Vintage Radio Power Entry Safety

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Vintage Radio Power Entry Safety

Post by jsweinrich on Sun Jul 02, 2017 1:55 am

I noticed something that when I was a kid fiddling with radios would not given a second thought, unsafe power entry. The power entry on this radio, a GE F-96 uses a power plug that is not polarized, the cord has no ground lead, and the set has no fuse. When restoring such beasts what do folks do to make them more safe? Of course I need to replace the entire power cord because it is falling apart but with what? I guess I could use a polarized plugmold cord and install a inline fuse inside the chassis on the hot lead to keep the chassis looking original on the outside. This radio also has a dual filter capacitor inside the chassis that connects to both power leads to chassis ground that has power applied to it the entire time the radio is plugged in. So I'm thinking that either putting the capacitor on the fused side or the switched side of the hot lead of the power cord and leaving the other cap connected to the neutral lead of the power cord.

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Re: Vintage Radio Power Entry Safety

Post by John Bartley on Sun Jul 02, 2017 10:23 am

This has been an ongoing debate in the antique radio community for as long as I have been on the internet ... almost thirty years? It's a personal opinion driven decision, and my opinion is that because there was no epidemic of people dying from electric shock for the fifty years that tubes radios were used in North American homes, my decision is that my radios will always be wired according to the factory schematic.

Unless the radio user is able to touch a line voltage carrying part of the radio .... and ... also touch a ground somewhere, they aren't likely to experience any problems.

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Re: Vintage Radio Power Entry Safety

Post by jukeboxman on Sun Jul 02, 2017 10:36 am

What John said---i never buy polarized cords -i buy rolls of 18 ga zip cord and non polarized plugs

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Re: Vintage Radio Power Entry Safety

Post by Chas on Sun Jul 02, 2017 11:18 am

I never alter the OEM configuration for a radios power input... Despite the apparent "danger" an alteration will give a false sense of security because no matter what is done to the radio there will be external circumstances that will make the alteration dangerous. Best alteration: Cut the cord off and set the radio on a shelf. Consider, as far fetched that an alteration is part of an inquiry after the fact. The alteration will come into question and if traceable the responsibility will fall on the technician.
Note, some AA5/6 radios will perform better when there is a RF path back through to neutral in the internal radio wiring, thus a non-polarized plug to allow the cord to be flipped in the outlet. At the time of the build of most of this type of radio, noisy, solid-state power devices did not exist and household power had far less electrical disturbances.

AC power system neutrals and grounds make terrible antennas...

GL

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Re: Vintage Radio Power Entry Safety

Post by jsweinrich on Sun Jul 02, 2017 11:50 am

All good points but I was more concerned about a fire hazard. That filter cap, the 0.01 uF @ 200 VAC one connected to both sides of the line 24/7 and made of paper. If it were ceramic it would be less of an issue but I've seen old paper caps make a nice little fire.

So, what you are saying that ANY changes to the design puts an increased responsibility on the technician making the change as seen by insurance companies. Experience tells me that insurance companies always look for pointing blame so they don't have to pay. I give this more concern because I live in forest fire country - Oregon. We are now in fire safety mode, same every year when the rain stops for good...

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Re: Vintage Radio Power Entry Safety

Post by John Bartley on Sun Jul 02, 2017 12:02 pm

jsweinrich wrote:All good points but I was more concerned about a fire hazard. That filter cap, the 0.01 uF @ 200 VAC one connected to both sides of the line 24/7 and made of paper. If it were ceramic it would be less of an issue but I've seen old paper caps make a nice little fire.

So, what you are saying that ANY changes to the design puts an increased responsibility on the technician making the change as seen by insurance companies. Experience tells me that insurance companies always look for pointing blame so they don't have to pay. I give this more concern because I live in forest fire country - Oregon. We are now in fire safety mode, same every year when the rain stops for good...

This (above) is a different issue than personal safety due to a live chassis. Someone with good knowledge should chime in here, but I think there are caps made which are designed and rated for this application and are designed to fail open?, along with other characteristics that make them correct for this job of bridging the AC line.

