I've been sorting out my pitiful stock of components and thought it was a good time to try out my capacitance meter.
I recently bought a new pack of 10 100uF 105degree supposedly good quality lytics.
Most measured somewhere near 100uF, but two of them show around 34 and 77uF.
Normally i would have used these and most likely never known anything was wrong.
Makes me wonder about quality control though.
Testing capacitors
#1 Testing capacitors
Much to learn there is.
#2
-- Al,
If they are electrolytic they might need reforming and make read better
when they've had some DC applied.
If you're going try try this, the best advice is to apply the DC in stages and bit by bit over a long period.
cheers,
-- Andrew
If they are electrolytic they might need reforming and make read better
when they've had some DC applied.
If you're going try try this, the best advice is to apply the DC in stages and bit by bit over a long period.
cheers,
-- Andrew
#3
I did wonder about that Andrew.
But happily they were cheap enough to simply discard the "dodgy" ones.
Surely the point here is that one shouldn't have to go to such lengths.
But happily they were cheap enough to simply discard the "dodgy" ones.
Surely the point here is that one shouldn't have to go to such lengths.
Much to learn there is.
-
andrew Ivimey
- Social Sevices have been notified
- Posts: 8318
- Joined: Mon Jun 11, 2007 8:33 am
- Location: Bedford
#4
By which time the fun has all but gone.
Because none of us have bucket fulls of caps to try, compare and experiment we can only build up anecdotal evidence. Here's an example:
we all know that Black Gates are the business and all other caps are not. With my new Cap meter, ((Hong Kong £14.99.... posiible hint?) I measured a couple of non-polarised 80mfd BG bruisers. They both measured only 60mfd. After hours of duty as cathode bypass they still measured 60mfd and are now doing service in the Dodd.Special.
Other caps I have measured, be they PIO, foil in oil, 'lytics and so on have measured oddly, spot on and within the specc'd tolerance.
So,
1) avoid caps if at all possible.
2) carry on using them where you have to.
3) there is no rule 3
4) when you have the time, make substitutions and if they sound
better, keep them.
5) Never cut the specs fine on PSUs unless you want fireworks.
6) Caps try to do their job no matter how many farads they are supposed to be. They will carry on doing this until their 'di-electric' breaks down. If it don't hum its okay (may not sound that good though so back to rule 4)
7) caps are most quiet either when they are left in the box or the amplifier is switched off.
Because none of us have bucket fulls of caps to try, compare and experiment we can only build up anecdotal evidence. Here's an example:
we all know that Black Gates are the business and all other caps are not. With my new Cap meter, ((Hong Kong £14.99.... posiible hint?) I measured a couple of non-polarised 80mfd BG bruisers. They both measured only 60mfd. After hours of duty as cathode bypass they still measured 60mfd and are now doing service in the Dodd.Special.
Other caps I have measured, be they PIO, foil in oil, 'lytics and so on have measured oddly, spot on and within the specc'd tolerance.
So,
1) avoid caps if at all possible.
2) carry on using them where you have to.
3) there is no rule 3
4) when you have the time, make substitutions and if they sound
better, keep them.
5) Never cut the specs fine on PSUs unless you want fireworks.
6) Caps try to do their job no matter how many farads they are supposed to be. They will carry on doing this until their 'di-electric' breaks down. If it don't hum its okay (may not sound that good though so back to rule 4)
7) caps are most quiet either when they are left in the box or the amplifier is switched off.
#5
And to add to the good list from Andrew
8. Caps that read low with no DC, may well reform within seconds to the expected value the moment they are in use.
Without the DC voltage causing the generation of the insulating oxide electrolytic caps are little more than a pair of wires in a pot of jelly
.
The good point Andrew makes is that the stated tol on most caps is -%50 + %100, so its always best to assume they can vary by that much and design accordingly. That does make a bit of a problem, when trying to replicate the carefully tuned suplies PSD will give you.
8. Caps that read low with no DC, may well reform within seconds to the expected value the moment they are in use.
Without the DC voltage causing the generation of the insulating oxide electrolytic caps are little more than a pair of wires in a pot of jelly
.The good point Andrew makes is that the stated tol on most caps is -%50 + %100, so its always best to assume they can vary by that much and design accordingly. That does make a bit of a problem, when trying to replicate the carefully tuned suplies PSD will give you.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.