1.8mH Iron Core Inductor

Hi All:

Have been away from the LHS forum for some time so I'm not up to speed on what you guys have been doing lately. I keep in touch with a few via phone and email but my on-line cruising time has been zero. I hope to spend some time looking thru the gazillion posts that I have not seen.

I've been procrastinating for over a year to make a post looking for an inductor that I need to repair a 3107 Network. Looks like today is the day. I need one 1.8mH iron core inductor, JBL part #50345, to replace a bad one in a pair of networks. This one inductor is keeping my pair of networks out of service (have been sitting on them for several years but later is better than never).

Anyone having one laying around or a parts cow network, please let me know.

Thanx - Rick

Rick,

What is the issue with the choke? If its open circuit it maybe repairable.

Hello Rick

You don't need the exact JBL inductor. All you need to do is measure the DCR with an ohm meter and order a 1.8mH coil with the same DCR reading. Between Parts Express of Madisound you should be able to find what you need.

Rob:)

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Originally Posted by saeman

Hi All:

Have been away from the LHS forum for some time so I'm not up to speed on what you guys have been doing lately. I keep in touch with a few via phone and email but my on-line cruising time has been zero. I hope to spend some time looking thru the gazillion posts that I have not seen.

I've been procrastinating for over a year to make a post looking for an inductor that I need to repair a 3107 Network. Looks like today is the day. I need one 1.8mH iron core inductor, JBL part #50345, to replace a bad one in a pair of networks. This one inductor is keeping my pair of networks out of service (have been sitting on them for several years but later is better than never).

Thanx - Rick

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I think that the easiest solution would be to manually 'unwound' the wrong coil and with almost same length of almost same wire wound another.

Regards
ivica

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I think that the easiest solution would be to manually 'unwound' the wrong coil and with almost same length of almost same wire wound another.

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You would just be guessing the value. When you unwind a 2mH to make a 1.8mH it's not as simple as a percentage of the windings. You really need to measure as you take the turns off. Been there done that.

Rob:)

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Originally Posted by Robh3606

You would just be guessing the value. When you unwind a 2mH to make a 1.8mH it's not as simple as a percentage of the windings. You really need to measure as you take the turns off. Been there done that.

Rob:)

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Hi Rob3606,

I can agree with You that, but I believe that if the same wire thickness is used, and about the same number of wounds per layer, and the same number of layer are applied, I believe that the error would be neglect-able, as network cutoff frequency is nearly proportional F ~ 1/N ( where N is total number of wounds).

Regards
Ivica

No - the number of windings and the inherent non-linearity of the interaction between the wire/gauge/material and the type/size/material of the core means it is NOT simply a ratio - and it is NOT close.

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Originally Posted by subwoof

No - the number of windings and the inherent non-linearity of the interaction
between the wire/gauge/material and the type/size/material of the core
means it is NOT simply a ratio - and it is NOT close.

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Sounds like the old rule - measure twice, cut once.

VELLEMAN DVM6243

* capacity measurements: 6 ranges from 1pF to 200µF
* induction measurements: 4 ranges from 1µH to 2H

$45 at eio.com

May find a cheaper solution (e.g., if you -already- have an oscilloscope or dvm and tone generator), but this is pretty cheap.

Quote:

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Originally Posted by subwoof

No - the number of windings and the inherent non-linearity of the interaction between the wire/gauge/material and the type/size/material of the core means it is NOT simply a ratio - and it is NOT close.

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Hi subwoof,

Any practical example: under the following circumstances:
-the same core
-the same wire thickness ( copper wire )
-the same number of wounds per layer,
-the same number of laye

What would be the expectable difference ??????

Regards
Ivica

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What would be the expectable difference ??????

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Forget the theory and just take one and try it. I have done it many times and always seems to take less turns than you would think. You have to remember you are pulling the turns off at the largest diameter of the coil. Who knows the wire length you take off might work out to a ratio compared to the total length but the turns from practicle experience don't. Even if the wire length was a ratio you have no way of knowing the length of wire used to wind the coil.

Under any circumstances to do it right you need to measure the inductance as you pull the windings off.

Rob:)

Quote:

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Originally Posted by Robh3606

Under any circumstances to do it right you need to measure the inductance as you pull the windings off.

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...and don't use your table saw as a work bench... I did once, and the coil sitting on the cast iron table had it's inductance increase markedly. In hindsight it was obvious and humorous, but I almost made a big mistake. ;)


Widget

Or use the table saw for working on high power amplifiers.
Still have a neat black crater on mine..:)

And it would be a nested, 2nd level calculus formula to even TRY to get at the expected result so just get an inductance meter..:)

sub

Here are a few options from Erse Audio. Just choose the one that is closest to your DCR. You may want to swap them out in both speakers to keep things even.

DCR = .137 Ohm
http://www.erseaudio.com/Products/Su.../ESQ55-16-1800

DCR = .178 Ohm
http://www.erseaudio.com/Products/IX.../ELC55-16-1800

DCR = .251 Ohm
http://www.erseaudio.com/Products/IQAll/ELC54-18-1800