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Old 18th Feb 2024, 7:48 pm   #21
Tractionist
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Default Re: Tar removal from Mica Trim Capacitor

It all depends what's under the gunge. Mica is a product of metamorphic rocks (a'la talc and garnet etc.) .... it's very inert and flame-proof etc. - but the trimmer body could be ceramic, plastic or even Bakelite. If it's plastic, very obviously you don't want to melt or damage the trimmer body. Soooo ..... my 'go to' would be white spirt - which as others have stated, is pretty benign.
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Old 18th Feb 2024, 8:09 pm   #22
emeritus
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Default Re: Tar removal from Mica Trim Capacitor

The only retail source of genuine turpentine I have found in the UK, is shops that sell art supplies, as it is used to thin traditional artists' oil paints. When we used to visit France, proper Turpentine was readily available cheaply in supermarkets' hardware departments, but it's more than 10 years since we were there. Incidentally, knowing how keen the French usually are to use their own terminology in preference to Anglo-Saxon, it was interesting to see that "White Spirit", is called "White Spirit"!
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Old 18th Feb 2024, 9:55 pm   #23
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Default Re: Tar removal from Mica Trim Capacitor

Here are the before and after pictures using odorless mineral spirits (OMS). Before applying the OMS, I tested a new working mica compression trimmer for its C value and its dissipation factor. Then again after application and set it aside to dry. There was no significant difference so I proceeded with hope. I checked the after C value and it was in its target range of 15-75 pF and its DF is 0.019, not great but not unreasonable for 1932 technology! A modern day mica compression trimmer comes in at .005 or better. I suspect and careful cleaning of the mica strip might get this factor down a little, not sure its worth the effort. I did put the trimmer on the network analyzer sweep to 3 MHz and it looked nominal, nice. Since the C trimmer is applied at 600 kHz, I felt relieved.
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Old 18th Feb 2024, 11:38 pm   #24
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Default Re: Tar removal from Mica Trim Capacitor

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I've also used the wife's acetone - the stronger stuff.

Aub
Is that nail varnish remover ?

David
Yes David. She has two types. One is a lot stronger than the other and therefore better at removing the longer lasting varnish she sometimes has.

Aub
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Old 19th Feb 2024, 12:34 am   #25
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Default Re: Tar removal from Mica Trim Capacitor

It looks like OMS (~White Spirit) has worked.

I'd guess the the league table of "cleaning" solvents, starting mildest first, is this;

alcohols
car windscreen de-icer (alcohol +?)
white Spirit

(there's quite a gap here)

xylene
acetone
MEK


I know there are others, like cellulose thinners, but cannot comment on them.

Halfords car de-icer I believe is mostly alcohol with a bit of glycol. It seems to work quite well with paper labels and over-spray paint on plastics (does not dissolve them, but makes them easier to 'de-bond' with say the edge of a credit card).

B
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Old 19th Feb 2024, 4:08 pm   #26
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Default Re: Tar removal from Mica Trim Capacitor

Did someone suggest using Diesel oil already ?
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Old 19th Feb 2024, 10:51 pm   #27
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Default Re: Tar removal from Mica Trim Capacitor

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The only retail source of genuine turpentine I have found in the UK, is shops that sell art supplies, as it is used to thin traditional artists' oil paints. When we used to visit France, proper Turpentine was readily available cheaply in supermarkets' hardware departments, but it's more than 10 years since we were there.
Available from hardware stores and most supermarkets in NZ.
https://www.mitre10.co.nz/shop/searc...sort=RELEVANCY
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Old 20th Feb 2024, 12:31 am   #28
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Default Re: Tar removal from Mica Trim Capacitor

It may be an EU thing, where they have tried to restrict some materials to usage by professionals (I think Creosote timber treatment falls in this category).

Back in the days when the ozone-depleting chloro-fluorocarbons solvents were banned, there was a brief period when people were desperate to identify other agents which would clean as well as the CFC's. Some manufacturers tried marketing terpenes, but many people complained that they did not want to use them (the strong smell was stomach-turning and people complained of generally feeling unwell. I think the terpenes pretty soon disappeared and very many people eventually replaced CFC's with new and highly effective water-based cleaners.

B
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Old 20th Feb 2024, 6:42 pm   #29
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Default Re: Tar removal from Mica Trim Capacitor

When cleaning anything like trimmers or variable-capacitors that involve ceramic insulators or mica, my #1 concern is whether the solvents also include any non-volatile oily components that will stay behind and compromise the insulation.

Mention has been made of nail-varnish-remover: it seems {following a conversation with a female dog-walking friend who spent some time starring in various 1980s TV dramas} that some of these also include a 'moisturiser' to help keep your cuticles in good condition after the varnish has been removed. Pragmatically, the last thing I would want to use on anything electrical would be something containing a 'moisturiser' !

And yes, the general availability of effective solvents has been curtailed by various regulatory measures in the last few decades.

COSHH and REACH being examples. Some of these are annoying, others [such as getting liver-damaging nasties like Carbon Tet and Trike out of general circulation] are good.

We have to use what we can get.
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Old 20th Feb 2024, 6:52 pm   #30
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Default Re: Tar removal from Mica Trim Capacitor

Speaking of nasties, I recall using benzene in the open chemistry lab at school. It was widely used by Joe Public for all kinds of jobs.

Arriving at University a couple of years later, we were told that benzene could only be used by trained research staff who had a note from the Head of Department accepting their need was essential.

Carbon tet was similar.

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Old 22nd Feb 2024, 12:54 pm   #31
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Default Re: Tar removal from Mica Trim Capacitor

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White spirit is just one of a huge number of petroleum distillates, so it's not that far removed from petrol/gasoline or paraffin/kerosene. It's volatile so it evaporates leaving little residue. 'Turpentine substitute' is basically the same stuff, and old school WD40 is mostly white spirit.
I'm not sure that turpentine should be regarded as the same stuff as White Spirt. It contains (some) terpenes, quite strong and stinky solvents. Just looking on Google, none of the Sheds seem to sell a product they call turpentine, but they can still be found (trades use? I suspect it was more common when we were kids!).

Odour-free mineral spirits seems to imply that some low levels of aromatic compounds have been removed, but I suspect the mixture will still handle tar. I always have some WS at hand.

B
In Oz, real turpentine was pretty much the province of artists suppliers, but "Mineral Turps" is ubiquitous.
It is seriously smelly.

"White Spirit" is not as common as it was but can still be found.

At my old work, we had what was labelled "Range Fuel" which we used to clean crud off the guts of our old Marconi TV transmitters---it smelled & looked like "White Spirit" but came in 4 or 5 gallon square drums (like the very early petrol & kero).

"The past is a different country"----- the cloths we used with the "Range Fuel" were called "singlet ends", which is apparently exactly what they were---offcuts from a singlet factory!
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Old 26th Feb 2024, 8:08 pm   #32
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Default Re: Tar removal from Mica Trim Capacitor

If you want good genuine balsam turpentine, I can recommend this stuff as I use it a lot with linseed paints. The paints Brouns sell are very good too.
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