Marakanetz`s point with the black residue inside the glass is not correct. The black "stuff" is normal in any working tube. One more the other less, so no sweat here. But you should keep away from EVERY stuff which cleans your pin by adding some chemicals may it be Pepsi or Coke or whatever!!
Try it with very fine sanding paper. Get somebody to carefully hold the tube because you need two hands to guide the paper around the pin and then carefully pull gently back and fro.
From what you describe I strongly recommend to get rid of that tube. A bad contact in one of my McIntosh MC2000's tubes took the amp down by dying because you NEVER will get back full contact once the pin is corroded. So you bettter avoid trouble with your amp with a new tube.
Good luck!
Try it with very fine sanding paper. Get somebody to carefully hold the tube because you need two hands to guide the paper around the pin and then carefully pull gently back and fro.
From what you describe I strongly recommend to get rid of that tube. A bad contact in one of my McIntosh MC2000's tubes took the amp down by dying because you NEVER will get back full contact once the pin is corroded. So you bettter avoid trouble with your amp with a new tube.
Good luck!