Re: OT question about oil filled caps

ebrucehunter
 

Speaking of reversed electrolytic capacitors, several years back, while working on a piece of test equipment and checking voltages, I founda mis-connected selenium bridge rectifier was causing the polarity of the 12V DCfilament supply for a critical vacuum tube to be reversed. This forced the 3000 mfd/15 V filter capacitor (a Sprague TVL-1170clearly marked "can negative"), to operate with reversedpolarity. The instrument had apparentlybeen functioning this way since leaving the factory in 1965. Surprisingly, the capacitor measured 2420mfd and exhibited low leakage current in this reversed polarity operation. WhenI experimentally tried applying the proper polarity to the capacitor, theleakage current soared. It appears that at the factory the relatively highinternal resistance of the selenium bridge rectifier might have limited theleakage current sufficiently until the capacitor could reform itself for a lifeof reverse polarity operation.

Bruce, KG6OJI

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