Anyone Have a Dead L2 Adjustable Inductor?

[trag]

I am looking for an L2 which is too broken to use. Anyone have one with a demolished core (tube) that just can't be used in a Mac any more, but one whose wire coils are still in tact?

I'm looking for an L2 from which I can unwind the wire, while counting the turns, but I don't want to destroy a usable L2. I also want to remove a sample of the Litz wire and run it by an expert (if I can find one) to determine its gauge and number of conductors per thread. I may be able to do this last part myself with magnification.

I have found a source of 1/4" X 3/4" threaded ferrite slugs. I don't have time to test them, so if someone else would like me to send them a few to test, that would be great --

provided you do the test and report back.

They should fit in L2. The question is whether their permeability is in the proper range and whether one slug will do or whether one must insert two end to end.

The 1/4" inner diameter cores do not seem difficult to find. So, if we can determine if these ferrite slugs are usable, and find the gauge, conductor # and number of turns of litz wire, then we should be able to make our own replacement L2 coils for Mac analog boards. Winding the coils will be a bit tedious, but what else are hobbies for?

 

[bbraun]

I believe I have one with a bad (or at least crumbled inner core) L2 from the pile of compacts. I could probably also swap cores on another L2. I might not be able to do much for a week or so, I've got some other responsibilities coming up, but should have a lull in the activities sometime next week or so.

If someone else is faster, go for it!

 

[mcdermd]

I have one sitting on my desk at work. PM me an address.

 

[onlyonemac]

What's wrong with those compacts? I thought they all worked.

 

[James1095]

Easier to measure the inductance and select a similar standard part. Should be able to salvage something that will work from a junk TV or monitor. The wire doesn't have to be identical, anything close will work as long as the core is similar. In a pinch you can make Litz wire by twisting together a dozen or so strands of ordinary enameled magnet wire using a drill chuck.

Lacking access to a L/C meter, you can sub in something that looks close and give it a try. Either it will work, or you won't be able to get the width adjusted within range.

 

[trag]

Easier to measure the inductance and select a similar standard part.

Well, you would think. But Wally measured the inductance on a working L2 and I have never seen an adjustable inductor in the needed range on any of the surplus electronics, radio, and ham sites.

Litz wire seems easy enough to get without winding one's own. At least, there's a guy on Ebay who sells quite the variety. Using the same gauge and number of conductors will help match the total resistance and current capacity more closely.

 

[tomlee59]

Thanks for undertaking this project, trag. I'm very interested in what you find out! I'm also interested in the measurements that you mentioned (the ones that wally may have made). Wally is an extremely careful, excellent engineer, so I trust his data.

 

[James1095]

Isn't this the horizontal width coil? Almost every CRT display has something similar. You can also get ferrite cores from other coils, or if you can find all the bits, they can be glued back together.

 

[trag]

Isn't this the horizontal width coil? Almost every CRT display has something similar. You can also get ferrite cores from other coils, or if you can find all the bits, they can be glued back together.

A highly motivated vintage Mac owner might sort through old CRTs (if he can find any) looking for a compatible inductor. Similarly for gluing the bits back together, or salvaging slugs from other hunted-down coils.

The average vintage Mac person is probably willing to do some soldering repair, but isn't going to accumulate a junk yard in the garage in hopes of finding a compatible part. I think offering either a pre-built part, or a ready supply of the components needed to wind his own, makes it much more likely that old analog boards will be repaired rather than junked.

I've been hunting these components off and on for about two years. Most folks aren't going to spend a similar amount of time to fix one old machine. (Although it is true that I have a very small Duty Cycle for said hunt.)

 

[trag]

Here is a link to the thread in which Wally publishes some relevant measurements from L2.

http://68kmla.org/forums/viewtopic.php?f=7&t=18725&p=176740&hilit=ferrite#p176740

 

[uniserver]

why do the cores get brittle and fall apart?

is it because they are vibrating?

 

[James1095]

They're made of powdered ferrite held together by a resin binder. The resin, like most plastics, deteriorates with age, heat, ozone, etc and becomes brittle. Also the former it screws into can shrink or warp slightly causing binding making it easier to break.

I haven't had to replace one myself on a Mac, but I've had them fall apart on arcade game monitors. The Electrohome G07 width coil is/was still readily available. I haven't looked into whether it would be a suitable replacement for a Mac.

 

[trag]

I haven't had to replace one myself on a Mac, but I've had them fall apart on arcade game monitors. The Electrohome G07 width coil is/was still readily available. I haven't looked into whether it would be a suitable replacement for a Mac.

It would be great if it was. It would be much nicer to just buy a manufactured coil rather than mess with fabricating our own. If you remember, would you please post the specs. the next time you run across them?

 

[tomlee59]

why do the cores get brittle and fall apart?
is it because they are vibrating?

The problem isn't so much with the cores themselves (they don't seem to get appreciably more brittle with time -- at least, in my experience). The main problem seems to be that they bind against the inside of the coil form (Wally notes that the teflon-like tape had degraded in the specimen he analyzed), so that you can't apply enough torque to turn the cores without breaking them.

 

[tomlee59]

Here is a link to the thread in which Wally publishes some relevant measurements from L2.
http://68kmla.org/forums/viewtopic.php?f=7&t=18725&p=176740&hilit=ferrite#p176740

Thanks, trag, and thanks, Wally!

 

[tanaquil]

Sorry for the thread necro, but I am wondering if any progress was ever made on this. I searched the forum for "L2" and "width coil" without much success (at least half the hits were me complaining about the destroyed width coil in my SE/30).

Long story short: I now have two analog boards with destroyed width coils (an SE/30 and a Classic). The first one was my fault - too much force applied with the wrong tool, years ago - but the Classic one (which I just discovered yesterday) was crumbling before I even poked gently at it with my plastic TV alignment tool.

I can fix the problem by swapping in another working analog board (already done for the SE/30, on my list today for the Classic), but I hate to see donor boards piling up in my workshop just because of these wretched width coils. Anyone had any success sourcing or manufacturing a replacement for the L2 coil?

 

[trag]

Anyone remember the inductance range that Wally measured back when?  The linked thread seems to be one of the one's lost in the software update.

I have not made any meaningful progress -- as with all my projects.

The (ICF) 94-530-1024  at https://www.surplussales.com/Inductors/Ind-SlugTu/Ind-SlugTu-4.html

is probably the best candidate I've found for a coil form.

I was hoping that one or two of these (ICH) SLUG-4  at https://www.surplussales.com/Inductors/FerPotC/FerPotC-1.html

will work for the ferrite slug adjustable core.

I don't have a current supplier bookmarked for Litz wire.  I recommend reading the Wiki article (assuming it's still there) to learn about the parameters involved.   

All that should be necessary is to take one of your broken inductors, carefully unwind it (maybe mark a stripe down the outside) and count the windings.  Then examine the wire under magnification to determine the number of conductors in the bundled wire.   Litz wire comes up pretty easily in searches, or it did a few years ago.  The trick is knowing what you need.

Then wind the same number of coils on a form in about the same pattern, insert one or two of the ferrite cores, and see if it works or works with adjustment.

This link https://www.electronicsurplus.com/inductors/inductors-coils/page/3

also has some parts that might be good candidates -- if I knew the inductance range.  But the 7-142 might be good even if one must unwind it and rewind it with Litz wire.  It looks like the form is pretty similar in shape.