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Old 1st Feb 2021, 9:40 pm   #1
Alan_G3XAQ
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Default Ultrasonic cleaning solution for variable capacitors

I have a number of airspaced variable capacitors that need cleaning. None have inbuilt mica compression trimmers. There is the usual accumulation of dirt, superficial corrosion, dried grease on the bearings, and so on that I would like to remove (without making the capacitor unusable).

Materials seem to be brass, aluminium, galvanised steel frame, steel ball races and the odd ceramic terminal post.

I have a big old ultrasonic cleaning tank that I was given some years ago. The drive unit is valve powered and is itself a nice piece of vintage kit. What I'm missing is anything definitive about the best non-destructive cleaning solution for this specific job.

Any suggestions? Those based on practical experience would f course be the most valuable.

Thanks.
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Old 1st Feb 2021, 9:59 pm   #2
David G4EBT
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Default Re: Ultrasonic cleaning solution for variable capacitors

I usually get mine from Allendale Electronics who I bought my ultrasonic bath from.

They sell as range of fluids for various purposes such as carburettor cleaning.

The one at the link below is recommended for ‘sensitive material’ - brass, copper, aluminium.

I recently used it with good results for cleaning the tuning gang of a DAC90A:

https://www.allendale-ultrasonics.co...cleaning-fluid

Hope that helps Alan.
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Old 1st Feb 2021, 10:13 pm   #3
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Default Re: Ultrasonic cleaning solution for variable capacitors

Another vote for Allendale. I used this one though:

https://www.allendale-ultrasonics.co...cleaning-fluid

It works well in removing rust and corrosion and 5L is only twice the price of 1L.
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Old 2nd Feb 2021, 12:40 am   #4
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Default Re: Ultrasonic cleaning solution for variable capacitors

I used to use ultrasonic cleaning extensively in my day job, so I know how effective it is.

However, using one on a home radio project, things went badly. I tried to clean a salvaged B9A valve base, so we had a combination of a plated metal skirt, the metal spring connectors, and the solder on them. This went in the bath using a mixture of water with a pH neutral additive at about 40'C and, being pH neutral, I left it unattended for good few minutes but on returning the metal skirt had changed from silver to black, and I could not see what the connectors looked like, but I decided to junk it.

Now, travelling back through time, the first solvent that everyone would use for ultrasonic cleaning was Freon 113, which was most wonderful, but destroyed the ozone layer. Eventually, extremely effective water-based cleaners came along, but these need to be used cautiously on components where there is combination of metals which could enable galvanic corrosion to occur.

Bottom line; if you use a water-based solution on a multi-metal assembly, start cleaning at ambient temperature and keeping a constant eye on things and then progress from there accordingly.

I'm sure the Allendale products are good ones, but take no chances!

B
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Old 2nd Feb 2021, 1:57 pm   #5
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Default Re: Ultrasonic cleaning solution for variable capacitors

I use diluted de-greaser leftover from doing car parts ('safer de-greaser' from Rustbuster), or washing up liquid in water. That works fine for chassis at 50 degrees C.For watch parts and odd smaller things found in electronics equipment I've made a few concoctions involving water, a drop of washing up liquid to break the surface tension and a glug of ammonia. Put same in a jam jar with the part and float it in the fluid normally in the cleaner. In my case, the de-greaser solution. That keeps the delicate parts separate from any residue in the main tank and saves using more aggressive solutions in large quantities.

There are innumerable formulations around, but for the amount of ultrasonic cleaning I do I haven't been able to justify spending a hundred quid on a bottle of special watch cleaner, especially when the MSDS suggests they're all just water, ammonia and a surfactant. There are lots of more or less complicated recipes available online, particularly among the horological community, as that's an area where tools and equipment are frighteningly expensive so there's quite a large incentive to DIY.

Rinsing with distilled water and wiping with alcohol are some ways to avoid bad reactions or water deposits.
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Old 2nd Feb 2021, 6:03 pm   #6
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Default Re: Ultrasonic cleaning solution for variable capacitors

For the little ultrasonic cleaning I have done I used a drop of Fairy liquid in plain old tap water.
 
Old 2nd Feb 2021, 6:49 pm   #7
Al (astral highway)
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Default Re: Ultrasonic cleaning solution for variable capacitors

Another vote for washing up liquid in tap water.


Washing powder is also next-level powerful stuff in combination with an ultrasonic bath.
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Old 2nd Feb 2021, 7:04 pm   #8
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Default Re: Ultrasonic cleaning solution for variable capacitors

These were two clamps I cleaned recently in the ultrasonic bath. Before they were rusted solid, after with a quick wipe over with an oily rag they are almost as good as new.
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Old 2nd Feb 2021, 7:18 pm   #9
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Default Re: Ultrasonic cleaning solution for variable capacitors

I've also used washing-up liquid, with addition of vinegar or Coca Cola.

So, slightly acidic, but it makes a good job of brass. Not had any problems, but I do it well supervised.

