[R-390] 390A contractors

[wb3fau55 at neo.rr.com]

So in the subject of contractors,  were there suppliers of just subchassis?  I have been told that Teledyne, Amelco, and Imperial all worked together  to build their radios.  So we know of 5 contractors of PTOs-  Collins, Cosmos, Motorola,Dubrow, and Progressitron.  Perhaps others?  
  So my real question is were running spares made up separate?  I know there were new IF strips made.  I saw some at a hamfest.  As always,  fascinating info.  73s Russ.