Author Topic: how to clean/lubricate old variable caps and (especially) roller inductor? (Read 10885 times)

cdev · « **on:** December 18, 2016, 01:19:39 am »

I recently got a good deal on a very old "differential-T" antenna tuner and visually its in fine shape but electrically the bearings are dirty. I am currently (no license yet!) just using it for SWL where it does clearly allow the tuning up of arbitrary wires to get a stronger signal- "impedance matching works!"

however, the conductivity of the roller inductor is patchy so as it rotates it cuts in and out- This can also be seen quite clearly on the (SDR) waterfall. Visually it looks pretty good, but it seems as if as it turns around half of it connects well and on the other side of the turn it does not make as good a connection. I bet that would also be the case with DC.

Someday before too long if I am going to use this thing without problems in my future ham shack, which was my intent, I am going to have to figure out what it needs in terms of cleaning/lubrication and fix it a bit better. What do people do?

So, I emailed the manufacturer with the question of what to do, not really expecting a response. But, they were actually quite nice. Its got a very long coil which has a counter which is also missing a little belt which they were kind enough to mail me a replacement for.

The manufacturer also mentioned a specific grease they use but - Googling, a bunch of people seemed to feel that the grease caused more problems than it solved for that manufacturer's products.

So, I ended up as confused as I started out, or maybe even more confused. This subject appears to be one of those subjects that people argue endlessly about.

However, some good news- It seems as if the roller inductor my unit has is better than the ones in the newer units, and it looks like its in fairly good shape considering that the thing appeared to have been sitting unused for a long time before getting sold to me. Which is probably how it got dirty. It had been sitting in one position so long that the belt on the counter had literally disintegrated.

This problem was actually why I had gotten it cheap. The seller had said that as he was unable to make it tune up his test antenna properly he gave me a good price.

It seems as if its also possible to touch up the silver plating on old silver plated parts.. so if I am going to disassemble it I might as well do that too.

But my main question is, what should I put on the bearings, and roller wheel? There is still a little bit of the original lubricant but I have a feeling its part of the problem. Acetone, for example, is a really good degreaser. So is that stuff made with citrus oil. 91% isopropyl alcohol, not as much .. but still useful.

I think the recommended grease contained graphite. I have some graphite, should I use that? In what? in some silicone grease? Or light mineral oil?

Also capacitors.. I am assuming its a similar application.

Just looking for more data points before I do something that could be a PITA to reverse if it doesn't work.

**Thank you!**

Ian.M · « **Reply #1 on:** December 18, 2016, 01:37:49 am »

Silicone grease or oil is a real P.I.T.A to remove and if there is ever any arcing it can form a glassy insulating layer on the contact surface. If you want to experiment with mixing your own grease use a hydrocarbon base. e.g. try loading Vaseline with graphite powder.

Does it have a spring holding the roller in contact with the coil? If so, maybe something's seized there and its not providing an even contact pressure, then any slight eccentricity would cause it to loose contact for half of each turn.

DimitriP · « **Reply #2 on:** December 18, 2016, 01:39:53 am »

Roller refurbishment fun here : http://www.eham.net/ehamforum/smf/index.php?topic=55297.0

cdev · « **Reply #3 on:** December 19, 2016, 01:44:33 am »

DimitriP - Indeed... thats the place I found all the chat about the issue.

Ian M, there are two sort of inverted U or M shaped springs, one at each end, but the pressure doesn't seem uneven

I am going to try a thorough disassembly and cleaning and then maybe a very little bit of graphite loaded vaseline, if further reading supports that idea and I'm feeling courageous.

Edit, at one point I squirted WD40 into the bearings and from reading more it seems that was likely a big mistake. So before I go any further I think job#1 is using some volatile degreaser and elbow grease - perhaps with q-tips to try to remove the WD40 residue.

