Ceramic capacitors are used in amplifiers for different applications
Aging does not have a destructive effect on the first both applications, but it may have a significant effect on the last application, because the resulting unwanted oscillation can destroy the transistors of the output buffer stage of a power amp.
This is because during this oscillation - as with an interrupt between the base of the Vbe multiplier transistor and pot for idle current - the maximum possible current that the mains transformer is capable of delivering flows through the power transistors of power output buffer.
This means that the power transistors will be destroyed instantly unless fast fuses provide protection.
There are to find a wide range of different versions for the ceramic caps at this place and from the first impression it is not possible to assume which dielectric material is used in the capacitor in question - thus there is no way to assess the effects resp regarding drift of critical parameters due aging after 10, 20, 30 and 40 years.
My first thought was to generally use for replace MICA caps for this application (known to have negligible effects from aging)
but in post #10 under
https://www.diyaudio.com/community/threads/is-this-vishay-mlcc-good-for-compensation-cap.300559/
I read, that MLCC is to prefer against MICA according this paper from TI:
https://www.ti.com/lit/an/slyt796a/slyt796a.pdf
similar in post #6 under
https://www.diyaudio.com/community/threads/is-this-vishay-mlcc-good-for-compensation-cap.300559/
examples for MLCC and NP0
https://www.vishay.com/docs/45171/kseries.pdf
https://www.kyocera-avx.com/products/ceramic-capacitors/surface-mount/c0g-np0-dielectric/
and Mica (in German language "Glimmer")
https://www.cde.com/resources/catalogs/STD-DIPPED.pdf
What kind of caps should one prefer in general for the aim of compensation in vintage power amplifiers in order to maintaining good RF behavior and also in order to maintaining good long-term stability - that is the main question for me in the moment.
Perhaps there are certain empirical values regarding this question - thank you very much for an information.
Currently I ask this in order to replace various ceramic caps of unknown kind in a power amp from Horch Elektroakustik model "3.0s" which provide unwanted oscillations around 2-3MHz on both channels - schematic and various images from PCB of this model under
https://www.diyaudio.com/community/...d-3-0s-what-to-3-power-output-devices.379808/
and I have heard from an other owner, that several years ago the manufacturer itself in such cases always replace all the ceramic capacitors.
This URL's don't provide the wanted information.
https://www.allaboutcircuits.com/te....-a-concise-guide-to-ceramic-capacitor-types/
https://www.diyaudio.com/community/threads/mlcc-vs-silver-mica.263994/
https://www.diyaudio.com/community/threads/ceramic-capacitors-in-audio-signal-paths.317685/
https://modwiggler.com/forum/viewtopic.php?t=156157
- a bypass for electrolytic capacitors on voltage regulators
- for low-pass filtering at the input and
- for compensation to avoid unwanted oscillations (e. g. Cdom in the Vas stage, output load of VAS stage and bypass cap in parallel to the NFB resistor between output and input).
Aging does not have a destructive effect on the first both applications, but it may have a significant effect on the last application, because the resulting unwanted oscillation can destroy the transistors of the output buffer stage of a power amp.
This is because during this oscillation - as with an interrupt between the base of the Vbe multiplier transistor and pot for idle current - the maximum possible current that the mains transformer is capable of delivering flows through the power transistors of power output buffer.
This means that the power transistors will be destroyed instantly unless fast fuses provide protection.
There are to find a wide range of different versions for the ceramic caps at this place and from the first impression it is not possible to assume which dielectric material is used in the capacitor in question - thus there is no way to assess the effects resp regarding drift of critical parameters due aging after 10, 20, 30 and 40 years.
My first thought was to generally use for replace MICA caps for this application (known to have negligible effects from aging)
but in post #10 under
https://www.diyaudio.com/community/threads/is-this-vishay-mlcc-good-for-compensation-cap.300559/
I read, that MLCC is to prefer against MICA according this paper from TI:
https://www.ti.com/lit/an/slyt796a/slyt796a.pdf
similar in post #6 under
https://www.diyaudio.com/community/threads/is-this-vishay-mlcc-good-for-compensation-cap.300559/
examples for MLCC and NP0
https://www.vishay.com/docs/45171/kseries.pdf
https://www.kyocera-avx.com/products/ceramic-capacitors/surface-mount/c0g-np0-dielectric/
and Mica (in German language "Glimmer")
https://www.cde.com/resources/catalogs/STD-DIPPED.pdf
What kind of caps should one prefer in general for the aim of compensation in vintage power amplifiers in order to maintaining good RF behavior and also in order to maintaining good long-term stability - that is the main question for me in the moment.
Perhaps there are certain empirical values regarding this question - thank you very much for an information.
Currently I ask this in order to replace various ceramic caps of unknown kind in a power amp from Horch Elektroakustik model "3.0s" which provide unwanted oscillations around 2-3MHz on both channels - schematic and various images from PCB of this model under
https://www.diyaudio.com/community/...d-3-0s-what-to-3-power-output-devices.379808/
and I have heard from an other owner, that several years ago the manufacturer itself in such cases always replace all the ceramic capacitors.
This URL's don't provide the wanted information.
https://www.allaboutcircuits.com/te....-a-concise-guide-to-ceramic-capacitor-types/
https://www.diyaudio.com/community/threads/mlcc-vs-silver-mica.263994/
https://www.diyaudio.com/community/threads/ceramic-capacitors-in-audio-signal-paths.317685/
https://modwiggler.com/forum/viewtopic.php?t=156157
New ceramics instead of old ceramics must work another 50 years I guess. That's good for me. Nobody can tell surely about a longer time.
As for MICA: they are usually larger size physically and temperature stable so film caps (possibly PP/FP or any other) must be a good replacement considering all perspectives. Of cause it is ok to replace MICA with a NP0 ceramics too but the latter is usually too small so it can be hard to fit properly or nice. A relatively larger film cap looks better instead of a large Mica than miniscule NP0 cer.cap.
As for MICA: they are usually larger size physically and temperature stable so film caps (possibly PP/FP or any other) must be a good replacement considering all perspectives. Of cause it is ok to replace MICA with a NP0 ceramics too but the latter is usually too small so it can be hard to fit properly or nice. A relatively larger film cap looks better instead of a large Mica than miniscule NP0 cer.cap.