Tube Life Artifacts


I've been using the same tubes for almost 12 years. They are RCA EL84s (6bq5) in 1959 Leak TL12 plus monoblocks. Recently, I have noticed that one channel seems to be "deeper" in soundstage, almost like there was more reverb on that channel. It's a mild difference, more noticeable on some recordings than others. This difference is consistent with both vinyl and CD, and switched sides when I switched the speaker connections.

Is this evidence of tube deterioration? I have a set of unused Philips tubes somewhere in the basement (made by Mullard, I believe) and I'm about to switch them. If I can find them...
dragunski
They are Philips brand tubes. The seller told me they were made by Mullard, but he was Chinese and I may have misunderstood. The amps were recapped in the 80s and may need it again, but for now, they seem to be working well. There's a little hissing when they power up, but it goes away pretty quick.

Yes, tomorrow I will dig around again in the basement. I'll be mad if I don't have them anymore. I found all sorts of cool stuff down there including reel and Elcaset tapes, so I think I'm getting close.

Ok, I found those NOS Philips and swapped them in. Maybe a slightly better treble, as the cymbals are louder and seem to fade slower.

But the RCAs are back in. They have much better bass and mids. More balanced across the whole spectrum. I don't hear a difference in width or height. 

My girlfriend doesn't hear any difference, even though she's got better ears. She thinks I'm crazy.
I haven't decided if the better cymbals with the Philips is real, or just a consequence of a suppressed and less liquid midrange. But it's true, the Philips only have about 12 hours on them. The Chinese guy raved about them, but then he was selling them, so...

At any rate, I'm looking for more RCAs on the net. Then I find that there's at least 4 different kinds. It's never simple, is it?