I was poking around for information on the Casio MIDI guitars, when I came across some discussion about problems arising from capacitor "forming". In particular - and this is the part that threw me - unused electros deteriorating "seven times faster" than used electros of the same vintage. The web-source linked to this document/discussion as support: http://antiqueradios.com/marc/service2.html
Interesting, I must say, but I'm not in a strong position to give it the EE seal of approval, or deny it that standing. What say you?
It would certainly have implications for the relative merits of NOS vs cannibalized caps, the potential for "noninvasive cures" for some pedals, and a host of other things.
I worry about this.
In Febuary I stocked up on stuff for this adictive hobby then a couple months later I joined a new band.
Between band parctice ,school,and family I havent had time to build anything I planned for this year.
So I worry about all the high voltage electros I bought at discount,will thay still be good in a couple of years ?
I have read somewhere that electros that have sit for more than a year past their projected first use-
Have to be charged with a certain percentage of their voltage rating for X amount of time to re-stabilize them,
otherwise they will fail in short time once used.
Is there any truth to this ?
I was told the same thing by a distributor.
Also off topic sort of... What about breaking in film caps by hitting them with AC for 24 hours straight prior to installing them?
Doest his really break them in properly VS having to play your amp X amount of hours to "break it in" ?
"vintage" high voltage caps should be treated with suspicion...however, I never had ANY problems with modern cap's ( early 80'ties onwards)..and that include my 12 years as pro audio repairman in my earlier career. the caps are "formed" at manufacturing and moder electrolyte is stable enough not to eat through the aluminum oxide.
J
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Quote from: Brymus on December 06, 2010, 02:47:30 PM
Also off topic sort of... What about breaking in film caps by hitting them with AC for 24 hours straight prior to installing them?
Doest his really break them in properly VS having to play your amp X amount of hours to "break it in" ?
That would seem to contradict what's in the attached article:
"The secret for forming is to increase the voltage slowly and limit the current in the process so as to not boil the electrolyte."
I believe in the latter.
We experimented with this one day in college. One of my instructors was having a battle of wit with another (drunk all the time) student (who was twice our age.) The instructor said, "Okay then. Let's try your method of 'safety testing' these motherboards and hook up a 9V battery to them to see what happens." The pops and crinkles sounded cool.
Anyway, that led into a discussion about how once they're set, they're set, and conditioning them by applying current and slowly turning up the voltage made them... well, not necessarily more stable, just more able to work like they were supposed to on the first try. That's not to say it can't drift a little in the future, but from one day to another it won't.
Of course you can't just go around doing this to every cap too. But I've read at least one pedal maker that says you have to give the pedal a few days of playing to break in all the caps for them to sound better. Bollocks. The dielectric is set at first power on. They don't keep breaking in, like a speaker for example. It would be splitting hairs, at best.
...that was kinda fun to revisit that. I'd forgotten about that. :)
Quote from: ayayay! on December 06, 2010, 03:22:15 PM
Bollocks. The dielectric is set at first power on. They don't keep breaking in, like a speaker for example. It would be splitting hairs, at best.
I've always assumed it's anything that moves or has a filament of some sort. Speakers, guitar tops, transformers I suppose (vibration???), tubes; that sort of thing. I think the old way of thinking of electrolytic lifespan was 8 to 10 years, and I'm pulling that number out of questionable brain cells. That said I've serviced amplifiers with 5yr old aluminum electro's that were knocked way out of whack, and nice old amps from the 40's and 50's that had caps that looked like miniature toilet paper tubes dipped in wax that were spot on.
Quote from: Gordo on December 06, 2010, 04:16:29 PM
I've serviced amplifiers with 5yr old aluminum electro's that were knocked way out of whack, and nice old amps from the 40's and 50's that had caps that looked like miniature toilet paper tubes dipped in wax that were spot on.
And that would seem to be the basis for a great deal of superstition and impromptu theories about caps. That sort of thing DEMANDS an explanation, doesn't it?
I really don't know about the Electro's
So I am hoping for more input about that.
I do check every cap with an LC meter before soldering it in.Will that really give an indication of longeveity if it's within spec?
Same with breaking in caps,
I don't notice anything with Orange Drops sounding differen't as they get played more,
But with the Mallory 150's they definetly get brighter and more musical sounding after they break in,and I've heard the same said about Sozo's as well,they dont sound right until they are broke in.
