Radial X2-AC Safety Capacitors (Question)

oldschool · 2017-08-24T16:19:50+00:00

I want to replace the original capacitor which is located across the AC power line in a Zenith Trans Oceanic (tube radio). The original cap is a .047 at 600V (standard capacitor). I was told that these days, standard caps are no longer used across the AC power line. Instead, they use these Radial X2-AC Safety Capacitors. What I'm finding is that these caps are available, but I am not finding any of them rated at 600V. All I can find are rated at 250 or 275VAC, and I did find some .1uf on ebay for 300VAC. Sal's Capacitors has a .047uf at 275VAC on their webpage. One rule I never violate is the voltage rating of parts. I'll go OVER but never UNDER the original voltage rating. However, the old caps were rated at DC voltages, whereas these Safety Caps are rated at AC voltages. I would think that 275V is sufficient to use across a 120V AC power line (which is what they are made for). Therefore, is is safe to use these to replace the original cap, since I can not find any rated at 600V? I know this will not be the first radio needing a replacement cap across the power line, so if I order one of these caps, I'd rather order several so I have them on hand. That leads me to a second question: How critical is the uf rating on these line caps? In other words, if I use a .1uf instead of a .047uf, will that cause any problems, or is the .1uf offering more protection against power line spikes? Thanks

Aug 24, 2017 23 Replies

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tabbypurr 8 years ago

275v ac = 389v peak, which can be withstood by a 389v rated capacitor. The reason they used 600v was to improve safety & reliability. However time showed that it wasn't good enough. X & Y caps are much better attempts to address the failure/safety issues.

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rickman 8 years ago

You are very good at math, but not so good at electronics. You don't need to consider the peak to peak voltage because the cap doesn't see them both at the same time. It sees one peak, then it sees the other peak. The fact that they are opposite polarity doesn't mean you need to add them to consider the capacitor voltage rating.

Rick C Viewed the eclipse at Wintercrest Farms, on the centerline of totality since 1998

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tabbypurr 8 years ago

Sorry but that ain't so.

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Phil Allison 8 years ago

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** Nonsense, the DC rating is not exceeded by a reversing voltage.

** False.

It's simply that 600V rated caps survive much better.

AC supply and load bridging involves spike voltages that can break down the insulation.

..... Phil

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