Ok people, I'm starting this thread because I didn't find old posts about this.
Bought a stock of old electrolytic capacitos, even knowing that these degrade or gone dry with time, expecting that at least some of them still work, because i think they look cool, specially those TESLA with the screw on the base. The problem is as you would imagine they are built in a country that no longer exist as such (Czechoslovakia) and others made in England which still exists, though my guess is these are at least 35 to 40 years old.
Tried a few 16mF + 16mF tesla brand with 100V DC and they get warm, possibly behaving more like a resistor than a capacitor.
I have a good analog multimeter and a digital multimeter that measures capacitance up to 22mF. Still I don't know a proper way to determine if a cap is good or not to be installed.
Ideas?
Pics are related.
dirt.
Bought a stock of old electrolytic capacitos, even knowing that these degrade or gone dry with time, expecting that at least some of them still work, because i think they look cool, specially those TESLA with the screw on the base. The problem is as you would imagine they are built in a country that no longer exist as such (Czechoslovakia) and others made in England which still exists, though my guess is these are at least 35 to 40 years old.
Tried a few 16mF + 16mF tesla brand with 100V DC and they get warm, possibly behaving more like a resistor than a capacitor.
I have a good analog multimeter and a digital multimeter that measures capacitance up to 22mF. Still I don't know a proper way to determine if a cap is good or not to be installed.
Ideas?
Pics are related.
An externally hosted image should be here but it was not working when we last tested it.
dirt.
An externally hosted image should be here but it was not working when we last tested it.
Here are my thoughts,
The reason noboby has probably asked is...old caps can contain dangerous chemicals (PCB)...The warm caps you refer to could heat up and explode covering you with hot electrolyte..
I have seen people opening caps and using the can with new caps inside...This is dangerous you are exposing yourself to unknown chemicals..
You could try reforming them...however I would not do this..
You could put them on a variable DC supply with a current limit and run them up slowly watch the heat and current...any leakage is a sign that they are damaged or faulty..don't put them on a bench and just look at them...I would put them behind a screen or use enclosure..
This is not a good Idea...life of the caps is going to be unknown..so cut a hole in the chassis for an old component that is not available?
Regards
M. Gregg
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Gregg, thank you for your reply, I was considering opening them up, specially the Tesla ones for the reasons I stated, they look neat screwed in the chassis along with the valves but now that you mention that is dangerous I think is a stupid idea. Also just checked them with my analog multimeter and most of them discharge completely after less than a minute, as opposed to my brand new capacitors of similar rating that retain the charge for several minutes. So I think I will toss them away. 
Gregg, thank you for your reply, I was considering opening them up, specially the Tesla ones for the reasons I stated, they look neat screwed in the chassis along with the valves but now that you mention that is dangerous I think is a stupid idea. Also just checked them with my analog multimeter and most of them discharge completely after less than a minute, as opposed to my brand new capacitors of similar rating that retain the charge for several minutes. So I think I will toss them away.
Some of the chemicals can be very dangerous..(PCB is an example)
I understand why you want to do this, however I am concerned for your safety.
Remember you may need special disposal...some countries can fine you if you just throw them away..
Regards
M. Gregg
I'm not aware that electrolytic caps ever used PCBs, only oil filled HV and motor caps. Still, worth checking. If you power these up with a DC supply and a large value resistor, they should (maybe) improve. If the leakage doesn't drop to normal levels after a day or so, they're probably junk. Though I still need to update it with several people's good suggestions, you might enjoy the capacitor article on my web site (click my name).
It all depends at which level you are trying to restore something.
At level 1 (The Ultimate level) only original components will do the job.
At level 2 (Looks the same) then you can disassemble cans and put different bits inside.
At level 3 (It works) you can just substitute.
Which level are you trying to achieve ?
At level 1 (The Ultimate level) only original components will do the job.
At level 2 (Looks the same) then you can disassemble cans and put different bits inside.
At level 3 (It works) you can just substitute.
Which level are you trying to achieve ?
To make them look old equipment, for instance I'm going to use Rimlock base valves (41,42 types), a modern capacitor simply won't look nice, I suppose I'll hide it beneath the chassis.
Opening anything up with chemicals inside it will always be hazardous.
I've never known a capacitor to be deadly though, so as long as you dont eat or breathe the contents you should be fairly safe.
