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Oil cap questions

8/29/1999 2:27 PM
Pat F Oil cap questions
I remember some time ago, R.G., I think made some remarks about the large oil filled caps being good for tube amp power supplies. I found cases of these things at a local electronics salvage place. Most of them are 16uf, rated 480 VAC? These are new and they want $3.00 each for them. My question is, if they are rated 480 VAC, what does that translate to in VDC? And are there any premade mounting type clamps for these? They are quite large.
8/29/1999 2:59 PM
Michael Cameron

Pat, I have seen folks claim that you can go 40 to 100 per cent higher for dc than the ac rating of the oil cap. You should be fine treating these caps as 650vdc caps. The clamps are available from Nebraska Surplus, or you can make your own if you can braze some flat stock steel to a bolt. Nebraska Surplus 1-800-244-4567. Great Catalog, takes for ever to get though. $3 bucks is a pretty good price for the caps if they are in good shape.  
If they don't say NO PCB'S on the caps you can assume they are filled with PCB tainted oil., if they start leakin, do not touch the oil , it is carcinogenic.  
8/29/1999 3:13 PM
Pat F
Thanks for the pointer about the PCBs Mike. I'll keep that in mind. These are all brand new (in the original cardboard cases). I'm assuming that since these aren't like standard electrolytics, they don't have to be reformed since the dielectric is the oil, right?
8/29/1999 5:09 PM
Michael Cameron

Yup, no need to reform an oil cap. Since my last post I just stripped some old theatre amps. Loaded with oil caps. They were rated 660vac/1550vdc. Anyone want to build a PP 805 guitar amp ? Sucker had 1500 volts on the plates.. Wow!  
later MC
8/30/1999 12:13 AM

q}Anyone want to build a PP 805 guitar amp ? Sucker had 1500 volts on the plates.. }  
HOLY "HIGH END" BATMAN! that sounds mighty harsh on the ears from here (ha, ha)  
8/31/1999 8:43 PM

This type of capacitor can be subjected to much higher ripple current than electrolytics. They are ideal for the first filter section after the rectifier where the greatest ripple amplitude is present, and will have a net smoothing effect of electros 3x their capacitance. I have a load of old caps like this, and so far not a one of them has leaked any oil. I guess if they were made today in some low labor rate country, they wouldn't remain as leak-tight. One thing about the US...they do (did?) know how to make a good sheet metal can.
9/1/1999 10:25 PM

Hey Doc - owe you an e-mail or two, but..  
A question: Is there any initial differenece in the charging current that an oil cap draws, i.e., is there any adjustment that need be made in the value of the first filter following a tube rectifier?  
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