UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - When is a capacitor not across the mains.

Ed_Dinning · 14th Jan 2021, 10:34 pm

Hi Chris, most Xcaps use a very thin metal film, so when a short develops in the cap, that area melts and seals off. Generally this short is of limited energy so can happen many times before the fuse will fail. It does however isolate part of the cap and reduce the capacitance as can often be seen if an old X cap is measured.

When used as a capacitive dropper this may ultimately result in the circuit not functioning as the Z of the cap is now much increased. It will not normally allow large currents to pass for a long time period, so can be used with confidence as a capacitive dropper in miniature sets.

Ed

14th Jan 2021, 10:34 pm	#18
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,195	Re: When is a capacitor not across the mains. Hi Chris, most Xcaps use a very thin metal film, so when a short develops in the cap, that area melts and seals off. Generally this short is of limited energy so can happen many times before the fuse will fail. It does however isolate part of the cap and reduce the capacitance as can often be seen if an old X cap is measured. When used as a capacitive dropper this may ultimately result in the circuit not functioning as the Z of the cap is now much increased. It will not normally allow large currents to pass for a long time period, so can be used with confidence as a capacitive dropper in miniature sets. Ed