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when do you replace capacitors?

I have read that capacitors last around 20 years. So, do you just have caps replaced as they go bad, or at what point do you replace all the caps in an amp? Do resistors or other parts (other than tubes) degrade, so replacing caps will just lead to some other failure? Is it like trying to keep an old car running?

Asking because I still enjoy the tube amp (Baron) I've had for 16 years. Not the best, but American made, still supported by Mesa, and I am not convinced that newer is better re: tube amps, or at least, not within semi-rational budgetary constraints. Equivalent performance from new production could cost dearly.
lloydc
face
516 posts
 
As Elizabeth mentioned, unused is worse.

But the correct way to reform capacitors is with a variac.
jallen
502 posts
 
i replace them if they re crap caps. I like v-caps if you have room, the REL RT, or Theta caps. Big sound difference over stock caps if they used junkers.
palasr
453 posts
 
Resistors are inert and don't really change over time (they can drift in value from thermal stress, but that's another matter).

Capacitors are a different story. Electrolytic capacitors are the ones to change; film types tend to last a very long time and rarely need to be changed. Electrolytics contain a semi-liquid dielectric compound that dries out over time (used or not) leading to catastrophic failure. Electrolytics tend to be larger in value (over a couple of microfarads); film type caps tend be much smaller in value (under 1 microfarad).
elizabeth
6,726 posts
 
Variac is the porper way to restore a cap. If your electronics item is worth a lot of money, and you have the money to spend getting it variac'ed. Do it. Otherwise the turn on style will do "in a pinch" or if you are just too cheap to get it done right. It is a 'dirty' method, but works. (than means it is not approved by anyone who actually does this stuff for a living, because it cuts into the bottom line)
face
516 posts
 
Not because it cuts into the bottom line, because it's much safer.
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