Here is a photo of Paul McCartney's Yamaha BB1000S Bass and a couple photos of my Yamaha Bass as well.
Macca's Yamaha Bass
I believe Paul went back to his Rickenbacker 4001S after the Tug of War and Pipes of Peace sessions. In 1983/84 when he began work on his film Give My Regards to Broadstreet, he was, again, using his RIC. He used his Ric during his 1987 live performances in Europe to promote All the Best. It was after this period that he went back to his Hofner and the WAL 5 string for Flowers in the Dirt and the World Tour
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I think you will find that this bass is a Yamaha BB1200 with just one split pickup. You are right about the "Back to the Egg" use. He also used it live when he did the "Concerts for Kampuchea".If you ever get a copy of "MUSICIAN" player & listener No.26 from Aug. 1980, Paul talks about the Yamaha bass and how he started playing it only because it was given to him for free. There was also a Record(LP)put out in 1980 called "The McCartney Interview" which is the full version of this conversation! I have some old "ClubSandwich" issues with lots of pictures of the Yamaha B1200.