Taking vintage Sansui amps as an example, there are several guys on Ebay who work on them. There seems to be three camps. The first will “service” the unit, which can mean anything. Unless you know what was done, in some detail, you run the risk that nothing much was done or, worse, that the unit was damaged by someone who did not know what they were doing. (I learned this the hard way.) The second guy will replace only what needs to be replaced to bring the unit up to spec. The third points out that electrolytic capacitors typically have a life of about 35 years, so for vintage equipment built before the mid-Eighties they all need to be replaced rather than wait for the next one to fail. And this is just the beginning of what will be a strip-it-down-and-build-it-up-again project that results in a unit that should be good for another 30 to 40 years.
I have a restored Sansui AU-717 integrated amp (sold 1977-79) purchased from an Ebay seller based in Olympia, WA, who is in the third group. His listing is for restoration services—you supply the rebuild candidate—and my understanding is that he rarely offers a restored unit for sale. His listing gives a detailed summary of the extensive rebuild that he does.
The Sansui is in a horizontal bi-amp setup with a Sherwood S-6040CP power amp (1983) and a Marchand XM9 active crossover. These are both dual-mono amps, and together they easily best the McIntosh equipment I previously used, a MAC 4100 receiver and MC7100 power amp. Due mainly to dual mono, I think, separation and detail are much improved. Along the way I also purchased a used McCormack DNA-125 power amp and McCormack RLD-1 preamp. They were transparent and detailed, but no match for the Sansui and Sherwood combo.
I bought the Sherwood for $125 on Ebay. So far as I know it has not been serviced or restored, and thus may not be performing at its full potential, though it sounds good.
I also have a Harman Kardon 730 receiver in a smaller system in a back room. I bought it from a guy who had brought it up to spec but did not do a full restoration. That’s how I got started pursuing dual mono.
So I guess you could say I am in all three camps—fully restored, brought up to spec, and “as is.” But if anything fails, I will look for a complete restoration.
I think that trying to re-create the original sound is a hopeless quest unless you have the original parts in their original condition—and given what we know about capacitor rot, this would require a miracle. Where are you going to hear the original sound, anyway? The unit that was just pulled out of a box and has never had anything replaced will not sound the way it did when new. If we don’t have an example of how it sounded when new, then talk about how new parts will change the sound is just unverifiable speculation. All anyone can do is meet spec, and if it can be done with parts that better withstand heat or last longer, it’s a win.