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

[Flowertime01 at wmconnect.com]

Tim, 

You wrote,
> 
> 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/
> 
> 

---------------
I think yo are on to something here. Some of the foampucky could be doing a 
short to chassis. Not a dead short but enough to act as an input source for 
some hum.

I have on easy way to test for such a condition. Unsoldering the filter 
inputs is a long grind to trouble shoot the problem. We do expect the input and 
output to be essentially open from the coils of the filter to ground. Once 
you lift the leads it is easy to get a meter reading. But to undress all 
those leads on a witch hunt is work.

At some point Jon may think it would be worth the effort.

Roger AI4NI