Hello.
I've bought a lot of old but useful parts, and some of these parts are old and large capasitors (You can see a picture of them here.
I would like to use these in the powersupply for the Hiraga "Le Monstre", but because these capasitors are old and large I'm afraid they'll blow up when I turn on the power.
How, if possible, can I revive these in a safe way?
Thanks in advance.
Eirik A
Norway
I've bought a lot of old but useful parts, and some of these parts are old and large capasitors (You can see a picture of them here.
I would like to use these in the powersupply for the Hiraga "Le Monstre", but because these capasitors are old and large I'm afraid they'll blow up when I turn on the power.
How, if possible, can I revive these in a safe way?
Thanks in advance.
Eirik A
Norway
Try charge them to 2/3 of working Voltage through a 10K to 100K resistor. If they take charge, then disconnect the power and see if they can keep the Voltage. If so, then decharge them again through the same resistor, and then try charging to near working Voltage through the same resistor again. If everything seems ok, try charge them without the series resistor.
Good luck
Good luck
Hi, and thanks for Your advise.
What You see in the pictures is'nt even all the stuff I bought.
I also got 7 pairs of the original Toshiba 2SD844/2SB754 transistors for the Monster.
That's why I wonder how to revive the capasitors.
However my first goal is to make this amp. It's the amp in the pictures in my first post.
I'll keep you posted.
What You see in the pictures is'nt even all the stuff I bought.
I also got 7 pairs of the original Toshiba 2SD844/2SB754 transistors for the Monster.
That's why I wonder how to revive the capasitors.
However my first goal is to make this amp. It's the amp in the pictures in my first post.
I'll keep you posted.
Looks like a lot of good stuff. But the caps I would be worried about. If they are old and have been sitting, they may not work for very long. I just replaced some 22000 100volt caps that were about 30 years old. Is there any way to judge their age? I would hate for you to put them in the monster only to have one rupture and spill its acid.
I have had two capacitor failures in different pieces of equipment this month. Both were from mid 1970's. One was the large DC capacitor I described above, the other was a non-polar axial high voltage AC capacitor that shorted and took out some other circuitry with it during it's explosion. Both pieces of equipment get used daily for many years. I am now thinking of replacing all my old caps.
I have had two capacitor failures in different pieces of equipment this month. Both were from mid 1970's. One was the large DC capacitor I described above, the other was a non-polar axial high voltage AC capacitor that shorted and took out some other circuitry with it during it's explosion. Both pieces of equipment get used daily for many years. I am now thinking of replacing all my old caps.
I've been collecting test equipment forever, and some of it is going on 50 years old. My audio stuff is only from the '70s. Every once in a while I'll get something with a bad cap, but very rarely. I'd never consider randomly replacing "old" caps, as most of them won't fail any time soon. More damage would be done to circuit boards and disturbed wiring, than would be prevented by having new caps. The only pieces of equipment that seem to consume caps on a regular basis are my Keithley HV power supplies, and an old Tek transistor curve tracer. The few other cap failures I've had have been as much low voltage circuitry, as power supplies. What fails most often are the very low voltage electrolytics, like 500uF 6.3V caps. And very old tantalums. One secret to long cap life is to run equipment at least a few times a year. Don't let it sit around unused. Also, don't expose electrolytics to chlorinated solvents like pot and tuner cleaner. If anything gets by the seals, the damage process is self- accelerating.
CBRworm said:
Never seen guys in a dump store shake electrolytics ?
If the caps are really dried out they feel/sound like an old walnut.
NOS military caps are cool, wrapped in aluminum foil and in a cloth bag they're well protected, i've rejuvenated 50 year oldies without a single goner.
A second physical check-up after reforming them is to measure the leakage current.
I still have this link about reforming caps in my favorites
http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm
http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm
I am reforming some big caps 68KuF/75Volt that are about 15 years old. They were purchased as NOS about three years ago from another member. Following this link provided
http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm
I hooked up as per illustration using a power supply and a 30K/5Watt resistor in series off the positive side of the PSU and a meter to monitor the current drain at the resistor.
The formula calls for 5 minutes at rated power (75V) and one minute for each month of storage, roughly 180 minutes for the 15 years.
I observed the voltage drop across the resistor go from 75 volts to 8 volts at the end of reforming!
After discharging the capacitor the next morning I hooked up the Cap again and watched it drop about 12 volts in a 30 minute period, better than the initial reform. The articles mentions that a new cap should go up to its rated voltage and drop maybe 10% and hold there.
I’m wondering if this type of voltage drop during the reform process is natural, it seems excessive to me. Keeping in mind that these cap 68,000/75V are quite large and old they may not be able to reform or perhaps should take multiple reforms or???
