[R-390] 60 Hz Hum Output from R-390A IF Module

[Tim Shoppa]

> Of more significance is a marked change in hum output for certain 
> mechanical filter selections.

Can you use an ohmmeter to check for leakage between
filter can and terminals? The usual symptom is a false actuation
in AGC action between different filters, but this could also
I suppose manifest itself in terms of hum (maybe AGC action
is hiding a source of hum?)

Some of us with still working, but leaky filter cans, have isolated
the can from ground to help alleviate this. But this is at best a workaround.
The real solution is to open the can and clean out the foampucky.
(I'm presuming that is the correct technical term for decayed foam!)
The really adept have done this as well as repairing damaged filter
coil winding, e.g. http://www.delphelectronics.co.uk/filter390a/

Tim N3QE