NOS electrolytics

[Aurora]

Somehow as an extension to the fake capacitor threads, how about NOS electrolytics?
I see some of you guys mentioning using those. As an EE i'd usually be quite wary about using old electrolytics, but even I have quite a lot of the sort in my stash.....even som really NOS ATOMs with the orange paper wrapping.
Any experiences and thuoghts on this? Reliability issues?

[ckpop]

It really depends on the age of the cap. The proper way to really get the condition of a NOS cap is to reform, test for leakage and other tests to know whats going on. NOS capacitors are more or less a gamble until checked correctly.

[paulster]

Hmm, what happened to yesterday's posts that disappeared?

Larry (novosibir) has posted a great method for slowly reforming caps over at the Metroamp forums. You can also heat them in hot water to break down the electrolyte crystal before slow forming to get them back in tip-top condition.

It clearly works in his amps which all use NOS LCR caps and sound amazing.

If you can't find it I'll dig out the relevant posts, or Larry might spot it here and chime in (he's a member here as well).

[Aurora]

Hmm, what happened to yesterday's posts that disappeared?

Ah- you did see it? I was wonderind if I had a real brainfart, as I was quite sure I wrote it before wandering over to some friends for dinner last night...

[paulster]

Ah- you did see it?

I did, and you had a couple of replies. I think it was Roe that was recommending the same method as me.

[C Moore]

Reforming on a VariAC over several hours or days, soaking in hot water (with a secret ingredient..??)...
They are just capacitors for crying out loud, why not buy new ones.?
How much magic can possibly be in these old over the hill components.?
Thank You

[C Moore]

Reforming on a VariAC over several hours or days, soaking in hot water (with a secret ingredient..??)...
They are just capacitors for crying out loud, why not buy new ones.?
How much magic can possibly be in these old over the hill components.?
Thank You

[paulster]

Reforming on a VariAC over several hours or days, soaking in hot water (with a secret ingredient..??)...
They are just capacitors for crying out loud, why not buy new ones.?

Take a vintage Marshall that's been well maintained and not left off for months at a time for instance and swap out the LCRs for some new caps and see how the tone changes, even with really good caps like F&Ts.

Old caps had their nuances, which is why people like John at Sozo are coming up with old-style electrolytics that use thicker foils but suffer higher ESR than new production.

These days it makes sense to design around new production components but when you're restoring something old or recreating an old design then you want to get as close as you can, and the power supply caps do play a part in that.

Old caps aren't necessarily no good either. They won't perform as they should if you suddenly start using them after years of storage because the electrolyte will have crystallised but this can be worked around.

Aurora - here's the original quote I was referencing:

I'm doing it this way, before I put my NOS LCR's into a new build. A small PT - rectified - then a 220K/3W to ground, to give the PT a pre load - and from there I go through each a 220K/1W to each 50+50/500 double can - always four at a time in parallel. They're sitting about 16-24h for forming, while I continue building the amp. Then the formed and discharged caps go in the amp

And moreover every 2-3 years I'm forming my complete stack of NOS LCR's, to keep it 'healthy' - they are from 1992

Before forming I put the caps (solder lugs upside) into hot water for about 20-30 minutes, to decristallize the electrolytic inside. It's similar as what you have to do with hard, old honey, to make it fluid again - and this pre procedure helps much to reduce the forming time.

[argonaut]

I've been cleaning the cave and found some NOS TVA Spragues still in their original packaging. They're all beginning to bulge and I was just going to toss them (responsibly, of course ), but thought perhaps I could try reforming them.

If they're bulging (or showing the first signs of) are they already too far gone? Or, is it possible to bring them back using a hot water soak and then a slow forming?

I think I'll give it a shot for my own curiosity's sake. Plus they're useless anyway as they are.

[Cliff Schecht]

I use a lot of NOS and even used vintage can and other types of caps quite often in my builds. It's what I have lying around and most of the time, the caps are perfectly fine. Here's the method my dad sent me when I asked him a while back. It works great and has brought quite a few "dead" caps back to life.

Here’s how to reform old caps (assuming they’re salvageable):



Take the unformed or old cap and measure its capacitance value with a Fluke DVM. Be CERTAIN that you haven’t charged the cap prior to doing this. It may read fairly close to its rated capacitance value but there’s a good chance that a lot of the dielectric has deformed and the cap will leak a lot of DC current when put into service.



Reforming the cap rebuilds the dielectric layer that the manufacturer established on the cap when it was new. Once reformed, the cap will not only have its rated capacitance but it will also leak very little.



