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 Post subject: Extract cracked slug from coil form? Or?
PostPosted: Dec Fri 09, 2022 6:07 pm 
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Joined: Mar Thu 22, 2012 8:19 pm
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Location: New Albany, IN 47150
In working on my Kenwood TS-520 I've discovered several slug tuned coils that can't be tuned because (apparently) a previous owner damaged the slugs. Yes, I have tried applying heat and a drop of oil but seemingly cannot budge them.

Terry (K9TW) suggests: "If careful you may be able to use a series of step increasing drill bits to drill out these cracked cores and then can ask Walter Dilley KD7DNY to harvest good replacement cores."

Maybe. Though I feel I would be lucky to pull that off, even if I where able to source some replacement slugs.

Maybe you have other suggestions of either how to get these slugs to tune, or to extract them?

If interested you can see a 27 comment thread (with photos) about the project here:
https://kenwood-hybrids.groups.io/g/mai ... n/95322049

Thanks,
Keith

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Keith Ostertag
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 Post subject: Re: Extract cracked slug from coil form? Or?
PostPosted: Dec Sat 10, 2022 1:38 am 
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Location: Lincoln City, OR. 97367
Greetings to Keith and the Forum:

I read your thread on the Kenwood group. The photo of the broken slugs indicates the problem.

I just read a post somewhere on the ARF within the last few days on this subject, but now I cannot find it. Perhaps the author or someone else can provide a link. The essence of the post was insert a disposable tool (cheap Allen wrench perhaps) into the slug along with some cyanoacrylate adhesive (super glue). The idea was to apply the super glue sparingly with a needle or similar tool so that it enters the cracks in the slug and the interface between the tool and the slug without using so much that it runs out to the edge of the slug. I would suggest as an addition that you put a Ty-Wrap around the coil to squeeze it if possible. Allow the glue to set. Remove the Ty-Wrap if installed. Then attempt to back the slug out.

Hopefully, the originator of the idea will jump in to claim his due credit and amplify on the process if necessary.

As far as replacing the coil form entirely is concerned, this is probably not as difficult as might first appear. I had to replace a coil in a Hallicrafters SR-400 Cyclone where the coil was inside a mechanical mounting and shield assembly that could not be accessed in place. It proved a fairly simple matter to remove the band switch shaft entirely from the radio. The individual coil pack could be extracted by un-soldering a couple of wires and a tin shield, then removing four small screws.

A similar technique is probably applicable to your Kenwood. Just be sure that you do not rotate any of the switch wafers while you are extracting the shaft. Based on your photos, I would replace at least the coil that has the huge hole in the side of the form.

Good Luck,

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 Post subject: Re: Extract cracked slug from coil form? Or?
PostPosted: Dec Sat 10, 2022 10:09 am 
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If its only the top slug, and sometimes is from an amateur twidler, then have you tried unscrewing the bottom slug right out? Then you maybe lucky and find the top slug has a slot on the bottom as well that you can use to wind it out with.

Gary


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 Post subject: Re: Extract cracked slug from coil form? Or?
PostPosted: Dec Sat 10, 2022 12:51 pm 
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I would wonder at a normal drill, some of that ferrite is that hard you can only grind it. even Tungsten-Carbide cant cut it.
What tends to happen is that any attempt to turn it causes it, once broken, expand & therein lies the problem. I have got a couple with holes down the middle out by gluing a rod into them with a scant amount of epoxy resin. That stops it expanding.

No escaping the fact that once broken, they can be a real swine.

Marcc


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 Post subject: Re: Extract cracked slug from coil form? Or?
PostPosted: Dec Sat 10, 2022 11:59 pm 
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I too have had some limited success using a tiny dab of crazy glue on the tool inserted into the slug. Worth a shot to try.

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 Post subject: Re: Extract cracked slug from coil form? Or?
PostPosted: Dec Sun 11, 2022 12:14 am 
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Joined: Mar Thu 22, 2012 8:19 pm
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Location: New Albany, IN 47150
Thank you gentlemen.

Yea, I anticipate they will be a "real swine" as Marcc says.

It will take me a few weeks to procure some replacement coils/slugs, very difficult to find! And I won't begin till I have those replacements in hand. Some of the Kenwood Hybrid group guys are helping me with that.

I think I will try the super/crazy glue approach first, and if that doesn't work I might see about using a dental burr in a Dremel to cut through some of it... since those burrs are designed to cut ceramic maybe they will be effective.

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 Post subject: Re: Extract cracked slug from coil form? Or?
PostPosted: Dec Sun 11, 2022 12:16 am 
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Joined: Jun Fri 01, 2007 8:46 pm
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Location: Chattanooga, TN
I'm one more who removed a broken core by using epoxy to glue a tool (actually an ordinary machine screw) into the hole in the slug. I'd be afraid to use super glue period. Some of that stuff can wick through the slightest crack and then you are worse off.

Vince


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 Post subject: Re: Extract cracked slug from coil form? Or?
PostPosted: Dec Sun 11, 2022 12:27 am 
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Joined: Mar Thu 22, 2012 8:19 pm
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Location: New Albany, IN 47150
Hi Vince- yea, I do wonder that it might be difficult to not get superglue between the slug and the form, which of course would be game over for that coil.

When you say you used an "ordinary machine screw" I'm guessing you sized it just slightly smaller than the size of the correct hex tool for the slug? Because the point is to not spread open the cracks, right? What's your favorite epoxy- I'm thinking maybe to use E6000?

