[R-390] please help

[wb3fau55 at neo.rr.com]

OK guys,  some years  back I read someone quote a noise floor of -141 DB for a "golden" R-390A. Please, if someone would,  convert that to microvolts.  I think it was in ER magazine.  I think they also quoted
-139DB for 75A4.  Then someone installed  a 6GM6 in the 75A4 and it  was now as good as the R-390A. 
  Entertainment-  HF is coming  back to life,  I have heard beacons on 10m for 3 days now! 73s Russ.