On Mon, 1 Dec 2008, Ross, NS7F wrote:

Date: Mon, 1 Dec 2008 20:27:52 -0800 (PST)
From: "Ross, NS7F"
Newsgroups: rec.radio.amateur.homebrew
Subject: uses for exotic capacitor types?

Dear List,
I am looking for your wisdom and lore regarding uses for some of the
more exotic capacitors found in my junque-box. I have been a ham for a
whole sunspot cycle now. I know what an NP0/C0G capacitor is and when
to use it, I know electrolytics, tantalum, and about the use of
Temperature Compensating capacitors. I have checked the usual places
(books, ARRL TIS, the archives of this list, etc) and none of these
resources tell me several important things: what they look like and
where would I use them in ham homebrew circuits. Here is my list:

UNKNOWN TYPE AND APPLICATION:
1. Blue, really shiny, flat, and small like a disc ceramic.

2. Orange and shiny- definitely not electrolytic or tantalum. Both
bulgy and flattish.

3. Green and shiny- both bulgy and flattish. (I've heard these are
either mylar or polyester film. How do I tell them apart?)

4. Dark orange (maybe brownish?) and bulgy.

5. Yellow rectangular blocks.

KNOWN TYPE, UNKNOWN APPLICATION
6. Labeled "monolithic dip"- what do I use these for?

7. "Mallory DC Film" (250V)- what do I use these for?

8. What's the difference between the following three types of mica
capacitors?
* Dipped silver mica

Capacitance should be more stable with temperature change.

* Old-style micas (colored dots and physically large rectangular
blocks)

Cheaper than silver mica.

* Modern, not dipped-silver micas

Should be larger (?) and more for higher currents (RF) and maybe
voltages.

Micas should be very resistant to the kind of ageing in paper dielectric
caps (leakage, change in value, short, open). And, also, some capacitors,
such as electrolytics have capacitance changes as a function of voltage
applied, and thus are very non-linear.

Thank you VERY much for any input on this matter.

If this is important to you, then it would have been more helpful to us if
you gave some specific dimensions of an example or two, and described any
writing or other markings (such as bands, "+", "=" ), and voltage and
capacitance numbers or even code numbers. Many new caps don't have
specific characteristics on them any more, just code numbers and you have
to guess or know what they mean.

Another possiblity would be to obtain catalogs, even current catalogs,
from parts suppliers. Often they have pictures or line drawings that can
give you hints.

I don't know about the newest ARRL handbooks, but many of the old ones
have typical pictures of examples and you can go by that.

Be aware that some of the newer caps do not have forms or colors that are
as standardized as they once were and the external appearance might not
give you a good clue as to what you have.

Capacitor color codes (six dots) on the old caps are also "decoded" in
some of the older handbooks.

73,
Ross, NS7F