@almarg Thank you for your perspective, Al.
As always, you raise an excellent and most salient point in regard to rectifiers.
As I considered what you said, I HAVE noticed the differences between types ("normal diodes" vs HexFred, 5AR4 vs 5U4 vs 5R4 vs 5Z3 vs 5Y3 vs...) far more prominent than variations within those types. I’m sure no one will say that’s noteworthy. While I have clearly observed the differences in voltage drop between them, I now realize I’ve been a bit too sloppy to not have more carefully measured the variation within a type. Thank you for providing a new rabbit to chase down!
Difficult question, I admit, and you could maybe just chalk it up to tubes in general, and why folks compete for valued ones, but do you have any opinions on why different tube rectifiers of the same type exhibit not much difference in performance, yet such wildly different tone? By that I mean, even friends who love to tell me, "Oh, I could never have a decent system because I’m just not good enough to ever be able to hear the differences..." can easily discern changing out a Sovtek vs Shuguang vs JJ vs Mullard 5AR4