I picked up a nice green US Emerson a while ago.
Tonight I decided I would give it a once over. Turns out it is an AC/DC set, no problem it has a back cover.
Pity about the screws holding the back on, and the chassis in.
I mean, only a small chance the non polarised plug could be plugged in and make the chassis live!
I do have a 240/120 isolated transformer to give it a run, but is 120v really that much safer to have exposed screws in it?

Personally I don't think so, and will go hunting for some plastic screws. The metal dial pointer is also able to be touched by those with small fingers.

What is the standard with US power sockets? What side of the socket is active?

I do have a couple of US 3 core IEC leads I can use, but I don't think putting an earthed cable on something that shouldn't be earthed is a good idea. Anyone have a source of US plugs, or a pre-made 2 core cable? I'm not a fan of the single insulated fig 8 flex on it at present.

Thoughts???

Ben

32 volts AC and 110 volts DC is usually enough to puncture skin so, no, it is not safe. Any voltage that can get through the first layer of skin and pump 50mA across one's chest is sufficient to kill the victim.

The active is on the right, neutral on the left and earth at the bottom for the standard US socket.

Another area of possible exposure with live chassis sets is metal grub screws on the knobs. These were usually sealed over with wax.

Anyone have a source of US plugs, or a pre-made 2 core cable?

Element 14 has NEMA 1-15P to IEC cords listed:

http://au.element14.com/volex/2166h/power-cord-nema-1-15p-iec-c7-1/dp/2133919.

I'm intrigued by this two, as I bought a 1950 Sylvania 510-H AA5 AC/DC radio. It's DOA, but probably because of all the wax caps and carbon resistors inside.

Chris

Another area of possible exposure with live chassis sets is metal grub screws on the knobs. These were usually sealed over with wax.

Fortunately this set has push on knobs.

Chris, it may also have an open circuit valve filament. These sets run all the filaments in series, bit like Chinese Xmas lights. Be carefull.


ben

The catch 22 with AC/DC sets is that you cannot earth them unless the mains or DC is "floating" above the chassis, which I believe they did on some later mains sets.

But then on the majority of both transformer and transformerless radios & some instruments, they used capacitors to chassis to ensure that there was a 50/50 chance of it becoming live when the cap failed.

I have noted the dangerous situation of the lack of accessibility to US (NEMA) Plugs & sockets and have seen (& bought) stuff with 240V plugs, that really was not legal to sell.

I have two plug tops, and these were actually brought in as luggage from the States. I refuse to put anything but a 110V plug top on a 110V device.

You can just wire in the two wires, but you have to make sure that the socket is wired, per convention. On a proper two pin US plug top that cannot be inverted neutral is the big pin and the three pin plug top has silver & brass coloured pins. The earth is "C" shaped (round) brass coloured & in the same position as ours. The big /brass coloured pin is neutral.

Like us there are a few variants based on the current, some have a small pin and a (low current) socket to match (albeit that they are tidying things up and banning unearthed mains sockets)

I should point out that Clipsal make a press fit plug top with US pattern pins however these plug tops are not polarised and can be inserted with the active to the left or right. For applications like AC/DC sets I think it is important to make sure a polarised plug top is used. As Marc said, the left pin is slightly wider than the right which ensures that a two-pin version of the plug can only be inserted one way.

While there is no real excuse now for plugs to be wired inverted. It is a good idea to to get one of those plug in neon light type testers to ensure that your plugs are correct and the switches are actually switching active.

That way shifting power points does not cause inverted phase. Wiring of an auto transformer, or transformer can cause it to invert, so do check that as well.

Apparently with the looser regs (if any) in the US 2pin wall sockets & 3pin with out earth (to save costs) exist.

As pointed out US & Canada are trying to clean up their act. They seem to be under the misconception that 115 Volts cant kill you


Marc

In all reality this radio will not get a lot of use. I have 2 240/110 transformers. One is isolated and one is not and are clearly labelled as such.
Had I known it was ac/dc I probably wouldnt have purchased it.
I think I have a solution for the exposed screws. Car trim christmas tree plugs. I bought a few packets today and will see if they are up to the job of securing the chassis.
The dial pointer has already been covered in heatshrink.

Looking at the way this thing has been put together it screams of cheap, mass produced product.

At the end of the day if I cant make this thing safe, it will be display only, and tagged as such.

I can appreciate ac/dc sets are part of our history, but its not worth ending up in a wooden box over it

Ben

Had I known it was ac/dc I probably wouldnt have purchased it.

I treat any old US radio as probably AC/DC. The yanks loved that configuration back in the day.

And you are right in treating it with due caution.

AC/DC radios did get safer over the years. In the early days (1930's) the line was directly connected to the chassis, and that chassis was exposed to the user. Later (1940's), an improvement was done, some isolation using a cap between the line (as the B - line) and chassis. Most recently (mid 1950's), these radios were completely enclosed inside plastic cabinets, with knobs that you could not remove if the chassis (or circuit board) was not removed first. And mounting methods that didn't have exposed screw heads to the user, and interlocks that remove the power when you remove the back.

Almost no consumer radio used grub screws in their knobs.

I have an example of the oldest AC/DC set, and I made it less dangerous by replacing its power cord with a polarized one, and rewiring the radio power switch to switch the hot side of the line (the side that connects directly to the set's rectifier to make the B+). Thus the chassis is always connected to the powerline neutral (assuming the outlet is wired correctly!). An American polarized 2 pin plug has a wider pin on the neutral side, as well as the outlets.

In sets that use one, replace the B- to chassis cap with an X rated one. Don't use one more than 0.1μF to avoid allowing excessive shocking current to pass.

Nowadays, switching power supplies are in a sense partially hot chassis. The primary side has a rectifier, and a switching transistor and oscillator, all hot to the powerline. It's not been an issue, as this circuitry is completely shrouded inside a grounded metal box in your PC, or a plastic box for the wall wart power supplies.

Oh, you should check that your 240 to 120V autotransformers place the 120V output in such a way that one side of it isn't hot with 240V to ground.