Trying to troubleshoot a hardly used cube 60 from the '70's. Seems to have distortion or maybe reverb that won't shut off. Speaker looks perfect and brand new. No obvious burn marks or failures on the board. Sprayed all the controls with cleaner and it's maybe a LITTLE better. I'll try it again tomorrow with some different guitar pickups[acoustic] and preamps and see if it's still acting up. Any suggestions?