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How best to inexpensively clean degraded variable caps?


Steve Ratzlaff
 

Now we need to find the least expensive method of cleaning variable caps not requiring (very) expensive DeOxit spray cleaner. Would cheap drugstore isopropyl alcohol work well enough? Maybe used in a spray bottle? Or perhaps something less expensive from the hardware store? I don't have any degraded variable caps to test cleaning methods on, so someone else will have to try.

73,

Steve

On 7/10/2020 2:56 AM, Gary DeBock via groups.io wrote:
Thanks Steve (and Dave),

The possibility that the "Q" of older variable caps degrades over time because of environmental factors is interesting, and I appreciate your experimentation regarding this. That would certainly explain why the brand new variable caps from Mike's Electronic Parts always seem like hot performers out of the box, while the older ones installed years ago seem like duds by comparison. By coincidence I had replaced all of the variable caps in the larger Rockwork Cliff "DXpedition" FSL antennas prior to last year's trip, and did notice improved tuning performance.

<<<   This is beginning to lend credence to Dave Aichelman's comments about these caps seem to deteriorate in selectivity/Q when used in FSLs that are exposed to cruddy conditions such as coastal salt air, and that cleaning the cap can restore it to "as-new" condition.   >>>

I should thank Dave personally for this information, since during the past week I've had several requests from DXers who want me to replace the variable caps in their FSL's with the latest models, and now it seems that this type of work can be done by the DXer himself, without any effort on my part :-)

As for the "cruddy conditions" such as coastal salt air, Steve, I can certainly appreciate how that would accelerate the degradation of a variable cap. But in reality those kind of coastal locations frequently are ideal DXing venues for the compact FSL antennas, such as the wacky Rockwork Cliff in Oregon, where Tom R. has completely shattered the west coast record for South Pacific NDB's received during a DXpedition. Overseas salt water beaches are also prime FSL DXing venues, and they frequently combine extreme heat and humidity along with their salt air corrosion. I suppose it's a situation similar to pushing a race car constantly for top performance-- before you show up at a challenging race track, you need to "pay the piper" with new tires, new brakes and a perfectly tuned engine in order to be competitive. Before using FSL antennas at an exotic beach involving some serious travel $$, installing a brand new variable cap (or detailed cleaning of an old one) should be considered mandatory.

73, Gary

  


 


daiche
 

Hi Steve and all!

I first tried DeOxit D5, with a spray alcohol rinse afterwards and lastly spray air to dry off the residue. I have also tried spray alcohol by itself, which seemed to work fine by too. I always used spray air to blow off residue afterwards.

As far as what the residue is, could be salt spray, especially for those who hangout at ocean cliffside locations. I was thinking more the type of crude found in typical city pollution, which gets into everything over time and leaves a film. I will leave it to the chemists among us to figure out how it affects variable capacitors, but it seems to affect the Q, dulling the response. Sounds like we need a drive-thru capacitor washing service. I am sure there is lots of money to be made there, to freshen those dull variable capacitors! Your mileage may vary, depending on where you live and hangout. Ha!

Dave Aichelman     N7NZH     Grants Pass, Oregon


daiche
 

As far as expensive, yes DeOxit isn't cheap, but then it doesn't look like you need to buy a new capacitor at $20-$60 either and can refresh existing ones multiple times, instead of replacing. Alcohol is cheap and seems to work good too. Both can be used without cap removal in many cases. Dawn soap, water and a fine long-bristled brush would work too, but you would need to remove, clean, dry and possibly relube the bearings and gearing before reinstalling the cap. I like the spray clean and canned air dry method the best!

Dave Aichelman     N7NZH     Grants Pass, Oregon


Phillips
 

It would be good to prevent the oxidisation in the first place.   This would need a hermetically sealed environment with a desiccant but getting a device that needs manual operation into a sealed box is difficult.  

For the microcontroller-minded, a stepper motor,  EasyDriver module and code adapted from BrainyBits could be a good starting point for remote operation.  https://www.brainy-bits.com/stepper-motor-easy-driver/ The whole shebang could be kept in an air-tight box with only the controller and wiring being outside.  It does, however, put a substantial mass of ferromagnetic metal near the FSL.

A compromise might be to keep capacitor exposure to air to a minimum.  This means keeping the FSL in an airtight enclosure with desiccant as much as possible and exposing it to air only during use.  Won't eliminate oxidisation but should slow it down.

Back in the dimdarks, when vacuum-tubes ruled, we used copper sulphate crystals as desiccant to keep moisture-sensitive components dry.   When the crystals turned pink, they were refurbished by being dried out in a box with an incandescent lamp (only set fire to the workshop once).

 


From: main@UltralightDX.groups.io <main@UltralightDX.groups.io> on behalf of daiche via groups.io <daiche@...>
Sent: Saturday, 11 July 2020 4:19 AM
To: main@UltralightDX.groups.io <main@UltralightDX.groups.io>
Subject: Re: [UltralightDX] How best to inexpensively clean degraded variable caps?
 
As far as expensive, yes DeOxit isn't cheap, but then it doesn't look like you need to buy a new capacitor at $20-$60 either and can refresh existing ones multiple times, instead of replacing. Alcohol is cheap and seems to work good too. Both can be used without cap removal in many cases. Dawn soap, water and a fine long-bristled brush would work too, but you would need to remove, clean, dry and possibly relube the bearings and gearing before reinstalling the cap. I like the spray clean and canned air dry method the best!

