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Old 31st May 2019, 7:06 pm   #1
William
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Location: Maidstone, Kent, UK.
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Default Ferrite core

Well it's happened again, admittedly not for a long time but after performing an alignment on a communications reciever the ferrite core cracked a lodged good and proper inside the oscillator coil former.

I managed to break up and free the remains of the old ferrite core and usually can replace as I keep spares.

Sadly the core is a mix of ferrite I do not have. I've been trying different ones all afternoon, but I have nothing to match or come close to the original.

If anyone can help with my probably I'd be very greatful. EBay hasn't been much help. There's plenty of OSC screened cans on there, but it's a bit pot luck. I really need a bag of a few different ferrite types.

The type I have and need is Hex fine thread 11.5mm X 5mm

Thanks on advance
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Old 31st May 2019, 10:07 pm   #2
Radio1950
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Default Re: Ferrite core

Please tell us the receiver type, manufacture date if known, and confirm that it is the oscillator coil which needs the ferrite core.
Do we assume that your core is 5 mm diameter, 11.5 mm long, with internal hex adjustment hole?
If it is an old rx, the core may be imperial and not metric.
Can you measure the thread pitch of a good core?
Have you checked the Neosid range?
Good luck. Some of us here have been in your predicament, or similar.
I just hate that sinking feeling you get when a core breaks, or when it cracks and jams.
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Old 2nd Jun 2019, 3:10 am   #3
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Default Re: Ferrite core

Are you really sure that core is ferrite?

Dust-iron is much more common and is more likely to go crumbly. Tuning slugs were made in a few different grades of iron dust, and also a few different grades of ferrite.... as well as the obvious matter of mechanical size.

Ferrite cores were used when much higher permeability was needed than the usual grades of carbonyl iron gave, but they suffered from greater temperature dependence.

If you use some magnification, the fracture faces of an iron dust core look, well, dusty, while in ferrite they look more often sort of crystalline and shiny.

If we knew what the receiver was, someone might have one out of a scrap set, which would be your best chance of getting a core which would work.

David
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Old 2nd Jun 2019, 11:30 am   #4
William
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Default Re: Ferrite core

Thank you both for your replies. To answer the questions that have arisen from my post.

Reciever type: Codar CR70A
Date: 1974
Coil type: Qoilmax
Band: 4 (broadcast MW)
Thread Pitch: Imperial?

I'm not 100% sure if indeed it is Ferrite or Iron dusted cores. All I do know is that for Bands 2,3 and 4 the cores are the same and can be swaped. For band 1 the core is different and I have plenty of those, they look the same apart from 2,3 and 4 which look slightly darker material.

Hope this helps a bit, can provide more info if needed..

Thanks to all

73 William 2E0KKQ
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Old 4th Jun 2019, 1:15 am   #5
Radio1950
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Default Re: Ferrite core

Hi again,

the solution may be difficult as originals are probably unobtainable.
You may find an old Codar set for "ratting".

Seems Qoilmax made both ferrite and iron dust cores.

I would experiment with various materials to see if you can approximate the old core, even using smaller diameter cores to see if it "tunes" close enough.
You need a big junk spares box, or a supplier from whom you can buy one of this and one of that.
Try 4mm ferrite beads etc. just to approximate the material.
You have prolly done all this already, but, just for the onlookers ...

Have a look at Neosid, MMG and Toko for possible cores.

if you kept the old core pieces, I would crush them up to a fine dust, make up a new cylinder type core with no thread, and glue it up with PVA glue or shellac.
Use a 6mm ID tube very lightly coated internally with some release agent eg light oil or similar.
You have to make "it" of a diameter that will just fit inside the original coil former. Guess the length.
Then glue this "core" to the end of a plastic or nylon threaded section eg 8mm long. Use brass as a last resort.
The threaded section has to match the original former.
Cut a cross slot for adjustment in the top of the threaded section.
The coil former probably is M6x1.0 or could be imperial 1/4x20.
Test this with known screws.
You may have to be creative.

Very good luck.
I am sympathetic as I am having troubles with cores also, albeit a different problem.

This is interesting
http://www.milair.co.uk/qoilmax.html

If I had to guess, I think your MW core might just be iron-dust.
But I make a lotta mistakes.
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Old 4th Jun 2019, 9:18 am   #6
Radio1950
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Default Re: Ferrite core

Or .... you could just mould up a "new" core from the old crushed core dust, in a threaded identical plastic coil former, with release agent,let dry, and then cut the coil former away.
Maybe poke a suitable screwdriver in one end of the nearly dry new core for an adjustment slot.
Maybe don't use shellac as a binding agent in moist environments; your choice.

Voila! Comme on dit en France.

But ... you may not have the old core anymore?

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Old 5th Jun 2019, 3:11 pm   #7
William
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Default Re: Ferrite core

Thanks Radio1950 for your advice and suggestions. I think I might be in luck.

Purchased another codar cr70a receiver off ebay, it's wasn't very expensive and just hope with fingers crossed that the cores aren't missing or damaged in it.

It'll be handy for other spare parts in the future should I need them.

Also you said you require cores, which ones as I might be able to help.

73 William
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Old 6th Jun 2019, 1:08 am   #8
Radio1950
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Default Re: Ferrite core

Hi William,

my problem resolved - thanks for offer.

Exeunt R50
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Old 6th Jun 2019, 1:40 pm   #9
William
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Default Re: Ferrite core

That's good you managed to find the cores you needed.

The codar off ebay came today and managed to salvage the core I needed. Also a couple of other bits came in handy.

My receiver is now happy again and so am I.

Added a picture of the Codar and the remaining bits from the donor.
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Old 7th Jun 2019, 2:07 am   #10
Radio1950
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Default Re: Ferrite core

You have a very nice job of that receiver.
Well done!

Just out of curiosity please, as it is an English set, with 1970s assembly, did the manufacturers use BA, imperial, or metric fasteners?
(and just for the purist onlookers, we already know that BA has a metric heritage).
.
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