^ I do know that much. I don't, however, know much about the mods. anyone want to give a go at describing the Cali mod? also, keep in mind, it's a JMP '74 Super Bass, not a JCM 800 Bass. dunno how much dif that makes.
A buddy of mine found a '73 superbass years ago super cheap. It was the only non-master volume type amp I ever played and it was really cool. I'm of the opinion that amps like that should be left relatively stock and use an attenuater or a load, to control it. If your looking to mod something it seems like you could find cheaper alternatives...