The AM Forum
March 29, 2024, 11:46:46 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1] 2   Go Down
  Print  
Author Topic: Capacitor plate corrosion  (Read 13558 times)
0 Members and 1 Guest are viewing this topic.
k7mdo
Contributing
Member
*
Offline Offline

Posts: 420


« on: April 23, 2014, 10:44:07 PM »

Browsing in my junk box I have been able to find enough parts for one of G3BDQ's SPC antenna tuners.  The only problem I have is that one of the variable capacitors has a little corrosion on the blades.  I am wondering what, if anything I can do about it or should I just look for another cap to fit the bill?

The cap is a Millen 16520-a and measures 14-209 pF.  I have others but none as close to 200 as this.

 The plate spacng of both of the shown units is about .085" and that should work fine for my 100 watt Johnson Viking II.

Any ideas of a fix or the severity of the problems I will face using the unit?

73, Tom


* Tuner cap 1.jpg (242.06 KB, 944x630 - viewed 476 times.)

* tuner cap 2.jpg (197.81 KB, 944x630 - viewed 509 times.)
Logged
KA2DZT
Member

Offline Offline

Posts: 2192


« Reply #1 on: April 23, 2014, 11:00:44 PM »

The cap is not that bad, I see no reason why you would have any problems.  You could try using a wire brush to clean it up a bit.

Fred
Logged
KA0HCP
Contributing
Member
*
Offline Offline

Posts: 1188



« Reply #2 on: April 23, 2014, 11:12:02 PM »

I would wash in warm water with dish soap, and dry in a warm spot. 

Do NOT use a wire brush.  This will scuff up the soft aluminum and create high points that will lower the arc voltage.  Use nylon brush.
Logged

New callsign KA0HCP, ex-KB4QAA.  Relocated to Kansas in April 2019.
W7TFO
WTF-OVER in 7 land Dennis
Contributing
Member
*
Offline Offline

Posts: 2521


IN A TRIODE NO ONE CAN HEAR YOUR SCREEN


WWW
« Reply #3 on: April 23, 2014, 11:27:43 PM »

You might pull it apart and hit it a lick with some mag wheel polish.  Shiny plates arc over less...

73DG
Logged

Just pacing the Farady cage...
Chuck...K1KW
Contributing
Member
*
Offline Offline

Posts: 167


« Reply #4 on: April 23, 2014, 11:46:17 PM »

Use as is...you will have no issues at all!  Compared to the air gap between the plates, that miniscule amount of corrosion is totally insignificant.

Best,

Chuck
Logged

73, Chuck...K1KW
flintstone mop
Contributing
Member
*
Offline Offline

Posts: 5055


« Reply #5 on: April 24, 2014, 06:39:19 AM »

A lot of directions to go here. I wouldn't do anything either, unless there is arcing.
Any rough treatment like a steel brush would not be good.
Cooking the unit in a pot of tomato sauce will get it cleaned up like new. The former HUZ man suggested that to me a few years ago.
Just rinse thoroughly and dry in a warm oven for a few hours. Check the lube in the bearings.
Fred
Logged

Fred KC4MOP
k7mdo
Contributing
Member
*
Offline Offline

Posts: 420


« Reply #6 on: April 24, 2014, 09:11:48 AM »

I do have stuff to etch and alodine aluminum...  so far from the posts, I think it would be just for looks.  It does seem like the other capacitor has an alodine tinge.

I think the tomato juice would etch as well. 

Anyway, thanks all for thoughts.  Tom
Logged
WBear2GCR
Member

Offline Offline

Posts: 4135


Brrrr- it's cold in the shack! Fire up the BIG RIG


WWW
« Reply #7 on: April 24, 2014, 09:35:34 AM »

Trip through the dishwasher might brighten it up... dishwasher stuff seems to have somewhat magic properties...

Lacking success with that, I like to use a slightly alkaline cleaner. We have a few brands around here, Mean Green and Thunderbolt are two. The next step up is "grille cleaner" which is more or less buffered Sodium Hydroxide (lye) and one level up from there is straight up spray oven cleaner... the last two yield a matte finish, but free of corrosion...

