If there's an electronic part that seems "marginal" based on how it works, it's got to be an electrolytic capacitor. Instead of having plates electrically isolated by a separate insulator, electrolytics depend upon a very thin film of oxide forming on one plate to insulate it from the other. Normally that insulation is very good, and electrolytics are a proven capacitor to use when one needs a lot of capacitance in a package that is only a fraction of the size of a capacitor of similar value made using more conventional designs. But that thin film of oxide insulation is easy to destroy.
Even so, many electrolytic caps from the 1940's and 50's are still working just fine today. Unfortunately, our electrolytics today are *not* Grandpa's electrolytics. We no longer expect most electrolytic caps to handle several hundred volts, as they did routinely in vacuum tube circuits half a century ago, but we expect even more capacitance and more advanced performance characteristics such as lower equivalent series resistance (ESR) from today's electrolytics. And, as before, size matters. In old gear, we were happy with an electrolytic that was perhaps 1" x 4" in size, compared to an average capacitor of much smaller value being one-quarter that size or smaller. Nowadays a big electrolytic is perhaps 1/4" round by 1/4" long, but that's still a huge part compared to the sizes of other modern electronic parts. The pressure is constantly on to make them smaller. Even so, most electrolytic caps can be depended upon to work for decades. The problem is with those that don't. Grandpa usually knew when his electrolytics were bad because the gain of a stage would drop dramatically or he'd start hearing lots of 120 Hz hum in the loudspeaker (electrolytics were used then, as now, to filter the output of the power supply rectifier). Lacking those symptoms, he could be confident his electrolytics were good. We're not so lucky. As before, most electrolytics are used as "bypass" capacitors whose function is to keep electrical noise off of d-c circuits by bypassing the noise signal to ground while allowing the d-c to remain unaffected. Unless the capacitor shorts (which will usually cause a the associated circuit to stop working entirely) it's often hard to tell when an electrolytic capacitor isn't working, or isn't working correctly, unless it happens to be on in our power supply. Usually some extra noise on a d-c circuit won't cause an obvious problem that is easily traced to a bad capacitor without doing some serious troubleshooting with an oscilloscope in the hands of a knowledgeable technician. As the writer of the post Doug referenced, it's often very hard to tell by operating the equipment that a cap has failed until it's replaced. There is another situation that didn't exist back in Grandpa's day either. Advanced state-of-the-art chemistries and manufacturing processes are constantly being introduced to produce smaller and smaller electrolytic capacitors. As a result, today's electrolytics tend to come from only a few factories and they use new secret, proprietary chemicals and processes. So if something goes wrong at one plant, everything goes wrong across much of the electronics industry using those caps. A few years ago an employee stole from a Japanese manufacturer the formula for the chemicals used in their electrolytics and sold the formula to a company in Taiwan. The Taiwanese company began supplying electrolytic capacitors in huge numbers to a hungry marketplace. But the thieves had not taken the entire formula! They left out a few key elements, and that omission made the chemicals unstable. After a number of months in use, those electrolytics began to fail: millions and millions of them in computers, radios, TV's and all sorts of electronics all over the world. As we constantly "push the envelope" on electronic components, we're launching a new "Titanic" almost monthly and hoping there aren't any icebergs out there, this time. Usually there aren't any, just as in 1912 Captain Smith had reason to believe the way ahead would be safe. But, sometimes... That's why buying electronics from a company with an unblemished, proven record of supporting its users over time is so important today. If you care about how well it works, if you invested enough that you don't want to throw it away if it seems "bad", you need a supplier you can trust to step up with in-depth support. I'm not an Elecraft employee, but I've had the opportunity to work closely with Wayne and Eric on many projects and have watched them provide that level of support to their customers. People who have followed the reflector have seen it happen right here time and time again when someone reports some odd situation that they don't understand, and Wayne or one of the engineering or technical support team jumps in to work with that customer to get to the bottom of the issue. Do other companies support their customers as well? I'd like to think so, but I don't have personal experience with most amateur radio manufacturers. I can say, from a great deal of personal experience, that Elecraft does. Ron AC7AC -----Original Message----- This post caught my eye. http://lists.contesting.com/pipermail/tentec/2007-September/076862.html Here is the link for the monthly archive http://lists.contesting.com/pipermail/tentec/2007-September/date.html de Doug KR2Q _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
