Orientation for the non polarized plug in vintage audio

[pollock0424]

I replaced the line/neutral to chasis caps with Y1 rated 4.7nF 500VDC/750VAC rated caps.

 

[Soandso]

I bought a used vintage energizer that supplies bias for an electrostatic headphone. A week later I asked the seller whether there was some old internal energizer component causing the hum I was hearing through those headphones. His suggestion was to try plugging into my electrical socket the 2 prongs of the energizer's cable one way and then the other way. I found one orientation did resolve that hum.

 

[pollock0424]

Yes, it helps! Are you sure that you had a line/neutral to chasis capacitor on both the line and neutral in your case? Or was it only on one side ?

In this case, i have it on both the sides, whenever I reversed the plug, I did not notice any difference.

 

[rdenney]

I replaced the line/neutral to chasis caps with Y1 rated 4.7nF 500VDC/750VAC rated caps.

That was the correct move, and what I had just typed until I read your post. Y-rated capacitors are specifically rated for line-to-ground applications and they fail open only. They are specifically designed and rated to never fail short.

If the chassis is available to be touched from outside the enclosure, I would find a way to modify the case to prevent such. The traditional strategy for allowing a two-prong plug was to "double insulate" the device so that even if the chassis became electrified it was protected from the user.

For line-to-neutral applications (not your case but others may see this), the correct replacement is an X-class safety capacitor that is designed to fail short (and NOT catch fire or blow apart) to blow the device fuse or the branch circuit's breaker.

Lots of vintage test equipment uses these capacitors for EMI filtering and I've replaced a number of them.

Rick "don't use RIFA safety caps without putting them on a strict 10-year replacement cycle" Denney

 

[DVDdoug]

If I want to keep it stock, does the isolation transformer make it the second best solution?

A proper more-modern plug shouldn't hurt the value. If you're concerned about that replace the whole chord and save the old one in case anybody wants to "restore" it.

 

[pollock0424]

The whole unit is encased in a wooden cabinet and the knobs were made of some type of polymer.