Help with mcintosh mr 67

I have aquired a mcintosh mr 67, this tuner sounds flat in stereo, rich and full in mono. There is also a constant tone sound, all tubes light up, the osc-6ab4 appears weak(very little light.) Any and all help would be appreciated in solving this problem.
Its 1 thing for the tubes to light up, another for them to be good, need to probably check and replace the bad ones, and you probably have a few, before you go another step. Check the solder joints at the RCA outputs, could be a bad one causing your hum, but bet on bets its the tubes. Then its probably going to need alignment. Then you will have a pretty good tuner.
Thank you,I talked to audio classic and have ordered a new osc(6ab4)will give it a try.
Try calling around to a few TV shops and get all the tubes tested. that Stereo demodulator is not the best in any case. If it needs service. Use expert service only. Call MAC and see who they would recommend. I do not think they service Tube tuners anymore..

Good luck