[apERNA1985]

I have a philco 46 - 420 code 121. When I got it the antenna was missing and I eventually bought a parts set just for the antenna. However after a full recap and alignment it hums like crazy, I also get squeeling and motorboating with the tuning capacitor almost closed. I posted this problem in another forum and someone thought it was electrical interference in my house. I ran a dedicated line from my electric panel to the upstairs in my house. I used 12/2 Romex with a brand new receptacle, I even cut it in the wall. This will be the dedicated line for my AM radio. Then I went downstairs and I shut off every breaker in the house except for the dedicated line running the radio and the hum never went away. Does anybody have any ideas on what it could be? Oddly enough last Saturday at about 8:00 in the morning I turned the radio on and it played perfectly for three and a half hours. I had clear audio no hum at all and it actually sounded pretty good. I shut it off and went outside to do some yard work for a few hours. By the time I was done it was almost time for cousin Brucie so I turned it on and the hum was back. I've tried turning the plug but it made no difference. The tubes all test moderate, I replaced the 7A8 because I had a brand new one, I've tried switching the tubes from the parts set into it and haven't seen any kind of a difference either. I attached some pictures of my work on the chassis feel free to critique my work I love doing this stuff so I want to get better at it.

Here is a clip on youtube you can hear the squeeling and motor boating along with the hum between stations.

[Video: https://youtu.be/vwVZ24rrWPo?is=NvYa9JFY78nPgHqL]

[462ron]

Hi apERNA, what you have sounds like typical AM reception with noise at my location. That repetitive sound you had around ‘60’ on the dial is exactly the noise I have that I traced back to my electric meter, it’s the kind that sends your reading back to the utility company. Did you try a different radio where your Philco is? Take a portable transistor radio and go around your service meter and listen for that noise. When I did that at my house, the interference was so bad that’s all I could hear, it drowned out all reception! Otherwise, your radio sounded fine as you went up the dial!

Ron

[tbone]

I have the same noise on my radios, and it’s from the neighbors light dimmers. We don’t have smart meters here, so at least for me, that’s not the problem.

I have radios that simply are worse than others with respect to the noise. AC/DC sets are the worst. Sometimes I can reverse the plug in the wall to help lessen the effect.

This is the sign of the times.

[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.

[morzh]

Interference.

There are places where the station comes clear without the interference, so this is not the radio.

See if you have a USB converter nearby, or an LED light, or...any radio will have some of that; I agree yours is a bit more intense, but given the clear places on the dial, this is from the outside.


Are any other similar radios exhibit the same behaviour when plugged / located at the same place?

[MrFixr55]

Hi Pholks,
I added more info to my previous post (#4) because I did not have enough info there.

[radiorich]

Hello Guys,
I agree with Mr. Fixxr’s comment: “I think it got worse when the power company installed the remote-read meter two years later.” I’ve noticed the same issue, and when I use a transistor pocket radio near that side of the house, it disrupts not just part of the AM band but even parts of the FM band.

Sincerely Richard

[apERNA1985]

Thank you all for your responses. The power meter is on that side of the house. And it is the type that we've all discussed. But I've tried the radio all around my house and haven't seen much of a difference. I also own a 1970 Ford LTD, it's got the factory philco AM radio in it. My hippo starts to gain noise above 1010 wins, that's a radio station out of New York. It gets louder and louder and basically drowns out all the other stations. So I parked my car in the driveway and tune the radio to am 12:50 which is pretty much the only music station there is anymore except for when they put Cousin Brucie on on 770 Saturday nights. In my car I can hear 1250 fairly well it's a little bit of a week station but it's Audible. I put the hippo on the hood and the humming was so loud I could not hear the station at all. I took a small transistor radio and walked around the house with it and as some of you have said some radios are more susceptible than others, but I can usually get 1250 I'll be sometimes a little weaker or a little stronger but the hum isn't as overpowering as it is on the philco. I'm not sure if this helps. I have a Bendix AM radio that I can pull out of storage that hasn't been recapped but still works somehow on original electrolytics I can try that out next to the hippo.

MRFixR55

First that's a lot of information thank you. I'm actually an electrician by trade so I know exactly what you went through. I actually wired my parents addition at 12 years old, but it did take 3 tries to pass. One thing that is bothering me, I remember one of paper wax capacitors had wire wrapped around it. If I remember right the term for that is a gimmick. I did not reproduce that when I replaced that capacitor, I just installed a new cap in its place. Could this be the cause of my issue? Also I snapped a screenshot of the schematic I'm using. Is this c402 that you're speaking about? Is there any benefit to increasing the capacitor value on that particular one? I honestly wonder if there is a filtering or ground shielding issue that's causing all this. One thing I noticed is after using the radio for a while it seems like the hum gets worse. The tubes all test in the low to Middle range of good on my Sencore tc-136 and none of them have grid leakage but I'm wondering if one of them is breaking down, or if I just happened to get a bad capacitor and maybe as the radio is running it's letting more and more leakage come through. I am considering recapping the parts chassis. Other than the little terminal strip where the antenna Loop and the ground that goes to the chassis mounts the chassis itself is in good shape. Someone dropped the cabinet and broke the bakelite badly, that's why it became a parts set. It is a different revision I can get the number when I get home, but it still has the field coil speaker. I'm wondering if the loop antenna could have changed values during revisions? I was also considering doing all the revisions in the schematic. The schematic I have mentions each revision that was done to the chassis before they went to a permanent magnet speaker, I'm wondering, considering mine is the very first one maybe it will help with noise and fidelity?