Stan
edit:
from the article -
If the amount of current flow (voltage drop across the resistor) is great initially, that is not a problem. If it doesn't start dropping within five minutes of application of voltage, a definite hazard exists. The current flow indicated that energy is being dissipated within the capacitor, in the form of heat.
Within an aluminum electrolytic there is a large area of aluminum foil and an electrolytic paste. As the voltage is applied, current flows until aluminum oxide forms on the surface of the foil, because aluminum oxide is a very good insulator.
http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm
I hooked up as per illustration using a power supply and a 30K/5Watt resistor in series off the positive side of the PSU and a meter to monitor the current drain at the resistor.
The formula calls for 5 minutes at rated power (75V) and one minute for each month of storage, roughly 180 minutes for the 15 years.
I observed the voltage drop across the resistor go from 75 volts to 8 volts at the end of reforming!
After discharging the capacitor the next morning I hooked up the Cap again and watched it drop about 12 volts in a 30 minute period, better than the initial reform. The articles mentions that a new cap should go up to its rated voltage and drop maybe 10% and hold there.
I’m wondering if this type of voltage drop during the reform process is natural, it seems excessive to me. Keeping in mind that these cap 68,000/75V are quite large and old they may not be able to reform or perhaps should take multiple reforms or???
Stan
edit:
from the article -
If the amount of current flow (voltage drop across the resistor) is great initially, that is not a problem. If it doesn't start dropping within five minutes of application of voltage, a definite hazard exists. The current flow indicated that energy is being dissipated within the capacitor, in the form of heat.
Within an aluminum electrolytic there is a large area of aluminum foil and an electrolytic paste. As the voltage is applied, current flows until aluminum oxide forms on the surface of the foil, because aluminum oxide is a very good insulator.
Re: Reforming Caps
Hi, if you are using a bench power supply to reform the cap, by slowing turning up the voltage on the power supply to the rated voltage of the cap would be the same as using a variac. Seems like a good idea to me on the old caps.
If you are applying power for the first time to an old unit with its own power supply to see if it still works I'm sure a variac would be a good idea.
Stan
sondguy said:
Hi, if you are using a bench power supply to reform the cap, by slowing turning up the voltage on the power supply to the rated voltage of the cap would be the same as using a variac. Seems like a good idea to me on the old caps.
If you are applying power for the first time to an old unit with its own power supply to see if it still works I'm sure a variac would be a good idea.
Stan
Old Caps - No No No !
Ean72
I have just replaced the 20 years old electrolytic PSU caps in one of my amps and the sound improvement is incredible. In fact I cant believe the amp is sounding so good.
I would not struggle with old caps. Especially not with equipment I value.
Forget sentimentality- caps are not really that expensive compared to the risk and cost of damaged equipment.
Jozua
Ean72
I have just replaced the 20 years old electrolytic PSU caps in one of my amps and the sound improvement is incredible. In fact I cant believe the amp is sounding so good.
I would not struggle with old caps. Especially not with equipment I value.
Forget sentimentality- caps are not really that expensive compared to the risk and cost of damaged equipment.
Jozua
Jozua: I totally agree.
The only reason for me to do this is learning by doing.
And right now I have a lot to learn and a lot to do.
I'm just curious on how it works and if it works. And if it sounds right as well, then I'll start over with new caps and high quality parts. Or something.
So thanks a lot for useful input, I've got a lot to read up on.
The only reason for me to do this is learning by doing.
And right now I have a lot to learn and a lot to do.
I'm just curious on how it works and if it works. And if it sounds right as well, then I'll start over with new caps and high quality parts. Or something.
So thanks a lot for useful input, I've got a lot to read up on.
Re: Old Caps - No No No !
No sentimentality here, just need them for testing and possible usage, if I can get 4-8 big caps working for peanuts compared to the cost of new ones - why throw my money away especially if you cannot hear the difference.
Did you try reforming your old ps caps before throwing them away to compare or was your wallet listening?
Its just learning.
Stan
Jozua said:
No sentimentality here, just need them for testing and possible usage, if I can get 4-8 big caps working for peanuts compared to the cost of new ones - why throw my money away especially if you cannot hear the difference.
Did you try reforming your old ps caps before throwing them away to compare or was your wallet listening?
Its just learning.
Stan
I rebuilt caps in a Marantz 10 (not 10B) after 42 years since construction. It was difficult, but I did it with a Variac. I slowly brought up the voltage and tested the cap temp with my finger. It worked, and the tuner still works today. A good way to keep a cap from overheating is to hit it with freeze spray while you are turning off the unit for awhile.
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