Michael A. Terrell wrote on 8/29/2017 7:12 PM:
wrote:
On Tuesday, 29 August 2017 11:02:29 UTC+1, Michael Terrell wrote:
wrote:

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 http://www.tuberadios.com/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

People, learn to do the math.

600VDC/2.828=212VAC, so the 275 volt rated capacitor would be equaL
to a 777VDC capacitor.

2.828 is the peak to peak factor on a RMS sine wave. That is
1.414 volts peak, on each side of zero

Erm... no. Firstly 275v ac is 389v dc peak, so a 389v dc rating. Secondly
the 2 ratings are not comparable, even after conversion to dc. The 600v
cap has no fusing and most likely no double layer safety feature, the 275v
ac one has both.

Think again. You have a negative and a positive peak, not just a single
peak. You have to add them together. That is why the original DC cap was
600V, not 300V.

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