Hendrix and Clapton and all those great innovators used a much higher amp gain when playing live than the inventors of those guitars had anticipated!!! I will never forget seeing Jeff Beck take his guitar off his back at the Marquee (must be about 1967 with the Yardbirds) and spin it slowly on its end strap button, making it feed back a whole symphony of notes!
The only other modification I made, some years later, was to turn the innards of one pickup (the Bridge one, I think!) upside down – and reverse the wiring.
This has the effect of making the bridge pickup and the centre one HUMBUCKING (ie cancelling out local radio noise) when they are in phase – which is the position I use the most (for Tie Your Mother Down, Hammer to Fall, etc .. )
This modification also allows the fingerboard and centre pickups to hum-buck when they are out of phase – which is another favourite combination I use … for the Bo Rap solo, for instance.
This means that, even though most of the other pickup combinations do anything BUT hum buck, if I am in a situation where the noise signal in the air is strong, I can get by for the gig, by just using those two favourite settings. It still works ! but these days usually someone is clever enough to minimise the noise pick up too.