For the past yeat I have been working for a company in the TV set-top-box market. We had a problem with a supplier substituting caps of a lower temperature rating. Since these things live permanantly switched on this was a problem and many failed after only 6 months service
We really dug the drains up on this issue an gained a fair amount of knowledge. For instance; increasing the operating temperature by 10Deg celsius halves their life time. The life time of our particular caps is 4000hrs at 105 deg. (therefore 8000 hrs at 95deg).
but the real thing that woried me is that the shelf life is around 10 years. Now, Bass player and PA guy that I am, I have some fairly old gear: 20 year old bass amp, 23 year old power amplifier. Should I be worried?
Some of this gear lives in a shed. It gets below freezing in the winter. NOW should I worried? Does anyone have experience of this?
We really dug the drains up on this issue an gained a fair amount of knowledge. For instance; increasing the operating temperature by 10Deg celsius halves their life time. The life time of our particular caps is 4000hrs at 105 deg. (therefore 8000 hrs at 95deg).
but the real thing that woried me is that the shelf life is around 10 years. Now, Bass player and PA guy that I am, I have some fairly old gear: 20 year old bass amp, 23 year old power amplifier. Should I be worried?
Some of this gear lives in a shed. It gets below freezing in the winter. NOW should I worried? Does anyone have experience of this?
Pbassred,
Part of the lifetime factor of an electrolytic is how often and for how long it is used. Caps in daily use maintain the oxide structure. Where as caps idle tend to eat their own oxides. I !think cold storage retards this process but I know there is a low enough temp where bad things happen.
Now, 20 year old gear, yeah, I would think about recapping. I am in the middle of rebuilding a Leslie 122 and a Hammond B3. I hadn't played/powered them for 10 years and the caps are 25 years old (I had recapped these in '80). Neither would come to life and all I heard was cracking and popping.
Knowing all this about caps, I shut things down before anything bad happened and started the rebuild. The bummer is that when electrolytics fail; they can take out your trannies... your... old... precious... impossible to replace... trannies.
Caps are cheap... really... tubes...so-so... trannies... OUCH
Part of the lifetime factor of an electrolytic is how often and for how long it is used. Caps in daily use maintain the oxide structure. Where as caps idle tend to eat their own oxides. I !think cold storage retards this process but I know there is a low enough temp where bad things happen.
Now, 20 year old gear, yeah, I would think about recapping. I am in the middle of rebuilding a Leslie 122 and a Hammond B3. I hadn't played/powered them for 10 years and the caps are 25 years old (I had recapped these in '80). Neither would come to life and all I heard was cracking and popping.
Knowing all this about caps, I shut things down before anything bad happened and started the rebuild. The bummer is that when electrolytics fail; they can take out your trannies... your... old... precious... impossible to replace... trannies.
Caps are cheap... really... tubes...so-so... trannies... OUCH
Pbass,
Interesting question... I don't know enough
There are, of cours, obvious symptoms of partial failure; heat, yes, I have often use a gloved finger to find humming caps. And hum itself ... well duh!
I supposed you could measure leakage current; it will increase with loss of oxides... but that's a hassle. Likewise with measuring capacitance it will drop with loss of oxide and electrolyte... again, a hassle.
I think the key thing is don't leave old equipment turned on when your not around... if a cap does go... you'll be there to shut it off before you fuse your trannies.
You know you can recap a bruiser of an amp for 30-40 bucks as long as you stick to quality stuff rather than silly stuff. In a lot of cases that is half or a fifth the cost of one tranny (think about an Ampeg SVT)... IF you can get it...
I spose another thing if you're holding onto relic's... make sure they get powered-up 3-4 times a year for a few hours... while your listening to them... that will restore the oxides to the extent the remaining electrolyte chermistry will allow.
Interesting question... I don't know enough
There are, of cours, obvious symptoms of partial failure; heat, yes, I have often use a gloved finger to find humming caps. And hum itself ... well duh!
I supposed you could measure leakage current; it will increase with loss of oxides... but that's a hassle. Likewise with measuring capacitance it will drop with loss of oxide and electrolyte... again, a hassle.
I think the key thing is don't leave old equipment turned on when your not around... if a cap does go... you'll be there to shut it off before you fuse your trannies.
You know you can recap a bruiser of an amp for 30-40 bucks as long as you stick to quality stuff rather than silly stuff. In a lot of cases that is half or a fifth the cost of one tranny (think about an Ampeg SVT)... IF you can get it...
I spose another thing if you're holding onto relic's... make sure they get powered-up 3-4 times a year for a few hours... while your listening to them... that will restore the oxides to the extent the remaining electrolyte chermistry will allow.
Hi Pbassred,
Sometimes there is no obvious warning. A filter cap will get warm as it gets closer to dying. They may just short.
Look at the bottom of the cap. If you see anything leaking out, it's a goner. Maybe not today, but soon. White crusty stuff around the bass of a can cap tells you to replace it.
Don't leave tube gear running unattended. Fuses are good, foil "cigarette" paper is bad.
-Chris
Sometimes there is no obvious warning. A filter cap will get warm as it gets closer to dying. They may just short.