Of course this is in amp's ,I suppose it could apply to pedals if using the same type of caps.
Quote from: Mark Hammer on December 06, 2010, 02:30:32 PM
I was poking around for information on the Casio MIDI guitars, when I came across some discussion about problems arising from capacitor "forming". In particular - and this is the part that threw me - unused electros deteriorating "seven times faster" than used electros of the same vintage. The web-source linked to this document/discussion as support: http://antiqueradios.com/marc/service2.html
Interesting, I must say, but I'm not in a strong position to give it the EE seal of approval, or deny it that standing. What say you?
It would certainly have implications for the relative merits of NOS vs cannibalized caps, the potential for "noninvasive cures" for some pedals, and a host of other things.
Ha, those danged guitars, I'm STILL trying to get my PG-380 working right, it seems that mine was more than just the caps in the little black door but on all the boards, I didn't order enough caps to get the job done.
That certainly is an interesting article, because mine isn't fixed yet it just sits and waits for me to tinker with it.
It's just chemistry.
The reaction that makes electrolytic capacitor insulation is one of forcing oxidation of the base metal driven by an electrical force. This makes the reaction proceed faster, and to a greater depth than is possible by the simple reaction of oxygen in the air with the base metal. It may also force a slightly different oxide or crystal format that open air oxidation. I don't remember THAT much chemistry.
A lot of this is in the Tube Amp FAQ at GEO, by the way.
The electrical force is combatted by the growing oxide thickness. If X thousandths of oxide thickness grows in just air, then X +Y thousandths grows by electrical forcing. Since the oxide is an insulator, the growth insulates itself as it gets thicker, and V volts grows Y thickness and then stops. If V is a bigger voltage, it causes a bigger Y thickness and stops there. Any voltage up to about 500V or 600V is possible; it gets impractical or impossible to grow aluminum oxides thicker than that.
The oxides grown on the foil of electro caps is a bit of an unnatural one, otherwise it would grow in air. So all by itself, it UN-grows with time, relaxing back to the more natural state. How long this takes depends on the conditions the oxide is in. If it were kept in liquid nitrogen, it might last for a very long time. Keep at room temperature in a semi-wet electrolyte, it un-ravels enough to make the manufacturers not want to warranty caps after about 5-10 years of shelf life. That means they think that there's a fair chance that the cap will no longer hold its rated voltage if it's suddenly applied after that time.
In a circuit, the voltage across the cap is in the correct direction to re-form the oxide. So there are competing effects between aging and heating UN-making the oxide and the electrical voltage RE-making it to some degree. Weak spots form, the voltage stress at the weak spots is higher, and it re-forms more at the weak spots. So eventually the oxide un-forms down to a voltage resisting level that the applied voltage will repair, for as long as the voltage and electrolyte chemistry can repair it.
Using something with an electro cap in it in a way that does not get it hot enough to outrun the re-forming process is the best way to get long life. Sticking the equipment in a closet unpowered is the same as leaving the capacitors unused. The oxide has no competing repair process for the inevitable deterioration. Electros last longer if they have a voltage applied. Overheating them can overwhelm that process.
As for the question of
QuoteThat said I've serviced amplifiers with 5yr old aluminum electro's that were knocked way out of whack, and nice old amps from the 40's and 50's that had caps that looked like miniature toilet paper tubes dipped in wax that were spot on
Capacitor making changes over time. The electrolyte chemistry, foil thickness, and other issues are different with new caps and caps from the 40s and 50s. There is also the "survivor effect". You only see amps with surviving caps. To make a comparison, you'd have to know the history of the units being serviced, and compare the manufacturing processes. A lot of progress in modern manufacturing is to make things last as long as they have to, and to not spend money on making them last longer. Sad but true, and one consequence of what I call "MBA Disease" in businesses. Some caps are effectively immortal just because they are. Some caps die early. You definitely see the recent failures because there are more units with them and more units surviving to be repaired. The weak brother units from the 40s and 50s are all in landfills, or rebuilt.
I acquired a small power supply used to power battery tube radios that had an output of essentially rectified AC (peak voltage = 169.7 VDC for a 120 VAC input). The output started at 88 VDC and rose at about one volt every three seconds due to capacitors forming up. This continues up to about 138 VDC at the output after which I terminated the experiment - you can reform capacitors but they may not stay reformed for long. A better idea would be to replace the capacitors and in my other hobby of restoring antique radios, we run into bad capacitors often enough that many restorers do a wholesale capacitor replacement for both electrolytic and paper capacitors.
