[R-390] oscillation in my R-390 IF

[Flowertime01 at wmconnect.com]

David,

Have you had a chance to get out the nut drive, small wrench and Philips 
screw drive to massage all the hardware in the IF deck? A lot of problems arise 
from loose and corroded hardware points. These are old receivers and your R390 
is older than the R390/A. Not a sure fire cure but a place to start. Also get 
the bolts that mount the tube sockets.

My R390 TM is still packed in moving cartons from July 2004 so I do not have 
it for reference. As the R390 filaments are in series you just cannot unplug a 
tube and divide the deck into neat sections to divide the problem down.

The IF cans have a bunch of solder joins in them. You can get the covers off 
and do an eye ball and remelt of the solder points. 

You are just going to find a sorry solder joint some place that is a high 
impedance point. You likely cannot find it with an ohm meter as the point will 
measure under an ohm with a meter and be open at 455Khz. Some point should be 
filtered by a cap. The point is not getting the filtering it needs because of a 
solder joint. That point radiates some signal around under the deck and it 
feeds back to oscillate.

Does changing the band width switch give you any clues?

Not an easy problem to resolve.

Roger AI4NI