Replacing Mica Caps

[Winky Dink]

I know that conventional wisdom is that mica caps rarely need replacement, but I've come across several in recent months which positively read fifty percent--or more--higher than they're supposed to. And I also sometimes break off the leads. When I do replace these, what should I use? I've been using 630V polystyrene and 500V silver mica caps--whichever gets me closed to the desired value. Any better suggestions?

Thanks,
Henry

[Findm-Keepm]

Me, I'd stick to the dipped silver micas, with possibly NP0 ceramics as a backup. The silver/clear polystyrenes like to crack and open up. We serviced a lot of Sharp and Hitachi B/W sets back in the 80s that had only one problem - the polystyrene caps in the horizontal oscillator would crack, change value, and we'd replace them with "close in value" silver micas - they had some odd values like 700pf and 850pf in the larger screen sets.

NP0-tempco ceramics don't have a drift factor - so are suitable, stable alternatives to silver mica caps.

[Winky Dink]

Thanks. I will heed your recommendations.