F&T Cap shelf life question
Moderators: pompeiisneaks, Colossal
F&T Cap shelf life question
Three years ago I started a new amp build that for several reasons got postponed until now. I purchased the parts I needed back then including new F&T caps for the power supply. I live in Arizona so my garage can get up to 95 degrees in the summer. I have an AC that I run when I'm working out there but the rest of the time it's pretty hot. I'm wondering if the lengthy exposure to heat may have shortened the working life of these caps. Buying a new set won't break the bank, but I'm curious what some of you seasoned builders/techs think? Am I overthinking this or is it worth it to get a new set.
Re: F&T Cap shelf life question
That 95F temperature will degrade the electrolytic capacitors a lot quicker than normal room temperature if they have not been formed yet. Since they are fairly affordable I would just spare myself the worry and just replace them.casey73 wrote: ↑Wed Aug 05, 2026 2:07 am Three years ago I started a new amp build that for several reasons got postponed until now. I purchased the parts I needed back then including new F&T caps for the power supply. I live in Arizona so my garage can get up to 95 degrees in the summer. I have an AC that I run when I'm working out there but the rest of the time it's pretty hot. I'm wondering if the lengthy exposure to heat may have shortened the working life of these caps. Buying a new set won't break the bank, but I'm curious what some of you seasoned builders/techs think? Am I overthinking this or is it worth it to get a new set.
Cheers
G
Re: F&T Cap shelf life question
For only 3 years of storage, they'll be fine.
I've got 20-year old unused electrolytics that are still OK. I won't sell them in a repair job because that's just wrong. But I'll use them for my own projects.
When they're that old, I usually bring them up to full rated voltage slowly and let them sit while I measure the current. When the leakage current drops to whatever is in spec, they're good to go. I can't remember the last time I had a bad one.
I've got 20-year old unused electrolytics that are still OK. I won't sell them in a repair job because that's just wrong. But I'll use them for my own projects.
When they're that old, I usually bring them up to full rated voltage slowly and let them sit while I measure the current. When the leakage current drops to whatever is in spec, they're good to go. I can't remember the last time I had a bad one.
Re: F&T Cap shelf life question
Nuke's process will work.
Another good way is to put a 100K resistor between the full rated DC voltage and the cap. Watch the voltage across the cap. It should decrease over time. When it gets down to 10% of the rated voltage (that is, the cap is supporting 90% of rated voltage) The cap can be used at full rated voltage. The 100K resistor limits the current in any "soft" places in the cap so that the current builds insulation instead of burning it out.
This can be quite slow, depending on the cap's condition. If the cap already supports 90+ percent of rated, it's still good to use. Any excess leakage can be re-built during use.
Another good way is to put a 100K resistor between the full rated DC voltage and the cap. Watch the voltage across the cap. It should decrease over time. When it gets down to 10% of the rated voltage (that is, the cap is supporting 90% of rated voltage) The cap can be used at full rated voltage. The 100K resistor limits the current in any "soft" places in the cap so that the current builds insulation instead of burning it out.
This can be quite slow, depending on the cap's condition. If the cap already supports 90+ percent of rated, it's still good to use. Any excess leakage can be re-built during use.
"For every complex problem there is an answer that is clear, simple, and wrong"
H. L. Mencken
H. L. Mencken
Re: F&T Cap shelf life question
Thanks to all who replied. I will do the reform route since this is a personal project, not something I'm building for someone else.
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flemingmras
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Re: F&T Cap shelf life question
Shelf life for electrolytic capacitors is 2-3 years.
I have some that I installed in an amp I still haven't finished building since I started it in 2015. It's been through several moves, stored in a garage, then in my bedroom, etc. Finally getting around to finishing it up this year. I ordered a brand new set and cut one open. The liquid had congealed and the paper was beginning to dry out. Would not have attempted a reform.
I have some that I installed in an amp I still haven't finished building since I started it in 2015. It's been through several moves, stored in a garage, then in my bedroom, etc. Finally getting around to finishing it up this year. I ordered a brand new set and cut one open. The liquid had congealed and the paper was beginning to dry out. Would not have attempted a reform.
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Re: F&T Cap shelf life question
The shelf life thing needs some interpretation.
