[wplash666]

I have a 20 yo. 9B-ST and noticed  the volume in one channel was a good bit lower than the other channel i was using ( using as 2 ch. only.)
was thinking it had to be age . Switched to another channel and everything evened out. Just curious. Thanks.

[JeffO]

There are formulas for determining the life span of a capacitor that depend on the operating temperature and applied voltage verses rated voltage.  I would assume given the 20 year warranty Bryston has designed their amps with a significant margin so the capacitors will not degrade much over that period.  That said the materials used in capacitors do degrade over time and 30 years is good life span.  I have an old 32 year old amp that I use occasionally and I get nervous every time I start it up.   

In a way I was lucky with my 9B-ST in that one channel failed after 19.5 years and Bryston replaced all the transistors and capacitors while it was in for warranty service.  Got to love Bryston's service.   

As for how to tell when to replace, I have only seen an issue when they start to leak. 

[Jozsef]

Firstly, we are talking about electrolytic capacitors invariably aging and degrading with time, not plastic ones, which is not to imply that plastic caps are immortal but they are pretty reliable and stable. The specific characteristic at issue is dielectric absorption which gets much worse as the years go by. This is a well documented, measurable and audible phenomenon rather than any mysterious audiophile thing and it sounds truly muddy and dirty when present in excess. Ten year old electrolytics generally need replacing but I understand that Bryston's choice of exceptionally high quality caps means they will last for 20 years. Their charge for doing this is very reasonable and I routinely take in old 2B and .5B units for friends. If the currently used parts actually work well for 30 years, that would be very good. I simply don't know, but some years ago I was told 20 years. Desoldering and testing these caps for DA is obviously far more trouble than it's worth for any end user so I always err on the side of tossing old caps.

[CanadianMaestro]

If the currently used parts actually work well for 30 years, that would be very good. I simply don't know, but some years ago I was told 20 years.

That would explain the 20-yrs warranty of Bryston amps.   

[Jozsef]

That would explain the 20-yrs warranty of Bryston amps.   

A reasonable hypothesis but my understanding is that it was arrived at through an elaborate set of calculations involving the cosmological constant in order for it to harmonize seamlessly with the solar system. (And regions beyond, of course.) No expense was spared to avoid any dissonant factors even of a peripheral nature. These are not careless people.

[konut]

If your caps are old enough to vote, they are suspect.

[maty]

[Jozsef]

While I don't pretend to know what the terms on the graph mean, I'm pretty sure it's about service life. In a control circuit, electrolytics can last a very long time but in an audio application we are concerned with the deleterious sonic effects of an increase in dielectric absorption which happens much sooner than any loss of capacitance or other failure such as swelling or leakage. These eventualities are estimated by graphs of ambient temperature vs time.