It's not going to explode as you open it up.
Be careful with Cadmium though. It's not a common component but was used by the Americans a lot. It is toxic when it is oxidised ( identified as a white dust).
Cadmium though is still OK if you work in a well ventilated area and DO NOT ingest the stuff. (WASH EVERYTHING THOROUGHLY)
I've never known a capacitor to be deadly though, so as long as you dont eat or breathe the contents you should be fairly safe.
It's not going to explode as you open it up.
Be careful with Cadmium though. It's not a common component but was used by the Americans a lot. It is toxic when it is oxidised ( identified as a white dust).
Cadmium though is still OK if you work in a well ventilated area and DO NOT ingest the stuff. (WASH EVERYTHING THOROUGHLY)
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They did not. PCB's were used in oil caps to improve the dielectric. PCB's were not used in electrolytics.
Electrolytics did contain some strong alkalai's that eat components and PC board traces if they leak. They can violently explode if overheated. I know this from experience. The old ones did not have vents to prevent explosions.
Old electrolytics can and do dry out. They can become leaky with age. This is why they get hot. DO NOT use one in a circuit if it gets hot. It can EXPLODE. A cap that gets warm can sometimes be cured by "re-forming". Connect it to a variable DC power supply that has a current meter capable of reading 1 to 10 mA. Slowly turn up the voltage until the capacitor draws a small current (1 or 2 mA) or the rated voltage is reached. Let the cap sit at this voltage while watching the current meter. It should go down with time. If it does, turn the voltage up some more. Repeat this process until the rated voltage is reached and the capacitor draws less than 1 mA. If the cap increases current with time, or doesn't decrease, don't use it. It will explode.
This whole business about exposure to toxic materials is somewhat over-exaggerated when compared to the other trash around in society....UK immigrants tipping sump oil down drains.. smelly cars, smoking fags...energy saving lamps with mercury in the trash... plus all the batteries....Cadmium based plating is universally used on most hardware washers, bolts etc; one can find plenty of toxins in ones living room.. one doesn't have to look hard either, asthmatic formaldehyde is everywhere in furniture and buildings so no point getting scaremongered about the gylcerine alkali in standard electrolytics....good ones should have a rubber bung to release pressure, if wrinkled and like a boil,a sure sign of end of life..others have a deliberate triangulation indented in the can usually at the opposite end..to the same effect....
High voltage is our forum business and even more dangerous...and some of us work at quite high potential with plenty of Joules and have a beer at the same time......put it all in perspective. One is not going to get any work done if one is obsessive & petrified about hazards.Electronics is a dirty profession, no escape from it......rare metals used in mobile phones and beryllium oxide used in RF semi's are by far the worst toxic offenders...and yet widespread and easily obtained.
Electrolytics caps have the lowest life expectancy of all the components, life halves for every 10°C temp rise....so I trash any electrolytic over a yr old unless I've known it's history...the WEEE local directives deals with their disposal if required. SOme are organic and can be simply binned.
I can assure you in the 1950-60's it was not unusual to come across power tubes with radioactive cathodes used in TV line output stages and in transmitter tank/outputs circuits in radio and diathermy equipment. The natural gamma radiation from the rock in my vicinity is quite high, 20-40 counts per minute on a GM counter (some locations in the world way worse and people live quite normally without any side effects)... What can I do about it ? Nothing.. Carry on as usual. Life is too short anyway.
richy
High voltage is our forum business and even more dangerous...and some of us work at quite high potential with plenty of Joules and have a beer at the same time......put it all in perspective. One is not going to get any work done if one is obsessive & petrified about hazards.Electronics is a dirty profession, no escape from it......rare metals used in mobile phones and beryllium oxide used in RF semi's are by far the worst toxic offenders...and yet widespread and easily obtained.
Electrolytics caps have the lowest life expectancy of all the components, life halves for every 10°C temp rise....so I trash any electrolytic over a yr old unless I've known it's history...the WEEE local directives deals with their disposal if required. SOme are organic and can be simply binned.