If you're manufacturing electronics in high volume, most eletrolytic capacitor datasheets will say the parts need to be used within one year. Some capacitor makers offer re-processing services for high-volume customers so they can send back inventory and have the parts re-formed and re-certified if they're approaching that year mark. (for a fee of course)
There are other considerations for that reasoning, like solderability of leads and especially for surface mount factors like MSL (moisture sensitivity level). A lot of SMD parts have to remain in their sealed packaging, right up to the point they get fed into the pick-and-place machine. If they're out of the package for 24 hours, they have to be baked for hours at specific temperatures. Others are days or weeks or months.
Same goes for circuit boards, which have a limited life once they're fabricated, or they are likely to have a high fallout during high-volume soldering process.
That's for statistical reasons in high-volume manufacturing mostly. The cap company asserts a certain life and performance for their parts, and their customer who's inserting them on the assembly line, designed their end product to hit certain reliability figures at the minimum of cost. They know that if they make 1-million car stereos, some will sell right away, some will take months, some may even taken years to get sold to the consumer.
Some electrolytics, like the old Sprague Atoms, were designed specifically for repair shops. They were made to survive for years on the shelf and still work fine. I have a bunch of these that are over 20 years old (when I was more active in repairing and modding amps). Even after all this time, I've yet to encounter a bad one. I'll run them up to full rated voltage make sure, but not a single one has failed or tested outside of usable parameters. They may not test as new, but they all were plenty good enough. I do have the means to test them too. Later production Atoms appear to be cheaper grade caps jammed into the old axial cans. I don't trust those.
Now I also have some of those grey colored ICC caps from the same period, that I have tossed a few out. They're kinda suspicious, being the same ones that Fender used that leak and drip goo in their re-issues and "Blues xxx" series.
Don't have a lot of F&T's, but I recently used a couple that were about 10 years old and no problem at all. Just as good as the older Sprague Atoms.
So 5 years old or less, I'd just use them, unless they're some weird off brand, or known for problems. Scuff the leads clean of oxidation and go to town. Test them at voltage if at all possible.
Now, I will NOT sell old-stock electrolytics on a repair job. If someone pays for a re-cap, they're getting a re-cap with fresh parts that are tested before they go in.
But for my own noodling around, I'll use 'em with no worries.
If you're manufacturing electronics in high volume, most eletrolytic capacitor datasheets will say the parts need to be used within one year. Some capacitor makers offer re-processing services for high-volume customers so they can send back inventory and have the parts re-formed and re-certified if they're approaching that year mark. (for a fee of course)
There are other considerations for that reasoning, like solderability of leads and especially for surface mount factors like MSL (moisture sensitivity level). A lot of SMD parts have to remain in their sealed packaging, right up to the point they get fed into the pick-and-place machine. If they're out of the package for 24 hours, they have to be baked for hours at specific temperatures. Others are days or weeks or months.
Same goes for circuit boards, which have a limited life once they're fabricated, or they are likely to have a high fallout during high-volume soldering process.
That's for statistical reasons in high-volume manufacturing mostly. The cap company asserts a certain life and performance for their parts, and their customer who's inserting them on the assembly line, designed their end product to hit certain reliability figures at the minimum of cost. They know that if they make 1-million car stereos, some will sell right away, some will take months, some may even taken years to get sold to the consumer.
Some electrolytics, like the old Sprague Atoms, were designed specifically for repair shops. They were made to survive for years on the shelf and still work fine. I have a bunch of these that are over 20 years old (when I was more active in repairing and modding amps). Even after all this time, I've yet to encounter a bad one. I'll run them up to full rated voltage make sure, but not a single one has failed or tested outside of usable parameters. They may not test as new, but they all were plenty good enough. I do have the means to test them too. Later production Atoms appear to be cheaper grade caps jammed into the old axial cans. I don't trust those.
Now I also have some of those grey colored ICC caps from the same period, that I have tossed a few out. They're kinda suspicious, being the same ones that Fender used that leak and drip goo in their re-issues and "Blues xxx" series.
Don't have a lot of F&T's, but I recently used a couple that were about 10 years old and no problem at all. Just as good as the older Sprague Atoms.
So 5 years old or less, I'd just use them, unless they're some weird off brand, or known for problems. Scuff the leads clean of oxidation and go to town. Test them at voltage if at all possible.
Now, I will NOT sell old-stock electrolytics on a repair job. If someone pays for a re-cap, they're getting a re-cap with fresh parts that are tested before they go in.
But for my own noodling around, I'll use 'em with no worries.