Cap wear on Ceramic Disc caps?

[davidsrsb]

I have always been aware that Z5U type (class III) should only be used for decoupling. When I first used X7R (class II) ~40 years ago, the age stability and voltage dependence were not widely discussed. I was only aware of poor tolerance at the time.

 

[JMFahey]

My policy with old equipment is not to mess around until there is a specific problem or solution.
The rest is all in the mind, the expectation that if this is done, it will be better.
Like coffee brewed in different places from the same beans...

Sorry but can´t back you on that one.

Exactly same beans can give WILDLY different taste, aroma, the works, and I mean from sublime to horrendous. 😀

 

[NareshBrd]

Exactly...
Like changing op amps and capacitors without modifying the circuit...
Or insisting that metal tab TIP41 are great, the plastic ones are not...it seems MJ series has better transistors.
The expectation is in the mind, and if it is satisfied, the result is perceived to be better. And it is seen as the result of action taken.
I feel the silk and hemp filled capacitors are a fad, so are B&O stereos, but they have their fans...

I lived in South India, coffee is great there.
Here, they don't know the different kinds of coffee, or the roast types. Just Plantation 'A' and Plantation 'B'. which they are not able to explain means Arabica and Robusta beans, or what A and B stand for...at a local coffee shop, they roast the beans, but that is it, they do not know anything more.

I get my coffee from a shop that sells South Indian things, he gets packed roasted coffee powder to be percolated or boiled, from South India.

South India. they add chicory to the coffee. In Africa, they add 50% Peaberry it seems.

Anyway, it was just a comparison, because I was trying to explain that like coffee, the results of messing around with a circuit, without any real need, can be, let us say. unpredictable...

 

[A Jedi]

My policy with old equipment is not to mess around until there is a specific problem or solution.
The rest is all in the mind, the expectation that if this is done, it will be better.

Yup. I'm doing all this specifically because there is a problem. The amp started sounding very dark some months ago and recently it started losing power (turning volume past a certain point no longer gets louder). I'm replacing all the caps regardless if some may not need it because while I have the whole thing in pieces, I might as well.

 

[A Jedi]

Looking at the schematic, the ceramics are mostly used for RF bypassing of inputs, so you should be fine there. Other places where a low cost amplifier might have used ceramics, NAD seem to have used metalized foil. From my superficial look the coupling and bypass caps, etc, seem to be quite generous values, so replacing like for like electros should be fine. Choose an audio grade, and if you want to be fussy replace any electrolytic capacitors that have very small voltages across with bi-polar capacitors (e.g. in interstage stage coupling). If anything the main supply capacitors could be larger. If it were my amp I would be looking for 4 x 22,000µF that will fit, or at least 4 x 15,000µF.

Thanks for taking a look. The main caps unfortunately have very tight space constraints so putting in bigger (physically) ones is not possible. The only ones I found available of the same size but higher capacitance are some Mundorfs that are more than I want to spend. I ended up ordering some CDE 10,000uF.