Whats the best vintage Yamaha amp to invest in?

the old M series were class A rated and amazing. The one with the meters was the m-80. What a monster, it would power up to 3 pairs of almost anything. The 35, 60 & 70 are great too with the matching pre-amps. They compare to threshold in sound quality (not build quality). Otherwise, I'd go with the sanui 717 listed here.

I had one of them and sold it after six months. The sound was very thin and bright. If you want something from that era you should check out Luxman. The ones with the rosewood cases. I had the model r-3045 and it was night and day compared to Yamaha.

A friend sold Yamaha and Luxman side by side for years in the late 70s and early 80s and hands down the Luxman gear was better sounding..... also higher priced. I have owned several pieces of both vintage Yamaha and Luxman and they were consistent with price points. The Luxman 1020A was the apex of highend receivers. Crappy speaker terminals, but everything else was amazing.

The Yamaha 620 and 820 are fabulous budget receivers. The Yamaha 2020 is great stuff, but rather, and I mean rather large and heavy.

Realize that with any vintage receiver, the electronics are old and often need cleaning, capacitor replacement, and restoration. You really won't get the "best" sound out of any receiver unless you have it re-capped and restored. And when you consider this into your budget, you'll potentially go over the $500 ceiling you placed. This doesn't mean vintage gear won't sound great as is, just not "best."

I agree that the Tandberg receivers are tops in sound, but the TR-2080 has been selling lately for quite a bit more than the $500 and under range as listed by the OP. I believe there's still a TR-2060 or TR-2040 for sale on eBay in the $400 range. Other options are the Sansui receivers - 8080, 9090 or 9090db - excellent sounding receivers that have haunted me ever since hearing my first 9090db. The 8080 has sound on par with the highly respected 9090 at a fraction of the cost, and will leave your wallet room to have it recapped for a really great investment.

Now, if you're set on the Yamaha natural sound, I'd personally skip the receiver and go to the amps. Check out the M-80 (one of Yamaha's best that's often available) then send it to Legendary Amps dot com for a complete upgrade and restoration. Yes, this will cost you more than your current budget, but you'll have a bulletproof amp with top notch sound for generations to come. These vintage Yamaha amps were built like tanks. Even if you don't go this route, you might want to call up those guys for a little chat. And they may be able to help steer you in the right direction for your vintage Yamaha needs.

Best receiver Yamaha made was the CR 3020.
It was massive and built in the late 70s.
It weighed like 90 pounds and was 170 watts.
The tuner section was also great.
I see them on Ebay once in awhile.