The AM Forum

   Looking through a plastic bin of various high voltage transmitting type caps earlier this evening - doorknobs, micas, ceramics - and noticed a little drop of oily liquid on one of them. Traced it to a cylindrical axial lead cap: a Plessey, marked 20KV and 1000pf, with threaded studs on either end. Looks to be weeping around one of the studs. I've bought a few of these caps in recent years, at Nearfest. Not sure what the internal chemistry is - probably some sort of oil-impregnated paper or film. I don't get the impression that they're old enough to contain PCB's, but I'm being cautious.
   I usually associate PCB's with larger metal can capacitors, but I suppose smaller form-factor caps could have it as well. Anyone have any experience with this?

Found this picture:

I can't support it with footnotes and references, but it's my recollection that General Electric was the main maker of PCB high voltage oils and they marketed it under their Pyranol brand name.  I have seen one of the typical gray canister oil caps with a minor seepage that was identified to me as being PCB and it seemed to have a faint moth ball smell that is reputed to be a signal.  Not all oil filled caps have Pyranol and your unit may be good old highly purified mineral oil as there was much of that out there.
Proper chemical analysis would be more expensive than buying replacement capacitors.  Does any of the assemblage here have more info on who made PCB transformer oils?
73 de Norm W1ITT

I recall working on several power supplies for our old SYA-4 PPI's having axial capacitors with PCB oil in them. They were actually sealed in glass with O-rings at each end but they were rated at 7KV and were of the same size as shown in the photo. The SYA-4 system came out ~mid 60's and I worked on them from 1982-1987 without any failures.

Certainly spending the money on getting the leakage analyzed isn't an option. I'm not going to worry much about it, either; PCB hazards are mainly related to long-term exposure. This is probably just mineral oil, anyway. I've cleaned up the small amount that leaked, tossed the offending cap, and that's it. In the meantime, just to satisfy curiosity, I'll keep my eyes open for some actual specs on that part.

PCB oil falls into the same category as asbestos and lead.

Don't stir, grind, breathe, or eat it purposely and you'll not have a problem. ::)

It's not like the critter in Alien, just waiting to jump on your face and burrow in. :o

73DG

Like the Heathkit SB-230 linear amp, with the beryllium oxide heat sink. It amazes me how many hams I've come across who were really freaked out about that stuff. Beryllium oxide in its solid form is not even considered hazardous waste; you can legally toss it right into the trash bin; even dunk it in your cornflakes if you took a notion to. Now if you took a die-grinder to it and blasted the dust all around your shop - especially on a regular basis - that's a different story.

There is a guy on the web selling a steampunk art made of half of a 4CX250B he has sawn in two with some sort of low speed diamond saw.

He claims that there is no hazard from the BeO during or after this process. Here it is:
https://www.ebay.com/itm/273863615778

I do not know what to say. I don't want one. I have whole ones and they work much better.

as far as axial caps, I have had some that felt oily or greasy but nothing around the cap was soiled/oily. If it seemed the stuff was coming from the cap then I replaced it. It's simple to wash hands if there is a concern.

I was directed to the website below where the fellow has laboriously investigated what sort of dielectric assorted brands and models of tubular capacitors use.  I think I bought some Russian .01 mfd caps on eBay years ago which now may be revealed as paper types.  Blast it.

http://crasno.ca/articles/capdielectrics.htm (http://crasno.ca/articles/capdielectrics.htm)

Well, it could also be a Class I ceramic pile (multi-layer) doorknob.

Phil

AFAIK, the ceramic tubes, including the 4CX250 use regular ceramic, not Beryllium Oxide.


                            _-_-bear

I could swear I have seen the BeO warning on the sheet that comes with a new one. LOL next time I poen a NOS canned one I'll confirm or deny.  Could have been some other tube.

Patrick,
I do not believe that you are wrong on this. I began using 4CX250Bs since 1964 and the label in the Eimac package warned that one should never cut or grind the ceramic insulator because it contained BeO and that it was toxic.
I think that I still have a couple of surplus 250s still sealed in the brown foil paper.
I will see if the label is still in those tube packages.

I would never cut or grind or even hit the stuff after the Eimac warning, even after 58 years. 😬😉
I will also get back on this. What are the chances two separate old geezers would suffer the exact same delusion-right? 😉😂
73, Mike

Possibly so! Some newer parts might use aluminum oxide ceramic which has poorer heat transfer: 30 W·m−1·K−1  vs.  330 W/(K·m) for beyrillium oxide. I don't know which.

LOL every time something works best, it gets banned by the freakout folks because it's bad when interacted with by the hoi polloi. The result is things that work poorly and have higher cost of ownership.

beyrillium oxide on big tubes with handles
carbon tet toothbrush for scrubbing Ward-Leonards
R-12 that keeps me on ice all night long
These are a few of my favorite things

PCB oil in my caps and transformers
1-1-1-trichlor for cleaning those sliders
Radium dials for a simple check source
These are a few of my favorite things

Yes, the whole point of BeO was that it was a great heat transfer material compared to other ceramics. Seemed like a small price to pay, not to. Grind aroumd on it to have reliable seals that were far better than the old glass metal seals.

Yes- all those effective chemicals plus Methyl Chloride, Carbon tetrachloride, and glove muffs made of asbestos. It is a miracle that all us ole geezers are not dead or our brains are eaten up….. or maybe that is what is wrong with my memory?? 😉😂😂
Kids dug asbestos out of steam pipe bundles and stuffed it down other kids shirts when I was in grade school- who knew?😉

Ok- finally located the Eimac warning text that Patrick and I were remembering about BeO ceramic.
I know it speaks of conduction cooled tubes, but tjis was in the 4cx10000a datasheet which uses fins, not conduction cooling, but apparently has BeO in tje Ceramic seals. BeO was used for it’s thermal conduction characteristics
See the attachment. 73, Mike