I think the tubes are very sensitive and can respond unpredictably to even slight changes in the way they are held down or damped.
For example, my Vali arrived with a moderately loud ring that came primarily from the left channel. This ringing would dissipate after about 20 seconds or so.
After talk of detached adhesive pads and tubes hanging above the board, I checked mine and one tube was, indeed, hanging above the board (with the pad attached to it). I pressed it back down.
An interesting thing happened after I did that. The volume, or loudness, of the ringing went down quite a bit, but now the amp was a lot more sensitive.
After pressing it down, just about anything sets off the ringing now. I didn't have much of a ringing issue from touching the volume control before, but now even brushing or putting a finger on the knob would trigger the ringing (not even turning the knob). Even the movement of the headphone cord across the table would set if off. So lower ringing volume, but now much more sensitive.
In Jason's reply, he mentioned that the tubes were pressed down onto the pads during construction. I'm assuming they soldered in the tubes with straight leads. The residual spring tension from the bending, and the cold weather, is probably what cause the adhesive to detach and the tubes to hang in the air. Jason said they were now pre-bending the leads to take the tension off.
Taking a cue from this, I opened up my Vali and carefully pulled the tubes off of the adhesive pads (do at your own risk. At room temps, the pads are very soft and sticky, and there's a good chance you'll rip one). I put a gentle bend into the leads of the tubes to eliminate the tension (so now they don't spring back up even without adhesive). Then I pressed them to the adhesive pads.
Well, joy! I couldn't believe it. I was actually shocked. The ringing had subsided so much, I could barely hear it in the background. And I really had to rap the the top of the case to get it to start.
I had read those reports from owners who could barely hear ringing or get their amps to ring, and now here it was right here. The amp actually sounded more "together" for lack of a better word. I was very, very happy... for a few minutes.
After reveling in the improvement and listening to several upbeat songs, I swapped albums. Uh Oh.....
Now I could hear a persistent ringing that would not stop. Damn. The improvement was undeniable and huge, but I had set up a situation where the now low level ringing just would not stop. It was unlistenable with the constant whine in the backgroud.
I gave up at that point and plugged in my Magni to listen for the evening.
So, yeah, these tube are very sensitive and give vastly different results regarding ringing. But it's very touch and go and unpredictable what will happen.
More tweaking to do....
Edited by K.T. - 1/2/14 at 9:40am