Have not done the acidic baths for aluminum myself, but have for steel/rust. Tomato juice is acidic.

                        _-_-
Logged

_-_- bear WB2GCR                   http://www.bearlabs.com
KA0HCP
Contributing
Member
*
Offline Offline

Posts: 1188



« Reply #8 on: April 24, 2014, 12:01:59 PM »

http://www.aircraftspruce.com/catalog/cspages/alumiprep.php

If you want to be professional, a bit of Alumiprep 33 and a nylon brush will clean this up in less than 60 seconds and leave a clean bright surface.
Logged

New callsign KA0HCP, ex-KB4QAA.  Relocated to Kansas in April 2019.
k7mdo
Contributing
Member
*
Offline Offline

Posts: 420


« Reply #9 on: April 24, 2014, 12:39:08 PM »

The capacitor has already been through the diswasher and it did clean it up a lot....  but I do have aluma-prep and will give it a dilute bath to see what happens... then a quick dip in the alodine.

I have a neat chassis that will allow a lexan front panel which will show off the internals of the tuner.  This is part of my reason for cleaning the cap up a bit....  and since the other cap has a tinge of color it would be nice if they both did... heck of a note when "looks" is starting to play a roll in these projects!

Thanks again, Tom
Logged
WBear2GCR
Member

Offline Offline

Posts: 4135


Brrrr- it's cold in the shack! Fire up the BIG RIG


WWW
« Reply #10 on: April 24, 2014, 10:03:56 PM »

Just to mention... that alumiprep stuff is 0.1-1.0% Hydrogen Fluoride.
Looked at the MSDS.
Forget about the high percentage of Phosphoric Acid, kids stuff there...

Exceedingly dangerous stuff.
Ought not to be used without significant care and safety precautions.

Jes' sayin...

                   _-_-

Logged

_-_- bear WB2GCR                   http://www.bearlabs.com
k7mdo
Contributing
Member
*
Offline Offline

Posts: 420


« Reply #11 on: April 26, 2014, 02:21:51 PM »

Yes, I am aware as I built a kit airplane years ago and got used to using the stuff "outdoors".  Oddly there are few warnings on the gallon jug itself.

On the capacitor corrosion, the etch (phosphoric acid) really cleaned up the vanes of the unit but of course did not really touch the corrosion itself.  And then curiously the alodine did not "take" to the vanes.  It appears the alloy used is not significantly aluminum.  I have seen this before.

All that said, the whole capacitor cleaned up pretty well with the processes and I am moving forward with the tuner and using it.

My plan is to use lexan (which I have a lot of) for the front so the concern was twofold in that I want the tuner to work but the capacitors inside the unit need to look good too!!

As any homebuilder knows, it is the sheet metal work and alignment of the parts that take the time!

73, Tom

Logged
k7mdo
Contributing
Member
*
Offline Offline

Posts: 420


« Reply #12 on: May 22, 2014, 12:32:15 PM »

Well, the tuner construction progresses!

I ended up not using the capacitor with the corrosion as it simply would not fit in the "re-purposed" housing I have on hand.

Even with my experience building things it still always amazes me how much time it takes to do the parts selection, the layout and the assembly.  I have attached the photo of the progress as of last night of the tuner as it is going together. 

I have not laid any wire in yet as I am not sure if I have suitable size.  I have 16 AWG siver plated copper but I think it is a little small for the application and I am now dithering on whether or not to just go to the hardware store an purchase some solid bare 12 AWG. I only have 100 watts to run now but maybe someday 200 or so.

I built the base and front out of lexan (scraps from where I work).  That solves some of the grounding issues in the circuitry.

Anyway, still having fun.

 


* antenna tuner 003.JPG (77.92 KB, 712x534 - viewed 564 times.)
Logged
N0WEK
Contributing
Member
*
Offline Offline

Posts: 790



« Reply #13 on: May 22, 2014, 06:32:11 PM »

Very  nice work...if something arcs in there you'll certainly know where!
Logged

Diesel boats and tube gear forever!
W3GMS
Contributing
Member
*
Offline Offline

Posts: 3063



« Reply #14 on: May 23, 2014, 07:19:09 AM »

Very nice work Tom! 

