Where the cap is from the line to the chassis, you might consider using Y rated safety caps, especially if selling or giving the radio away. While metalized film caps have a very low rate of failure, the Y cap may protect against possible shock hazard due to short. Actually, with a cap connected to the chassis there will always be a shock hazard. However, it increases with short. Regarding the article I read from Just Radios, if no cap is connected from the line to the chassis in a transformer powered AC radio, this does not mean that the radio has no RF connection to ground. There is still capacitive coupling through the transformer. However, a capacitor from the line cord to the chassis may improve reception and reduce some hum troubles.

The reason why I feel that safety caps aren't necessary across the line is because there is nothing in a capacitor that could short out the line severely enough to cause a fire, at least that I know of. I've seen old-style paper caps split and sizzle, and even had one blow up like a 10 pack of firecrackers in my ear, and looked like pages in a book afterward. However, they contain very thin foil, which isn't going to draw enough current to overheat wiring, but, instead, will melt on its own. There may be more concern where the cap is exposed to a wooden cabinet, but even then the chances of fire are highly remote. With metalized film caps current draw would be even less because we are dealing with a film of metal instead of a foil.

It would be wise in all cases to wire a replacement across-the-line cap after the on-off switch so that it is cut out when the radio is off.

Safety caps afford the highest margin of safety, and if you wish for that margin of safety, by all means use them.
T.

:::Need some understanding, what kind of cap is this, was this noise what you call motorboarding, even though it said DC on the cap-the AC cap is working, confused about this?
:::But glad the radio is working well now.
:::Thanks
:::Mitch

Hi Mitch:
Caps that say DC on them such as a paper cap that may read " 0.1 UF @ 630vDC" does not specifically mean "only" DC.
As long as the dielectric is not an electrolytic chemical or liquid in nature such as that found in Electrolytic DC only caps.... you can use them in AC too.
The ones with electrolyte in them are polarized and the electrolyte acts as a dielectric only when properly polarized. So THEY must only be used in DC.

When using capacitors with household AC voltage, one must consider that the value given for that voltage is its RMS (root mean square) or voltage that would heat a resistor the same amount for an equivalent steady state DC voltage. That is, 120 VAC RMS heats a resistor the same amount as 120 VDC. The actual sine wave has a peak of about 170 VDC.

Also to consider is stray spikes on the line that can often reach several hundred volts. ...So, for good protection you want a capacitor that will be able to handle these spikes without failing.

Others on here have pointed out that capacitors with a chemical dielectric must be used on DC only, but otherwise to understand the DC rating and what a capacitor does, a capacitor is basically two plates brought close together, but not touching, with a dielectric between them. There is no conductivity between the plates, but charges on one plate can affect those on the other, much like when you have static on a balloon it will raise your hair. Changes in voltage on one plate will cause corresponding changes on the other. The line capacitor in your radio, if across the line, is used to nullify small RF interference found in the wiring of your home. Its value is chosen so as to be large enough to pass high frequency RF waves well, but not the low frequency 60 cycle current in your home. The capacitor's DC rating is the maximum voltage (plus some margin of safety) which the dielectric can withstand without breaking down. While you are using the line cord capacitor on AC, at any one instant (a snapshot in time, if you will), the capacitor has varying degrees of DC voltage on it, and it must be able to withstand those voltages, how ever high they may be. If this doesn't make sense, look at a sine wave and follow it with your pen. You can stop your pen like a snapshot in time and take note that at any one point in time the capacitor would have various amounts of voltage on it of a certain polarity, making that instantaneous voltage DC. However, since time moves on, that voltage and polarity are constantly changing, at 60 cycles per second to be precise, and so it becomes AC.

T.

The noise you describe is not what is sometimes called 'motorboating'. You had 60 Hz AC line voltage hum, with a strong 120 Hz. second harmonic. Motorboading is a low frequency oscillation that sounds like a motorboat, typically caused by unwanted feedback between various stages in the radio. This is often caused by open filter / bypass capacitors. It is also a common problem where electrolytic capacitors have dried out with age, and no longer have the required capacitance value. Ed M
::
::Hi Mitch:
::Caps that say DC on them such as a paper cap that may read " 0.1 UF @ 630vDC" does not specifically mean "only" DC.
::As long as the dielectric is not an electrolytic chemical or liquid in nature such as that found in Electrolytic DC only caps.... you can use them in AC too.
::The ones with electrolyte in them are polarized and the electrolyte acts as a dielectric only when properly polarized. So THEY must only be used in DC.
::
::
::
:Thank you all,
:I have a good direction and not confused about this issue after all the good input and reading just radios article on safety with caps. Info is always great from this forum and will move forward with advice, these radios are for my grandchildren, will be the safest.
:Thanks again
:Mitch
:

One can learn a lot by taking a few capacitors apart, and looking at how they are made. Also, try to find a copy of "The Radio Amateur's Handbook" between about 1935 and 1955. (Try the internet, talk to a ham radio operator, or look for a 'Hamfest'. You will find a wealth of information on capacitors, other components, and how radio circuits work. Ed M

