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Why do Electrolytics sometimes need replacing?

Many customers ask about the benefits or the need for replacing electrolytics in vintage amplifiers. Unlike many components in a typical amplifier electrolytic capacitors are the one component with a finite lifetime.


Manufacturers usually specify such a component in terms of how many thousands of hours the components parameters will meet original specification at a certain ambient operating temperature. A typical figure is 2000 hours at 85 deg C. This lifetime generally halves for each 10 deg C increase in temperature (and likewise roughly doubles for each 10 deg C decrease). In an amplifier it's not unusual to find hot running components such as resistors, heatsinks, transistors etc running at 55 to 65 deg C. A poor component layout by the designer which places electrolytics close to such heat sources will adversely affect lifetime therefore. As an example in a Cyrus Two there are a number of small 85 C rated capacitors all clustered around a regulator heatsink which runs at 55 to 60C as soon as a powered mains lead is inserted at the back (i.e independent of the front power switch). These capacitors therefore are all 'slow cooking' in 24/7 temperatures of around 45C if you never switch off at the wall socket. A typical lifetime of 2000 hours at 85C is increased to around 32000 therefore in this case. This may sound a lot but if you never switch off the mains at the wall when not in use then these electrolytics could reach their end of life in barely 5 years in the worst case!. 

The symptoms of failing or failed electrolytics are varied but can include poor bass response, low level, hum or ripple on all outputs. In some cases they can even go with a bang and fire their innards around the inside of your amplifier. When replacing electrolytics those areas where failure is more likely will have longer life higher temperature ones fitted here at ARS to improve future reliability in contrast to those fitted at the factory.


Some amplifiers such as the Musical Fidelity A1 run very hot with internal temperatures of 60 deg C or more and it's always wise to have electrolytics replaced in these.  For those customers looking for an economical repair though then generally those few components known to fail prematurely are always replaced under the basic fixed price overhaul. For the best sound quality though it's best to replace all and add the full replacement option to your overhaul.

Some customers ask "can you let me know if they need replacing?" This isn't really feasible as to check each one has to be desoldered and individually measured on test equipment. By then you may as well solder a new one in having removed a 30 to 40 year old one!

A capacitor is basically two metal plates spaced apart with some form of dielectric in between, the simplest being air. However that will only result in a few tens of picofarads of capacitance at most. An electrolytic achieves a very high capacitance per size by still using two plates but these are very long instead, spaced apart by an 'electrolyte' soaked paper and then rolled up into a tube and 'canned' as in the pictures below. This 'can' needs to be well sealed as otherwise the electrolyte will quickly dry up and then the capacitance vanishes! As you can imagine the better quality longer life components almost certainly have a far better seal to avoid this happening especially when intended to be used in a hot environment.

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