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 Stuck Tuning Cores

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FrankB
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FrankB

Join date : 2010-11-22

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PostSubject: Stuck Tuning Cores   Stuck Tuning Cores Icon_minitimeDecember 8th 2018, 11:29 pm

Some radios, especially the AA5's using the miniature tubes have a hexagonal cored ferrite IFT tuning slug.

Quite often these were sealed in place with wax. Trying to move them with a plastic "wiggle wrench" Tuning tool, can cause the core to break.

 I found that taking a cheap, metal hex/Allen wrench and heating it, then inserting it into the core with pliers can often times cause the wax to soften just enough to allow you to back the core out with little problem. Be VERY gentle using a metal Allen wrench. The cores are extremely fragile.
 I have had friends tell me they used a heat gun to loosen the core, but you run the risk of damaging the coil form, windings, or other components in the IF can.  
  I have also used a cheap- dollar store type straight tip soldering iron applied directly to the core to loosen it up, but if you use this method, just heat it enough to get it to move. You can easily burn/melt the coil form or overheat the wire on the form.
   Some of the coil sealing materials can emit acrid smoke when heated also, and so it's a good idea to do this outdoors or with a lot of ventilation.

I have a drawer full of salvaged cores I use to replace broken cores where someone got too "animal" with them.  Old TV and commercial tube radio chassis are good sources of spare cores. They do come in several different diameters, lengths, and ferrite compositions too.
 Some cores are even aluminum and some are brass too! I have seen them as small as a 4/40 thread, and larger than 5/8".
  If you have one that is way too long, you can cut them down or grind them down carefully, to the right length too.

Use extreme care when trying to adjust or remove any ferrite core. They break so easy, it can be annoying at times. 

Please don't try to adjust them with any sort of metal tool. It throws the alignment tuning off and can easily break the core.

GC (General Cement) made a "Ferrite Cement" that I have used on broken antenna ferrites and a couple of times on cracked cores. It does work sometimes, but does change the tuning properties slightly. I have not had 100% success with it when I have used it.

Some coils used a strip of rubber "band" like material to hold the core in place in the threads. I have seen Glyptol, paint, epoxy, and hot glue also used to keep the cores from moving.

I find that plain old beeswax works just fine if needed. You can even salvage it from the old wax caps you remove, by heating them with a heat gun over a metal can and the way will usually run off of them. Typically you can get enough to "lock" a core back in place from just one old wax capacitor.
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ve1arn
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ve1arn

Join date : 2010-11-23

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PostSubject: Re: Stuck Tuning Cores   Stuck Tuning Cores Icon_minitimeDecember 9th 2018, 7:09 am

Frank.... Could holding a hot metal Allen key too long could also make the ferrite expand and possibly break the form as well? Just wondering. The idea is a great one nonetheless.
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FrankB
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FrankB

Join date : 2010-11-22

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PostSubject: Re: Stuck Tuning Cores   Stuck Tuning Cores Icon_minitimeDecember 10th 2018, 5:06 pm

I suspect that is possible. Somewhat of a judgement call. The idea is to soften the way holding the core enough to turn the core, not melt it out.
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Cliff Jones
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Cliff Jones

Join date : 2010-11-22

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PostSubject: Re: Stuck Tuning Cores   Stuck Tuning Cores Icon_minitimeDecember 10th 2018, 7:56 pm

i WONDER IF REMOVING THE CORE AND ADDING A TRIMMER PAD EXTERNALLY WOULD SUFFICE. YOUR THOUGHTS PLEASE.

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FrankB
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FrankB

Join date : 2010-11-22

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PostSubject: Re: Stuck Tuning Cores   Stuck Tuning Cores Icon_minitimeDecember 11th 2018, 5:39 pm

I am not sure that would work, as removing the core would really change the Q and tuning range of the coil. A trimmer cap might not be good enough to do the job.  It would make an interesting experiment though.
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PostSubject: Re: Stuck Tuning Cores   Stuck Tuning Cores Icon_minitime

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