There was a fellow here a while back who “inherited” an r390 and was looking on advice to get it up and running. I came up empty. I havent seen one in 25 yrs.
These new receivers really are neat. pop a video decoder in the PC and you can pick up video transmissions as well.
I got lucky- when the Naval Air Station here closed, the airport part of it turned in to had one of those "old guys" open an avionics repair shop, and he kept mine tuned and repaired. A lot of military technicians seem to have worked on them while in service.