I can assure you in the 1950-60's it was not unusual to come across power tubes with radioactive cathodes used in TV line output stages and in transmitter tank/outputs circuits in radio and diathermy equipment. The natural gamma radiation from the rock in my vicinity is quite high, 20-40 counts per minute on a GM counter (some locations in the world way worse and people live quite normally without any side effects)... What can I do about it ? Nothing.. Carry on as usual. Life is too short anyway.
richy
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I think I will put the aluminium can of the larger ones in the freezer to drink vodka shots.
Hehe. There are videos on YouTube where you can see capacitors exploding. One did blow up on me because I overdid its voltage rating, it was a modern one and it died in a spectacular fashion, lots of smoke. I have some vintage caps from old tube radios. Yes, they look cool but after seeing the explosion of a metal electrolytic can on YouTube I'm afraid to use them even though I'm not easily scared. Electric shocks are OK explosions are not. I agree with richwalters, this hobby is not for the faint-hearted.
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Just for fun,
Little caps with modern vent for overheat..
Some of the old ones don't have a vent..wonder what would happen//
Capacitor explosion from excessive voltage - YouTube
Regards
M. Gregg
Little caps with modern vent for overheat..
Some of the old ones don't have a vent..wonder what would happen//
Capacitor explosion from excessive voltage - YouTube
Regards
M. Gregg
Another small cap
Capacitor Explosion #2 - YouTube
Wonder what a big one would look like..
Regards
M. Gregg
Capacitor Explosion #2 - YouTube
Wonder what a big one would look like..
Regards
M. Gregg
Modern caps have a vent that is supposed to split open if too much pressure builds up inside the can. In normal overloads that slowly build up pressure the vent works releasing steam, a sticky white goo that tends to eat PC board traces and stink, lots of stink. I have "let the smoke out" of quite a few modern caps. If you clean the PC board with a toothbrush and WD-40 shortly after the event, all can be fixed. The wife complaining about me stinking up the house lasts longer than the cleanup. The old can caps HAVE NO VENT!
Modern caps can and will explode with enough violence to hurt you and damage a lot of stuff if you violate their ratings in a spectaular enough manner to cause pressure build up faster than the vent can open. I have done this twice that I can rememeber.
The most recent event occured when I had Pete's DCPP board on the bench connected to a bench power supply and I was exploring the upper limits of some small sweep tubes. My power supply is rated at 0 to 650 volts at 1.5 AMPS! It can deliver tens of amps into a short circuit for a brief moment before the current limiter kicks in. I was cranking the supply up while watching the tubes and the wattmeter trying to find the melting point of a 6JN6 without really paying attention to the voltage. I was somewhere around 600 volts on a 450 volt cap when there was a very loud bang. There was a large black stain on the red PC board where the cap was. There was no trace of the cap, and I have been finding fragments scattered all over the room since it happened.
About 25 years ago a bunch of us pooled our money and bought out a computer vendor that had gone out of business. We had about 200 PC-XT power supplies that were returns. Some worked, some didn't. After sorting out the dead ones, I began the process of repairing the easy ones. Many just had blown fuses or bad fans. The fuse was on the PC board soldered in. I adopted the stupid habit of opening up the supply jumpering the dead fuse with a clip lead, and testing. I replaced the fuse if that made it work. This was fine until I met the first power supply with a shorted rectifier. This connected a large snap in electrolytic directly across the line with no fuse. As soon as I put the plug into the wall I knew there was a big problem since the lights got dim and the plug became one with the power strip. In a matter of milliseconds the cap exploded with enough force to split the PC board in half and embed the can into the sheetrock ceiling of my workroom. The crude patch that I made remains over my head to remind me never to do that again. I made a fixture with a 100 Watt light bulb for jumping fuses, got power strips with circuit breakers in them, and made a big red panic button that kills the bench power.
I bought a cubic station wagon full of vintage electronics from an antique dealer that didn't know what the stuff was, or what to do with it. I wanted the tubes, and most of the other stuff went on Ebay. There was a large lot of NIB Sprague and Mallory twist loks. I explained that they had been in a hot warehouse in Florida for 40 years, but someone in Hong Kong paid more for the caps than I paid for the whole lot. I won't use these things in my amps because I know how big of a bang they make.
Modern caps can and will explode with enough violence to hurt you and damage a lot of stuff if you violate their ratings in a spectaular enough manner to cause pressure build up faster than the vent can open. I have done this twice that I can rememeber.
