20 Year Old Amplifiers compared to 2017

OK sorry I missed that.
I`ve heard of such "scientific" blind tests before and don't care to read their reports because I`m 101% confident that I hear clear differences between different amps, preamps, sources etc.

They probably used some muffled speakers and veiled preamp in their blind test so the results LOL :))

Lafayette KT-550 ? Yes, I rebuilt a couple of those and their smaller cousins
many years ago. They were really good as was the frequently disregarded Bogen equipment of the time. There has been a rampaging snobbery to the hobby for years and equipment like that old Lafayette tends to be considered junk both because it's old  and because it wasn't expensive when it was made. Bravo for mentioning it!

@plutos 
I agree with you 100%. I hear the differences between amps, preamps, tube sets. And measurements aren't everything.

Dan D'Agostino, in his Stereophile interview, said, point blank, that some of his Krell offerings measured better than his current stuff. He specifically chose sound quality over measurements in his highly acclaimed breed of new Momentum components.

Older amplifers should be refurbished, of course. The first thing that has to be replaced would be the power supply caps, as these do degrade and can fail wtih nasty consequences. As I said earlier, with luck you can fit larger modern ones as they tend to be more compact for the same value. If the amplifier has been designed competently a slow ageing of the other components should not degrade sound, or not much.
I am currently using two refurbished Quad amplifiers (a 606-2 in the main system and a 405-2 in my study). The service engineer simply replaced all resistors and capacitors, arguing that these days quality components cost very little and labour is expensive. Why test a resistor if a new one costs peanuts?