Yes, its amazing when you consider the number of components being just a few, how long it takes.   

When you get into the project details, especially when you want to make it look professional, the hours just fly away!

Now you know why the OT'ers just screwed stuff down on wooden boards!

Joe, GMS
Logged

Simplicity is the Elegance of Design---W3GMS
k7mdo
Contributing
Member
*
Offline Offline

Posts: 420


« Reply #15 on: June 04, 2014, 01:49:24 PM »

I have finished the preliminary wiring and testing of my NEW
antenna tuner... kind of interesting education.

What with all of the equipment I have now days, the testing has presented
some interesting results.

I have a non-inductive 50 ohm load on the tuner and my variable frequency
antenna analyzer feeding the thing... now the "theory" is (in my mind) that at any given frequency within the parameters of the installed capacitors and
inductors, I should be able to achieve, while tweaking the knobs, a
"match" which results in "1:1" SWR.

The reality is that it is not yet the case!  I am unable to actually get
very near the magic match between input and output and at this point I am
not sure why...  I understand that the range of the tuner is bounded by
the values of the inductors and capacitors but even when I get to a frequency where I start to get some appearance of resonance of the tuner it still will show
some reactance (unable to tune it completely out) along with some
approximation of 50 ohms resistive.

I am starting to wonder if my design limits the effectiveness or if I am
making some fundamental error in thinking about the way it works.

I have an input variable capacitor, an intermediate variable inductor to
ground parallelled with another variable capacitor to ground and then a variable
capacitor in line to the antenna (in this case the 50 ohm load).

Wouldn't you think there would always be some combination of adjustments
that would achieve a good match for any desired impedance?

Anyway, just rambling...  I will report my progress as I tinker with
the thing...  Tom
Logged
WD5JKO
Member

Offline Offline

Posts: 1996


WD5JKO


« Reply #16 on: June 08, 2014, 03:27:20 PM »


What with all of the equipment I have now days, the testing has presented
some interesting results.

I have a non-inductive 50 ohm load on the tuner and my variable frequency
antenna analyzer feeding the thing... now the "theory" is (in my mind) that at any given frequency within the parameters of the installed capacitors and
inductors, I should be able to achieve, while tweaking the knobs, a
"match" which results in "1:1" SWR.

The reality is that it is not yet the case!  I am unable to actually get
very near the magic match between input and output and at this point I am
not sure why...  I understand that the range of the tuner is bounded by
the values of the inductors and capacitors but even when I get to a frequency where I start to get some appearance of resonance of the tuner it still will show
some reactance (unable to tune it completely out) along with some
approximation of 50 ohms resistive.

I am starting to wonder if my design limits the effectiveness or if I am
making some fundamental error in thinking about the way it works.

I have an input variable capacitor, an intermediate variable inductor to
ground parallelled with another variable capacitor to ground and then a variable
capacitor in line to the antenna (in this case the 50 ohm load).

Wouldn't you think there would always be some combination of adjustments
that would achieve a good match for any desired impedance?

Anyway, just rambling...  I will report my progress as I tinker with
the thing...  Tom


  Tom, There are several antenna tuner topologies out there. I've never seen this SPC version used before. Is this what you are using:

https://rsars.files.wordpress.com/2013/01/spc-antenna-tuner-160m-6m-g3wme-1-31.pdf

The more common version is a simple 'T' network like MFJ and Heath have used for a long time. It would be easy to adapt yours to a 'T' as a test. My Heath 2060 is a simple 'T', and it does a pretty good job from 160-6m with my 80m OCF dipole. Many have criticized the 'T' though as it suffers from poor harmonic reduction since it acts somewhat as a high pass for the upper harmonics.

Then there is the old "Ultimate Transmatch" that has always done a good job.

http://www.arrl.org/files/file/Technology/tis/info/pdf/7007024.pdf

Go ahead and play with fixed resistors, like 47 , 220, 470, or maybe even 22 ohms. Using carbon film, carbon comp. Even a WW on the lower bands might be tunable. You should be able to get an exact 1:1 SWR null so long as your signal source is clean. If the signal source has significant harmonics present, then the SWR null will never get to 1:1.

