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  #1  
Old 18th January 2017, 08:34 AM
Riggers Riggers is offline
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Default Longevity of modern passive components

Hi All
There have been a few posts re how to know when valves will need replacing. I would like to know how long one could expect the bulk of the passive components in a modern amp to last, (ie. Capacitors and resistors).

Looking around the web at people servicing/fixing valve equipment built in the 60's and 70's the 1st thing that seems to been done is to replace ancient/decrepit electrolytic caps. Given that I own a WD88VA XL built early 2015 populated with modern high quality parts such as Soniqs polypropylene caps and the like, what sort of serviceable lifetime (barring catastrophic failure) should I expect.

Cheers

Phil.
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  #2  
Old 18th January 2017, 09:19 AM
bob orbell bob orbell is offline
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Default Re: Longevity of modern passive components

Easy answer Phil, almost a life time, only the power supply electrolytic capacitors may not do so well, but at a guess even they should exceed 40 years. BOB
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Old 18th January 2017, 10:09 AM
John Caswell John Caswell is offline
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Default Re: Longevity of modern passive components

Hi all,
The first thing to bear in mind is that there is this "disease" doing the rounds that pretty well any old equipment needs all the electrolytic capacitors and other changing "cos "Joe Bloggs" says so. I refer you to various other forums.
This is not necessarily so and often causes more problems than it is worth, as something that was working, albeit not too well, is often rendered useless.
Whilst i would be the first to admit that old capacitors should be viewed with suspicion, it doesn't necessarily follow that all old capacitors are in the same boat.
There are certain make of capacitors especially the should be deemed suspect, the Red/Black Plessey type , the Maroon ROE as used in Quad, the dark brown WIMA as used in various German products , the black HUNTS type used in the UK.
Modern products are much more reliable and will probably last the lifetime of the unit, but with elcos the thing to watch out for is temperature, overtemp will cause premature failure. When I am repairing a unit I always try to fit in 105C elcos as i do not know what environment the unit will be in.
Resistors fall into much the same categories, a modern 1/4 watt resistor is very small in comparison to one of 30 yrs ago, so for a given dissipation it will get much hotter possibly reducing reliability, so once again if space allows fit a physically larger resistor, and also bear in mind the limiting voltage placed on resistors.
I always suggest replacing output valves on a yearly to two yearly basis depending on use, but small signal valves seem to last forever.
With modern components i do not think you need to worry too much.

John
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Old 18th January 2017, 11:14 AM
Richard Richard is offline
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Default Re: Longevity of modern passive components

Long answer Phil ,

I agree with Bob and John about modern film resistors and plastic film caps. A lot of the long life is to do with newer materials (plastics, epoxy, plating etc) sealing the device. Care should be taken not to compromise that by bending the legs close to the body or leaving the gear in damp or humid storage etc.

Electrolytic caps though may have a shorter life which is usually defined in their specification. Whilst construction is better these days, sizes have become smaller, so we should check the spec.

We are familiar with seeing 85 or 105 degrees C on them and the spec will also say such as 1000, 2000, 5000 hours life.

The temperature shows the cap will work OK at that level and the hours will say for how long at that temperature. If they are de-rated by running cooler their life doubles for every 10 degree drop in temp. (Thus a 105 cap of 1000 hours rating would have equal life to an 85 cap of 4000 hours rating, all else being equal, but bear in mind an 85 cap may not work at 105 if you plan on using it that high!)

In the larger uF sizes, a good high temp 105 cap might be 2000 hours at 105. If our gear runs at 45 degrees then it would do that for,

2000 hours at 105
4000 at 95
8000 at 85
16000 at 75
32000 at 65
64000 at 55
128000 at 45

divided by 8760 hours = 14.6 years at 45 degrees

If it were the more common 85 cap in a large mF size for smoothing rated at a similar 2000 hours it would only last 3.6 years. Some are 5000 hours at 85 which would be 9 years etc etc.

Then the gear most likely will be off for a lot of the time so the temp will drop to 20 ambient and life will increase.

Putting this into practice I've recapped quite a lot of 90's solid state gear over the last few years. On several there were already blown or bulging caps and the one time I didn't do it a cap blew. But yes you can also see how some almost-unused gear from a dry cool home can have good caps at 40 years if it has been turned on every week or two to let the caps reform.

Valve gear runs warmer. I measured 48 inside my Kit88 so look to be changing electrolytics at anything over 10 years if used for long hours. Smoothing caps certainly, and cathode bypass caps also, have a hard life
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Old 18th January 2017, 06:50 PM
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Phil Y Phil Y is offline
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Default Re: Longevity of modern passive components

Hello Phil,

My experience of modern components is generally pretty positive but there are 2 things which I view with suspicion. One is paper-in-oil audio caps which I have seen electrically leaky several times and I have not had that many through my hands. I expect some brands are better than others but personally, I would never use them.

The other, in a more general sense is electrolytic capacitors. Having lived through the capacitor plague ( https://en.wikipedia.org/wiki/Capacitor_plague) in a professional environment and having with colleagues, to change large numbers of bulging and leaky caps in a "service and repair" role, I think I will always view electrolytics with skeptic eye.


Phil.
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Old 31st January 2017, 12:29 AM
bikerhifinut bikerhifinut is offline
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Default Re: Longevity of modern passive components

My WD 88VA was built by me in 2007 and the ONLY problem I have had was a bad solder joint (of my making). All coupling caps are polyprop and the electrolytics are the originals. Hope that allays any fears to anyone reading this who is worried. I get the distinct impression that the latest amp designs are much more reliable than the earlier WAD ones?
I'll also add that I haven't "fiddled" with the amp and its pretty much standard but with a few WD approved upgrades basically soniqs polyprops and Schottkies on the DC heater feeds although I ain't sure that they are proper ones as the voltage is bang on without a pi filter. Whatever, I dont care as it sounds bloody ace!

A.
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Old 31st January 2017, 10:48 AM
Richard Richard is offline
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Default Re: Longevity of modern passive components

Hi Andy,

Good to hear yours is going well. There must be many WAD and WD amps out there still going strong and we tend to only hear when folk have a problem or want to upgrade.

Time flies though and many are 20 years old now. WAD's various 300Bs and K5881s are well over 20 years - mid 90's - and many KEL84, KEL34, KIT88s etc are from the late 90's and early 00's.

Your amp is a mere spring chicken at 10 years but I'd be changing C12, C13 and C7, C8 in the next year or two rather than risk it
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Old 31st January 2017, 12:32 PM
bob orbell bob orbell is offline
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Default Re: Longevity of modern passive components

Hi Andy, if you are changing C12-13 as Richard has suggested in the near future , go for Evox Rifa, low ESR, they improve the sound no end, a bit tricky to get in due to their size but I can recommend it . BOB
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