:The noise you describe is not what is sometimes called 'motorboating'. You had 60 Hz AC line voltage hum, with a strong 120 Hz. second harmonic. Motorboading is a low frequency oscillation that sounds like a motorboat, typically caused by unwanted feedback between various stages in the radio. This is often caused by open filter / bypass capacitors. It is also a common problem where electrolytic capacitors have dried out with age, and no longer have the required capacitance value. Ed M
:::
:::Hi Mitch:
:::Caps that say DC on them such as a paper cap that may read " 0.1 UF @ 630vDC" does not specifically mean "only" DC.
:::As long as the dielectric is not an electrolytic chemical or liquid in nature such as that found in Electrolytic DC only caps.... you can use them in AC too.
:::The ones with electrolyte in them are polarized and the electrolyte acts as a dielectric only when properly polarized. So THEY must only be used in DC.
:::
:::
:::
::Thank you all,
::I have a good direction and not confused about this issue after all the good input and reading just radios article on safety with caps. Info is always great from this forum and will move forward with advice, these radios are for my grandchildren, will be the safest.
::Thanks again
::Mitch
::
:

All:
May I suggest anyone who wants to understand the AA5 and it's components a lot better, go to a site called "Fun With Tubes". This guy knows his stuff, believe me. I go there every so ofter for a refresher course myself.
Lewis

:::
::
:

T.

::Good grief! My under-cabinet halogen light dimmer produces tons of noise. All of my dimmers produce noise! My cell phone chargers produce terrible noise! My television produces a little noise. My wireless internet DESTROYS my AM reception.
::
::T.
::
:
:Interesting- but the trolly lines, fan motor, washer, (with the wringer, remember getting your hand caught in it), refrigerator, etc. don't. It's interesting that these devices you mention are causing so many problems. I own these same devices and have NEVER had any of these problems. Perhaps there is another issue at work. Anybody else have this same experience?
:Terry
:

Ha ha. I've been using candles since the power went out in May. Thank goodness for the bicycle generator.
seriously-
I'm not saying that these problems don't exist, just that I don't have them.
I have two florescent lights, a dimmer on the lights over my collection, 3 TV's, (sometimes on at the same time), and wireless internet. I have 8 AM radios on display. I often have all of them on at the same time to show them off. Sometimes I use my AES transmitter. The main problem I have is squealing from the oscillator as I tune one. I guess I'm lucky to have products produced since the RFI standards were introduced.
Almost every electronic device manufactured has the notice that "...this device complies with the FCC rules of operation". Even my coffee maker has it.
Hummm, coffee sounds good.
T.
:
:::Good grief! My under-cabinet halogen light dimmer produces tons of noise. All of my dimmers produce noise! My cell phone chargers produce terrible noise! My television produces a little noise. My wireless internet DESTROYS my AM reception.
:::
:::T.
:::
::
::Interesting- but the trolly lines, fan motor, washer, (with the wringer, remember getting your hand caught in it), refrigerator, etc. don't. It's interesting that these devices you mention are causing so many problems. I own these same devices and have NEVER had any of these problems. Perhaps there is another issue at work. Anybody else have this same experience?
::Terry
::
:

My wireless internet and cell phone chargers have the FCC Part 15 thing on them, but they still destroy my reception.

T.

...But plug in a cell phone charger next to your radio sometime and see how it doesn't destroy your radio reception.

T.

:::The trolley would make static. Your Mixmaster would possibly make static, though mine has built in RF suppression filters. ...The vacuum cleaner, blender, electric coffee grinder. ...But not the wringer washer. This usually uses a brushless induction motor.
:::
:::...But plug in a cell phone charger next to your radio sometime and see how it doesn't destroy your radio reception.
:::
:::T.
:::
::
::Check this out- it might be the answer to all your troubles
::http://cgi.ebay.com/Vintage-Aerovox-Radio-Interference-Eliminator-/130450196994?pt=LH_DefaultDomain_0&hash=item1e5f700a02
:::)
::Terry
::
:Terry,
:You do have a great sense of humor, this one is rare.
:Mitch
:

Cell phones are nice to have, though. I also like texting. It is less invasive than calling, and so I can get information from people without having to start a big conversation and bother them. It's really great for organizing get-togethers. Text back and forth to see where each person is, get to a restaurant, find out it's a long wait, find a new restaurant, and all the while keep everyone informed of the changes.

Regarding the wiring in my apartment, it is all correct. Most of it is original from 1930, in excellent condition, and in fireproof grounded conduit. Still, even with the conduit, there is interference. The interference travels inside of the wires and into the radio. I have found that I can minimize it by placing chokes on the radio's line cord, and then placing a capacitor across the radio side of the chokes. If two are used, all RF grounding through the line cord is lost, and an external ground will be necessary. However, supression is better than with just a choke on the hot side of the line. I find that capacitors across the line cord side of the chokes increases interference, so I only place one on the radio side.

T.