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Old 28th Jul 2020, 7:06 am   #1
FrankB
Hexode
 
Join Date: Oct 2005
Location: Olympia, Washington, USA.
Posts: 475
Default Stuck Ferrite IF cores.

We all have run into this from time to time.
I ran into a lot of this in TV servicing and old radios.

That "delightful" hex hole core was stuck. Often from hot glue, or more commonly beeswax or silicone seal.

Getting a stuck core out can try the patients of a Doctor (LOL).

I found sometimes pouring some denatured alcohol into the core would loosen it, but more often digging out the silicone seal, or hot glue- and heating the coil carefully with a heat gun to melt the bees wax out.
Sometimes putting in a nail filed to the core shape and heated would loosen the beeswax quite quickly too.

Then comes that sound we all dread... Crunch! When the core breaks into a pile of ferrite pieces.
I learned decades ago that this was way more common than I liked. So I started removing the adjustable ferrite cores from old TV and radio chassis, 2 way radios, etc.
I would carry a box of them of assorted diameters and lengths in my service kit. (GC- General Cement, used to make a kit of assorted replacement cores).

The core you need too long? File it down or use sand paper to reduce the length. Too short? Put 2 cores snug with each other, and cement together with ferrite cement. Then put in the coil form.

Now I never found any problem with ferrite mix causing a problem in the coils. Sometimes I'd have to adjust the core to a different spot to get the correct adjustment, due to the replacement core being a bit longer, shorter, etc; but it never failed me.

Oh, and carry a few VERY thin rubber bands in your kit too. Some cores used a thin strip of rubber band to "lock" the core in place. No glue, silicone, or beeswax needed. I did carry a small ball of bees wax to seat the cores with and wax dial cords too.

The very last thing I wanted to do was replace a good coil with a replacement just because of a broken core.
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