sorry..... this began as a duplicate post, because my browser crashed with the edit page open...
sounds like you have bad regulators. these will usually be some TO-220 cased transistors with some zener diodes nearby. the ground on the regulator could be flaky (let me guess? they used the 18ga stranded wire which is wire wrapped to tall posts with a square cross section, to make connections between boards? this was a popular wiring method between about 1970 and 1985.). or the xeners could be bad, or the regulator transistors shorted E-C. dried out electrolytic caps in the regulator can also make it operate in some bizarre ways. normally that would be a good call on the volume control, but once again, what type of wiring method is used. if it's the wrap/posts, you probably have a lot of flaky connections' it's best to remove the wraps, and solder the wires onto the posts the way you normally would if you were building the amp yourself. i have never seen the wire wrap tools that were used for 18ga stranded wire, but they must have been common in Japan because everybody used them.. even if the wrap/post wiring method wasn't used, it's still likely you have one or more bad grounds. i didn't find a CA-65 schematic, but found a CA-30..... switching in the CA-30 was done with real switches, so this is probably not a whole lot like the CA-65... but the regulators for the analog stuff is done with only zeners. if they did it with zeners here, it's likely they continued using that method for a while just a few thoughts, hope something here points you in the right direction