[R-390] R 390A RF Deck problem

[triode45 at aol.com]

Hi Gents,

I am new to the list, I 
  am not a Ham but I am a SW Listener and retired EE.? I have a question 
  that has probably been asked before. 
I have 2) R 390A's and one is very 
  sensitive and the other is not. After considerable testing the newer EAC has a 
  sensitivity, MDS, of less than half a microvolt. The older unit Motorola is 
  more like 2 to 3 microvolts. I have checked all tubes on the RF deck and have 
  swapped tubes from one deck to the other and the symptoms did not change. If I 
  swapped the RF decks between the two receivers the problem moves, Now the EAC 
  has poor sensitivity. I have changed the recommended capacitors recommended and 
  suggested from several web sites. All voltages seem to be OK. 
Any 
  recommendations on what to check next.

Thanks is advance and as you 
  guys say, 73,

Alfred? 

SW and Ham Band 
  listener