Hi, my first post on this forum.  Thanks for the details and pictures!  I remember seeing the ads for Series 20 in the hi-fi magazines.  They said: "It takes guts to be more expensive than McIntosh." 
  
I see that there are a lot of Yamaha power amps that can be run in Class A and are much more readily available!  I'd be interested in hearing of any reactions on their use for this application. 
  
Thanks!