Capacitors

[Enzo]

Here is a little article I found interesting. Talks about things other than capacitance and voltage rating.

http://www.analog.com/Analog_Root/st...ml?ref=ASC1422


And under the article are some links, this one from among them is more in depth .

http://www.analog.com/library/analog...ersary/21.html

[Rigormortis]

I have a question so simple that nobody has it on their website:

What is the capacitance designated by the underlined numeral on a basic ceramic capacitor?

I have a bunch of ceramic capacitors with underlined numerals. I was assuming they were nF.

Here is a picture:

[Bruce / Mission Amps]

Originally Posted by Rigormortis

I have a question so simple that nobody has it on their website:

What is the capacitance designated by the underlined numeral on a basic ceramic capacitor?

I have a bunch of ceramic capacitors with underlined numerals. I was assuming they were nF.

Here is a picture:

I think I can see .03uF .0022uF, .001uF, 47pF 10pF, 7pF.... . etc

example:
222 should mean 2200pF or .0022uF 102 = 1000pF or .001uF

[Rigormortis]

What about one that has just one numeral, like a 1? Is that a 1pF?

47pF is .047nF and .000047uF, etcetera; so I think all these are of the same range, either all nF, or pF. I'm doubting whether they are using the 3-digit system, since most don't have 3 digits but all share the underlined numeral.

So if it says "1", what does that mean?

[Enzo]

To expand on Bruce's, it usually reads just like a resistor color code - two digits and a multiplier. I never think of it as a multiplier, I think of it as the number of zeroes. The units is almost always in pf. for under 100pf, they often omit the multiplier, so 22 would mean 22pf. But 221 would mean 2-2-0 or 220pf, 222 means 2200pf or 0.0022uf if you prefer. But sometimes they leave in the third digit on a small cap. I have seen an 82pf cap labelled 820 - just as a gray/red/black resistor would read 82 ohms.

Nanofarad is relatively recent, no one used it when I was learning electronics, oh way too long ago. I never use the term, though I understand it fine. Nowdays it is more common usage and you will see parts labelled with nf but still not a lot. I'd say measure your #1 and see. 1nf would surprise me, but then 1pf would as well. But if I had to vote, I'd go with 1pf.

Where did these parts come from, they look suspiciously like a kit? And if it is a kit, what values are listed as coming with the kit?

[Rigormortis]

All I have here to get electronics from is Radio Shack. That was a pack of assorted caps with absolutely nothing on the package to give me a hint.

I think I have the system figured out now. I was resisting the idea that they were all in pF because I didn't think caps that large could have such small values. The 200 pF I'm replacing is a third the size of the 1pF. I don't really know how to test for capacitance and have to go by the numbers printed on them.

[Enzo]

1pf is extremely low capacitance a 1" piece of zip cord probably has as much. In fact in old RF circuits we sometimes needed to tweak a value and a couple pieces of insulated wire twisted around each other could be soldered to things to act as a small capacitance. That was called a "gimick" capacitor.

If I had no cap meter, I could set up an RC circuit, apply a voltage to it and see how long it took to charge the cap. SInce 1pf and 1nf are different by a factor of 1000 it should be easy to determine which it is.

Or I could send an audio signal through it - tack it across a pot in typical brite cap style. A 1pf would do pretty much nothing, while a 1nf would have substantial effect.

[Rigormortis]

I'll try the pot method. I have a couple of old ones that don't fit anything.

For now, I've put that little 1pF away and used some with 3 numerals that I know the value of. Check out my thread on reverb options for the whole story. Thanks so much for your help in my reverb mod, BTW--a very successful mod thanks to you guys.

[bbartilson]

Originally Posted by Enzo

1pf is extremely low capacitance a 1" piece of zip cord probably has as much.

Indeed, it is, and indeed, it probably does. But the zip cord is a lot harder to put in a pick and place machine - not to mention the debate over which one is the 'more shielded' side... ridged, or plain?

Hi 'Zo.

At any rate, I got curious so I went and bought one of those cap assortments while I was out earlier today. Took me a while to find any marked '1'. There are about 50 10pf caps in there.

At any rate, I finally found a couple of them. Unsurprisingly, they don't measure at all on my cap meter. However, with a 180pf cap already in place, the value does indeed change by exactly 1pf when you shove one of these into the test terminals along with the other cap.

When we were partners, that was one of my favorite activities - solving the little mysteries.

I guess we can check that one off.

-Bill

[bbartilson]

As soon as I posted that, I happened to think:

"Wait a minute - the whole mystery really isn't solved. We don't yet know about the zip cord."

I measured out 6" in order to get a decent reading. 6" of zip cord is 10pf or so.

So an inch has 1.6666667 pf by my calculations.

So, now it's solved. Or is it?

[Enzo]

Um... well I used METRIC zip cord... yeah... 1pf


Hmmm... outside foil on a zip cord cap...


Hey Bill! Mysteries-R-Us. or were.

BB here used to be my shop partner and pretty much whenever some interesting mystery cropped up, everything else stopped.

[Rigormortis]

BB--That's cool you got one of those packs to check it out. My pack had three of those blue 561 in there. That's the one I used to up the value of--exchange places with--a 100pF.

When you add up two capacitors in place of a higher value, do you do that with them in series, or parallel?

[Enzo]

Caps in parallel add the same way resistors in series add. Caps in series divide the same as resistors in parallel divide.

[bbartilson]

Originally Posted by Enzo

BB here used to be my shop partner and pretty much whenever some interesting mystery cropped up, everything else stopped.

I surely hope that's still the case, even though I'm not there.

And frankly, it took a lot less than an interesting mystery to bring things to a halt. Remember the month we had that battery operated lectern in the shop?

It had an astonishing ability to make people a block away think you were talking directly to, and only to, them. And it ran on C cells or something.

But I'll save the better stories for later.

[bbartilson]

Originally Posted by Rigormortis

BB--That's cool you got one of those packs to check it out. My pack had three of those blue 561 in there. That's the one I used to up the value of--exchange places with--a 100pF.

When you add up two capacitors in place of a higher value, do you do that with them in series, or parallel?

I'm not sure I'd ever seen a 1pf cap before. Enzo has already told you - solving the mystery once interrupted all else. Fortunately over the years I learned to get something done in between solving them. As it was, I was out and about and driving by the 'Shack. I just knew they'd have one of those packs in stock.

As it was just a random pinch of caps, I was fearful that my pack wouldn't contain any... but I eventually found a few.

So a 560pf in place of a 100pf? What's it doing? Bright cap across the volume control or something?

And, as Enzo already answered - Caps in parallel add up, caps in series divide. Just like resistors, but exactly the reverse.

-Bill