New Chassis Fabrication Pics and Capacitor Question

[Vespasian]

Having a great time with my latest project and wanted to show off a bit with a couple pics. I was going to try a hole saw but a friend let me borrow an old punch and it is working out ok...








Re: Vintage Caps
I'm thinking that it's not a good idea to rely on any old capacitor to perform properly but was wondering, if I attach one to 300vdc and put a 10ohm between it and ground and measure 5mv, can it be considered ok? The CP Manufacturing multi sections work great but the prices aren't cheap.



This PLANET was guaranteed for a whole year - back in 1960...


Cheers, Ed

[Brian Beck]

Originally posted by Vespasian
This PLANET was guaranteed for a whole year - back in 1960...

Well, that's easy. Just mark out the old date code with a marking pen. Make it 2007, and you're good for another year

[kevinkr]

Seems like you are going to a lot of effort just to have to replace all of those caps in the pretty immediate future. I just trashed a huge stash of these things because I don't believe they would be reliable in service. Some of them reformed ok, but a lot of them didn't.

You're asking a lot of 47 yr old cap whether used or not. They're too old! Rated shelf life was just a few years, and anything over 5 - 10yrs old is very iffy. They aren't perfectly hermetic and still dry up over time, it just takes longer when not subjected to self heating or external heat sources.

I'd use some of the current crop of JJ multi-sections, they're inexpensive and readily available. Dual sections won't cost you more than $8 - $9 if you shop around and last a lot longer IME than the current expensive FP twistlocks that seem to be good for about 5yrs or so.

Another excellent option are Solen films purchased directly from Solen in Quebec.. This is my preferred choice and should last a life time without replacement barring mis-haps. They aren't expensive either when purchased in reasonable quantities.

[frank754]

That's what I was wondering too, are NOS can caps which are 40-50 years old but never used, trustworthy in the long run, or can they fizzle out at any time due to the technology and age?

I've also seen "new" can caps they say are very recently made but "made on original Mallory equipment", not cheap. Does this give them a nice 30-40 year run, or is the technology still a bit inferior to new-design caps?

Among my old radios, I've got two (one a Westinghouse dual band from 1938, and an Emerson 78RPM AM radio with 78RPM phonograph from 1940), both with old can caps and original paper, but they both work fine, though I'm in the process of putting in new caps under the chassis and just leaving the old cans for appearance.

[SY]

Electrolytes dry out over time. Nothing to be done about it, just trash the old caps. Modern cap technology is vastly superior, so take advantage and put in better, more reliable caps that are smaller. I use 105 degree rated units exclusively. JJ are very good, so are some of the Chemicon series (e.g., KMH); both are very reasonably priced. And they'll go at least 10 years unless you abuse them.

[stokessd]

I wouldn't waste your time with antique electrolytic caps. I sell a lot of circuit boards to replace old twist lock caps with modern PC mount ones. People aren't buying them because their caps are good. You've put a lot of time and effort into your project so far, you should use good modern caps. Aside from the reliability issue, modern caps are just plain better caps than the old ones.

Sheldon

[frank754]

Great, thanks, that was my general impression.
For real "purist"- type folks, I've also read a few articles about taking apart the old cans, scraping them out, and putting modern components inside. That's another route, but it sure sounds like a heck of a time-consuming job...

[tubelab.com]

Modern caps have a much lower ESR and hold it over a far greater frequency range than the old stuff. It is also possible for the old caps to develop leakage current as they heat up, which then causes the cap to heat up more, raising the leakage current. Every once in a while one will catastrophically fail. They usually spew their guts out the bottom, but I have seen the can explode. The "stuff" inside is caustic and will really mess up your amp. When repairing vintage equipment, I mount a modern Panasonic electrolytics on perf board under the chassis, and leave the old ones on the top for looks..

I saw a quart size "computer grade" electrolytic blow up violently enough for pieces to penetrate the side panel of the rack and imbed into the adjacent wall. This was a large industrial UPS on the factory floor where I work. The rocket scientists that designed it had 4 large caps wired across 84 volts worth of car batteries with no fuse.

[stokessd]

I've done the scooping out thing, it's a nasty job, but not very hard. The cool thing about technology advancing is that you can easily fit the same capacitance in the can with room to spare.

The hardest part of the process if gently unwrapping the crimp at the bottom so you can reuse it. I would run a bead of JBweld around the re-crimp for integrity when I was done.

I only did the re-capping a twist-lock can a few times (one was all 5 cans in a Citation II), then I started to put circuit boards under the chassis.

Sheldon

[Vespasian]

Thanks for the advise gents - I do have some JJ's and CP Manufacturing multi sections put aside for this project and plan on putting them inside the chassis as it is 3 inches deep.

Kevin, Sy, I will check out the solens / chemicons next time I need to order something - thanks.

But regarding my test question, would like to have a reliable way to test newer caps that may be questionable. Could someone describe a simple way to test 400+ volt caps for leakage - perhaps something like I described above?

Thanks again, Ed