Dear Sirseedy, very strange you post this problem now, because I have the SAME problem occuring recently, and we have quite similar systems ! I am also on the diagnosis pathway, and I never thought of a tube problem . I swapped
recently the 12AX7A NOS Telefunken for military grade Mullards , and wonder if they are the culprits.It is like a big electrical discharge occuring every 10 minutes, but only with my analog system . I borrowed a PS Audio Premier Power plant and proceeding by elimination, apparently it is the phonostage headamp who is picking up AC noise when my REFRIGERATOR switches on. When I unplug the frig this not occuring anymore. Hope this helps.
recently the 12AX7A NOS Telefunken for military grade Mullards , and wonder if they are the culprits.It is like a big electrical discharge occuring every 10 minutes, but only with my analog system . I borrowed a PS Audio Premier Power plant and proceeding by elimination, apparently it is the phonostage headamp who is picking up AC noise when my REFRIGERATOR switches on. When I unplug the frig this not occuring anymore. Hope this helps.