N.B.
They last longer if the re-forming operation is quite slow. You need to limit the current in the "weak spots" so the forming current doesn't do collateral damage. One good way is to attach the cap to the desired end voltage through a 100K or so resistor. You monitor the voltage across the 100K resistor, which both limits current and tells you what the current is. You can go to full voltage when the voltage across the 100K drops below 10% of total end voltage - alternatively, when the voltage on the cap is over 90% of max.
One thing I've read that maybe someone (RG) could verify, is that the shelf life of unused caps can be extended by warming them to 150F or so every year or so. Don't know if it's valid, but it sounds plausible enough to ask about.
If the electrolytic chemistry is perfect, electrolytic caps last a very long time.
The chemistry is never perfect.
It took time to discover how perfect it had to be. My father says radios from the 1930s usually need a cap-job in 5 years.
Many of the potential contaminants were known by the 1940s. Of course knowing of a long-term problem, and fixing it, depends on what your customers will pay.
It can be very good. We know of caps from the 1950s, some idle for decades, which still meet orioginal specs for tolerance and leakage.
OTOH, about 6 years back many PC motherboards were failing in 3 years due to contamination at cap factories.
My observation is that caps after 1980-1985 are mostly pretty perfect, in service or in a decade of storage; with a few exceptions which make headlines.
However it is folly to buy caps for long-term storage. Not electronic folly but economic folly. You have cash tied-up in an object you can't eat and can hardly sell. If you put that cash in investments (even a savings account, most years), you can buy the cap you really need and earn interest besides.
> shelf life of unused caps can be extended by warming them to 150F or so every year or so.
That seems unlikely. Most chemical reactions happen twice as fast every 10 deg C hotter. I can't put a finger on it now, but I have seen storage guidelines and hot is said to be bad.
I remember reading something about shelf life getting real bad after 130F which is why I bring my electronic stuff outa the garage in summer.
So what someone could measure to attest the degree of forming ? ESR, leakeage and frequecy response ?
I would almost be ready to say shelf-life is a non-issue for us DIY-stomboxers...in a big factory it would probably be a big Issue. why?. if the tv-plant stuffs 1000 caps/minute and 1/10000 is crocked. that would be bad. 1/1000 tremendously bad. 1/100 bankrupsy-bad...how many caps do any of us stuff every minute?...how many times did you pull a cap up at random when breadboarding, and found a bad one?...non-issue...stop worrying...
..and as PRR once stated in a non related thread on a different forum a long time ago..."if you can't handle minor disasters, don't mess around"....
J
Yes well said, Johan. My "Bollocks" comment above was aimed at one's claim a pedals electrolytic caps "break in to sound better" over the course of a few days. I just don't see that being a valid argument, nor one worth pursuing.
...and if it changes that much, then wouldn't a few days of not playing it also 'adversely' affect the tone? What if it's still holding a charge? What if it's NOT, and the dielectric has changed! *gasp*
...and what's to say it's 'better' (that nasty, relative, conjecture of a word) when the caps are newest? When they're oldest? When they're warmest?
So in context of pedals, I still say it's not an issue I'm going to lose sleep over. Of course given time, heat, and current, clearly they do change, but what's to say that makes it worse? Or better?
Still it was a great article and a great discussion. :D
[PDF] The Electrolytic Capacitor Alexander M. Georgiev 1945
http://ebooksgo.org/engineering-technology/ElectrolyticCapacitors.pdf
The guy who made electrolytic caps good by 1945, and his thoughts about how they could be made better (they were).
Does not directly address long-term shelf life, and it is dated, but still The Bible.
I bought a large bag of mixed caps (mainly NOS early 70s electrolytics) from a local electronics store that was closing down. Salvaged about 200 polystyrene caps out of it an put the electrolytics to one side, intending to throw them out someday as I didn't trust them. It turns out that this was a misunderstanding on my part and they all measure up within capacity tolerance, except the leakage on some is unacceptable and they need to be formed. I use spent 9v batteries with a series resistor and a couple of croc clips. Once reformed they're fine and I've been using them up without problems.
But how I wish I'd bought the lot. The shop must have had 50 bags being sold for 10p each. Some must have contained thousands of polystyrene caps as well as really nice electrolytics and other types.
Anyone remember Worthington's, Newcastle, Staffs, England?