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Old 20th February 2013, 08:06 AM   #21
ODougbo is offline ODougbo  United States
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Well that's a huge difference!! I do find the 2mh and 20mh settings are slightly different, but not much a 0.1 e.g. (not bad at all, and there is the lower setting). I've been checking "store bought stuff", and it seems to work fine.

The cost of copper is crazy, the inductors can cost more then manufactured drivers! Been trying to make up bobbins quickly, these went really fast, just a few minutes; the center "dowel" is 1" so used a flat spade bit and had a nice fit.

The sides are 3-1/4", the ID width is 1", which will make a nice/neat 1.5mh 14g inductor once finished.

Clear epoxy seems to work better than CTA.
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Last edited by ODougbo; 20th February 2013 at 08:22 AM.
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Old 20th February 2013, 12:33 PM   #22
oshifis is offline oshifis  Hungary
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Quote:
Originally Posted by JMFahey View Post
Yes there is.
Very much used in UHF transmitters or receivers.

Sometimes referred to as "U" turn or "U" coil, for obvious reasons.

Just cut and pasted from UHF schematics and datasheets:

or
This is OT here, but anyway. 1/2 turn exists on paper, it is the visible part, there can be magnetic field and flux in a closed loop only. Similarly you don't see stray capacitance at UHF but it is there nonetheless.
Neither has importance in audio...
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Old 20th February 2013, 02:44 PM   #23
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by oshifis View Post
1/2 turn exists on paper,
On paper?
Tell that to the UHF transmitter/Ham/TV/Satellite/Radar/etc. guys who build them in the flesh.
Ok, in the copper

Quote:
Originally Posted by oshifis View Post
there can be magnetic field and flux in a closed loop only.
Sorry but maybe you mised that class in Electronics 101.
A "0 turn" coil, a.k.a. straight wire, can and does have inductance.
Inductance of a Straight Wire: A Calculator

Is it "irrelevant" at audio frequencies?
Not at all, the page cited above says:
Quote:
This can be important if you are dealing with low impedances (< 1 ohm) at high frequencies (> 10kHz).
Meaning it must be taken seriously in, for example, power rails, speaker out and **GROUND** when an "unseen" but very real 1 ohm frequency dependent impedance may be the cause of instabilities and oscillation.

Maybe there is a reason, after all, why decoupling caps must be placed as close as possible to the part being decoupled.
Might it be another dread of that evil straight wire inductance?

A very real and practical everyday problem.

Quote:
Originally Posted by oshifis View Post
Similarly you don't see stray capacitance at UHF but it is there nonetheless.
"you don't see means it does not exist there?
"but it's there" Contradicting.

Quote:
Originally Posted by oshifis View Post
Neither has importance in audio...
Just explained the importance of stray inductance in Audio.
Now you say that stray capacitance is also irrelevant in audio?
People struggling to get correct trouble free layouts might disagree with your blanket statements.
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Old 20th February 2013, 06:39 PM   #24
oshifis is offline oshifis  Hungary
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Well, English is not my native langue, but if I am not mistaken, the word "circuit" is related to "circle"...
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Old 20th February 2013, 06:58 PM   #25
tvrgeek is offline tvrgeek  United States
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I have an old used B&K. Works fine.

"Maybe there is a reason, after all, why decoupling caps must be placed as close as possible to the part being decoupled.
Might it be another dread of that evil straight wire inductance? "

The term is parastatics. Yes, very real.
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Old 21st February 2013, 12:00 AM   #26
ODougbo is offline ODougbo  United States
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So my little ploy worked pretty good - Son and I did this in a few minutes and good for him since he's in electrical school (then he can explain inductance to me )

Made up a drive tool for the battery drill - I think a good tip may be let the "Axel" stick out on both sides that can be trimmed later. That way the nuts/bolt won't crush the sides and break glue joints on spool.
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Old 22nd February 2013, 01:18 AM   #27
ODougbo is offline ODougbo  United States
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Found some plastic spacers (black parts) in the junk barrel - this will hold. Also the lead wire going thru the spool can be used to keep things from spinning.

The magnet wire cam be found here: McMaster-Carr
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