To start: Put a resistor in series with the cap you’re going to reform. Choose the value of resistance to limit the short-circuit current to no more than a couple of milliamps (watch the resistor power rating as well, in case the cap is shorted and stays that way).



Next, hook the cap up to a variable power supply (minding polarity, of course) and slowly bring the voltage up to a value that’s a bit under the rated WVDC of the cap. IF you don’t have a variable high-voltage supply, you can hook the RC setup to a non-variable HV supply and just switch the thing on, although it’s preferable to apply the forming voltage slowly. Leave the cap hooked up to the HV supply for a few minutes and then check the leakage current flowing into the cap (measuring voltage across the limiting resistor and computing the current works fine). The cap’s leakage current shouldn’t be more than a couple of milliamps…some of the older ones may leak up to perhaps 10mA.



After the cap has sat under the charging supply for a while, disconnect the HV supply and then discharge the cap through a low enough resistance to run it down fairly quickly without making a lot of sparks while doing so. Don’t dead-short it to discharge it; it makes a lot of neat sparks and noise but the high surge current is really hard on the internal structure of those older caps. Then hook the cap up to the HV supply again (through the limiting resistor), leave it for a few minutes and then check the leakage current before discharging as above. Repeating this process a few times usually reforms just about any old cap that’s still in usable shape.



After the last forming run, discharge the cap one last time through a resistance and this time, place a shorting wire across the output for several minutes. A lot of electrolytics exhibit enough dielectric absorption to allow them to recharge themselves to significantly high voltages if left unshorted after being charged and that charge can fry your capacitance meter when you go to check the capacitance one last time.



So, after the cap has sat with the short across it for several minutes, remove the short and check the capacitance with your DVM. It should read within its tolerance limits. Since it’s been reformed, it won’t leak much either.



The term “dry” electrolytic is a bit of a misnomer. Modern, polymer dielectric electrolytic are truly dry in that sense but the older aluminum-foil and paper electrolytic all had some liquid in them. They were called “dry” since they didn’t have liquid sloshing about in them. Instead, the electrolyte was typically held in a paste form. If properly stored, some pretty old caps are still usable today. It’s easy enough to check the seals to see if they’ve broken or become embrittled and a capacitance/DC leakage test will also tell you whether they’ve survived or not.



If the electrolytic caps you have were used, then it’s probably best not to try to salvage them. The heat they endured for the years they were in service in tube equipment was usually enough to compromise their integrity or even kill them. NOS parts are worth trying to reform unless they’re really old (WWII or earlier).

[selloutrr]

If you have enough caps that it makes sence to buy a tester. sencore makes capacitor testers that can reform and test to lab spec. they just released a new model that does in circuit testing so the previous model is selling cheap! was over $2500 - . If you have under 50 caps PM me can test them for you.

[VacuumVoodoo]

I'd never use NOS or ANOS electrolytic caps in anything other than a lab prototype. Electrolytics are delicate devices, dropping a can cap on a hard floor can damage it enough to cause a fatal failure later on.
You don't know what happened to the old NOS caps over time, how they were stored etc.
I returned 250 caps to the distributor without even trying to test them because they were just thrown into a plastic bag and not in manufacturers original packaging. I suspected a reject from another customer was just resold to me.
I use Panasonic TSUP series snap-in caps in most of my designs. They come in sealed individual bubble foil bags. And they're damn good too...just study the specs for the 500V caps.

[FYL]

I use Panasonic TSUP series snap-in caps in most of my designs.

The TS-UPs are really good caps. The TS-HAs, rated at 105°C, are even better and cost only slightly more.

[argonaut]

Cliff- thanks for the additional info.

Selloutrr- Thnks for your generous offer, but I actually have an old LC53 that I use for testing. Since these caps are already bulging, I didn't want to zap them with the leakage test. I figured the slower, gradual method might work best.

VacuumVoodoo- I agree with you, I prefer to use new electrolytics from a distributor (I still test them though). This is more of an academic exercise for me.

[VacuumVoodoo]

I use Panasonic TSUP series snap-in caps in most of my designs.

The TS-UPs are really good caps. The TS-HAs, rated at 105°C, are even better and cost only slightly more.

TS-HAs end at 450V rating. Using 500V rated TS-UP used to give me (see below) just as good life time. It's a matter of juggling specs and derating or uprating what is inconsequential in a particular application. For really tough working conditions and lifetime exceeding your own by a couple decades use 140°C Sif-Safco caps. Very expensive caps that end up being cheap in the long run, if you can get a customer to pay the entry ticket.

Anyway, both TS-UP and TS-HA caps are discontinued and obsolete and my "private reserve" stock is almost depleted.
There are new 450V rated long-life snap-ins now that are pretty good too.