[Collins] 75S-3B hum (yes, again)

[Craig Roberts]

My "new" 75S-3B is humming -- and it's not a merry tune.

I konow this topic's been covered before, but -- well ---

My hum is low level and independent of volume control setting. It's 
there with the gain all the way down.  My receiver has a new 40/40/40 uf 
electrolytic can and IF filter shields top and bottom. 

The hum seems to mimic the vibration of the power transformer.

The hum MAY have appeared or increased after I performed a mod, i.e., 
replacing the inductor L-16 in 75S3-B with an 820 ohm resistor to reduce 
audio distortion (as suggested in a Reflector post some time ago).    
I've noted on the schematic that the original RF choke was magnetically 
shielded.  Could this have done it?

Many thanks and 73,

Craig
W3CRR