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Old 28th March 2013, 03:00 PM   #1
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Default rare inductor needed where find ? 0.7uH

HI guys

I search anywhere on google - ebay - digikey - solen.ca and I don't find anywhere this amplifier output INDUCTOR value it's 0.7uH or 700nH for output of LM780 board.

OR Can I change this RL circuit (10ohm resistor / 0.7uH) by RC ?

thanks in advance !

nicK
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Old 28th March 2013, 03:20 PM   #2
hpeter is offline hpeter  Europe
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https://www.elfa.se/elfa3~tr_en/elfa...0-14&toc=20335
7A enough?
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Old 28th March 2013, 03:50 PM   #3
AndrewT is offline AndrewT  Scotland
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Get a AA battery. Or any mandrel of similar diameter.
Get a length of 1mm diameter enamelled copper wire. 200mmm gives just enough for short tails.
Wind 10Turns around the battery.
Slide the copper turns off the battery.
You now have a ~0.7uH air core inductor
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Old 28th March 2013, 04:33 PM   #4
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Default thanks :) !!!

thanks hpeter but I don't know if the sound is good with this type of inductor VS air core ?

thanks ANDREWt it's a good idea but I don't have inductor tester

I try this anyway !


THANKS !

nicK
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Old 28th March 2013, 05:04 PM   #5
DF96 is offline DF96  England
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It is very unlikely that the inductor value has to be exact. There are inductor design tools on the internet, and various formulae. If you carefully make an inductor you can expect that it will be within about 10-20% of the intended value.
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Old 28th March 2013, 05:09 PM   #6
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10 Turns AWG-22 insulated, solid core wire wound around a 1.5V AA battery. Measured on Thurs 28 March, 1700 GMT. (1300 EDT in New York City).

Measured inductance was 696 nanoHenries on an AADE LC meter
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Old 28th March 2013, 07:38 PM   #7
GoatGuy is offline GoatGuy  United States
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Nice! However it would have been over 700 nH had the coils been more tightly adjacent to each other. [DF96]'s point stands: its hardly likely that the exact value is critical. GoatGuy
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Old 28th March 2013, 07:42 PM   #8
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WOW THANKS TO ALL FOR YOUR QUICK REPLY !

I have crossover inductor in stock and I take that wire it's 20 AWG

but do you glue or other tips to get all wire loops very close together ?
on the pics of GOATGUY the loop is not close but it work well too

nicK

Last edited by nickthevoice; 28th March 2013 at 07:51 PM.
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Old 28th March 2013, 07:56 PM   #9
GoatGuy is offline GoatGuy  United States
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Quote:
but do you glue or other tips to get all wire loops very close together ?
on the pics of GOATGUY the loop is not close but it work well too
Just start with REAL STRAIGHT wire. If its wiggly, bent, not really straight, you're not going to get nice close windings. But if its straight-straight, then by hand you can wind this and have it look beautiful, in a minute or two.

If you're using magnet wire, stripping is a problem that has a not-so-obviously solution. Alcohol flame. Burns off the enamel, and you can quench the hot copper in another diluted bit of alcohol. Work on an area that is going to be safe for flaming alcohol (its not overly dangerous, just ... things happen). You can even make a quick-and-dirty alcohol burner from a piece of aluminum-foil about 3cm x 3cm. Wrap it over the tip of your finger (or that AA battery!) and make a small cup. fill with 5mm to 10mm isopropyl alcohol, and put in 1 little wad of glass wool (from wall/ceiling insulation).

It'll burn for awhile, long enough to do the stripping. Its pretty safe, and you can just chuck it when you're done. the problem with commercial isopropyl alcohol is that it is 30% water. So, the lamp becomes "water logged", and won't burn after a few minutes. Safe!

GoatGuy
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Old 10th April 2013, 08:36 PM   #10
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RF guys use "Coil Dope" to keep their hand-wound coils mechanically stable, so the inductance value and the Q remain constant. Google shows a number of homebrew recipes for making Coil Dope at home; the top two appear to be
  • Polystyrene ("styrofoam") packing peanuts dissolved in toluene or acetone
  • Clear glossy polyurethane varnish (for wood floors or wood boats)
Here is a cool website where they tried 4 different ways of stabilizing a coil, plus a fifth coil as a control. The before-and-after experimental results are:

Click the image to open in full size.
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