[apERNA1985]

Just an update I was thinking about caps by memory and confused 402 with the cap in this , which was the one that had the wire wrapped around it. I actually never changed 402 because I did not have a mica cap. Here's a picture of the unrestored Parts hippo chassis you could see both capacitors I'm talking about. The one with the wire wrapped around it doesn't seem to be on my schematic. It's a .2 microfarad that goes from pin 4 on the 7B7 goes to the ground on the terminal strip then is connected to pin number 1 on the 7c6 through a 120k resistor. Both chassis did have that.

[MrFixr55]

Hi apERNA,

Yes, that's C402  [Edited 07/11/26] 401 on the schematic section that you posted.  That's the cap that "grounds" the chassis to the B- "Mecca" that I described.  I wouldn't call the wire wound around it a "gimmick; a gimmick is usually connected only at one end and was very common in the RF transformers of the early 1930s 4 tube TRF radios.  Here, I think it acts as a choke. It and the cap are in series.  I have only seen these in Philcos.

If using the chassis from the parts set as a comparison, change ONLY the electrolytics, jumper the power switch and install a polarized power cord to ensure that the chassis remains at neutral - ground potential  More on that later.  The reason why I am recommending to not recap the paper caps at this point is because paper / foil caps are wound like a Swiss roll.  This causes one plate of the cap to be "inside" the other.  The "outer foil" goes to ground (B-) on "bypass caps" or to the plate of the previous stage in coupling caps.  For example, in the audio stage, the cap that couples the triode plate of the 7C6 to the grid of the 50L6, has the outside foil connect to the plate of the 7C6 and the inner foil to the grid of the 50L6.

The reason that I want you to jumper the power switch is this.  Consider for a moment if C402 401did not exist or was shorted and the chassis was directly connected to one side of the AC Line.  In just about every AC-DC radio, the power switch switches the B- / chassis ground to the power line.  This causes a d**ned if you do / d**ned if you don't situation.  If the plug is in the AC outlet in such a way that the chassis is at neutral v/ ground potential with the power switch closed, all is well.  However, when you turn the set off, the chassis is now hot, through the tube heater string.  The heater string is less than 100 ohm when cold.  Reverse the plug and the opposite happens.  The chassis is safe with the switch open and hot when the switch is closed.  Since you are working with an exposed chassis, this is dangerous.  In fact, I modify all transformerless sets in my collection so that the B- /ow end Heater String "Mecca" is hard wired to the neutral conductor (large pin) and that the switch is between the rectifier plate and heater connection and the Hot leg of the power cord (small pin).

Tuning caps were quite standard in radios of this period.  the AA5 or AA6 radio had an RF stage cap whose value was almost always at 365pF with plates closed, 10pF with plates open, making the antenna loop value pretty similar from model to model.  The only difference is that in the Philco AA5s and AA6s, there is an RF coil in series with the antenna loop that allows the user to connect an external antenna to the set (the green wire).  However, if no external antenna is used, the green wire is grounded to the chassis, thereby at the RF level, shorting out the coil at RF frequencies.  Therefore, you could possibly replace the loop with a loopstick if you find one from a radio using a 10-365pF.  So I don't think that there is any real difference between the loops from your restored radio and your parts set.

It is sounding like much of your problem is coming through the power line.  The Philco radio in your LTD (I wonder if they were actually made by Philco or by Bendix?)  are "permeability" (coil and slug) tuned.  Ford radios in the late 1950s to early 1960s came either from Bendix, Motorola or possibly Philco.  From about 1968 or so, the Ford radios had "Philco" instead of Ford on the dial, as Ford owned Philco from about 1961 to 1974.  I am fairly sure that the radios in

