The design of many of these amps is timeless & in many ways as good as almost anything today. The parts quality on the other hand is all over the place w/ some good & some not great that can be really improved w/ better parts which many people have done.
The Conrad Johnson Premier Four which I owned in 1985 was probably the best 3 dimensional imaging amp I’ve ever heard & beautiful mid range & tone if not slightly rolled off in the extreme frequencies. The Dyna Stereo 70 I grew up w/ was overall similar sound just much less power. Both are true classics!