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 Post subject: Re: Extract cracked slug from coil form? Or?
PostPosted: Dec Sun 11, 2022 12:44 am 
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keithostertag wrote:
In working on my Kenwood TS-520 I've discovered several slug tuned coils that can't be tuned because (apparently) a previous owner damaged the slugs. Yes, I have tried applying heat and a drop of oil but seemingly cannot budge them.
Yes they are not stuck because of wax, glue or dirt. They are stuck because someone cracked the core (don't ask how I know, grrrr). The people who suggest putting something inside the core to glue the core to this tool are on the right track (epoxy or maybe Duco cement, but definitely NOT Superglue). The problem with other methods is they simply cause the crack to spread open and jam the slug inside the coil form because the diameter of the slug gets bigger.

Put a thin film of adhesive on the tool then carefully slide it inside the core. You don't want the tool to fit tightly otherwise the tool will jam open the crack all by itself. Then let things dry.

With the core adhered to the tool it shouldn't spread and should allow you to "turn it out". Success cannot be guaranteed, but it is one of the safer options.

Drilling also can work, but there is a high risk of having the whole thing "self destruct" on you.

Curtis Eickerman

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 Post subject: Re: Extract cracked slug from coil form? Or?
PostPosted: Dec Sun 11, 2022 3:08 am 
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Location: Queensland, AU
"I think I will try the super/crazy glue approach first" Good Lord

Don't put Cyanoacrylate glue anywhere near it, it will track into the fracture & the threads and glue your slug into the former, most likely, unless perhaps it was the Gel variety & don't attempt to drill or grind the slug, you will destroy the former.

I have been over this before on the forum, of how to remove fractured slugs with the hex hole.

The reason that they don't unscrew is that the tool causes expansion of the two halves with rotation and the sharp edges of the slug halves simply bind in the threads.

If any lubricants have been added they must be thoroughly cleaned out with contact cleaner (CO contact cleaner by CRC works well) initially.

Once that is done you need to hand carve an Allen key with a scalpel, No 11 blade on a handle is good, I use a wooden Chopstick as the wood is fairly strong and the surface a little absorbent . Then apply a small amount of 24 Hr epoxy resin (JB weld) just enough so that when this wooden key is fitted the faces on the on the wood are glued to the faces on the inside of the slug. You don't want the resin tracking into the threads. The application is to prevent the two halves separating with rotation. I have only ever used the wood, so I cannot comment on the success rate using a metal key or a plastic key & the resin. Make sure it is positioned when it is drying so that the rod/tool is parallel with the long axis of the coil, not tilted over to one side or the other, which will cause a problem when you attempt to manually rotate the tool & remove the slug later.

Leave it to harden for 24 Hrs. Then you can apply some lubricant if you wanted and gently start rotating the slug clockwise and anti-clockwise, a little at first and more and more, and you will be able to unscrew it.

I have been removing broken slugs like this for decades and was surprised that many people on the forum didn't know how to do it. Its like the other situation of people not knowing how to safely remove/dissolve the Pitch/Tar from components that were potted in it and causing a lot of damage, but it was common to dissolve it in mineral turpentine (paint thinners), for the last 60 years in NZ, but oddly nobody in the USA or UK involved in radio & TV restorations had heard of the method.

The primary reason why these slugs get cracked is that people reach for a metal tool, the local forces on the metal surface vs the Ferrite cause the fracture, it seldom happens with a proper plastic tool.


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 Post subject: Re: Extract cracked slug from coil form? Or?
PostPosted: Dec Sun 11, 2022 6:10 am 
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There is also the preemptive strike with some of those hollow ones that love splitting: glue an adjuster in first. then install it.

Marcc


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 Post subject: Re: Extract cracked slug from coil form? Or?
PostPosted: Dec Mon 12, 2022 12:48 am 
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Joined: Jun Fri 01, 2007 8:46 pm
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Location: Chattanooga, TN
Then there is the challenge of holding the coil/former tightly enough so that it doesn't turn but gently enough so it's not damaged.
Proceed with caution, don't be in a rush.

Vince


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 Post subject: Re: Extract cracked slug from coil form? Or?
PostPosted: Dec Sun 18, 2022 4:17 pm 
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Joined: Mar Thu 22, 2012 8:19 pm
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Location: New Albany, IN 47150
To report back- As it turns out I did not need to extract those broken coil slugs- someone on the Kenwood Hybrids forum generously sent me a set to replace all four 28meter band coils. I am so grateful for that gift, and also for not having to extract those coils. Of course there will be a time when that will happen so thanks to all for your ideas on how to do that!

It also tuns out that replacing those coils not only did not solve the problem but made things slightly worse. Several people on that forum have been helping me with the issue but so far little joy. Part of the issue is my lack of knowledge, and part is the RF boards are vertical in a tight spot and can't easily be removed.

If any of you might be interested in helping troubleshooting that would be greatly appreciated. At this point it looks like the problem could be located on the Ant Coil Unit of the RF section. For some reason four of the five Ant coils do not respond to their slug adjustment, and the fifth one just barely. You can read the current story here: https://kenwood-hybrids.groups.io/g/mai ... n/95681623

Thanks,
Keith

Attachment:
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kenwood_ts-520_ant_coil_schematic_detail.jpg [ 101.23 KiB | Viewed 257 times ]

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Keith Ostertag
New Albany, IN 47150


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 Post subject: Re: Extract cracked slug from coil form? Or?
PostPosted: Dec Sun 18, 2022 6:21 pm 
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Joined: Mar Thu 22, 2012 8:19 pm
Posts: 951
Location: New Albany, IN 47150
Just now found part of the problem with the Ant coil adjustments- found a bad solder joint and now all coils are responsive to their slug adjustments. Other problems still to resolve, but for now this one is mostly resolved.

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Keith Ostertag
New Albany, IN 47150


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