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Old 18th May 2012, 09:45 AM   #11
DF96 is offline DF96  England
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Join Date: May 2007
If you think your replacement caps may have sat on a shelf for some years then a gradual increase in voltage will avoid any accidents. Low voltage caps are generally better in this respect than those used in valve circuits, but gentle reforming won't do any harm and might do some good.

The easiest way to do this is to use an external power supply and just let the caps charge up gradually through a resistor. Monitor the cap voltage. If it rises steadily following the usual CR curve then the caps are fine. If they slow down and then creep up they are reforming themselves. Any fizzing noises switch off and leave the room! Discharge fully through a resistor before putting them in the circuit. After discharging, leave a short across them for a while. Don't use a short to discharge them!

ooops, sorry forgot that some of them are higher voltage caps - definitely reform before using unless you know they are factory-fresh

Last edited by DF96; 18th May 2012 at 09:47 AM. Reason: add oops
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Old 19th May 2012, 04:23 AM   #12
oneir is offline oneir  United States
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Thanks, this is very helpful - I didn't know how it was done. [QUOTE=DF96;3027838]If you think your replacement caps may have sat on a shelf for some years then a gradual increase in voltage will avoid any accidents. Low voltage caps are generally better in this respect than those used in valve circuits, but gentle reforming won't do any harm and might do some good.
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