BTW, what model LTD do you have.  I had a 67 Country Squire that Dad gave to me for my 21st birthday in 1976I rebuilt the 390 and replaced the rotted frame on.  Drove it for about 70K miles (160K miles) total when I sold it and bought a 69 Falcon wagon because the cost of the gas was getting to me.  The 69 and later full size Fords had stronger frames because they were made of heavier metal.  Unfortunately, the FE engines were replaced with the 351M / 400 which was nowhere near as good an engine.  Had the Falcon wagon with a 302 (really a Fairlane with 2 headlights and less trim), sold that in 1983 when I got my wife a 78 Fairmont wagon with a 302 2bbl.  That went as fast as lightning, especially for a malaise era car.  wish it had fuel injection!  Put 160K miles on that. It rusted out by 1992 and sold it for $100.  Bought an 80 Lincoln for $450, kept that till 2004.  Bought my 91 Aerostar company car when it went off lease and gave to my wife, the Linc to my son.  Still have the Aerostar.  Replaced the Linc with a 2000 Explorer in 2004 for my wife, son drove the Aerostar till I took it away from him.  My daily driver is my Mom in Law's 2003 Taurus 3.0 Vulcan.  166K miles on it, it's 23 years old but it came from the south and /runs like a Rolex watch! I don't drive it in the snow, so no rust.  I drove the Aerostar instead.  But I would love to have a 70 LTD.  However I collect radios because Ms. Fixr does not let me collect cars.

[MrFixr55]

Hi apERNA,

Me again.

The terminal that the wire coil end of C402 401goes to is likely the terminal on the trip that is riveted to the chassis. Do make sure that that rivet is not loose or corroded.  The resistor you describe also goes from the
B- / heater string "Mecca" to chassis ground.  This is needed, because the cap stator and frame and the IF cans have to be at ground potential, as well as the metal bases of the Loctal tubes, as any shields used on the tubes have to be grounded, and they are grounded through the base.

Try what I suggested before about changing the electrolytics, put the antenna back on the parts chassis, jumper the switch, make sure that the chassis is at neutral potential and fire it up.  THen compare to the other set.  If they both perform the same, thenthe problem is definitely through power.

BTW, there is usually a cap, C100, a 0.04uF cap across the power line downstream of the power switch.  If this cap is open or gone, this can increase noise.  The cap that you need to use is a Y2 Safety cap.  The cap is fused so if the cap shorts, the fuse opens to prevent fire.

Forgive me, there is a problem with the document from the Philco Library that I was using.  The document is for Model 46-420; the pic is of the "Hippo" cabinet, the chassis is a 6 tube job, the sectional schematics are likely correct, but the complete schematic is for a 46-200.  Can't write to Philco to correct it, the company does not exist, the buildings are gone and the engineers are in the afterlife.

[apERNA1985]

MRFixR55

I'm going to give everything a shot this morning. What schematic are you using? The schematic I found was some kind of philco service bulletin I don't really care for it because it seems to have a lot of shortcuts and not a lot of detail.

Also considering I've lost that little choke is it worth trying to rewrap it around my capacitor? I thought the new style capacitors were better shielded and didn't need this that's the only reason I didn't transfer it, but seeing as it acts as a choke it should be very necessary to the radio. Also I might just scuff the ground rivet on the terminal strip and solder it to the chassis to make sure it has a good connection.

By the way could a bad volume control be causing this? The radio never gets very quiet when i lower the volume all the way down. Then today I flipped it on to see if there was some kind of anomaly at 730am on Sundays but it had the same noise as usual. But now at low volume when the knob is about to push the off switch internally it started squeeling almost like feedback on a microphone. I jiggled the shaft of the pot and it would go away and come back.

The radio in the LTD is stamped Philco but I don't know if bendix made it for them. It's full of those kNetworks or Couplets That you find in the Predicta TVs so it might be Philco. It is slug tuned. The car is a 70 LTD Brougham 4 door. I've always been into cars, and we have a 1 year old daughter so I said it's time to get a cool 4 door. I love the hidden lights in the grill, and the weird dash. I was between that, a 70 Montego 4 door, and a 71 Satelitte 4 door.The LTD was the cliche old lady's car, 56k miles with receipts, a couple bumps from pulling in and out of the garage, but otherwise all original even the hoses say Ford. I felt guilty swapping the belts, hoses, and brake parts but I needed it to be reliable and safe.

[RodB]

The capacitor with coil (C401) is a wave trap roughly tuned to 455kHz to prevent nearby interference from other rf sources. Don't know when Philco stopped putting them in but you don't see them in later sets. My experience is there's always 8 turns of wire in series with the cap. You have 3 options; leave the coil out of the circuit, wind wire on a new cap, or remove it altogether. I think most use option 1 and put in the cap only. This is one of those things where you want to be a fly in the room during the design discussion. (Hamilton: "I want to be in the room when it happens!" )

[Paul Philco322]

Have you tried pairing it with a tunable AM antenna, like a Terk, select antenna or the like? Paul

[apERNA1985]

Real quick as a test I took the unrestored Bendix radio and put it in front of the hippo chassis on my kitchen counter. It has a little hum but that could also be because the caps in it are 70 years old or more, but it doesn't have that blow your head off hum that the hippo has. This is more like the am hum I expect. it even has a damaged antenna but still picks up most of the stations. Going to go replace the filters on the hippo in the basement later on.

This is it.
https://youtube.com/shorts/dR2oYQBDzao?i...8Nm_IESalM