The AM Forum

I recently acquired a very nice Millen HV power supply.  A few days ago, I found that one of the 0.5 uF @1KV oil bypass caps has shorted terminals, and so HV was shorting to the chassis.   I removed the cap and of course, the fault cleared.

Purchased a similar cap on-line.  It's a near-identical GE "Pyranol" type but unfortunately one of the corner seals has a hairline crack and a small amount of PCB oil is leaking to the surface.  I would like to keep the discussion focused on repair and not get into a long dissertation about the hazards of PCBs, environmental disposal procedures, etc.  I'm familiar with those issues having disposed of several hundred pounds of PCB caps through a GE-contracted vendor back in the early '90s.     

Is the sealed end of the cap made from tin or some alloy that will allow for re-soldering?  If not, has anyone tried using an epoxy as sealant.  Finding one of these caps with the right mounting structure took a lot of time; it was much harder to find a used replacement than I first thought.  I know I can find a modern equivalent, but for several reasons, I would like to keep the supply as original as possible.  Clearing out the inside of the cap and re-stuffing is not an option.

Apart from not using the cap at all, anyone have any other suggestions?

Paul, W9AC

I have soldered them up before   (CHOKE...Gasp)   do it where the smoke goes somewhere besides your nose....Good Luck

Out doors with a gentle breeze.  To make sure maybe you should start a smoky fire in a safe metal container as a sign where the wind is blowing.

Then using a big iron so you can get in and get out in a hurry, seal the leaky spot with solder.  You'll never get epoxy to stick what with the leak that has left a film over everything.  I'd wash that sucker well in some sort of detergent afterwards to make sure you have gotten rid of everything.

I'm assuming, of course, that the leak is minimal.  Otherwise, how about using eBay to find a healthy replacement?

Al

Hi Paul,
use a magnet and test the case. If the magnet attaches firmly to the case of the capacitor, it is likely to be a carbon steel alloy. Epoxy or acid core solder are both good fixes I would think of. It depends on where the crack is and how accessible it is. Was the crack caused by stress being near a mounting stud? Is the leak at a seam?

I would say if the crack is in the open I would sand and clean the area and solder the crack using a very hot iron, acid paste plus lead/tin 60/40 solder. If you choose epoxy, consider using a wire drill bit (.030" or so) with a manual pin vice. Drill a hole at each end of the crack. rough up the cleaned area to give the glue something to hold on to. A very good idea when using glue is to cut a patch out of a steel can. flatten and rough up both sides, cover the crack. Use glue on both sides of the patch. The small holes at both ends of the crack will stop the crack from getting longer and give the glue an anchor.

Good Luck!
Mike

Been there with an pyranol oil cap from a Johnson KW. Set the cap with the leak area highest. Clean with MEK, outdoors with plenty of airflow! MEK will dry very fast. If this doesn't remove surrounding paint, sand until paint is gone. Repeat MEK. Have a two part mixture of JB Weld ready to go. Spread JB Weld with leak area highest. Let set 24 hours.

NO LEAKS since. Note: On the Johnson KW the oil cap is held in place with two metal clamps. Do not over tighten, the cap grows as it warms.

Craig,

I've used engine degreaser to clean 'em. Then grab your American beauty and slober.



KLC

Thanks to everyone who replied.  The seals were definitely soldered.  I cleared the paint around the edges and what few small flakes I didn't get, the 200-watt Hexacon iron did. 

After heating the perimeter of the seal and applying solder, it's holding and the cap still measures fine.   I did use surgical gloves while working around the oil and avoided inhaling the smoke while soldering. 

Paul, W9AC

Be aware, GE Pyranol is PCB’s  . Nasty stuff and health hazard. ST

Also, Westinghouse ‘Interteen” is also PCB oil. Skull and cross-bones