Best vintage amps (late 70s / early 80s) under $3k?

I’ve spoken to someone who had an M-25. More power, inferior sound, and unfortunately just as much heat.

I know the guy who had the Tekton and M-22. He ended up getting a Don Sachs tube amp that he prefers. Tekton are very efficient speakers though, I used to own some.

I got a super experienced tech to refurbish my M-22. I asked about a new power cable, and he said "the line cord does not drop voltage when the power increases as it does in a class AB amp, so increasing the wire gauge buys you nothing. On the other hand, there are better quality line cords available. But again, I think the improvement will be subtle"... so I gave it a miss. I did get some Mundorf caps installed though, which are very nice. Gives the top end some sparkle, I think.

I concur with the recommendation to take a good look at the NUForce STA200 SS amps.  Check out the reviews on Absolute Sound, Hi Fi News, Stereophile, and the Audio Advisor website.  They have reduced the price to a rediculous cost as low as 449 each (Audio Advisor yesterday).  At 499 I purchased a pair to bi amp my Martin Logan SL3 electrostats.  I previously ran class A Stereophile recommended Creek 5350 SE’s, or alternatively a pair of restored and tweaked Harman Kardon Citation II tube amps that I spent a lot of money to completely rebuild and installed the best components and tubes available.  They sound awesome, until I acquired the NUForce STA 200’s.  They retail for over 1200 and were considered a bargain at that price, the sale price is rediculous.  Some pretty strong statements from users, that I agree with after they hit 20 hours..  My pre-amp is a tweaked out PAS-4 Dynaco tube (Panor 1995yr version) with the best Mundorf Supreme caps EVO Silver, gold, oil and using Vishay low uF bypass capacitors to refine the soundstage and the best tubes available including a quad of the HG Russian ‘75 6N23P’s and 60’s Grid Frame E83CC Tesla’s ( TeleF 803S grid frame copy) in the front end of the phono section.  The ML SL3’s electrostats have large panels that are extremely resolving to reveal the finest details.  There is no question to my ear that the NUForce STA200’s live up to the accolades  in users reviews and outperform anything else I’ve connected them to.  Fast, resolving, broader/deeper soundstage, clear, dead quite, unfatiguable.  And they run cool.  Eclipse my Creek’s and the HK II’s by a large margin that is very audible if not impressive.  I’m 65 yr old and have been running audiophile systems since I was 15 with my first tube Mac (cut a lot of grass for that).  I never thought I could be torn away from the tweaked HK Citations’s, but these NUForce amps are the best audiophile bargain and they are bran spanking new.  

@pts     Anything on my list that sounds like an M22 without running hot?  No. My old Sumo on that list is so significantly modified.  It is the best Sumo amp that I have heard,  Period.  The M22 won't hold up to this Nine.  Its been soooo long since I've heard a stock Sumo Nine, that I probably shouldn't comment between those,  but you can fry an egg on my Nine.  
The Old Heathkit's are really surprising, but again, they need a mod or two and better parts to stand up to todays amp,  but I really believe that you'd enjoy one of these models of Heathkit amps.. 
Remember, you are looking at very old amps.  Nothing wrong with good NPO ceramic disc caps, but these old amps are full of lower quality ceramic disc and all electrolytic need to be replaced to bring them up to par.... The Son of Ampzilla properly updated is also a nice sounding amp.  I actually own 3 amps on my list right now.  

pts, wasn't the Sumo Nine a class A design too?

There is a company in CA that refurbishes Threshold and Forte electronics.  http://www.vintageamprepair.net  I think they were former Threshold employees.  I've seen several online comments on the quality of their work.  Checking with them, giving your priorities, might be helpful.