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Old 25th February 2010, 02:46 AM   #21
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I replaced 12 electrolytics today, Hammond 1968 parts labeled "AO-xxxxx" and they didn't cut costs, mostly Mallory and Sprague parts with 66 or 67 production dates. After charging with a multimeter ohms scale, 4 were leaking pretty badly, dropping 10 mv or more per second on 2 volt chargeup. 8 were probably "Okay". Two of the leaky ones were tanalum 10uf caps with 77 date code. I could have put the "Okay" ones back, but I replaced them, mostly with plastic film 20 uf caps that will never need replacing. Three caps had 77 production dates on them, so a factory tech had been in this chassis to make repairs once before. Do what you want, if I go to the trouble to remove one end to measure a cap, I'm spending the dollar to replace it with something new and long life or reliable by design. Half the electrolytics in the organ were replaced with film caps if they would fit, or ceramic if they wouldn't. The 10000 hour caps I did buy look like the caps in the long life AB motor drives, with visible seals around the wires coming out the bottom.
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Last edited by indianajo; 25th February 2010 at 02:50 AM. Reason: More data
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Old 25th February 2010, 08:32 PM   #22
clm811 is offline clm811  United States
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Quote:
I've replaced a lot of 440 VAC motor drives...
Hi, Jo.
You sound like an experienced technician... I'm a bit curious about what kind of "motor drives" you're referring to(industrial)? What have you experienced with large (>5,000uf) can caps in power amps?

I have a few amps over 15 years old that still have original PS caps, which is why I'm looking at replacements.

Thanks.

-Chas

Last edited by clm811; 25th February 2010 at 08:34 PM.
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Old 6th March 2010, 03:15 PM   #23
PB2 is offline PB2  United States
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Quote:
Originally Posted by Conrad Hoffman View Post
I have literally thousands of capacitors, mostly surplus, from nearly new to as old as dirt. The only ones that show any signs of deterioration are the HV twist locs up at 450 volts or so. Anything else can be pulled from its box, bin or bag and used without forming or anything else. The HV caps need to be slowly formed if any reliability is to be had. Newer brand name caps are better, not because they're newer, but because they're just made better from day one. Technology has advanced. Newer off-brands should be approached with caution. As I've said many times before, the best practice is to build (or buy) a simple bridge and measure the things. If C and D are good, and leakage is low at full voltage, you've got nothing to worry about.

Conrad
How old is old as dirt? It is easy with vintage tube equipment to see 40+ year old caps. I prefer to be cautious about any electrolytic cap that is more than 15 years old less for those that are highly stressed.

I tend to agree with Sakis in post #17.
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Old 6th March 2010, 05:35 PM   #24
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Default historic rubber is dirt

Many electrolytics use some form of elastomer (rubber) as a water seal. Rubber deteriorates simply due to age and atmosphere. The US government is now issuing a warning about tires over 7 years old. If a 15 year old or older cap hasn't leaked yet, it might if stressed. There are some nice pictures of electrolytic explosions on the Hammond thread of organforum.com. When an electrolytic explodes on your pcb or chassis, it takes a lot of cleaning to get back to "insulation". Admittedly these are on tube circuits, which can pump a lot of energy into the cap and boil water when it shorts. My advice on historic preservation:Save the can and the sleeve, put new smaller guts in it, make it look good.
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Old 6th March 2010, 08:07 PM   #25
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Lower voltage caps will also ooze some very nasty materials. There is the bad caps issue also:
Badcaps.net - Badcaps Home

Capacitor plague - Wikipedia, the free encyclopedia
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