Chuck McManis <cmcmanis(a)mcmanis.com> wrote: Hi There are a couple of issues here. When electrolitics aren't used for a long period of time,they need to be reformed. This is an electro-chemical action. The way to do that is to bring the voltage up slowly. Now for the bad part. First many pieces of solid state electronics will draw higher current until the voltage properly biases things off. This is normally not a problem since the power supply usually comes up fast. Even worse, if the supply is a switcher and not a linear supply, bringing the AC voltage up slowly will most likely blow the supply. Many older switchers don't have brown out protection. Because of the way they work, the run the switching part hard enough to get the full output voltage and current. If the input voltage is low, the input switcher will draw more current until it meets the power requirements of the output. Since the input switching transistor(s) main limit is how much current goes through them, they will often blow out. If you fear the electrolitics are vary old, disconnect one lead and form them from a bench supply and a current limiting resistor. Dwight

At 12:49 AM 4/24/99 +0100, you wrote: I have. The ones in my PDP-12 were leaky enough that they drew too much current and took out the bridge rectifier. Had to reform them. --- Jay R. Jaeger The Computer Collection Jay.Jaeger(a)msn.fullfeed.com visit http://www.msn.fullfeed.com/~cube

Upon the date 12:39 PM 4/23/99 -0700, ss(a)allegro.com said something like: Variac is a trademark name for a variable transformer made by the old General Radio Company in MA which came into common usage like the Crescent brand of adjustable wrenches has. Anyway, being an old radio nut, there is much truth in what ss wrote as I've been restoring AC operated radios for just under 30 years. I can send privately some comments I kept from one of my radio email lists in reference to reforming electrolytics and what happens to cause them to fail. Not appropriate on-list as it would actually be off topic. I just have to hunt them up from either the list's archives or mine first. Those comments discuss the technical aspects of how an electrolytic capacitor will literally degrade over time and need to be reformed well during its next power-up. Reforming steps are also discussed. A shorted electrolytic as a result of the dielectric either deteriorating from disuse or even occasionally from just slamming its normal working voltage on it after years of being idle is not too much fun. Rather rare to happen, but trust me, not fun. The computer-grade electrolytics we usually see in our computer gear may not be immune to such failures but I haven't yet seen one yet. Incidentally, as for Crescent wrenches, the original Crescent Tool Company which began here in Jamestown made them. Invented by a Swedish immigrant in 1905 down on Harrison Street just off Brooklyn Square. Crescent was bought by Cooper Group in early 70's and everything hauled down to North Carolina where labor and other costs (especially taxes!) were cheap. Xcelite tools (nutdrivers, screwdrivers, etc.), from nearby Orchard Park (Buffalo suburb), met the same fate a bit earlier. At least Chan-nel-lock (adjustable gripping pliers) from neaby Meadville, PA is still in its home town. Everything headed South from the industrial Northeast during the 70's and 80's it seemed. That's my bit of off-topic info for the day :) Regards, Chris -- -- Christian Fandt, Electronic/Electrical Historian Jamestown, NY USA cfandt(a)netsync.net Member of Antique Wireless Association URL: http://www.ggw.org/awa

About ten years ago, I was using a 2 metre amateur radio power amplifier, that had been in storage for a few years. It ran fine for several days of intermittent use, but one quiet Sunday morning, as I was excitedly working another amateur station via the moon (this was EME operation where both hams use the surface of the moon as a passive reflector), two electrolytics in the amp's power supply exploded, sending a fireball and thousands of pieces of paper dielectric through the top of the amp and into my ham shack. Needless to say, the breakers tripped, and my contact was over. My wife heard the explosion, came to the hallway, and asked "what was that??" She still tells friends of my calm reply "Can you bring the fire extinguisher up here, please?". That afternoon, with a $5 expenditure on new electrolytics, the amp was operational again. Kevin -- Kevin McQuiggin VE7ZD mcquiggi(a)sfu.ca

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