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In Reply to: RE: Metallized caps require significant break-in time... posted by Steve O on March 27, 2017 at 17:26:26
I believe one has to approach cap ratings with caution when the cap is going across the AC line. Depending on mfgr, a cap rated for 600/630VDC may have a very much lower AC line rating.
I have actually seen those caps with a 1.2kv rating,mainly because of AC spikes.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
One does have to approach capacitor ratings with caution, but I am a professional amp tech with years of experience at this. Yes, capacitors do have different DC and AC voltage ratings, ratings that are usually noted on the datasheet. For example, most 1600 to 2000V DC rated capacitors are only rated 500 to 700VAC, but it's not a linear relationship. As the DC voltage ratings go up, the AC ratings plateau.
You frequently find 600V polyester film capacitors installed in guitar amps as "death caps." They could easily end up across the AC line, depending on how the ground switch was set or how the amp was plugged in. And some amps have capacitors across the output tubes plates in parallel with the output transformer. Those can see very high AC voltage swings.
For reference, both the 400VDC and 600VDC 716P types have a 200V RMS frequency-dependent AC rating. The rating starts to decrease around 12kHz, but at lower frequencies like 60Hz, the full rating applies.
...as a pro, you already know of cap rating idiosyncrasies and what might happen if not heeded. And that if used, a "death cap" should carry a type "Y" rating.
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