[R-390] bfo hum and s meter not on zero

[Perry Sandeen]

List, 
One of the least expensive trouble-shooting aids is a compete set of tubes.

They don't have to be new or special just good.  It is a PITA to pull all the tubes out and replace them one by one.  But if you have a very limited test equipment budget it  may be the only good choice that one has.
Also, spend time reading Roger R's comments in the Y2KR3 manual.  One won't become an expert overnight.  But over a period of time one will become more familiar of the way it works.  Seeing all the slugs go up and down as one tunes through the bands is intimidating.  But if the cams line up properly with the marks on the rear panel, you're probably good to go.
Really, the more you study and "spend quality time" with your radio(s) they become far less intimidating. (but still weight a ton)
BTW, remember the old car radios where you pushed the button to the station you wanted?  They employed a slug tuning system also.
The "A" just does it on steroids.
Regards,
Perrier