My experience has been primarily with Pass and a few other brands over fifty years. An amplifier made by the same manufacturer will show significant improvements in ten years and a huge difference in twenty. It is a competitive market and to stay relevant a company must keep improving the sound. So, in general they all have.
Companies typically have house sound, so, unless they took a turn (which could happen with a company like Yamaha) then you will get a similar but much improved sound with a much newer model.
I cannot comment specifically on recent Yamaha, the last one I owned was about 1980… it was supposed to be a high power amp (it weighed 75 pounds)… but the Acoustat 2 + 2’s electrostatic I owned drained it at low volume. The new Pass amp that I bought (Threshold s500), blew it away on power and overall tonal balance.
Companies typically have house sound, so, unless they took a turn (which could happen with a company like Yamaha) then you will get a similar but much improved sound with a much newer model.
I cannot comment specifically on recent Yamaha, the last one I owned was about 1980… it was supposed to be a high power amp (it weighed 75 pounds)… but the Acoustat 2 + 2’s electrostatic I owned drained it at low volume. The new Pass amp that I bought (Threshold s500), blew it away on power and overall tonal balance.