I'm interested in the solution to this problem jukie. I recently had my Melos SHA-1 modded by Carlo, and I just recently (2-3 days ago) started having a hum problem in ONLY the left channel.
The history of my issue:
Prior to the mod, I was also having noise in the left channel, which Carlo told me was due to the original design of the Melos routing the left channel through the power supply, but I was told that his mods fixed this issue. At that time, the noise would come and go, and sometimes if I switched the input selector switch, the noise would go away.
When I first got the amp back after modding, everything sounded just fine. But all of a sudden the noise is starting to come back. I don't think the noise is caused by the tubes, but I'm at a loss to explain why the noise is there. So if you could tell me how you fixed it, I can check to see if that's the cause of my problem or if there is something else happening.
Thanks Jukie!
Edit: Oh yeah, and Carlo already switched out the original volume pot for a stepped attenuator, so I know it's probably not the stepped attenuator that's causing the noise.