Midrange Increasingly Harsh

As Elliot recommended try an isolate the problem. Most likely its either the speakers or the tubes since you’ve replicated the problem with multiple sources. You’ll need either an alternative amplifier or alternative set of speakers and see if you can replicate the problem after replacing one of them. Also is this coming from both speakers or just one side?

When it comes to tubes its more about hours played then age, power tubes can last around 2500 hrs and preamp tubes about double that, but like any piece of electronic gear, they can fail at any time, if you have single tube or single driver fail the problem would more likely be in one side. If it’s gradual decay over time its would be on both sides. So first see if its the amp or the speakers, then go from there.

I listen at lunch and again in the evening with my adult beverage.  I have post-concussion phonophobia, which I suspected at first.  But my wife also noticed it so I can rule that out.  I don't have any sources for spare gear around here to swap in and out.  What I may try is plugging the CD player into other output taps from the amp, and fooling around with some different cables.  By my estimate I have over 5000 hours on these tubes, so they need to get replaced in any event.  I don't recall the brand but the were made in England and sounded wonderful for a long time.  Hopefully Upscale has my purchase history if I can't run down the receipt.

Yep, I’d do a full re-tube. Your power tubes are definitely shot and the pre-amp tubes are at the end of their life. Try to avoid using it until you get the power tubes replaced at minimum as the distortion from spent tubes can damage the speakers. Fortunately you don’t play at high volumes so hopefully the drivers are unscathed.

Congrats on averaging 1k hours a year of listening! That’s tremendous. I work from home and even then I doubt I’m half that.  I think I'll do some listening now and try and catch up lol. 

Even if it is not the tubes getting worn, it is helpful to have a full complement of replacement tubes.  Any time you suspect tubes are going bad, you can then do substitutions to see if that cures the deterioration.  Even when you don’t hear an obvious problem, performance can decline gradually and you may not notice this until you do substitutions.

Make sure ears are clean before passing judgement on gear.