The most recent event occured when I had Pete's DCPP board on the bench connected to a bench power supply and I was exploring the upper limits of some small sweep tubes. My power supply is rated at 0 to 650 volts at 1.5 AMPS! It can deliver tens of amps into a short circuit for a brief moment before the current limiter kicks in. I was cranking the supply up while watching the tubes and the wattmeter trying to find the melting point of a 6JN6 without really paying attention to the voltage. I was somewhere around 600 volts on a 450 volt cap when there was a very loud bang. There was a large black stain on the red PC board where the cap was. There was no trace of the cap, and I have been finding fragments scattered all over the room since it happened.
About 25 years ago a bunch of us pooled our money and bought out a computer vendor that had gone out of business. We had about 200 PC-XT power supplies that were returns. Some worked, some didn't. After sorting out the dead ones, I began the process of repairing the easy ones. Many just had blown fuses or bad fans. The fuse was on the PC board soldered in. I adopted the stupid habit of opening up the supply jumpering the dead fuse with a clip lead, and testing. I replaced the fuse if that made it work. This was fine until I met the first power supply with a shorted rectifier. This connected a large snap in electrolytic directly across the line with no fuse. As soon as I put the plug into the wall I knew there was a big problem since the lights got dim and the plug became one with the power strip. In a matter of milliseconds the cap exploded with enough force to split the PC board in half and embed the can into the sheetrock ceiling of my workroom. The crude patch that I made remains over my head to remind me never to do that again. I made a fixture with a 100 Watt light bulb for jumping fuses, got power strips with circuit breakers in them, and made a big red panic button that kills the bench power.
I bought a cubic station wagon full of vintage electronics from an antique dealer that didn't know what the stuff was, or what to do with it. I wanted the tubes, and most of the other stuff went on Ebay. There was a large lot of NIB Sprague and Mallory twist loks. I explained that they had been in a hot warehouse in Florida for 40 years, but someone in Hong Kong paid more for the caps than I paid for the whole lot. I won't use these things in my amps because I know how big of a bang they make.
Nobody has said the obvious. Electrolytic caps before about 1965 were sealed with rubber. Caps after 1965 sealed with anything but rubber were rare. Do you drive your 1965 Mustang on the freeway with 1965 tires? No, there is a reason, called oxidation. No matter how gently you "reform" the oxide on the aluminum of the capacitor, it doesn't put the amount of water back to the original. Nor does reforming improve the sealing power of the rubber seal. A little vapor pressure from use, the water can evaporate right out. Then hot spots develop, the cap boils and corrosive slime gets all over the inside of your device.
I'm buying radial lead caps rated 5000-10000 hours life at 105 deg C when I can get them. They are small enough now I can usually install them under the chassis without removing the old cap. Taking wires off the old cap is important, they can boil and short no matter how little the load is. But a deenergized cap may not be as prone to leak slime as one that is powered up. I pull the old cans and install vent screens over the holes, but almost nobody is buying an organ for its original appearance behind the cover. B3's over $7000 excepted.
I've had to recap my 1961 ST70 and PAS2 3 times since 1971 when I bought it for poor wattage and poor B+ voltage. I put a new cap in the ST70 in 1982, then put it away because I couldn't find new tubes in rural Kansas before the internet. I bought the new output and rectifier tubes last year, reformed the 1982 Cornell Dublier cap with 19 VDC, and listened to the blissful sound for one night last winter. The next night it blew the fuse immediately: the 1982 cap after ~3 hours total use had leaked out the water and shorted.
I'm buying radial lead caps rated 5000-10000 hours life at 105 deg C when I can get them. They are small enough now I can usually install them under the chassis without removing the old cap. Taking wires off the old cap is important, they can boil and short no matter how little the load is. But a deenergized cap may not be as prone to leak slime as one that is powered up. I pull the old cans and install vent screens over the holes, but almost nobody is buying an organ for its original appearance behind the cover. B3's over $7000 excepted.
I've had to recap my 1961 ST70 and PAS2 3 times since 1971 when I bought it for poor wattage and poor B+ voltage. I put a new cap in the ST70 in 1982, then put it away because I couldn't find new tubes in rural Kansas before the internet. I bought the new output and rectifier tubes last year, reformed the 1982 Cornell Dublier cap with 19 VDC, and listened to the blissful sound for one night last winter. The next night it blew the fuse immediately: the 1982 cap after ~3 hours total use had leaked out the water and shorted.
