The AM Forum

I've bought a couple large (7KV) EF Johnson bread-slicer capacitors.  The model numbers are 350D70 and 500C70.  The plates are pretty hefty, and the airgap on both is .175".  They turn freely, and only one of them needs a little plate alignment work (plates don't look bent).

Planning on using them in future E-rigs, but they're both pretty grungy.  Looks like they've sat uncovered in a garage for 40 or 50 years, including a few small areas that are slightly corroded.

So, I'm looking for some experienced advice on getting these things cleaned up and restored for high voltage service.  I prefer not to take them apart, but listening for the voice of experience!

Thanks, Karl

People run them through dishwashers with dishwasher detergent, and I hear good reports on the results.  Disassembly results in more uniform cleaning.  If you disassemble them before cleaning, use some sort of porous bags or containers that will pass the detergent and water, but contain the small parts.

I've heard of people soaking them in tomato juice, then washing them off...  gotta try it someday when the warden isn't home  ...... klc

I would take them completely apart and get scotch brite pads. polish them then reassemble. Very easy to do. You can run the parts through the dishwasher to get the heave crudd off. Don't do it if there is any mouse droppings on them.
With mouse droppings take dishwashing soap and throw them in a bucket of hot water and soak them. All the screws are brass so don't crank them up tight or they could snap. I use anti seize on all threads. The insulators have soft washers on either side of them so they wont crack. If they are damaged make new ones out of thin G10 or plastic/nylon washers.
They will look like new when you are done. gfz

i spray them with 409 let them sit for a few minutes then the dishwasher. When done from the dishwasher RINSE THEM WELL with hot hot water and shake them dry. You MUST get ALL of the detergent off of them or they will corrode. Once they have air dried completely put a few drops of light oil on the bearing surfaces and ur good to go!! Complete dissasembly is too much like work!! I only do that if I'm trying to save one that has nasty zorch-over marks and zots on it.

                                            the Slab Bacon

Frank, 409 in the dishwasher...that will make your egg plant taste good. I would rinse it off real good before I put in with the dishes....

409 is a great cleaner!

Scotch brite will polish off all arc marks and a small fine file will take off the real deep pits.

Poooey!!, now you know my secret ingrediment...................................

A slow simmer in the tomato sauce for a couple of hours is the way to go. Taking it apart invites more problems down the road. Just force some grease into the ends and make sure there is a good connection for the "ground side"
Looks beautiful. The sauce tastes funny though...............hi
Fred

Nothing like a little Aluminum Oxide to spice up your Spaghetti Sauce it adds a little bite to it!

Hey... since aluminum makes solid rocket motors burn hotter... I wonder what it'll do for my chili ?????

Big Johnson caps come apart very easily and a no brainer to reassemble. 

Hmmm.. Might be the answer we're looking for in alternative transportation! Eat a bowl of Chili in the morning, and launch yourself to work! Don't forget to bring some for the return trip!

Well,

I wasn't expecting to get such umm, interesting recipes from this post. :o    Guess it's my fault for using the term bread-slicer!

Seriously though, thanks much for the info.  Probably one will clean up nice without disassembly, and the other may have to come apart.

Thanks again,
Karl

Hey Karl,

I've been using wire wheel and spoke cleaner from the automotive store. Rinse well and dry thoroughly.

whats needed is a slyentific test
one with tomato juse
one with pisolene
one with nothin (the control)
run 'em all through the dishwasher.....   maybee time to go digin....   klc

The EF Johnson caps are a no-brainer to disassemble and re-assemble, but a REAL pain to align so that the spacing is the same between all the plates.

You need a perfectly flat surface to get all the rotor plates aligned with each other.  I use the platen from a defunct table saw.

With a split stator, the  challenge is to get the capacitance in each section exactly the same, so that both tubes in a pushpull amplifier run with balanced plate current.

If the plate spacing is not the same on each side of each rotor plate, the voltage rating of the capacitor will be degraded.  Sometimes, after everything is assembled and aligned as best possible, as a final adjustment you have to slightly bend some of the stator and rotor plates to get the spacing exactly right.

The split stator plate cap in my HF-300 rig is spaced at 0.175".  It is 240/240 pf.  Not a standard value from the factory, because I built it out of parts salvaged from three separate EF Johnson variables.  The rotor shaft, the rods that hold the stator plates together and the four connecting rods that go between the end plates came from a 150/150 pf BC-610  plate cap.  The ceramic insulators and end plates and rotor and stator plates came from a single section 500 pf @ 0.175" and a 50 pf @ 0.375".  Both capacitors were needed to get enough stator and rotor plates to fill the BC-610 cap with larger plates.  Once I got it assembled, it took a lot of tinkering to get the plate spacing between all plates even, and to maintain identical capacitance in each section throughout the capacitance range.

Another problem with my homebrew job was that one of the cannibalised capacitors was an older model than the other.  The ceramic insulators on the older and new ones are not the same. The older ones are perfectly rectangular, while the newer ones are tapered towards the ends.  The two are not compatible in the same capacitor; mixing them up will make the cap impossible to align.  Fortunately, I had another large EFJ capacitor with the older style insulators.  I swapped out the insulators, without having to cannibalise the fourth capacitor, giving me 4 identical ceramic insulators.

