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 Post subject: Chinese blue ceramic discs?
PostPosted: Sep Wed 16, 2020 1:27 pm 
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Joined: Mar Fri 27, 2009 8:57 pm
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Location: Alexandria Louisiana
Wondering if anyone has used these Chinese small blue ceramic caps(unmarked) in any of your radios? Are they reliable, stable, etc.? Thanks, Carl-Louisiana


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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Wed 16, 2020 1:43 pm 
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Aren't most capacitors now made in China? ....certainly true for all the ones I get from Sal's or JustRadios

The only blue ceramic disks I have seen are so-called "safety caps" used for line filters

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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Wed 16, 2020 4:18 pm 
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zenith1944 wrote:
Wondering if anyone has used these Chinese small blue ceramic caps(unmarked) in any of your radios? Are they reliable, stable, etc.? Thanks, Carl-Louisiana

Picture of "these" would help.

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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Wed 16, 2020 5:14 pm 
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The vendor should also have a datasheet which has voltage ratings, dielectric type (COG, NPO, X7R, Y5U, etc).

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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Wed 16, 2020 5:33 pm 
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pixellany wrote:
Aren't most capacitors now made in China? ....certainly true for all the ones I get from Sal's or JustRadios




God made the world, EVERYTHING else is made in China.


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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Wed 16, 2020 6:07 pm 
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Joined: Mar Fri 27, 2009 8:57 pm
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Location: Alexandria Louisiana
Am not sure what type they are; just that they were advertised as 10,000pf, .01 mfd, 10 nf. (1,000v). I want something to replace those Zenith caps in a AM/FM radio. 10,000pf is pretty hard to find for some reason. Those blue ones are available on EBAY, as well as others.I also understand those in the Zenith are by-pass and coupling, not in signal Carl


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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Wed 16, 2020 7:16 pm 
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Joined: Mar Fri 27, 2009 8:57 pm
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Location: Alexandria Louisiana
Would Mouser #D103M43Z5UL63L6R be suitable for this application? They say it is .01mfd.,500v, 20%. Z5U. Carl


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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Wed 16, 2020 8:02 pm 
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zenith1944 wrote:
10,000pf is pretty hard to find for some reason.

Someone please correct me if I'm wrong, but isn't 10,000pF = 0.01 uF ? That's a common enough capacitor.


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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Wed 16, 2020 9:42 pm 
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Joined: Mar Fri 27, 2009 8:57 pm
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Location: Alexandria Louisiana
I am aware that 10,000pf is the same as .01mfd, and also 10nf. I was more curious about the type of the cap mentioned from Mouser (Z5U). Carl


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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Thu 17, 2020 12:30 am 
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These are them.
Attachment:
IMG_20200916_172811_7.jpg
IMG_20200916_172811_7.jpg [ 577.5 KiB | Viewed 228 times ]

Not bad capacitors. Work like they should.

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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Thu 17, 2020 12:55 am 
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Z5U are the worst capacitors except for electrolytic. They change value with temperature, voltage, frequency, and just about everything else. They can also be microphonic. Their advantages are that they are very small and they are inexpensive. About their only use in most cases is for supply bypassing. I wouldn't use them for any signal circuit such as coupling, filtering, tone control, etc. Use a mylar or polypropylene instead. X7R ceramic capacitors are much better than Z5U but aren't available in large values. C0G ceramics are among the best capacitors you can easily get, considerably more stable than silver mica.

The color of a capacitor tells you nothing. You have to know what is inside which you can't tell by looking.

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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Thu 17, 2020 3:12 pm 
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yeabuttt.... they are blue, man. @&@. Throw some of those orange ones in there and view using 3D glasses.....

I'd not be replacing tubular capacitors with disks of any type, unless you're in a big hurry and can unreplace them later. Not sure if that's the application or not, just a general comment.

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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Thu 17, 2020 3:52 pm 
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If unmarked, they are probably safety cap rejects. From the small size, they are not likely to be a stable dielectric.

Jay


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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Thu 17, 2020 6:11 pm 
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Location: Long Island NY
Quote:
Z5U are the worst capacitors except for electrolytic. They change value with temperature, voltage, frequency, and just about everything else. They can also be microphonic. Their advantages are that they are very small and they are inexpensive. About their only use in most cases is for supply bypassing. I wouldn't use them for any signal circuit such as coupling, filtering, tone control, etc. Use a mylar or polypropylene instead. X7R ceramic capacitors are much better than Z5U but aren't available in large values. C0G ceramics are among the best capacitors you can easily get, considerably more stable than silver mica.


Temperature and voltage coefficients are not everything and are often used in circuit design to compensate for changes in other components. While Z5U ceramic is too unstable for most timing and frequency determining networks, it has the highest dielectric resistances of any material that can be used to make capacitors, and it offers a large amount of bulk capacitance in a small space. So it is ideal for bypassing and coupling applications.

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The color of a capacitor tells you nothing. You have to know what is inside which you can't tell by looking.


I fully agree with you there. The color is merely the epoxy coating on the outside of the cap. If a ceramic disc capacitor is not marked in some way that reveals what type it is, and its value, I would not bother with it. Different ceramic materials have vastly different performance characteristics and it is not worth playing guessing games just to save a few pennies.

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 Post subject: Re: Chinese blue ceramic discs?
PostPosted: Sep Thu 17, 2020 6:15 pm 
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Mr. Highlander wrote:
These are them.
Attachment:
IMG_20200916_172811_7.jpg

Not bad capacitors. Work like they should.


Depends !

As mentioned, most are made in China. But like kids, there needs to be some adult supervision. Get them, where you can get an associated datasheet.

I bought some 0.1uf 500V caps, that look just like those off of eBay. If you apply 500V across them, and even 1000V, they don't leak .... yet ! Put them in a circuit, and it failed in a few weeks, due to those capacitors leaking, latter.

Yes, they have "104" stamped on them, for 1 0 0000 pf (100,000pf). "1" "0" "0000". As is a common convention (but not universal), which fits nicely on PCBs silkscreen, with only 3 character.

If its for a critical application, I get them where I can trace it back to the manufacturer, like Mouser or Digikey.

If its in a non-critical area, so if it "shorts" or "opens up", nothing bad happens (prefferably nothing else breaks, and definitely no fire hazard), then I'll get the cheap ones, mostly based on physical size, as opposed to cost.

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