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

True story. Back then I purchased a preamp from a woman who worked for a terrific high end store west of Madison WI. As we talked, she related to me that she was into high-end. She told me that her theta amp was the best she had ever heard. She also related that she kept it hidden from her husband and pulled it out whenever he went to work. Ultimately, she was discovered and her love for her amp, led to her divorce....

Phase Linear are still great amps and some still sound great in relation to modern amps. If they still work your all set but if not there are a few places on E-Bay that will get them back to Snuff I use Circle Stereo in Texas. You had the 400's 700 and 500 and the newer ones had a B designation and had  different meters  and they still sound as good as most new amps and maybe better after being rebuilt. I still have all of these and I can't get myself to part with them. And by the way Pink Floyd used too use the 700's stacked so that goes to show how good they were. Look up the most influential amps of all time and you'll see the 400 as right up  near the top. Bob Carver was the guy who got the ball rolling as far as high powered good sounding amps. I am 72 and have heard them all. Most important is the Pre amp as that will make the big difference and a lot of new ones have made great strides as far as better sound.

I bought a Bryston 3B new, in and around 1985. It still works flawlessly, and has seen a tough life at times, but not once did it ever go back for service/repairs. It has now been passed along to my son for his system. I never strayed from the Bryston line. Owned many of the 4B series and now have a pair of 28B SST2's. Perhaps I'm stuck in my ways, but I feel loyal to the brand that has worked out so well for me, and being a Canadian, I like to support home grown manufactures whenever possible.

Agree strongly with the Electron Kinetics Amps. All of the Eagle 2 series power amps are stable down to 2 ohms. They became the building platform for all of the mono amps that followed.
I managed to purchase a pair of 11 prime mono blocks recently and will never look back!
I purchased a 7a dual mono amp from John Iverson and later he upgraded it to a 7b (only 22 exist) which I still have.
Used to own Thresholds, Accuphase, and briefly Phase Linear. None compared to EKSC Eagle, especially with dynamic loudspeakers.
The BEL (Brown Electronic Labs) were peerless and remain so when driven as mono blocks for Electrostatic Loudspeakers, especially Dayton Wright's.

I still have the Krell KSA 250 that I spoke of above. I had it updated to a 250S, sold it bought a 700C, sold it and ended up with the 250 again after the owner died. I have been using it quite a bit although I have a pair of Citation IIs running in balanced mono, it still sounds great.
I also have a Yamaha CA 2010 that sounds super and a Mcintosh MA 6100, a Bryston 3B, Transcendence 400, Belles 1, a pair of Audionics and various other Yamaha receivers. There may be others.