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In Reply to: RE: Question... posted by Jim McShane on February 16, 2017 at 19:08:59
Jim - this is about noise pickup by an unconnected piece of metal. These capacitors are big, so the shell, if not grounded one way or another, presents a good antenna for picking up stray electromagnetic fields. Same reason why transformer cores in low level audio transformers are electrically grounded.
One way to ground the shell is to strap it directly to ground. This is not good because this may add quite significant shunt capacitance to ground. The better way is to connect the shell to one of the leads, and use that lead as outer foil connector.
Follow Ups:
Okay - so you are assuming one lead goes to ground then, yes?
In your previous post, I don't think you made that clear, but it makes sense among the various alternatives.When the Russian Teflon capacitors (of all kinds) were "discovered" by TubeDIY aficionados, there were several posts about totally removing the metal casing, de-soldering the typical low quality leads in favor of better wire, and some even encased the capacitor in PVC tubing or coated them with epoxy. That's what I was trying to do when I killed an 0.47uF FT series (I think it's FT, anyway). The idea of doing this mod seems to have died on this forum, but I am willing to believe it would make an improvement to the sound, which is why I tried it once. In this thread, no one has mentioned the efficacy of doing that.
It occurs to me that if you are going to ground the case to the "outer foil", by which I think you mean the capacitor lead that is attached in the circuit AS IF it is the outer foil, do you also have to identify which lead actually IS connected to the outer foil? Because if you do, I found that to be impossible, possibly because of the metal case getting in the way. Catch-22.
Edits: 02/17/17
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