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RE: Film Capacitor Orientation Question

"Is this test not representative of actual circuit conditions?"

That is correct. The scope test is only useful for identifying which lead is connected to the foil. It doesn't represent actual circuit conditions. In actual use, the impedance of the capacitor itself reduces the differential induced across it. In addition, the outer foil is not a continuous, all-encompassing shield. Currents induced on the outside of the shield are free to travel to the inside surface, where they can, in turn, induce additional current on the adjacent layer. Even the scope test makes it evident that the outer foil is grossly imperfect as a shield. Connecting the probe to the inner connection does not entirely eliminate the external coupling, even when the foil is grounded. Consider how much less effective the shielding is likely to be when the foil is elevated above AC ground by the impedance of the stage driving the capacitor.

This is not to say that both ends of the coupling capacitor will be identically affected by voltages resulting from external fields. However, the real result is much less significant in practice than many people realize. In addition to these caps, unwanted pickup also takes place through the many unshielded component leads, vacuum tubes, etc. For all these reasons, "correct" orientation usually offers no real benefit in real world use.










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  • RE: Film Capacitor Orientation Question - Triode_Kingdom 19:12:55 07/13/21 (0)

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