Ian.M · « **Reply #4 on:** December 19, 2016, 02:07:51 am »

It may also be worth adding a trace of oleic acid to your home-brew grease.
see https://www.eevblog.com/forum/chat/any-suggestions-on-how-to-make-a-home-made-contact-deoxidizer/

VK5RC · « **Reply #5 on:** December 25, 2016, 08:22:32 pm »

I have a similar problem with my daughter's older car, the sockets holding the tail light bulbs,
can themselves, can be fully removed from the tail light assembly. The bulb and bulb holder come free with no attached wiring. The electrical contact between the bulb holder and the tail light assembly, a pair of wiping contacts, are erratic electrically.
I searched for 'electrically conductive grease' , my local electronic supply house offers something, when they open after the holidays I will try some. https://www.jaycar.com.au/conductive-carbon-grease-50g/p/NA1034

Ian.M · « **Reply #6 on:** December 25, 2016, 08:35:25 pm »

For a high current wiping contact that never moves while power is on, conductive carbon grease may not be the best choice as the carbon particles may cause 'hot-spotting' if there isn't good metal-to-metal contact, or may cause tracking across the insulator. Clean the s--t out of it and make sure both contact surfaces are bright and smooth, and that there is adequate contact pressure. After confirming correct circuit operation, apply electrical grade silicone grease.

Robert763 · « **Reply #7 on:** January 01, 2017, 03:31:45 pm »

Ian.M said " After confirming correct circuit operation, apply electrical grade silicone grease." DO NOT DO THIS. Silicone based lubricants should NEVER be used on electrical contacts. As mentioned previously, any arcing can convert the silicone into glass ruining the contat.

slicendice · « **Reply #8 on:** January 01, 2017, 05:18:55 pm »

I found this video on YouTube:

Hope that one helps getting your variable caps and the inductor cleaned and greased properly.

Ian.M · « **Reply #9 on:** January 01, 2017, 06:35:17 pm »

Quote from: Robert763 on January 01, 2017, 03:31:45 pm

Ian.M said " After confirming correct circuit operation, apply electrical grade silicone grease." DO NOT DO THIS. Silicone based lubricants should NEVER be used on electrical contacts. As mentioned previously, any arcing can convert the silicone into glass ruining the contat.

Silicone grease is *ONLY* suitable for *FIXED* contacts that are *NEVER* mated or disconnected under load. For *ALL* other applications, including the O.P.'s variable inductor,
you are right and the use of silicone grease will cause problems. However for fixed contacts exposed to a harsh environment with a large temperature range (e.g. marine and automotive connectors), it is far more effective at excluding moisture and vastly reduces corrosion. Without contact movement, there is no possibility of arcing so no glassy layer forms. It also is far more likely to be compatible with the plastics of the lamp housing than a hydrocarbon grease.

However for general maintenance it has some serious disadvantages - its extremely persistent, transfers easily on contact and even the slightest trace on a surface will cause fish-eyeing of new paint or adhesion failure for adhesives and cauks, and as previously mentioned, its use on moving contacts is a disastrous mistake. Your average 'trade school' mechanic absolutely can not be trusted with the stuff as one mistaken application can result in $EXPEN$IVE$ damage.

For:

Quote from: VK5RC on December 25, 2016, 08:22:32 pm

I have a similar problem with my daughter's older car, the sockets holding the tail light bulbs,
can themselves, can be fully removed from the tail light assembly. The bulb and bulb holder come free with no attached wiring. The electrical contact between the bulb holder and the tail light assembly, a pair of wiping contacts, are erratic electrically.

finding a suitable non-silicone grease that retains an acceptable consistency over the required temperature range, available in small quantities will be very difficult, and silicone grease will almost certainly provide the most durable corrosion protection of the lamp housing contacts.

cdev · « **Reply #10 on:** January 01, 2017, 08:11:01 pm »

maybe if in doubt the most sparing application possible?

Does anybody know what goes into the commercial products like "DeOxIt" and friends?

(some of which seem to sell for an arm and a leg, and also require more expensive or longer shipping)

I'm also wondering what's the best compound for getting old grease off?

Early on, I screwed up by trying a Radio Shack contact cleaner that is a lot like WD40 - into the bearings, etc. before really doing my research on it.. that didn't fix the issues and may have even made it worse..

Since then Ive tried to clean it with 91% IPA and that hasnt been really successful. There is a citrus based degreaser that Ive used on PCBs with decent success. (zep citrus degreaser which contains d-limonene and other chemicals http://www.homedepot.com/catalog/pdfImages/ca/ca91d217-a686-4142-ba23-71802e235447.pdf ) Its worked better for me on small PCBs that are fairly critical to clean well than isopropyl alcohol alone.. But of course contacts are different. I think the citrus stuff does contain a significant amount of water although they do claim its flammable.. It isnt sold to clean PCBs or do anything electrical, its just a good degreaser.. (also good for cleaning floors, bathtubs, etc)

I dont want to make the same mistake twice by using the wrong cleaner.. but it has seemed to work well (combined with a little brushing) for PCBs.

randsl · « **Reply #11 on:** January 17, 2017, 01:10:42 am »

What happens if we use WD40?

