[MrFixr55]

Hi apERNA,

First off, NICE JOB on this radio!

It is highly likely that the issue is interference.  It seems from your video that the sound is good on a strong station (Highly negative AVC, minimum Converter / IF gain) and between stations, no negative AVC voltage, max gain, you are picking up general interference.   I live not horribly far from you (Huntington area of Long Island) and interference is horrific, even on the car radio if driving along power lines.

A couple of things to try:

• Do you have another radio of similar vintage with a back panel loop antenna?  Try that and compare.
  
• You can compare to a transistor radio to determine if the interference is through the power line or over the air, but the ferrite loopstick in a transistor set is somewhat more resistant to certain types of interference.
  
• Rotate the radio to determine if the interference gets louder or softer.  If so, then the issue is definitely interference.
  
• To eliminate interference from the radio itself, short the RF terminal of the tuning cap to B- (the junction of the negative terminals of the electrolytics and the filament string at the 7C6 detector / 1st AF tube with the shortest wire possible.  Short AVC to the same point.  This should kill all signal coming into the set, but the local oscillator should be running.  I think that under these conditions, the radio should be quiet.  If so, the radio is good and all interference is coming from the outside.  If not, there is still a possibility that some of this could be coming in on the power line.  If you have an isolation transformer, try using it to see if the radio is now quiet under the above conditions.
  
• Consider replacing the electrolytics on the parts set if it was not cannibalized.  Transfer the antenna to the parts set.  Same performance?
  
• If the parts chassis performs better, verify lead dress and "outside foil polarity" of the coupling and bypass caps.  Caps used to be marked with a band denoting "outside foil".  The outside foil side connected to ground for bypass caps and to the plate of the previous stage for coupling caps.  Outside foil on the opposite direction than listed above could invite internal coupling, motorboating, etc., that may be more noticeable on weak signals when low AVC translates to higher stage gain in the convertor and IF stages.  I have heard that new caps are neutral in this matter but I'm not sure.  I just think that the "Middle Kingdom" does not bother marking outside foil.
  
• Verify correct connection of the antenna.  I believe that the innermost end of the loop connects to the RF section of the tuning cap.  The other end connects to AVC.
  
• Look at the C402 (0.2uF) cap that goes between the B- and Heater string "Mecca" and the chassis. This "Mecca" is the point where the negative terminals of the electrolytic caps, the cathode resistor of the output tube, the bypass caps, grid leak resistors and the cathodes of the 1st AF, IF, converter and RF tubes. (This is a "Warm Chassis" set, meaning that the chassis is connected to one leg of the power cable through a capacitor, C402 in this set..) There is a coil of wire that serves as a choke wound around the cap and is between the chassis and the terminal of the cap that does not connect to this B- "Mecca". Duplicate this.
  
• If you have a "True Sine Wave" portable power source, go out in the woods and try.  It has to be a true Sine Wave supply.  Tjhe "Modified" sine wave supplies wreak havoc on an AC DC set.  Between the power transformer and the full wave rectifier, AC sets are less prone to interference from modified sine wave supplies.  I have tried this and have found this to be true.
  
• When I was a Field Engineer for a Lab Instrument manufacturer, the use of power line conditioners with isolation transformers on sensitive instrumentation was popular.  The theory was that the low impedance of the transformers tended to block high frequency noise.  The use of an isolation transformer with a "Hopkins" filter may be useful.  Google "Hopkins" Line Filter for schematic and theory.  Most computers, digital TVs etc. have these as part of their power supplies.
  

It was a good idea to put in a dedicated line.  However, I don't think that it helps much, especially if it is type NM (Romex) cable as opposed to type AC (Armored Cable, that replaced the rather dangerous mis-engineered "BX" cable).  I would think that unless there were high power devices on the same branch circuit that cyclically loaded the line down, that the interference travels through all branches.
At least you can hang a room AC Unit or resistance heater off that line.  I added dedicated lines for all window AC units in my house, which was grossly underwired. (No grounds, 2 lighting circuits, boiler circuit, one appliance circuit for kitchen counters, refrig, washing machine and dishwasher!!!???!!!, 60A service, but that was the code in 1954).  

Needless to say, I upped the service to 200A, added dedicated lines for refrig and washer, 4 wire for stove and dryer, 2 more kitchen circuits.  BTW, did ALL of this myself and passed the underwriters inspection.  However, sure as heck, did not kill the noise!  In fact, I think it got worse when the power company put in the remote read meter, 2 years later.