Replacement ceramic caps.

[ThinkingGrenade]

ok, needed some replacement ceramic caps for a project.  replacing some 30 year old stuff, ordered and these arrived. ( small blue ones)

rated 4700pf at 3kv. - tested also, capacitance is accurate.  - am i being an idiot, or have components just shrunk? schematic for device doesnt list any other info than that.....

[Twoflower]

Yes, ceramic caps shrunk a lot. Just look at the SMD caps. I remember the time ceramic caps are only in pF ranges. Now you can get them up fo several µF. Not sure about the high voltage ones, but that one looks still reasonable.

But you should not use the blue one as to me it looks like the old one is an X-Rated cap . Unless it is X-Rated too which is not visible on the picture. Most likely the part sits in the mains input stage of the device. You must replace it with an X-Rated cap.

[ThinkingGrenade]

Yes, ceramic caps shrunk a lot. Just look at the SMD caps. I remember the time ceramic caps are only in pF ranges. Now you can get them up fo several µF. Not sure about the high voltage ones, but that one looks still reasonable.

But you should not use the blue one as to me it looks like the old one is an X-Rated cap . Unless it is X-Rated too which is not visible on the picture. Most likely the part sits in the mains input stage of the device. You must replace it with an X-Rated cap.

1kv EHT section of an oscilloscope. after the main PSU. on a separate board.

[wraper]

Unless you are replacing faulty parts, replacing such ceramic capacitors is a waste of time. Won't do any good and only could cause damage in the process. It might have less stable dielectric too. So simply buying same capacitance and voltage spec might be not good enough. Also if you bought it from china it may easily have fake voltage rating.

[wraper]

But you should not use the blue one as to me it looks like the old one is an X-Rated cap . Unless it is X-Rated too which is not visible on the picture.

None of them are safety rated. Also you might mean Y rated.

[magic]

LOL, 24Mpix and 3.6MB to show a pair of capacitors has to be the new record on this forum

And don't google what "X-rated" means...

[Twoflower]

But you should not use the blue one as to me it looks like the old one is an X-Rated cap . Unless it is X-Rated too which is not visible on the picture.

None of them are safety rated. Also you might mean Y rated.

I got suspicious as the original part shows an X before the value. Maybe I was wrong estimating the security rating.

Actually the right word is not rated but class. Sorry, if I caused some trouble...

[Benta]

IMHO, the old cap is not ceramic, but silvered mica... very common for high voltage safety approved caps. Personally, I wouldn't replace it with a ceramic cap.

[Gyro]

No, it's a standard ceramic disc. You never got silvered Mica in a circular form factor. I've never seen silver Mica used for safety applications, just RF and precision.

It's also pointless changing it unless it's actually faulty, which is unlikely. You can take a change old capacitors on sight fetish too far.