Recommended cheaper vintage SS Integrated Amps?

I own a KA-3500 and love it. Punches way above its 40 watts and has a wonderfully clean sound. It's often overlooked with people always going to Sansui or Marantz. I also have a Harman Kardon 330c receiver, and I think this is actually warmer than the Kenwood. Beautiful piece.

From the 70’s… more people had receivers than amps, At least among my peer group.
Nikko, Onkyo, Denon, Marantz, Pioneer (did they have the Quadraphonic system?)

I had that Kenwood as part of my first “serious” system. Nice amp!

   Sansui, JVC, Marantz, and some others are definite prospects. Like stated before, the integrity of components (caps/etc.) is a given. However, I would not purchase a vintage piece just based on the word that the previous owner had all components checked out and, if necessary, replaced. That can be a daunting task unless you personally know the seller.
   Many years ago I had a Pioneer receiver from the SX series which was a decent performer. While it was rated as a "receiver", given it's internal tuner, which was sub par at best, it still produced pretty good sound. All of the previously mentioned brands depended on the speakers they were mated with.
   One avenue you may investigate when it comes to vintage stuff.....Years ago Dynaco offer some products at very reasonable prices. Their equipment was offered as ready built or as kits for those with some degree of soldering skill and ability to read simple instructions. Some of those units sounded noticeably better than more expensive "name brand" products. Don't rule out Dynaco.
   Good luck in your search.
 
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I don’t normally post, but I can speak with experience on this topic, so I’ll jump in.  I’ve had a bunch of vintage pieces, and still have quite a few. Receivers are certainly more popular from that time frame. Based on your request and my use, I would recommend a Harmon Kardon 330c. Not a lot of power, but if your speakers are reasonably efficient, it should play nicely. I’ve compared this unit in stock condition, to quite a few higher powered units, and other brands, and it’s always been way better. Warm but clear, nice deep bass, and visually not as over the top as others from that time frame. They don’t fetch much money, as everyone is looking for Marantz, Pioneer, and Sansui. The 430 is reported to be even better, but I have no hands on experience with it. Good luck on your search. For what it’s worth, with the right speaker pairing and source, the 330c can be very satisfying. I have wondered more that once why I continue to spend more money on gear that doesn’t sound that much better.