[ARC5] Restuffing electrolytic caps - it won't work??

[Mike Hanz]

On 6/1/2014 4:52 PM, Kenneth G. Gordon wrote:
>> My problem with this:  When drilling out the old cap guts,
>> I can smell and even taste chemicals from inside them
>> which become aerosolized during the drilling.
>> I have no idea what I'm breathing-in during this process,
>> but I don't like it.  Anyone know if my head is going
>> to turn green and fall off??
> Probably. I sure as heck wouldn't do that.

I realize that the conventional wisdom these days suggests we all wear 
Hazmat suits whenever we enter the radio shack, but AB5S's experience 
prompted me to investigate the composition of electrolytic capacitors 
back in the early 1940s, and to dissect examples of both the 5uF and 
15uF caps in question.  It's easy to peel back the onion layers with a 
lathe and boring bar.  Here's the construction that I found in the two 
examples:

After removing the top using the pipe cutter tool, you are faced with 
the picture at http://home.netcom.com/~arc5/Restuff/IMG_3116.JPG  The 
reddish disk with the eyelet connection on top is actually made from red 
pigmented rubber - basically a red rubber washer 1/8" thick.  The next 
layer underneath that is a similar thickness disk of phenolic. This is 
where the smell come from - anyone who has drilled or machined phenolic 
is familiar with that lovely aroma.  It's also where the yellow 
"cornmeal" stuff comes from as you drill down through it.  Beneath that 
is a paper insulated rolled capacitor. Henney's Radio Engineering 
Handbook (1941) advises that this design is the latest in technology for 
electrolytics, and is composed of tightly controlled thickness aluminum 
foil that has been etched to increase the surface area, and the 
electrolytic portion of the paper dielectric is...are your Hazmat suits 
sealed?...wait for it...apparently just ionized water!  Placing a drop 
of the fluid in the can on a freshly sanded steel surface produced 
fairly quick rusting.  Okay, Hazmat suits off...:-)

At the bottom is a slim (.030" thick) circle of phenolic to insulate the 
bottom side of the rolled capacitor from the bottom of the can. Though 
not relevant here, Henney also advises that normal oil filled paper 
capacitors use either castor oil, cottonseed oil, or "transformer oil", 
whatever that was in 1941.

As Dave mentioned, the aluminum container for this concoction, including 
the top rubber washer, is pressed into the brass shell of the 
capacitor.  The connection of the outer foil to the aluminum can is 
apparently just direct contact with the can for 360 degrees.  The inner 
foil connection is through the eyelet.

I did not remove the pressed-in aluminum cup from either capacitor since 
everything came out so cleanly, but there is no other apparent ground 
connection - which begs the question of why there is a ground solder 
blob between the two screw posts on the bottom of the capacitor.  I 
hated to destroy one of these two examples, since they are prime 
material for restuffing.  I suspect there is a simple pressure contact 
in the bottom of the cup that enhances the ground connection of the 
inner can, but it will have to wait until I find a more suitable (badly 
corroded) example to investigate.  In the meantime, I would suggest 
simply solder sucking the blob off the bottom and drilling a .030" hole 
through the bottom of the aluminum can for the ground lead of the 
restuffed caps, then resoldering that ground lead like the original.

I'll put some photos of this dissection up at 
http://aafradio.org/garajmahal/Removing_command_receiver_capacitor_tops.html 
later on today when I get some time.

73,
Mike  KC4TOS