20 Year Old Amplifiers compared to 2017

I have a Krell KST 100 over 20 years, maintained not the best but so what. It plays well and stopped me from looking for the next best thing and thatt's all that matters.

what changed...
90's to today? nothing.
70,80's vs. 90's yes. changed a LOT.
If you open user manual of 1980 equipment and 1990+ equipment you will see HUGE differences.
First off circuit, block diagram, service manual isn't published anymore. That is due to I guess depletion of normal human intelligence or something stimulating that depletion. If earlier people were smart enough to get to the bottom of problem by reading service manuals, now they can't. Now they get zapped and sue the manufacturer so service instruction ain't no good no mo pal since 90's. 
My solution to this problem is using and servicing units that have circuit diagrams and user manuals and let the rest of crap disposed. So I assume nothing can possible beat 80's units that are the most advance, well built and serviceable. 

My take is that this one of the most informative threads on AG in a while with very thoughtful responses. I recently got an First Watt F5 amp, my first Class A amp, and it is a glimpse into music that I had never heard before.  I dunno if all pure Class A amps have similar performance to the F5, but it is the pinnacle of amps I have had over 45 years.  It is not as powerful as my McCormack DNA .05 amp, a Class A/B amp, but between the two of them, I am very happy.  I would be very keen to find an upgraded Krell KSA-250... it is the one Class amp for which I lust. 

I am a denier of the SQ benefits of Class D amps, but I have not heard the best of them. The ones I did hear seemed to be bereft of the total musical involvement I enjoy with Class A and Class A/B amps.   I am a lover of vintage gear myself.  Again, this a great and informative thread. 

I imagine that Nelson underclocks the First Watt amps to prevent them from competing with Pass Labs.