I bought a 1965 Ampeg SB-12 (with the rare 7868 tubes). The idea behind this was it was originally designed to be a multi-instrument amp. It has a bass input and an "instrument" input. Now I can play bass through it while only needing one amp. It has a very interesting, lush tone that is super revealing. I love it.
I've owned this same model as well as several other models of portoflex Ampegs. They offer a fantastic warm, full sound. Lots of acoustic bass and archtop electric guitar players LOVE these. Damn they are heavy, but wonderful tone. I especially enjoyed turning down the lights, playing and watching the tubes and plexi logo glow.