Bryston offers a 20-year warranty on our power amplifiers and preamplifiers. For that reason, we do a great deal of research of filter capacitors. We need to be sure they will last longer than the warranty period before needing service.
As with many electronic components, it turns out that the lifetime of electrolytic caps is dependent on temperature, with lifetime cut in half for every 10 degree C increase in operating temperature. Or, to look at it another way, if high temperature electrolytic capacitors are specified, their predicted lifetime doubles for every 10 degree C reduction in operating temperature below their maximum rating. It is for this reason that Bryston uses electrolytic capacitors rated for 105 degrees C minimum. These components are normally specified for 3000-5000 hours of operation at maximum temperature and current. Bryston amplifiers run at approximately 40-45 degrees C average temperature over their operating life. If we subtract 45 degrees C from 105 degrees C, we get 60 Degrees, or doubling lifetime 6 times, equaling a factor of 64 increase in lifetime beyond its 105 degree C specification. 3000 hours X 64 = 192,000 hours, or 22 years of 24-hour-per-day operation, worst-case.
It is very important to recogize exactly what is required to specify and produce a long-life, high-temperature electrolytic capacitor: First, the design must minimize flaws and impurities in all the separate parts of the complete component. Any impurities will lead to unwanted chemical reactions which would contribute to the deterioration, corrosion and degradation of the internal materials, especially as temperature rises, eventually destroying the component. Second, internal electrical connections must be made especially low-resistance, to reduce temperature rise with current-flow, (i.e., ESR must be extremely low, in the low milliOhm range). Third, seals and methods of excluding contaminating influences must be particularly effective and long-lasting to maintain stasis of all internal materials even under brutal conditions. In short, the closer to theoretically 'perfect' design and construction a capacitor is, the longer it lasts, and as importantly, the better it does its job. That means it also sounds better because it more effectively maintains the purity of the musical signal.
There are many 'exotic' capacitor manufacturers making expensive hand-assembled components, but we find that many times they don't stand up to tests of purity and long lifetime. If Bryston finds a better component, based on actual tests of performance and construction that guarantees long lifetime, we use it.