I doubt that this is a tube problem. My first guess would be that it is somewhere in the grounding or wires (IC's). Check to make sure all of your IC's are not near any transformers, etc and all connections are solid, especially grounds from your TT and phono stage.
Tubes trouble?
Need help and advice.
Have an ARC PH5 Riaa where the tubes were changed two years ago. Sometimes when I play there is a humming sound that changes character when I put my hand on the cabinet and all of a sudden I am completely free of interference again. Where do I start? Guess it's a tubes that's bad. How do I find which one? Can I change just one tubes or do I have to change all of them? Is there any placement of the four that is less critical if a pipe is in worse condition? Thanks fore comments and tips. // Niklas