DAMMIT!!!!!!
Had a long-ass reply and the friggin' board ate it!! I hate that!!!
Yes, still interested. I might snag a 9600 and rebuild the filter to act as a subsonic. Much more useful.
wjahn5, you may have a dirty switch or pot (easy to clean, unlike the Pioneer's I've worked on), or a dirty output relay. It's also possible that the bias current is too low, especially is the problem is more apparent the first half-hour that it is on. All the above are easy fixes. Every 70's Kenwood I have ever heard held its own vs any other manufacturer of that vintage, so unless the differences were more a matter of taste, then yours may need attention.