It's a tube amp turned up slightly past the distortion point. I don't know what Jerry used, but Doug Lubahn said that when he recorded with the Doors, he used a Precision with flats into the studio's B-15 and a DI. Does sound like a Precision. Amp I'm unsure, but the B-15 or the 200s will get the job done in style.
Ampeg Portaflex Club #1