Jim
Wd5JKO
Logged
k7mdo
Contributing
Member
*
Offline Offline

Posts: 420


« Reply #17 on: June 10, 2014, 03:24:06 PM »

I should have supplied the diagram in earlier post....  sorry, Jim.

The tuner is a copy of one developed by Jim Heys G3BDQ .... in about 1990.  It's claim to fame is that it does have a bit of capacitance to ground to provide a path for those pesky harmonics....  

I have played quite a bit with it both with a 50 ohm dummy and a 1/4 wave inverted "L" 80 meter antenna I use.... it is happy to provide an SWR of 1.5:1  but never closer....

The analyzer I am using is a kit one from Australia (VK....) and it would appear to work well in other applications so I doubt it is some fault of the analyzer.  

One thought I had while reading your post was that I should just lift the ground on the C2b capacitor, thus making it a "T" tuner and see what happens.  Tonight I will try it....

Thanks for your thoughts, Tom  


* Tuner diagram.jpg (134.74 KB, 944x630 - viewed 358 times.)
Logged
k7mdo
Contributing
Member
*
Offline Offline

Posts: 420


« Reply #18 on: June 10, 2014, 11:03:39 PM »

I lifted the C2b cap from the circuit and the result was pretty much the same....  I also tried a 400 ohm resistor as the antenna... same result... the SWR bridge will show only at best about 1.5:1 at any HF frequency I choose... other things look good... ie when I change to higher frequencies it requires a significant reduction in the number of turns on the inductor... by just about what one might expect.

I am in the process of working up an independent SWR bridge to cross check the unit...  the Viking II doesn't seem to mind some mismatch. (:>)

Tom
Logged
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 8308



WWW
« Reply #19 on: January 25, 2015, 05:57:24 PM »

Is this a good candidate for the above mentioned methods? It has not been washed yet at all. Want to know before I ruin a pot and stink up the place. I have vinegar handy, no tomato sauce right now but that I can get, and it is cheap. any brand?.

There's also this topic.

Is ultrasonic cleaning any good or will ruin it?


* capacitor-corrodeds.jpg (257.08 KB, 780x585 - viewed 377 times.)

* capacitor-corrodedc.jpg (456.27 KB, 937x751 - viewed 366 times.)
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
KA2DZT
Member

Offline Offline

Posts: 2192


« Reply #20 on: January 25, 2015, 06:30:27 PM »

Scrap it, the cap is in really rough shape.  Maybe take the whole thing apart and use Brillo or the other brand steel wool, you might end up with the best results with the steel wool.

Fred
Logged
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 8308



WWW
« Reply #21 on: January 25, 2015, 07:41:06 PM »

I've done good wet-polishing with the steel wool that has soap in it. Just thinking however to do that cap that way is about a gallon of elbow grease due all the separate pieces. If there's no better solution I'll save it for after the apocalypse when I have more time.

Maybe my friend's ammo brass polisher would help. I think it is functional.
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
KA0HCP
Contributing
Member
*
Offline Offline

Posts: 1188



« Reply #22 on: January 25, 2015, 10:12:57 PM »

Steel wool?  Argh!

The LAST thing you want to do is add more scratches and high points to condenser plates.  The manufacturer went to considerable trouble to tumble the plates in media to smooth it out.

Use a nylon brush and soap. 

Lye, such as Easy Off Oven Cleaner will also clean aluminum and slightly etch it. Don't leave on for more than a minute or two, then flush with copious water.  You can also use it to restore that original 'frosted' aluminum finish on IF cans, chassis, etc.

Logged

New callsign KA0HCP, ex-KB4QAA.  Relocated to Kansas in April 2019.
WB3JOK
Member

Offline Offline

Posts: 637



« Reply #23 on: January 25, 2015, 10:16:42 PM »

would it cause problems to gently glass-bead it?
Logged
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 8308



WWW
« Reply #24 on: January 26, 2015, 12:23:03 AM »

It has 0.2" spacing. I want to use it with a 4-1000 with 4500VDC on the plate. The cap would be isolated from plate supply DC by the existing doorknobs on the amp.
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
Pages: [1] 2   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone © 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.066 seconds with 19 queries.