90% of the capacitors I see at hamfests are visibly out of alignment.  I wonder how many came from the factory that way.

If you disassemble an EF Johnson transmitting cap, don't lose or omit the little black or white fibre washers that are inserted at the ends of the long connecting rods, between the rods and the end plates, and under the screw heads on the outside surface of the end plates.  They serve an essential purpose. Those are insulators that isolate the connecting rods, the screws and the end plates from each other, designed to break electrical continuity, to prevent circulating currents through the frame of the capacitor.  Larger Bud and National capacitors use ceramic spacers for this purpose.

Don,
I do the same thing and have built a number of caps from parts. I rearrange the two section cap so there is a low C section for 20, 15 and 10 then switch in the rest of the cap for the lower bands.
I have a life time supply of cap parts.

Tomato Juice is actually not as wacky as it sounds--the active ingredient being the acid in the juice. A less messy source of FB cleaning acid is to purchase Citric Acid powder (I used to get it at the apothecary) and use it in lieu of dish-washing powder. This will do 2 things--remove the scum form your dishwasher (works good in coffeepots too) and give you some really clean radio parts.
I think Dow chemical actually patented this at one time for cleaning pipes in industrial applications.

more than we all wanted to know

Hmmm.. Eats oxidation and gunk in pipes..
No wonder Tomatoes give me heartburn! LOL

In the past i've used various industrial citris degreasers.  One application was to clean out vent ducting and the louver assembly. Most of the assemblies were painted and were not damaged. Wish i had saved some of it. Its nice ' caus you can cut it with water for the proper strength. The stuff works good, and is is generaly "envyronmentally friendly".. The profit AlGore would be proud.... ..             klc   prophet in the suberbia

I wonder what temperature Al and Tipper keep their house at and the R value of their insulation....

I have no idea...   but,

"Public records reveal that as Gore lectures Americans on excessive consumption, he and his wife Tipper live in two properties: a 10,000-square-foot, 20-room, eight-bathroom home in Nashville, and a 4,000-square-foot home in Arlington, Va. (He also has a third home in Carthage, Tenn.) For someone rallying the planet to pursue a path of extreme personal sacrifice, Gore requires little from himself."   http://www.usatoday.com/news/opinion/editorials/2006-08-09-gore-green_x.htm


                 I always like a person with firm convictions.  that and a willingness to lead.. Like Jimmie Carter wearing  a sweater in the White Hose... 

and to be fair    "Sometimes celebrities do decide to just stay put--in which case, they're like to gobble up the neighboring properties until their once-modest single-family home has been inflated into a gigantic estate, eating up several plots of land. Radio-show host Rush Limbaugh, for example, who made our list as the 20th most powerful celebrity, started collecting the real estate surrounding his West Palm Beach, Fla., house in 1996, and now he reportedly has amassed five lots, which collectively are appraised at upwards of $26 million.                http://celebritytoys.com/homes.htm


I'm just sorry I CANT own one of the above homes !!!

Just one of the little people. I guess this is the type of home we could get    "A cardboard house places the least demand on resources and encourages people to shift their preconceptions about the “typical Australian house”.   Now to grab an oil can (Fosters) and chill out...
klc

I realize that it may be a very simple process to disassemble the slicer, but as Don mentions NOW you have possibly opened another can of worms for alignment and the degradation of the voltage rating of the cap.
The Tomato sauce works soooo well.
Fred

I think you're right Fred.  It wasn't the re-assembly that had me worried, it was getting the plates aligned correctly in the process.  After all think of all the caps you've seen over the years that looked screwed up...  Would they have looked like that if it was easy?

What I'm dealing with here is more grunge than corrosion.  I'll start with plain water and go from there.  The problem will be nooks and crannies.  If that doesn't work out it's the dishwasher or mamma's sauce pot.  The tomato sauce is good for eating at the aluminim oxide I assume, but is it also effective at de-grunging?

The one that I'm considering taking apart already has alignment issues, so if it won't line up without dissembly I'll just have to do it.  Good info from Frank and Don if it comes to that..


Thanks,  Karl

Westley's White Wall cleaner will clean it almost instantly.  Rinse well afterwards!

Toss in my 2 cents...

My faves for aluminum clean up are (in order of decreasing nuclear activity):

- oven cleaner (rinse after a short bit, eh?)
- industrial floor "degreaser" (an alkaline cleaner of some strength)
- "grille cleaner" (a step under oven cleaner and different formula than the above cleaner)
- Mean Green or '*something* Thunder' "degreaser/cleaners" (strong consumer alkaline cleaners) or similar brands
- Fantastik
- 409

I think these are are alkaline cleaners.

I have heard that people get very excellent results using Salt + Vinegar.
This supposedly cleans rust off steel and iron exceptionally well.

Tomato juice, of the canned variety, has both salt and citric acid... fwiw. Similar.
Works great on copper & brass btw!

            _-_-WBear2GCR
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