After replacing the tube and the fuse on my Peavey Triumph 120, I started getting a hum when the amp is fully engaged (not in standby). After watching this video on different causes of tube hum, I checked and found that the hum is not responsive to volume changes. I pulled out the chassis and swapped out each 12ax7 with a spare. I used the same 12ax7 to briefly check the 12at7 spot since I did not have a spare 12at7. I pulled 2 power tubes, check, replaced them, and then pulled the other 2 power tubes. None of this had any effect on the hum. I did notice that the noise level of the hum increased briefly from cold to warm, but leveled off quite quickly. Does anyone have any ideas at this point, or is it time for a tech?