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I also can indicate that the pcb reference for electrolytics is not relevant - a good reference on that topic is http://www.environment.gov.au/settlements/publications/chemicals/scheduled-waste/pubs/pcbid.pdf
An old reformed electrolytic will almost certainly have a higher ESR than a new cap. In some situations this is a benign issue - or can be sidestepped by using another new cap in parallel - I have used this method in restorations where I wanted to keep the original chassis mount can for aesthetics and to continue using the positive terminal (the bypass cap being placed under tha chassis).
I would suggest not using such old caps for the first capacitor after the rectifier where they will experience significant ripple current, or where it is in an inherently hot position, as the leakage current will naturally walk up in level.
Ciao, Tim
An old reformed electrolytic will almost certainly have a higher ESR than a new cap. In some situations this is a benign issue - or can be sidestepped by using another new cap in parallel - I have used this method in restorations where I wanted to keep the original chassis mount can for aesthetics and to continue using the positive terminal (the bypass cap being placed under tha chassis).
I would suggest not using such old caps for the first capacitor after the rectifier where they will experience significant ripple current, or where it is in an inherently hot position, as the leakage current will naturally walk up in level.
Ciao, Tim
My Philips Pm 3215 Oscilloscope from 1981 still has all of its original electrolytic capacitors and they appear to be working OK. I am looking to replace them asap so that I don't have to deal with any smoke bombs in the future though...
I agree with the members here though... I'd definitely stick with new capacitors but you can always stuff the old ones for that classic look!
I agree with the members here though... I'd definitely stick with new capacitors but you can always stuff the old ones for that classic look!
I had bought and tested various vintage capacitors from Russia (and countries in the area) in order to use them as upgrade parts in my repair (& upgrade) shop.
I had tried various electrolytics caps including tesla. I started testing them by applying to them voltage at about half of their rating and check for current draw, heat etc. Then i will up the voltage to 10% below their rating. If they passed that, i tested them with a modern capacitor meter and an LCR bridge. And if they seem good i then tested them in a compatible working circuit.
Without getting in details i have to say that -according to the samples that i got- most of the vintage NOS electrolytics are bad, have drifted alot from their ratings and the worst is that they are dangerous. Just like Indianajo said they use materials that are near disintegration so they are time bombs in your hands. Even if they work or sound good you dont know when are they going to fail.
And like Tubelab (george, right?) said you dont want an electrolytic explode in the same room as you! I had various electrolytics explode in equipment that we were powering for fault finding and they are very dangerous. As an example: a huge pro amplifier came in. The owner used it with a power generator. the moment we powered it to start troubleshooting one huge 10000mf/80v exploded. The tin can of the cap smashed to our concrete ceiling and left there a mark. We got sprayed with papers from inside the cap and the chemicals were so bad smelling that we had to stay out of the lab for more than an hour. Despite the smell, can you imagine that metal cap flying around your room?
So there is a big NO to those old caps, its time for them to get recycled.
Panos
I had tried various electrolytics caps including tesla. I started testing them by applying to them voltage at about half of their rating and check for current draw, heat etc. Then i will up the voltage to 10% below their rating. If they passed that, i tested them with a modern capacitor meter and an LCR bridge. And if they seem good i then tested them in a compatible working circuit.
Without getting in details i have to say that -according to the samples that i got- most of the vintage NOS electrolytics are bad, have drifted alot from their ratings and the worst is that they are dangerous. Just like Indianajo said they use materials that are near disintegration so they are time bombs in your hands. Even if they work or sound good you dont know when are they going to fail.
And like Tubelab (george, right?) said you dont want an electrolytic explode in the same room as you! I had various electrolytics explode in equipment that we were powering for fault finding and they are very dangerous. As an example: a huge pro amplifier came in. The owner used it with a power generator. the moment we powered it to start troubleshooting one huge 10000mf/80v exploded. The tin can of the cap smashed to our concrete ceiling and left there a mark. We got sprayed with papers from inside the cap and the chemicals were so bad smelling that we had to stay out of the lab for more than an hour. Despite the smell, can you imagine that metal cap flying around your room?
So there is a big NO to those old caps, its time for them to get recycled.
Panos
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