How to track down bad tube and what can it mean?

The distortion appears to be caused by one of the new tubes. Replace the new tubes - one at a time - with equivalent older ones, listening to the amp after each replacement, until distortion disappears. This technique should allow you to identify the bad tube. Hope this helps.

I had this problem. The first thing I did waw to reverse my interconnects to see if the sound moved from right to left. In my case it did not so the problem was in the amp.

Next, I reversed all of my tubes in the amp to see if the sound moved and i did this to see if indeed the problem is a tube or some other connection. The noise moved.

Then it was just a matter of time as I traded pairs of tubes until the sound moved again. I nest moved just one of the tubes and the noise moved again. Bingo!

With my ARC PH-3, I had a situation were I replaced all the tubes with NOS JAN Philips and everything seemed ok for a while. Then, problems with the right channel. My intention was to put back the original Sovteks one by one until the unit worked, but after substituting just one the situation seemed ok. Short while later, problems with the right channel again. So I brought the unit in to the local ARC dealer for an inspection. Turns out the mute switch was bad. They checked the two sets of tubes I had and they elected to put back the original Sovteks, declaring them way better than the just recently bought NOS. Moral of the story: NOS may not be the best road to go down (conversely, ARC dealers may be averse to using anything other than what ARC sells???) and more than one problem can surface at once making diagnosis/repair best left to qualified techs. Good luck.

I'm facinated with the fact that the hum level varies with the level of the music - the reason is that the tubes in the line stage and amp are constant and merely pass on, amplified, what passes thru them. Question - does this problem occur with any source you select, or just one?

Thanks folks. I'll have to spend some time this weekend on this detective effort. The sound, a buzz that reminds me of a blown speaker though I did nothing to effect the speakers this way, appears with whatever source I have selected. This morning I switched interconnects between preamp and amp and the sound was still coming from the left channel. I'll try switching the left and right tubes in the amp and see where that goes.

Do you use a Q-tip to clean the tube pins?

If necessary I'll take the amp in for service, but it weighs 100 lbs so it's a freakin pain in the arse.