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Old 4th Feb 2015, 1:43 pm   #1
Tyso_Bl
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Default Ceramic plated inductors repair

I've got a VFO here, its part of another unit but don't know what, it has ceramic coil formers but no wire windings. The windings seem to have been plated directly to the ceramic formers.

The unit has badly damaged by corrosion. I don't have pictures available as the unit is in long term storage.

Does anyone have any thoughts on what it may be part of and if DIY plating of ceramics is a feasable operation?
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Old 4th Feb 2015, 2:20 pm   #2
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Default Re: Ceramic plated inductors repair

What size/shape are they?

Ceramic formers with [silver]-plated windings were used in a significant amount of German WWII communications gear.
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Old 4th Feb 2015, 6:33 pm   #3
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Default Re: Ceramic plated inductors repair

Some years ago, I used to use an electroless nickel plating system that would pretty much plate anything. One of the uses we made of it was to put a metal layer down on top of silica and this was just a doddle. Unfortunately, I think that that particular product line (Canning's 'Nifoss 80') was closed down in the UK and I think it now exists in India. But as a general answer to your question, I reckon that a good electroless nickel system could be used on a DIY basis to plate ceramic.

B

Last edited by Bazz4CQJ; 4th Feb 2015 at 6:40 pm. Reason: typo
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Old 4th Feb 2015, 7:19 pm   #4
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Default Re: Ceramic plated inductors repair

Why not use silver loaded conductive paint?
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Old 4th Feb 2015, 8:02 pm   #5
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Default Re: Ceramic plated inductors repair

Why not wind wire round it?
 
Old 4th Feb 2015, 8:40 pm   #6
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Default Re: Ceramic plated inductors repair

Quote:
Originally Posted by merlinmaxwell View Post
Why not wind wire round it?
If it's a VFO there's clearly a reason for the designer going to the effort of speccing silver-plated 'windings'.

For one of my early-1980s free-running-oscillator designs I specced a grooved ceramic former and flat-section silver-plated windings fitted in the grooves. The process was quite specific - involving chilling the former to liquid-nitrogen temperatures and heating the flat-windings to 100Centigrade, winding under specified tension and anchoring/terminating the ends before the former reached -30 Centigrade.

The result was impressively thermal-stable - good-enough for a free-running VFO to be eminently usable on 2-Metres mobile SSB (though it was originally specced for AM VHF mobile-radio/airband service).

Where do you get silver-plated copper tape these days?
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Old 4th Feb 2015, 10:49 pm   #7
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Default Re: Ceramic plated inductors repair

Ok from memory, cylindrical formers, different heights, spiral groove like thread, different pitches. Dark stain on the ceramic where the winding should have been, so was assuming a plated winding as no sign if wire, Very heavy duty modular construction, but not much to salvage except the formers hence my curiosity.
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Old 4th Feb 2015, 10:58 pm   #8
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Default Re: Ceramic plated inductors repair

Inductors made from etched silver on a ceramic cylinder were available in the 70s and 80s, and I can't remember the maker's name. It might have been Oxley developments. THe flat conductor gives a high Q and a good SRF.

Oxley? Cambion? Coil-craft?

HP used some, and I believe R&S too.

David
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Old 5th Feb 2015, 11:00 am   #9
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Default Re: Ceramic plated inductors repair

If the coils are not in a high-power circuit, this may do the job, and is easy to apply.
http://uk.rs-online.com/web/p/solder-pastes/8352699/ Just a thought.
Higher power circuits will probably mean heavy electro-plating, or using normal wire. Tony
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Old 16th Feb 2015, 1:58 am   #10
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Default Re: Ceramic plated inductors repair

Why not silver plate some copper foil alarm tape, such that is used on windows? If the tape is too wide, simply make a wooden jig with a razor blade as a cutter and cut to width desired.
This method worked fine years back to cut wide computer tape rolls into the correct width for audio recorders.
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Old 26th Apr 2015, 2:28 am   #11
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Default Re: Ceramic plated inductors repair

Just an update on this, still not sure how to plate a silver spiral coil on a ceramic former, but I did manage to find the unit in question, and it has been identified as being from a WW2 german submarine transmitter. The person who identified it has a beter use in mind for it than I had so I hope he's happy with it.

Still interested in how to plate ceramics though.

Tyso
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Old 26th Apr 2015, 9:33 am   #12
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Default Re: Ceramic plated inductors repair

Start with an electroless plating process to deposit something that's conductive, then switch to electroplating to put down much better conductive metal.

Avoid nickel. Firstly, it's a poor conductor (Nickel features in most resistance wire alloys) AND it's magnetic. Both are undesirable in oscillator coils and filter coils.

Part way through, apply a resist to allow the stuff between turns to be etched away, then get on with the electroplating.

PCB manufacturers need an electroless process to make the insides of holes conductive so electroplating will build connections through plated-through holes.

David
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