ceramic caps for cathode bypass

[mxrshiver]

any reason why not? generally love to eliminate electrolytics when i can. eyeing these pretty affordable TDK FK20X7R1C156MR000, for example: https://www.digikey.com/en/products/detail/tdk-corporation/FK20X7R1C156MR000/2256763

currently doing extensive work on a 1986 Mesa Studio 22 (not the +) that's been a workhorse for 40 years, owner's hoping to get at least another several decades out of it. replacing tantalum cathode bypass caps so that there's no risk of them eventually failing short and taking out a tube or more. heat in this amp was crazy, we're adjusting the bias but i'd still like to avoid whatever electrolytics i can, especially close to tubes. so most of them are getting replaced with film, but there's two 15uF's, and available 15uF film caps are generally just too big to fit and pretty pricey, even with lower capacitance values in parallel.

the two reasons i've heard to potentially avoid these multi layer ceramics, are that they're potentially microphonic, and that the multi layered design makes the body vulnerable to failing short if it receives impact or the leads get torqued or bent wrong. both may be of potential concern here, though the second one worries me much more. my strategy would be to be gentle with them and make sure i only bend the leads well away from the body, bracing on both sides of the bend, and use a little electronics grade silicone to make sure it stays put.

what do you folks think about the applicability of these caps for cathode bypass, and the concerns raised? anyone been using them for a while? i'd love to use these more often in the future if they're viable. but i'm not sure if their seemingly delicate construction can even put up with the heavy vibrations of a combo amp.

[ac427v]

Mouser says "Not recommended for new designs". What is that all about?

[bmccowan]

Mouser says "Not recommended for new designs". What is that all about?

I think it means that its either not in current production or will soon be obsolete. So don't include it in your next rocket ship design.
Ya know, like vacuum tubes.

[acheld]

So, I generally like those caps, and they seem to hold up well in my builds.  I've not used them as cathode bypass caps, but no reason not to.

As always with ceramic caps, pay attention to the temperature characteristics.  Capacitance will change with increased temp.  X7R not too bad, about 15%.  As a cathode bypass cap, that would be acceptable to me.   

[stratomaster]

Mouser says "Not recommended for new designs". What is that all about?

I think it means that its either not in current production or will soon be obsolete. So don't include it in your next rocket ship design.
Ya know, like vacuum tubes.

Those tags are on the tried and true 1N400x rectifier diodes. 

I can already foresee the Gear Page posts in 10 years hunting these diodes down because the UFs don't have the same mojo. 

[mxrshiver]

didn't know about the temperature coefficient with most ceramic caps, thanks for the heads up acheld! wow, if 15% isn't much of a change by comparison, that sounds like it's usually a really significant effect overall... i usually use C0G/NP0 for the low microphonics, but it seems those are also basically completely stable in capacitance across their temperature range.

this is probably old news, but this makes me think that it's a major factor in some amps gradually sounding different after long periods of warming up...