i have enough in my store to last me thru the remaining years of my life....
btw, shorting the terminals of caps not being used anytime soon is a good practice...prevents accumulation of charge....
btw, shorting the terminals of caps not being used anytime soon is a good practice...prevents accumulation of charge....
Yes 100%
I used a variac and 10k 25W resistor to limit current, doubling as a metering shunt to measure leakage.
Somwwhere I have 8×3300uF Rifa, and about 200×470uF 250V Phillip's, which I need to reform - the latter caps should keep me going with valve amp builds for decades
I just put them in the circuit and power it on. They usually are connected to the supply through 5R though.
My son is coming over to the house on Sunday so we'll see. He rescued a bunch of rack mount and general networking / telco stuff from the dumpster too. Subsequent opinions in this thread indicate they can be used if cautious about safety, circuit, and taking the time to reform them in a controlled manner.
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For relatively “new” snap-in type caps that’s probably ok. The only two caps that I specifically reformed on my last build were the two 1000uf/450v soup cans I bought from Skycraft. All the smaller snap-ins and leaded caps got “reformed” during all the slow, careful buildup to powering up the 6550’s.
The black ones were pulls from a UPS so they had probably been used within the previous year... I've had them for 2 years or so as you can see by the layer of dust!
The blue one is from 88/41 if that's a date code. I bought it for 5$ at a surplus place. Who knows the history of it but I threw 330V at it and nothing bad happened.
What's the difference in taking an amp I built 5 years ago, and connecting it? Granted I don't leave my amps off for years at a time, but still 😀
The blue one is from 88/41 if that's a date code. I bought it for 5$ at a surplus place. Who knows the history of it but I threw 330V at it and nothing bad happened.
What's the difference in taking an amp I built 5 years ago, and connecting it? Granted I don't leave my amps off for years at a time, but still 😀
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"My son is coming over to the house on Sunday so we'll see. He rescued a bunch of rack mount and general networking / telco stuff from the dumpster too" Great! Loads of decent rack mount metal too, lucky sods. If you didn't live over the pond I'd have some of those caps off you, well worth saving, you want to look at the price of those things new, they'll be more than a £100 each.
Re old caps, I always test (for leakage) and reform old electrolytics especially ones that have sat in test gear for years, like in old Tek 500 series scopes on sat in drawers, most are ok, some aren't and go bang. Aside from that it's kinder, I'm 55 and if someone woke me up without coffee then asked me to run round the block or shoved 100v up my pipe to get me going I'd be a bit grumpy to say the least.
Andy.
Re old caps, I always test (for leakage) and reform old electrolytics especially ones that have sat in test gear for years, like in old Tek 500 series scopes on sat in drawers, most are ok, some aren't and go bang. Aside from that it's kinder, I'm 55 and if someone woke me up without coffee then asked me to run round the block or shoved 100v up my pipe to get me going I'd be a bit grumpy to say the least.
Andy.
The old 'Computer Grade' class of electrolytic cap was (is) hugely better than the cheap small-value radials. The electrolyte is pH neutral (rather than the acidic electrolyte used for small types) and this keeps them stable for longer duration.
They were good for tens of thousands of hours runtime, rather than 2000 for cheap types (at max. temp) and leakage current increases much more slowly.
Spragues, along with BHC made the best quality large-can types.
They were good for tens of thousands of hours runtime, rather than 2000 for cheap types (at max. temp) and leakage current increases much more slowly.
Spragues, along with BHC made the best quality large-can types.
Pulls from UPS’s also have been formed at one time, and have some running hours on them. This also stabilizes them. Old unused ones will not have that benefit and should be formed, as should anything you don’t know the history of, even if it ends up only being a precaution. I’d hate to lose a cap which would cost $27 that I only paid 4 for get ruined just because I got lazy. Would be even worse with a $150 cap.
speaking of pulls, i had Cornell Dubillier caps with part numbers that do not appear in their websites.....
i suspect they were special orders for special costumers....but they tested very good...
3300ufd/450 wvdc, no vent seals, 2.5 inch x 5 inch tall
i suspect they were special orders for special costumers....but they tested very good...
3300ufd/450 wvdc, no vent seals, 2.5 inch x 5 inch tall
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That's good to know, I have some oddball BHC hanging around too!
But those Rifa PEG series 3300uF are huge, probably 3 inch diameter and 8 inch tall
My other hobby is restoring vintage computers. The very large capacitors from the early 1970s reform well. The smaller ones maybe 1.5” in diameter are bad more often. I put them on a current limited supply and slowly raise the voltage and watch the current for a few minutes. If everything is good at this point the cap is fine.
I would never do this with small electrolytics though. Just replace them with aluminum polymer caps and they will outlive you.
I would never do this with small electrolytics though. Just replace them with aluminum polymer caps and they will outlive you.
it looks overkill alright, but consider this, the overall impedance of the power traffo even reffered to primary will be higher than that you find in SS amps, so that that alone will act to soft start the psu as the filaments brighten up....
also the dc resistance of the chokes, the series resistors installed all mitigate the start up currents....i even installed 10 ohm NTC's.....what's to be afraid of?
but the caveats follows, do not do this if you are unsure of what you are about to do......
me too, small electrolytics are not worth the effort, just replace then with new ones and when opportunity presents itself, and when film types can suit in, then by all means do it.....
i made a 16 kt88 triode mode pp amp years back, the separate psu block contained a lot of 470ufd/450volt caps wired in series parallel connection...
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That would be great for a can crusher Can Crusher - Magnetic Implosion | Harvard Natural Sciences Lecture Demonstrations
Nice amp there Tony & agree these big caps aren't for everybody. When you discharge them with a discharger you get a nice blue arc, if they get discharged accidentally with a SC they make you jump with a bang. One thing to watch is creepage distances, I had a PCB arc over using 1100u 450v caps. but these caps are nothing compared to the big bu**ers our transmitter brethren have to deal with. As long as you use your head, design some protection and whathaveyou into the amp design your fine.
"1400uF is too small to use. You need a few of these" Nice. Got a few spare : )
Andy.
"1400uF is too small to use. You need a few of these" Nice. Got a few spare : )
Andy.
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