I just replaced a power cord on a Philco 118. Since I have several standard 3-prone cords lying around, I used one, and soldered the ground wire to the chassis. After I did that, I start thinking if that's really a good idea. The radio has a power transformer so that the high voltage DC is isolated from the input AC. Now, with the chassis tied to earth ground, I defeated the isolation. If I touch a high voltage circuit while standing on the ground without good insulation, I could be zapped. I know I should never touch the HV but I believe the transformer does provide a safety net just in case.
What do you guys think? Should I disconnect the ground?

Gary,
This is a classic example of how it's done today. Some would say "don't redesign an antique", but others consider user safety first. Some older AC/DC sets (2 wire/transformerless) could be lethal if safety precautions were not observed, and Murphy lurked nearby. The 3rd wire is a safety ground to protect the user, and is not intended for circuit current flowing in the device. There could be leakage currents, but very small. Some GFI (Ground Fault Interruptor) safety devices measure this current, and trip the GFI breaker off if the design amount is exceeded. Others monitor balance between the line (hot) and neutral (common). An unbalance would indicate current flow via another path (ground fault), and trip the GFI circuit breaker off. Hope this helps.

marv

:I just replaced a power cord on a Philco 118. Since I have several standard 3-prone cords lying around, I used one, and soldered the ground wire to the chassis. After I did that, I start thinking if that's really a good idea. The radio has a power transformer so that the high voltage DC is isolated from the input AC. Now, with the chassis tied to earth ground, I defeated the isolation. If I touch a high voltage circuit while standing on the ground without good insulation, I could be zapped. I know I should never touch the HV but I believe the transformer does provide a safety net just in case.
:What do you guys think? Should I disconnect the ground?
:

What you did is to tie the metal chassis to earth ground which is a standard safety practice.

The only time you can't do it that way is when you are re-wiring an AC/DC set with no floating ground.

If you are using a 3 prong cord with a wide blade lug and if you connect the chassis to the wide blade lug you have safely now tied the chassis to neutral... yes that part is good. ok.

BUT.. if you also tie the green lead ( earth ground) to that same point on the metal chassis then you have effectively tied neutral and ground together.

This in not proper because the neutral leg must only be tied to earth at the service panel.

If you have a GFI outlet it will trip if it detects that earth and neutral are tied together.

So you can only connect the green earth ground lead to the metal chassis on sets with a transformer or those with a floating ground.

Basically you made the radio safer if you're touching the chassis, but not safer if you're touching the high voltage wiring inside. Grounding the chassis, as others have said, is common modern practice, especially in computers. Consider one other benefit: that is that you won't have to run a separate ground wire to improve reception, which can sometimes happen when this is done. However, it is typically better to connect to a ground source that's far away from AC lines to minimize interference.

...Personally, I'd never put a hideous modern cord on one of my radios, but other than aesthetics, you did nothing wrong.

T.

Not only for safety concerns, but a chassis ground may help reduce electrical 'noise' for better AM reception.
When it comes to 'keep it original', I wouldn't let a 3-wire 'made in China' plastic cord on an old radio bother me.
Although not original, putting seat belts and radial tires in the Studebaker makes it a better car IMHO.