Tuesday, May 15, 2012

interesting pulse capacitors

I picked up a few interesting capacitors at a local surplus store recently. It's pretty rare for me to bother carting home Yet Another High Voltage Capacitor these days, as I now have fairly narrow interests and very specific projects which make the vast majority of HV caps of little use to me. I've been enthusiastically getting rid of a great many large units in fact.

The first item is the one I'm most interested in investigating. The basic specs are there on the label. We don't know things like self-inductance, but given the apparently coaxial termination and the cylindrical can, and other clues (such as the areas of expertise which Reynolds-Teledyne has demonstrated over the years) lend one to believe it's a very fast cap indeed. Can you say "firing circuit assembly"?

Given what RI do for the defense and aerospace industries - having practically invented the EBW detonator, I would not be surprised to learn that this cap was an EBW initiator for say, explosive bolts somewhere. It doesn't have the look of flight hardware.

EBW caps can be made much smaller and are often made of film-and-foil with "wrap-and-fill" construction. RI sells those too.


Some salient features of these odd little beasties: the can is solid brass. The tip-offs (three on each can) are crimped and soldered. The can is very heavy, I strongly suspect oil backfilled under vacuum. The insulator on that connector is alumina ceramic. I doubt it's a standard connector. It is not immediately apparent to me whether the connection is meant to be coaxial, but the bare raise ring around the base of the alumina insulator - which is soldered to the can - suggests it might be. There is obviously another terminal connected to the case.

I don't know the diameter of the inner pin yet, I'll need to go at it with a selection of socket contacts. I can't get a pair of calipers in there.


I'll probably go through the motions of asking the Reynolds Industries division whether they have a company historian who might be able to help me out, but I would bet lunch that even if they have records of this old product somewhere, they might not be allowed to tell me anything about it.

I've got two of those little gems.

These next items I include more to show what's possible when scrounging of exotic parts than any other reason.

They are only mildly interesting reconstituted mica capacitors. They are not super-low inductance, they are obviously not intended for high currents (look at the lead size) and because of recon mica's poor loss tangent, it's unsuitable for RF or high rep-rate devices.

But recon-mica has a few singular advantages as well: tolerance to high heat and voltage reversal and other electrical abuses. This latter property of being a really robust dielectric in nasty electrical environments makes it nice for single shot pulse devices. It can be used to build higher current, lower inductance devices, these just don't happen to be that sort.

When I got these, the bigger one had a lead broken off right at the surface of that red epoxy. Annoying, but not a show-stopper, if the item itself is worth an hour or so of time. I felt it was. Dig down around the lead very carefully with an X-Acto knife (if you haven't got a working Dremel tool, which I hadn't) until you've exposed a 0.1" or so of lead. This is aided some what by the fact that the epoxy tends to have crept up the leads a bit during manufacturing. Solder on a new lead, then throw some epoxy (I'm fond of J-B Weld for many such purposes) around it to support everything mechanically. I decided to just replace both leads with stranded insulated wire.

Spending most of my time looking for work right now. More as it happens, but progress on science and hobby stuff is once again glacial until income comes back up. Mostly I have been pushing the gas handling apparatus needed to test the new switch, as well as back of the envelope design stuff for the water (load) resistor and agonizing over what to use for a trigger source.

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