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Re: Vintage Radio Power Entry Safety

Post by jukeboxman on Sun Jul 02, 2017 1:14 pm

http://www.tuberadios.com/capacitors/
he sells saftey caps for line use

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Re: Vintage Radio Power Entry Safety

Post by CaptainClock on Sat Aug 19, 2017 12:26 am

The 2 capacitors you are referring to that are connected to the power cord are NOT the filter caps, those are the one's that are in the metal or cardboard can that sits ontop of the chassis, what you are referring to are what are called "Safety caps" which are used to prevent electrical shorts/failures if there was some sort of power surge, those capacitors would fail open and the radio would not get any juice anymore (ideally, but I've seen safety caps fail and the radio still worked even with a blown out safety cap), all you need to do (and what is recommended by most antique radio restorers including me) is replace the old paper cap with an equivalen ceramic, mylar, polyester, or polypropelene capacitor and you shouldn't have to worry about anything, in fact all of the radio's paper caps need to be replaced by now as they are dried out and don't function properly anymore and replacing those old paper coupling caps and safety caps (especially the Bumblebee type) then your radio will function like brand new again, also you do need to replace the filter caps if they are original because they have long since dried out and will cause the radio to short out and take out your rectifier tube (and if it has a power transformer it will take that out as well). With any of these old radios especially the AA5/6 models there is no need to fuse or ground, or install a polarized plug on these radios because first of all as was already pointed out, it will ruin the performance of the radio, and secondly as long as the radio chassis is inside the cabinet with the knobs attached to it, you don't have to worry about electric shock because, yes even though AA5/6 radios have a hot chassis the user of the radio is protected from shock by the cabinet and the knobs because they act as an insulator and keep the electricity at bay, which is why it isn't recommended to run one of those radios outside of the cabinet unless you know what you're doing. Also as for Transformered radios you don't have to worry about electrical shock if you touch the chassis because the power transformer isolates the chassis from AC. So again you're kind of over reacting and if you want to have a radio that's got all of the "Safety features" you want in a radio then you shouldn't deal with antique radios then, and you should just stick with modern Solid state radios and stereo systems.

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Re: Vintage Radio Power Entry Safety

Post by jsweinrich on Sat Aug 19, 2017 1:00 am

Just to make sure you understand, the filter caps that I'm referring to are the ones that are connected in PARALLEL with the power entering the chassis. That puts them in the category as a filter. And if they open power would still power the radio. The use of filter isn't just applied to the power filtering function in the power supply circuit of the radio. Sometimes (in this case) they are used to filter noise coming in or out of the radio and sometimes they are used to filter specific frequencies (as in an LC filter).

Yes, power transformers do provide the isolation function and many electronic equipments did rely on that capability over the years. In this radio this application is applied works great and will continue. I am very familiar (I repaired them for a living many moons ago) with the 5 tube superhets of the 50's and early 60's where the tube filaments were wired in series eliminating the need for a power transformer for that function. The result was having to connect one side of the power coming into the radio to the chassis for the HV power supply. This is when the polarized plug came into being to help reduce electrical shock.

Since I had to replace the power cord I used a polarized plug because I wanted to fuse and switch the hot side for safety reasons, mainly fire. Hot side of power comes in, immediately goes through the fuse then switch, then to the filter cap and transformer.

With all due respect, I can work on anything I want to include antique radios, solid state electronics...

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Re: Vintage Radio Power Entry Safety

Post by easyrider8 on Tue Aug 22, 2017 5:11 am

CaptainClock wrote:The 2 capacitors you are referring to that are connected to the power cord are NOT the filter caps, those are the one's that are in the metal or cardboard can that sits ontop of the chassis, what you are referring to are what are called "Safety caps" which are used to prevent electrical shorts/failures if there was some sort of power surge, those capacitors would fail open and the radio would not get any juice anymore  
The two capacitors across the the incoming line act as filters and as a RF ground, they are not safety capacitors unless they have been replaced. They should be replaced with the new technology safety caps and nothing else. So called safety capacitors are simply capacitors that will fail in the open state and were not developed until recently. Most  of the AA5/6 have a resistor that acts as a fuse. I usually don't use polarized cords or rewire the hot side to the power switch, by doing this you introduce hum into the volume control and you are not able to reverse the plug for better reception.

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Re: Vintage Radio Power Entry Safety

Post by jsweinrich on Tue Aug 22, 2017 11:57 am

Exactly how would the hum be introduced into the volume control since the power on both sides of the power cord are isolated (via power transformer) from the chassis (except for the two filter caps to chassis ground)?

I would think that reception would also not be affected because of the aforementioned isolation. Now, if the chassis was not isolated or there was a asymmetry in the isolation then that would be a different story. The only asymmetry in THIS radio is lead dress, inner/outer power transformer primary winding (primary/secondary isolation), addition of a fuse, and the power switch.

Since the two filter caps act as a "RF ground", they provide a common mode path to both sides of the power cord and thus render the polarity moot. O course I'm speaking specifically about this radio design and not the AA5/6 or others that are different...

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