And after the aqueous clean, it's rinse thoroughly, and then ultrasonic clean in paraffin. Apart from removing any other residues, it clears out any water globules that have been trapped.
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Old 3rd Feb 2021, 10:56 am   #10
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Default Re: Ultrasonic cleaning solution for variable capacitors

Folks, are any of these liquids of any use in a puny maplins bought ultrasonic cleaner?

The manual for that states to only use water, but with water only it is next to useless. Im wondering if it needs a better liquid, or whether it was just a waste of money that should be scrapped?

Cheers
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Old 3rd Feb 2021, 8:42 pm   #11
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Default Re: Ultrasonic cleaning solution for variable capacitors

You can but try. I imagine the warning is to prevent them being responsible if people put petrol in! There are some warnings about vinegar that are reasonable, as it will attack the stainless steel container to some extent. Ammonia is a common brightener for brass, though there are endless discussions about whether it is damaging for certain old clock parts.

Make sure the objects aren't sitting on the bottom, as they'll dampen the vibrations from the transducers. Most come with baskets to keep the object suspended in the liquid for this reason.
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Old 3rd Feb 2021, 9:54 pm   #12
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Default Re: Ultrasonic cleaning solution for variable capacitors

The advice to use water is probably related to avoiding using alcohol, which some people do, but the concern is that ultrasonic baths are self-heating, hence the risk of fire when using a flammable solvent. Of course, some go down the route of adding some IPA to water as a "compromise". There's a difference between what you can do at home and what you can do in a 'workplace'.

I don't think vinegar attacks most stainless steels, but the term 'stainless' covers a range of materials.

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Old 4th Feb 2021, 11:44 am   #13
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Default Re: Ultrasonic cleaning solution for variable capacitors

Quote:
Originally Posted by PsychMan View Post
Folks, are any of these liquids of any use in a puny maplins bought ultrasonic cleaner?


Cheers
Adam
Sadly it won't make much difference the Maplins one is too feeble Ok for a bit of jewelry but I found it useless on encrusted radio bits. I bought a much more powerful one.
I normally use a drop of washing up liquid but have tried Brass clock cleaner (very good on brass and copper) Evaporust in a jar sitting in the warm water and JPL sea clean which turned my valve holders black . my advice is try a small part/area first otherwise stick with plain warm water.
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Old 4th Feb 2021, 10:02 pm   #14
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Default Re: Ultrasonic cleaning solution for variable capacitors

At work we use diswasher tablets in the ultrasonic cleaner. They seem to be quite effective for most types of oily grime
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Old 4th Feb 2021, 11:55 pm   #15
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Default Re: Ultrasonic cleaning solution for variable capacitors

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Originally Posted by chriswood1900 View Post
and JPL sea clean which turned my valve holders black . .
Two of us with blackened valve holders (see post #4) - seems like that is a no go area

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Old 7th Feb 2021, 3:12 pm   #16
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Default Re: Ultrasonic cleaning solution for variable capacitors

I have cleaned variable capacitors in a dishwasher and it worked beautifully. They were both from late 1930s sets so less substantial ones may not survive as well.
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Old 7th Feb 2021, 5:03 pm   #17
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Default Re: Ultrasonic cleaning solution for variable capacitors

Over the years I have also successfully cleaned several air-spaced variable capacitors in the dishwasher. Most integral trimmers can be partly dismantled and the mica insulators taken out for cleaning separately once the adjusting screw has been removed.

Whatever cleaning method you decide to use, remember to re-lubricate the ball bearings at each end and to put a few drops of switch cleaner onto the rotor's earthing contacts. Take care not to get switch cleaner onto the vanes otherwise you risk creating an additional dielectric. Good luck.

Len
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Old 7th Feb 2021, 5:11 pm   #18
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Default Re: Ultrasonic cleaning solution for variable capacitors

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Originally Posted by merlinmaxwell View Post
For the little ultrasonic cleaning I have done I used a drop of Fairy liquid in plain old tap water.
That's me too, a drop of washing up liquid in plain old room temperature tap water. Start like that. You can always go stronger, but not vice versa if you do damage..
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Old 7th Feb 2021, 6:08 pm   #19
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Default Re: Ultrasonic cleaning solution for variable capacitors

Before Maplin closed down, I bought a bottle of Seaclean 2 ultrasonic cleaning liquid, which is still keeping me going. I have also used the original green Fairy liquid in lukewarm water with excellent results. For heavily tarnished objects, giving them a wipe with cotton wool soon after removing them from the ultrasonic bath helps remove any tenacious residue.
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Old 8th Feb 2021, 12:29 pm   #20
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Default Re: Ultrasonic cleaning solution for variable capacitors

Quote:
Originally Posted by Bazz4CQJ View Post
The advice to use water is probably related to avoiding using alcohol, which some people do, but the concern is that ultrasonic baths are self-heating, hence the risk of fire when using a flammable solvent. Of course, some go down the route of adding some IPA to water as a "compromise". There's a difference between what you can do at home and what you can do in a 'workplace'.

I don't think vinegar attacks most stainless steels, but the term 'stainless' covers a range of materials.

B

I regularly use white vinegar with a drop of washing up liquid to clean all types of stainless steel and have never had any problems. None of this involved ultrasonics though.
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