: > > Thank you Bob. I did discover that they were chokes/coils, : > > as I had suspected, but your explanation of their construction : > > and how they are formulated made it very clear. I now know : > > what to call them and how to find out what their ratings are : > > when I reverse-engineer a circuit. Incidentally, is there an easy : > > method for taking a reading on them to find out their value? : >
: > Yes, you can buy inductance meters. I've heard a rumor that this is a good : > one: : >
: >
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: > If you have access to a signal generator, you can test them directly by : > observing the resonance frequency of a circuit with an inductor and a : > capacitor of known value, using the equation : >
: > L = 1/((2*PI*f)^2 * C) : >
: > There are also markings on them to tell you what their inductance value is. : > They use the same color scheme as resistors, except that the value depicted : > is in micro-henries (uH) rather than ohms. So, a 33uH inductor will be : > orange orange black, and then a color band for precision. There are other : > schemes for marking as well, see a book such as "Practical Electronics for : > Inventors" by Sherz at your library for more details on inductor markings. : > There are also websites that have this information. : >
: > Regards, : > Bob Monsen : : I have the above meter, and I think it's a good buy - a hundred : dollars for the kit. Or add $30 and get it assembled.
Aren't there any I can make for about $25? I am such a cheap-skate. ;-)
: There are as many different looking inductors as there are capacitors. : Some are obviously coils of wire on a core. Others look like blobs of : dipped plastic, AKA gumdrops, with three or four colored dots on the : top. Others have the values printed in letters, which can be cryptic : until you begin to understand it. Like he said, some look like : resistors, and they can be tricky because they may be wound with very : fine wire, which gives them a certain resistance if you measure them : with a DMM.
I had a few choke coils laying around that I had taken from some Apple II disk drive analog controllers. None of them gave any reading on the ohms scale. They are around 18 gauge solid wrapped around some kind of ring of unknown material painted yellow, with shrink-tube over the whole thing. The wires terminated at the same place on the ring but on opposite edges. Only 5/8" diameter and 3/8" thick, but fairly heavy.
: Some radiofrequency coils are just wire, which was wound on a dowel : and then the dowel was removed. Sometimes the maker adjusted the : coils at the factory by spreading the turns, so it looks like some kid : got in there and messed things up. Or the coil may have wax poured : over it to keep it from changing value.
I've seen these and wondered if they were a mistake, or placed there to trick people. So if the coils lose their shape, it can affect the circuit operation?
: And then there's _the_ ultimate coil, the TC, short for Tesla Coil. : Don't even bring that topic up, you get those fanatics started and : they'll never end! ;-) See URLs :
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I won't say a word, except for this: Why would anyone make that a serious hobby?, and, I'd think as a junior high project it would have been fun, once, maybe. Gee, hope I didn't stir up anything. ;-)
Bill @ GarberStreet Enterprizez };-) Web Site -
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