I can remember I've used WD40 to "fix" difficult to tune old transistor radios back in '90s. I made a small hole in the variable tuning capacitor plastic casing and sprayed WD40 while turning the knob back and forth few times. After that treatment everything worked well without a problem.

Ian.M · « **Reply #12 on:** January 17, 2017, 02:39:34 am »

WD40 is at best a poor lubricant. Its mostly Naphtha (lighter fluid), with a fairly small proportion of a sticky mineral oil. It tends to get everywhere you don't want it, attracts dirt, and the oil component readily oxidises, esoecially if exposed to ozone or ionising radiation to form a gum or varnish.

Its not bad for breaking down cruddy old lubricant and freeing off stiff moving parts - although plastics compatibility isn't wonderful, but unless you flush it out and re-lubricate with a more appropriate product its nothing but trouble. Its effectively addictive - once you've used it the mechanism wont stay working smoothly unless you either frequently give it another dose or get it 'clean' again. Also its low viscosity before the Naphtha has fully evaporated causes lubrication film breakdown and can cause rapid wear, especially of heavily loaded bearing surfaces.

1design · « **Reply #13 on:** January 18, 2017, 01:34:23 pm »

I am using this combination with very good results:
Clean surface: http://www.kontaktchemie.com/KOC/KOCproductdetail.csp?product=KONTAKT%2060
Remove cleaner: http://www.kontaktchemie.com/KOC/KOCproductdetail.csp?product=KONTAKT%20WL
Protect surface: http://www.kontaktchemie.com/KOC/KOCproductdetail.csp?product=KONTAKT%2061

Used it for trimmers, all sorts of connectors and contacts with long lasting results.

sidspop · « **Reply #14 on:** January 28, 2017, 11:32:28 pm »

I may be a little late in joining this thread. Try getting the caps Ultrasonically cleaned. Works wonders on crappy carburettors

cdev · « **Reply #15 on:** January 30, 2017, 07:51:51 am »

I wonder if this might work as an ultrasonic cleaner?

Flump · « **Reply #16 on:** January 30, 2017, 11:49:45 pm »

I have a palstar at2k which is a big expensive and well thought of atu

this is taken directly from the manual
Once every 4-6 months clean the roller coil with 70% isopropyl alcohol and a clean cotton cloth.
Do not remove the conducting grease on the rod that guides the roller wheel.
Do not transfer any of the conducting grease from the rod to the roller coil body,
as this will contaminate the windings.

phenol · « **Reply #17 on:** January 31, 2017, 01:02:29 pm »

BERULUB FK33 ....?

KD0CAC John · « **Reply #18 on:** January 31, 2017, 01:45:58 pm »

Using alcohol , what are the reasons for 70% vs. 99% ?

SeanB · « **Reply #19 on:** January 31, 2017, 07:27:33 pm »

70% will take ionic contaminants off which the low water 99% will not. The 99% ( you can get anhydrous ethanol by using calcium chloride, but that extra 0.6% is expensive, and 100% is impossible, it ceases being an alcohol) is good at removing non polar contaminants, but will strangely enough almost totally ignore ionic substances. You can store table salt in 99% ethanol with almost none of it going into solution.

KD0CAC John · « **Reply #20 on:** February 02, 2017, 12:19:01 am »

Thanks , another subject that I would like learn , chemistry .
What are some of the purposes of using 99% alcohol ?
On cleaning the inductor , DeOxit D5 is one of the highest recommended electrical contact cleaner for most hams / repair guys .
But double check , DeOxit comes I a large verity optional makeups .
If you can get a lint free wipe , I prefer just buying the liquid , and just use the spray to unreachable contacts .


EEVblog Main Site	EEVblog on Youtube	EEVblog on Twitter	EEVblog on Facebook	EEVblog on Odysee

Author Topic: how to clean/lubricate old variable caps and (especially) roller inductor? (Read 10885 times)

Share me