Post by Steve Deckert on 02/01/19 at 02:15:22
We use Sprague Atom, Nichicon and F&T electrolytic caps. The voltage in most of our amps is around 330VDC and the caps are rated at 450 and 500 volts. The caps are rated at 85 degree centigrade. We run them at less than 60 degree centigrade. The quality of these caps and the technology of the electrolytic is superior to amps built in the 1950's. We fully expect them to last between 40 or 50 years.
Film caps, often used in the signal path never fail.
Hope that helps!
Just for a perspective, we feel these three brands are the best there are. Using the exact same rating (450V) Ruby caps, which are no doubt re-branded Chinese caps, will fail in the first few years. We tried this brand back in 2004 and purchased 100 caps. Virtually all have failed and it is now 2019. These were very pretty capacitors with great specks and all the hype. After that experience we have never used anything but the three mentioned, and today we only use F&T from Germany because there isn't anything better for our application.
YOU CAN NOT TELL in today's world what is a good cap without experience.
Here is a picture of the RUBY cap I used as an example. As you can see it is actually rated at 105 degrees Centigrade! These temperature ratings are suppose to determine how long the caps will last in hot environments. If the electrolyte inside the cap dries out from heat or leaks out from pressure, such as has happened in the second picture, the cap will fail.
100 caps purchased, 100 caps failed. Not one saw a temperature above 59 degrees centigrade, nor did they see more than 330 volts, and none of the amplifiers osculated or shorted or presented anything other than normal operating conditions, so I guess the answer to the question should you re-cap and older amp, if it's Decware, no, if it's not, possibly yes.
In fairness, this issue wasn't really RUBY's fault except for their decision to rebrand a Chinese capacitor as their own with no way to grade their quality. RUBY rebrands Chinese tubes with EXCELLENT results over the years because they grade the tubes and keep only the ones that actually worked and dump the rest. No way to do that with capacitors without some really elaborate lab gear and even then, without watching the actual caps being made on site, and being a cap expert, you're just screwed. RUBY was no doubt lied to by the manufacture or the manufacture was incompetent... either way a lesson learned that probably cost me more than RUBY since each amp repair was a minimum 100.00 bench fee covered under warranty. Nevertheless I can still recommend RUBY tubes, but nothing else.
-Steve