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I am using a Hafler 9300 THX power amp which is now 16 years old. It has been turned off when not in use, and I would describe its usage as light over the years, by audiophile standards. By professional standards, that would be very light.I have been told to expect the electrolytic power supply filter capicitors to fail, maybe soon. My pedestrian research has revealed that these caps are specially sized and very hard to source even now, with worse prospects in the future. The power transformer is also specially sized, and I have been told by John Hillig not to expect to be able to replace it if it fails.
I may have a slight symptom of the capacitors or transformer failing, or it may be my imagination. When I turn the amp on, I hear a momentary hum from the amp (not from the speakers) that may have become louder than it used to be.
I would like to get another year out of this amp, at a usage level that would be about the same as in the past or a little more. Would these two components be placed under more stress by leaving the amp on or by turning it on and off, maybe 5-7 times a week?
Follow Ups:
the simple version of the way most electrolytic caps work is: there's an anode and a cathode, one is a post and the other the liquid in it. For a dielectric to separate the two and create capacitance, they rely on some type of oxide to form on the post while current is flowin, and this oxide *is* the dielectric. It takes some operation to initially form the caps, and continued operation to keep them formed. If they are good quality caps they might last 30-40 years if they are kept formed.
Power supply caps as Used in the Haflers (which actually use decent quality components) are long lived. Age is THE big factor in deterioration, as is long periods (years)of non use
IF paranoid visually inspect them for obvious leakage no subtlety there Leaky large PS caps make a mess. When the caps ae old and tired they often need to 'reform' when first turned on after periods of non use (actual length of non use varies with the condition of the caps).
This 'reforming' process is usually evidenced as a Motorboat sound.. Unpleasant and disturbing.. but usually short lived.
Also of note, is that any passably skilled Tech can check the PS caps for ringing.. as a precise indicator of their condition. Doesn't have to be magic.. there is lotsa science available :-)
Personally I wouldn't seriously worry about replacing those caps unless they motorboat at every or possibly every few turn ons.
Electrolytic caps lose the water from their electrolyte paste. Heat from other circuit elements in a poorly-ventilated cabinet, or internal heat from large amounts of ripple current, can raise the temperature and cause the water to be lost.This is the general reason for the limited life-span of electrolytic caps, but each unit will age at a slightly different rate. There are two ways to tell if your units are near death. Measuring the equivalent series resistance (esr) with a specialized meter is one. Another is to weigh them. All caps of the same model number should weigh the same. If one or more are significantly lighter than the others, then these have lost a lot of water and are closer to death.
I've found that a big electrolytic cap can lose a lot of weight and still show a low esr, so I consider the weight test to be more sensitive.
If your amp does not have a soft-start circuit, the hum you hear is the transformer being overloaded upon start-up. It would be worth checking to see if there is a surge-limiting device (a specialized thermistor) at or near the AC input. I don't know if these things fail to a short-circuit, but what you hear suggests that your amp has one and that it is failing.
Since an electrolytic capacitor is a sealed container, how does the water - as miniscule as it may be - disipate or evaporate?
What do you attribute measurable weight change over time to?
" ... Measuring the equivalent series resistance (esr) with a specialized meter is one. Another is to weigh them. All caps of the same model number should weigh the same. If one or more are significantly lighter than the others, then these have lost a lot of water and are closer to death. ..."Wow, what a great tip. Thanks so much. I can see how you are right here, the electrlytic drying out = lighter weight ... Good tip, keep 'em coming!!
While the same physical part may no longer be availble, individual capacitors are. IOW you can make up the required capacitance value(s) with individual descrete parts. The circut will function as intended but just not cosmetically look as before. If the unit has a cover, this inner appearance matters not. And due to modern construction technology permitting smaller physical packages than previously for the same capacitance value, there may be sufficient space under the chassis for the new individual descrete capacitors while leaving the original can cap in place (but disconected) to preserve original cosmetics. Per existing aged parts, I'd think the heat stress of 24/7 could be more detrimental than normal on-off usage.
In the last 16 years, 'lytics have gotten denser, so you may be able to find something of the same or smaller size that has the same or greater voltage and capacitance ratings.Good luck!
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