Dave Aichelman     N7NZH     Grants Pass, Oregon


radiojayallen
 

De-Ox-It is not the best way to clean dirty cap plates...it is a contact cleaner/enhancer designed to improve conductivity between two metal parts. I have successfully cleaned caps in vintage radios with 91% Isopropyl alcohol, blowing it out with compressed air. This is cured several tuning caps that crackled when tuned or even shorted out in places.

i recommend 91% Isopropyl mainly because it leaves less residue than 70% which may have other additives in addition to water.

I HAVE used De-Ox-It on the contact points in tuning caps, using the pinpoint applicator rather than the usual spray. That has worked well.

Jay
https://radiojayallen.com


daiche
 

Thanks Jay!

I don't think I ever used DeOxit without a 91-99% wash afterward because of residue. However, it seemed that DeOxit might do a better job of removing oxidation if used first. The alcohol wash seemed to work just as well, as an afterthought, and is certainly less expensive and with essentially no residue at all. By the way, I use 91-99% spray alcohol as a 'dry cleaner' for clothes and such all the time and it is a good contact disinfectant in this time of Coronavirus too.....

Dave Aichelman     N7NZH     Grants Pass, Oregon


Gord Seifert
 


   I will (eventually) put a large two section variable cap, with three to one gear drive, in my ultrasonic cleaner and see what happens. It was new old stock, so it isn't decades old and covered with nicotine and such, but it has been sorely mistreated, having been damaged in a tip over of a box loop. That required many hours of careful 'forming' to eliminate contact between plates and equalize the spacing. It works fine now. I want to try it in an FSL once my ferrite rods and Litz wire get here. Then I will subject it to ultrasonic cleaning and see if I can notice any difference afterwards. I don't expect to be able to notice any difference at all, but I am willing to be surprized.

   BTW, I found 50 meters of 200/46 Litz for only $28 US with free shipping. Nice for an inexpensive  3 or 4 foot air core loop to compare to the FSL. https://www.ebay.com/i/163918891324?chn=ps?_ul=MX

   Regards,
   Gord


Guy Atkins
 

My method has been 91% isopropyl alcohol, using a long bristle, very soft brush for working the liquid down between the vanes. I don't worry too much about washing out the bearing grease as I prefer to just re-grease the pivot points (Caig De-Oxit L260D lithium grease) after blowing out the remaining alcohol with compressed air.

The thought of using a micro-controller and stepper motor (mentioned earlier) to move the variable cap makes me shudder at the chance of creating RFI anywhere near these sensitive FSL antennas, much less the introduced mass of metal nearby. This approach was something I tried years ago while trying to create a viable remotely-tuned FSL, but I decided the complexity of motors etc. wasn't worth it. Varactor diodes aren't worthwhile either, as have been discussed at length in the forum. It's tough to beat the excellent "Q" of a top-notch air variable cap!

A simple enough approach to give a modicum of weather resistance to the caps--and forestall weathering-- is to build the FSL components inside of a tote box. I describe that method here: https://swling.com/blog/2017/01/a-new-approach-to-fsl-antenna-construction/

73,
Guy Atkins
Puyallup, WA


Gary DeBock
 

On Mon, Jul 13, 2020 at 07:26 PM, Guy Atkins wrote:
It's tough to beat the excellent "Q" of a top-notch air variable cap!

Amen to that, home town brother!

The reality is that when you spend some serious vacation $$ to show up at an ocean side cliff and/ or exotic overseas ocean beach with FSL antennas and completely depend on the FSL's tuned gain performance to give you DXing success, you had better deploy with with the sharpest variable cap(s) that you can track down. The cost of all-new variable cap upgrades is always less than 10% of the total vacation cost.

Of course I'm aware that most FSL users chase DX with these antennas in the shack, under far less demanding conditions. A variable cap that has minor issues because of oxidation or a less-than-successful cleaning attempt is not going to be a major deal breaker in routine, home town DXing. It's only when you are trying for something bordering on the "impossible" in extremely tough conditions (like chasing African AM-DX at over 8,000 miles at sunset in Hawaii on a 5" FSL) that a degraded variable cap will almost certainly shoot you down. These receptions are barely possible anyway, even with superior propagation and a razor-sharp 5 inch gain antenna.

<<<   A simple enough approach to give a modicum of weather resistance to the caps--and forestall weathering-- is to build the FSL components inside of a tote box. I describe that method here: https://swling.com/blog/2017/01/a-new-approach-to-fsl-antenna-construction/     >>>

Guy's approach is good, and would stop any degradation due to salt water air exposure. Even in all the FSL antennas previously deployed to ocean side cliffs and overseas ocean beaches there has always been a waterproof vinyl covering designed to stop rain from throwing off the variable cap tuning, but obviously some oxidation has still been occurring over years of time, throwing off the variable cap performance somewhat. DXers can address this issue any way they prefer, but for the FSL antennas heading for the Rockwork Cliff DXpedition coming up soon, not only will the variable caps be brand new, but the FSL antenna designs will be brand new, developed during the extended tinkering hours of the Pandemic. These combine powerful tuned gain with much lighter weight (and much lower cost) than the 15" and 17" Monster FSL antennas used previously. Shown in the attached design photos, they deliver equivalent performance in a much more user-friendly package. Their construction cost would probably still derail most hobby budgets, but is less than half of the $1K Monster FSL's.

Gary DeBock (in Puyallup, WA, USA)    

   


 

I'm a disabled veteran and funds are very tight. I can't really afford De-Oxit but, I have found a viable alternative. I use CRC QD Electronic Cleaner and it works just fine. I have used it to clean recycled variable caps from old radios as well as normal use such as sticky and scratchy switches and pots. I think I paid around $4 for an 11 ounce can not too long ago.
73's
Ron