20 Year Old Amplifiers compared to 2017

@whitestix 
Believe it or not, there's room for improvement with the F5. I've been tweaking and tuning mine since we last crossed paths. I replaced some shielded interconnect cable with some solid twisted wire for the input signal, replaced the silicone MOSFET insulators with split micas, dialed in the distortion a bit better, and cranked up the bias to 1.4 amp. This amp now delivers a 62 watt class A envelope into 8 ohm. The power is hardly the best part though. The thing with the F5 is you get pronounced sonic benefits as you crank up the bias until you get up past 2 amp. I doubt I'm going to squeeze more bias out of it in this chassis though. 
This thing has made me a serious believer in simple, heavy, high bias, class A amps with obscene power supplies. 

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

My Julius Futterman OTL3s are circa early 1980s. I recently had them converted from pentode to triode, and replaced all the caps with Jensen foil oil caps. They were tuned to my Altec 694Cs and to my room. 

I cannot imagine anything sounding significantly better for the money.

Good thread. I have an old Proceed Amp5 in need of TLC sitting around, that I've been debating back and forth about investing in a rebuild. It functions, but it's not working at its potential. Anyone have any thoughts?

I would think, that when comparing an older amplifier to newer designs, isn't it also essential to be certain that it still functions optimally? Maybe that's a dopey statement, but after 20 or more years, it's easy to neglect it and forget it might need refreshing.
In the case of my amp, it needs a good refurbishing, so I wouldn't dare compare it yet to anything. 

Kosst,
My F5 at the moment is being worked on very capable DIY'er, who, based discussions he has had with Nelson Pass, is doing some the upgrades you describe above.  It difficult to imagine the F5 improving, but it is logical thatat it will do so with the improvements you describe.  
Finally, there are lots of facts and opinions stated in the realm of audio blogs, but yours I consistently find the most logical and informed.  Thanks for sharing your information.  Whitestix