Jamerson's bass was recorded direct out of an Ampeg B-15. In fact, based on what I've read, the majority of studio recordings were done this way through the mid '70s.
Jamerson's bass wasn't recorded this way, as detailed earlier in the thread. Live he used a Kustom as well as an Ampeg.
Many different techniques were used to record bass in the '60s, including DI into through that tube preamp at Motown. Fender Concert and Showman amps were recorded mic'ed as much if not more than B-15s, too.
By the '70s I doubt many recordings feature a B-15 at all.