I'll get back to you with more detail after I try some different combinations tomorrow. I have also noticed that some tubes have showed more noise in the Vali2 than other amps, including Lyr1, which also has AC heaters. On the other hand, I have noticed that some tubes lost some borderline noise after use in the Vali2. My sense is that these are borderline tubes to begin with. As for power, you can at least test going direct to the wall sockets in several different locations. There are other options also.