From: peterwieck33@gmail.com   
      
   More information:   
      
   A well informed former HK rep sent some information:   
      
   a) Look for the ICs - they will be there, somewhere. They were, back of the   
   driver boards.    
   b) That S/N (alphanumeric) suggests that the unit was assigned to a factory   
   rep ahead of release to generate orders. Check the S/Ns on the driver boards.   
   Date codes are November of 1975.    
   c) Internal fuses, ICs mounted differently from production, alphanumeric   
   serial number = advance model.  In his opinion.    
   Icing on the cake: no codes on the filter caps. And the two output transistors   
   I checked were entirely blank.  They looked like they were cleaned, not issued   
   that way.  Two slightly different types of feet. An HK marked metal toggle   
   on/off switch    
   different from any others I have seen, and so forth.     
      
   And there it seems to be.     
      
   Peter Wieck    
   Melrose Park, PA   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)