Amps from the 1980's -- What gear holds up sonically? Reliably?

The first version of the Acurus DIA-100. I bought it along with the Acurus CD player (also the original version) right after they were available. I paired them with a pair of Snell E-IIIs and it was my first decent stereo system. I still have the DIA-100 driving a decent pair of outdoor speakers and the CD player is in a second home system. The CD player was also used as a transport in earlier main systems I had. Even the LED on the CD player still works and the DIA sounds great. I get compliments on how good the outdoor system sounds. The Snells I had re-foamed several years ago and the oak cabinets are still beautiful. Even have the original stands with the Snells. They are in storage and I need to sell them as I have another pair of Spendors I use with the surround system and swap those with the Logans every once in a while.  Recently I tried the Acurus in my current system, diving Martin Logan ESLs and was shocked at how good it sounded. For those that do not know - the DIA -100 was described as an amp with a passive gain stage (?, I think). I see no reason to sell the Acurus stuff. 

Amplifier design matured during the 1970’s and the better ones reached sonic perfection at the time. Of course, such technical instruments age, and the most problematic components are the power supply capacitors. Quality of those at the times was not as good as it now, and after 10-15 year many had already aged dangerously. So if you have an amplifier from those days, it pays to get it recapped. If you don’t, one day you may destroy your speakers.
The vast majority of the amplifiers mentioned here were never on the European market, so my experience has been with Quad: a 303, a 405-2 and a 606-2. I still have all three of them, and all three completely refurbished. The 303 is a bit old fashioned and is less usable for the lower impedance speakers that only came on the market after its introduction. But it was the ideal amplifier for my Quad esl 57 speakers. The 606-2 and 405-2 were bought second hand quite recently, and are now used to drive my Quad 2805 main speakers and Harbeth P3ESR desk top speakers respectively. Sonically, there are no differences at lower levels, but the bigger ones do sound better at higher levels.
The design criterion for ampifiers was defined long ago by Peter Walker, to be ’a straight wire with gain’ and that was indeed achieved by the better amplifiers of the period. After all, there are only three ways in which a well designed amplifier can sound different:
1 input sensitivity that is not matched to the output sensitivity of the source. This was a problem in the early days with no effective fixed standards for home audio. Hence Quad pre amplifers like my Q33 had variable inputs to precisely match the output level of the pickup cartridge, the tape recorder etc. If this is not done, there can be clipping of the input stage. This is quite common when you use these older amplifiers with modern cd red book standard sources with their 2.0V output (or more if the designer wanted to cheat). 2.0 V is way more than their rca inputs can handle. The solution is simple: inline attenuators.
2 Insufficient output power to avoid clipping of the output during dynamic peaks. Real dynamic music like a symphony orchestra may occasionally need hundreds of watts. Here, big power output rules, so beefy power supplies and big output capacitors. You can upgrade the latter, which is well worth it on the older Quad amps if you have them recapped anyway. Modern capacitors can be much smaller, so you can now fit bigger values in the same case.
3 load dependent frequency response. Real speakers are not just e.g. 8 Ohms, but their impedance varies quite a bit. The more the impedance varies, the harde the speaker is to drive for the amplifier. What this means is that the frequency response is not flat, but varies with the impedance at that particular frequency. To avoid this, amplifiers need a low output impedance, for a high damping factor (i.e. speaker impedance divided by output impedance). If this is not the case with real speakers of varying impedance over the frequency spectrum, the frequency response of the amplifier can vary quite a bit, giving that amplifier a signature sound like extra bass or a high frequency roll off for more ’warmth’. Many audiophile amplifiers are like this, thus deviating from the ’straight wire with gain’ criterion. Here, solid state amplifiers have a great advantage over most tubes.
So, to come back to the original discussion about older amplifiers, yes there are real beauties. Get one with sufficient power (there were some really big ones at the time), have it at least recapped, and probably get some inline attenuators to connect modern 2.0 V sources.

Funny, I'm finding myself squarely stuck in the 80's when it comes to audio gear and rather enjoying it.  Been a classic B&K guy for a long time as this is my 4th B&K amp (2 - ST140's, an EX442 Sonata & now an ST202), but would love to try Perreaux, VSP Labs, Moscode, Acoustat, PS Audio and maybe a couple others.  I like the sound of Mosfets too.  I had a Tandberg 3012 integrated that was lovely as well.  To me, nothing is as tubey, warm, and as reasonably priced as B&K, which is why I always tend to revisit this amp.  

Which 80's amps do you love and why?