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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: How long can electrolytic capacitors (in a tube amp) last? posted by Leslie Loh on September 28, 2004 at 03:00:30:
I can't speak to all the types and values used in every instrument, but I would not necessarily advocate a hard and fast time-based rule about changing out electrolytics.How conservative the designer was can play a decisive role in how long a filter cap should last. It doesn't surprise me that some of the high end instruments are seeing early failures; they are prone to be engineered less conservatively than the older classics. That's not to say that all vintage designs were conservative; there are some exceptions that are confirmed cap killers. But twelve years seems terribly short, under any standard. And almost $1,100 to replace a dozen filter caps sounds like typical high end theft to me - regardless of what designer cap brand they are.
The design of the capacitor itself is a substantial factor as well in determining its service life. In many of the vintage instruments I restore, it is typical for a 35 or 40 year old FP multisection can to reform up and operate perfectly fine at full WV. But is is also typical for most of the smaller electrolytics to be shot. You'll even get a fair share of failing small electrolytics with 20 year old gear.
But I would never advise anyone to recap something at a certain age per se without considering the instrument design and specific capacitors involved.
Don't condemn the filters because their plastic sleeves fell off; it's also possible that the sleeves themselves shrunk and broke open becuase of age and heat. Any fluid coming out of the seals of a modern electrolytic is a red flag. But "moisture" on the top of a radial cap would cause me to want to know what the fluid really was, as seepage through the top is somewhat unusual; the usual way the electrolyte gets through the top of a radial is when it explodes.
The best way to know if your capacitors are failing is to check the circuit on a scope for excessive ripple. If you hear a 60 hz hum, then you definitely have a problem. FWIW, the "power" of the power supply always comes from the power transformer; it's the job of the filters to keep up with the phase changes to hold the AC ripple under a specified threshold. If the ripple is below specification, then the filters are doing their job.
I'd find a local technician to check it out for you before you recap anything. Although it seems you have already.
Good luck!
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Follow Ups
- A word of dissent. - sgmlaw 14:00:21 09/28/04 (0)
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