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FrankB 28th Jul 2020 6:06 am

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.

SeanStevens 28th Jul 2020 7:54 am

Re: Stuck Ferrite IF cores.
I have a transistor radio that needs 3 or 4 cores replaced. They are not broken yet, but will be if I try any harder to get them out.

Does anybody sell slug replacement sets still?


Tractionist 29th Jul 2020 1:06 pm

Re: Stuck Ferrite IF cores.
Some people also recommend eardrops [i.e. those intended to dissolve and/or dislodge wax] .........? Hear! Hear! :laugh1::laugh1::laugh1:

TechyNYC 15th Jan 2021 4:28 am

Re: Stuck Ferrite IF cores.
The main ingredient in ear drop solutions is Hydrogen Peroxide. Works great on removing ear wax, bees wax and other things. HP is an oxidizer but it's non-flammable.

Sinewave 16th Jan 2021 12:51 pm

Re: Stuck Ferrite IF cores.
I've used WD40 in the past and worked a treat, then a few wraps of ptfe around it so that I can make the adjustments and leave it set without glue.

John Caswell 16th Jan 2021 1:49 pm

Re: Stuck Ferrite IF cores.
PTFE tape, now that's a good idea - why didn't I think of that:)


Oldcodger 26th Jan 2021 3:29 pm

Re: Stuck Ferrite IF cores.
In a second life I worked in MSDF ,mainly on the RT353. In the repair section we'd often get radios in any state of repair ( from poor reception to being run over by a tank). The latter we could do little with ,but in the case of realignment of the IF section cores, we used a heat source( gun/dryer) to melt out the core glue, then took out the cores before realignment. I don't remember breaking any in my few years in repair.

G6Tanuki 26th Jan 2021 5:28 pm

Re: Stuck Ferrite IF cores.
To lock cores my preference is the old very-thin-rubber-filament thing: elastic is a good source of this [though don't go cutting-up your other half's underwear].

Over time the rubber perishes, but the fragments still work to stop the core unscrewing - and if anything the perishing will make it easier to remove the core again in 20 years time.

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