[Texasrocker]

... to filter any AC outlet to rid AC line noise (line hash), this idea works. I isolated my vintage radio repair bench from incoming ac-line hash by doing this yrs ago. Its simple too!
* Take (2) .1 uf/ 600 v bypass ( orange drop caps), Lay them side by side. (parallel). Twist the ends together on one-end only. Solder a green colored single (ground wire) to those twisted caps ends. Attach that 1 ground-wire to outside grounding rod near your workbench.
*Attach a old 2-prong type AC cable with (male AC plug), (solder independant 2 wires) to other 2 caps wire-leads from the capacitors making sure they cant short together. Use good electrical tape or heat-shrink to these 2 separate capacitors connections opposite end of the ground wire twist.
* plug the male end of the AC cord you soldered to the caps directly into your service-bench power strip, or other female connection of your house plug that you are using for testing your old radios.AC line hash gone!!Any other noises would be nearby florescent lights transformers,etc that can be turned-off to isolate those type interferences.
My neighbor runs a "cracker-box" electric welder down the street sometimes.I can see him in his driveway when he works on his welding projects from my vintage radio repair bench. I fully "isolated",.. and got rid of his AC line hash noise by installing the 2 caps (parallel) suggestion above.