Look at the bottom of the cap. If you see anything leaking out, it's a goner. Maybe not today, but soon. White crusty stuff around the bass of a can cap tells you to replace it.
Don't leave tube gear running unattended. Fuses are good, foil "cigarette" paper is bad.
-Chris
Three years ago, I've built Cyril Bateman's tan-delta meter and tested many very old caps. I almost found no bad cap. I thought my Tan-Delta meter was wrong, so Cyril sent me some bad caps to test, my meter proved to give right indications. I tested about forty 1500 - 2200 µF 450 V caps coming from professionnal photographic flashes which have been intensively used for nearly thirty years, I think a flash is one of the most stressing demand which can be done to a cap. The main problem was a bit of oxydation which made good electric contacts sometimes a bit difficult to establish. All these caps proved to have a tan-delta less than 0.1, which means good. I wonder if such special caps which handles huge discharges couldn't do a lot of good if used in valve amps amps.
My conclusion is that electrolytics are incredibly reliable as far as they are not submitted to sources of heat.
~~~ Forr
§§§
My conclusion is that electrolytics are incredibly reliable as far as they are not submitted to sources of heat.
~~~ Forr
§§§
Photoflash caps are specially designed for the unusual demands made on them. I don't know the details (I'm sure someone will tell us), but they're not typical electrolytics.
Having said that, studios used to have to regularly replace the caps in their flash supplies (I'm talking about the big guns with seperate HV units), but that doesn't seem to be the case these days.
Provided there is no leakage of goop from the cap itself many of them that have been sitting idle for long periods can be re-formed. I have restored many early TV sets from the early 40's and I end up replacing very few electrolytics in them... all have been re-formed and work just fine. In general I do replace any coupling or small bypass caps in them though as todays caps are much better in general and the actual performance of some TV's can be increased.
Here is a good link to a site that explains just about every aspect of should I or shouldn't I replace them...
Link
Mark
Here is a good link to a site that explains just about every aspect of should I or shouldn't I replace them...
Link
Mark
ELECTROLYTICS
If the capacitor was formed propery by leaving it on for a minimum of 12 hours, it should last forever unless it got warm regularly, sat in a warm place with no power, or if it is physically small for its size. If it is a modern small one, then it will have a thinner dielectric. I know that most manufacturers of consumer equipment did not consider it, but HEAT IS DESTRUCTIVE NO MATTER WHAT, if it is formed properly or always on.
I recycle electronics for projects and test electrolytics regularly. A 35 year old Sprague from a hot power supply can reform to good condition if it was formed properly to begin with when fresh. It is actually just more predictable, that is it will test well or fail after a long reforming process. If your solid state amplifer has never been left on (NOT UNATTENDED) for a 24 hour period it will never see its true potential. (Assuming the capacitors don't get warm.) One reson many people think they like tubes so much is that SS uses 1000s of UFs, and tubes rarely use a capacitor over 100 UF. It actually takes a week of constant (and clean) power to form a high UF capacitor. But once it is formed (especially if done when capacitors are fresh) it will be good to go forever, unless it is using those capacitors that the TV companies needed to put lower temperature ratings on.
Unfortunately, it should never be left on unattended, for safety, but turning it off is the worst thing for a capacitor, unless it is in a warm environment.
If the capacitor was formed propery by leaving it on for a minimum of 12 hours, it should last forever unless it got warm regularly, sat in a warm place with no power, or if it is physically small for its size. If it is a modern small one, then it will have a thinner dielectric. I know that most manufacturers of consumer equipment did not consider it, but HEAT IS DESTRUCTIVE NO MATTER WHAT, if it is formed properly or always on.
I recycle electronics for projects and test electrolytics regularly. A 35 year old Sprague from a hot power supply can reform to good condition if it was formed properly to begin with when fresh. It is actually just more predictable, that is it will test well or fail after a long reforming process. If your solid state amplifer has never been left on (NOT UNATTENDED) for a 24 hour period it will never see its true potential. (Assuming the capacitors don't get warm.) One reson many people think they like tubes so much is that SS uses 1000s of UFs, and tubes rarely use a capacitor over 100 UF. It actually takes a week of constant (and clean) power to form a high UF capacitor. But once it is formed (especially if done when capacitors are fresh) it will be good to go forever, unless it is using those capacitors that the TV companies needed to put lower temperature ratings on.
Unfortunately, it should never be left on unattended, for safety, but turning it off is the worst thing for a capacitor, unless it is in a warm environment.
My understanding is that the warning signs of a failing electrolytic are:
1. getting warm, due to increasing leakage current
2. reduction in value, or rise in series resistance (due to drying out)
3. casing bulging, or signs of chemical seeping out (due to sign 1 being ignored)
It may be that some recently manufactured electrolytics will not last as long as older ones. Technology may have improved, but care in manufacture has declined in some places. There are also some outright fakes around, which sometimes find their way through official supply chains.
1. getting warm, due to increasing leakage current
2. reduction in value, or rise in series resistance (due to drying out)
3. casing bulging, or signs of chemical seeping out (due to sign 1 being ignored)
It may be that some recently manufactured electrolytics will not last as long as older ones. Technology may have improved, but care in manufacture has declined in some places. There are also some outright fakes around, which sometimes find their way through official supply chains.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.