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Old 26th Sep 2021, 6:16 pm   #1
mindburner
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Default Capacitor leakage.

hi I have some old TCC metalpack PIO 0.1uf capacitors - rated 350v

I have tested them at 300v, the highest my power supply goes up to and I get
150uA. A new Vishay equivalent is around .5 uA This on A Fluke DVM, inline current limiting resistor

I wanted to know if this leakage is acceptable in an audio circuit as I wanted to keep the authenticity of the amp (RDG1046)

many thanks and sorry for the noobish question

Last edited by mindburner; 26th Sep 2021 at 6:34 pm.
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Old 26th Sep 2021, 6:34 pm   #2
snowman_al
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Default Re: capacitor leakage

I would not trust a Metalpack for coupling duties (''that cap'' duties).

Try another test. Put the cap in series with a 1MΩ resistor. Now feed 300 volts into the cap and ground the bottom of the resistor. Measure the voltage across the resistor. If you measure any volts the cap is U/S.
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Old 26th Sep 2021, 6:51 pm   #3
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Default Re: capacitor leakage

Stick with the modern types, much better, if they where available when the amplifier was designed they would have been used. Paper In Oil, posh for the day, now rubbish.
 
Old 26th Sep 2021, 6:51 pm   #4
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Default Re: capacitor leakage

Quote:
Originally Posted by snowman_al View Post
I would not trust a Metalpack for coupling duties (''that cap'' duties).

Try another test. Put the cap in series with a 1MΩ resistor. Now feed 300 volts into the cap and ground the bottom of the resistor. Measure the voltage across the resistor. If you measure any volts the cap is U/S.
hi thanks for the reply. Yes in the past I have just stuffed them. They look great and I have the peace of mind of a new cap in there.

I did the test you suggested
.120v
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Old 26th Sep 2021, 6:51 pm   #5
Lucien Nunes
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Default Re: capacitor leakage

300V / 150μA = 2MΩ insulation resistance, definitely unusable for anything with that kind of voltage on it and disastrous for any output valves coupled from it. One would expect @snowman_al's test to produce around 100V across the resistor and 200V across the capacitor.

Even for decoupling duty they would be likely to drag voltages down significantly and might get worse with time as there will be some undesriable effects going on inside.

I fear most Metalpacks are in this condition now, they held up better than some but no longer trustworthy in general.
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Old 26th Sep 2021, 7:53 pm   #6
Craig Sawyers
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Default Re: Capacitor leakage.

At 300V that is only 2Meg insulation resistance. That is not high at all. I'd put them in the duff category.

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Old 27th Sep 2021, 8:34 am   #7
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Default Re: Capacitor leakage.

The 'Super Metalpack' version of these caps are far better and may be a suitable replacement. These were made for much tougher applications, higher temperatures and have ceramic end-seals.
They are usually in good electrical condition too - far more durable than the ordinary 'Metalpack' types.
They are quite pricey though, as many collectors of vintage amps have the same idea to use 'SuperMetalpack' to replace the standard 'Metalpack' caps...
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Old 27th Sep 2021, 10:05 am   #8
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Default Re: Capacitor leakage.

These capacitors are now over 70 years old with a design life of a guaranteed 10 years. They are now untrustworthy and useless causing damage to expensive valves and transformers.
I don't care how you test them, they are now rubbish!

To give you an example. I completely brought back to life a Murphy V114 television [1947]. I replaced all the usual paper caps but left the two .5uf 350V oil filled ones in the frame and line timebase. They were spot on value with excellent insulation but the lack of height that scanned 50% with the height control on maximum turned out to be one of the oil filled caps that tested 100%. They are not a perfect oil seal allowing tiny quantities of damp air to enter over a very long period. Oil filled line output transformers suffer the same problem.

Just restuff them as suggested. Whatever caps you use they will be 500% better than the ones employed in the 1946 RGD 1046 radiogram. They only had paper, wax, pitch and oil as insulators all of which love to absorb moisture. If you are a BVWS member you can purchase excellent caps at moderate prices and there are of course many other suppliers of good quality components. No need for fancy expensive brands. John.
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Old 27th Sep 2021, 11:08 am   #9
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Default Re: Capacitor leakage.

I have military packed bags of Metalpack caps. I keep them to show beginners of what sort of caps to replace and not use.
The above comments are pretty obvious!! CHUCK em out!!!

Sorry, mods,

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Old 27th Sep 2021, 2:35 pm   #10
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Default Re: Capacitor leakage.

thanks all for the replies. Interesting about the 'supermetalpack' versions.
I think I will just replace all 3 of the blocking PIO caps with stuffed ones. I have spare 0.1 metalpack so can include those if ever selling the amp's.
I will try and reforum the 15 and 30uf electrolytic caps
Whilst not perfect the 'stuffed' caps (pictured) look pretty decent and have a good modern equivalent inside.
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Old 27th Sep 2021, 4:03 pm   #11
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Default Re: Capacitor leakage.

Yes definitely replacement is the sane thing to do, not only in coupling roles but decoupling too. 2Mohm of leakage can really mess up the behaviour of an AGC line....
When I see metalpacks or their smaller friends metalmites in always remove them and replace with some of mr. Vishay's nice yellow goodness. Doing this turned a Pye C12 transceiver from a deaf underachieving lump into a much more usable beast.
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Old 29th Sep 2021, 5:27 pm   #12
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Default Re: Capacitor leakage.

Quote:
Originally Posted by G6Tanuki View Post
Yes definitely replacement is the sane thing to do, not only in coupling roles but decoupling too. 2Mohm of leakage can really mess up the behaviour of an AGC line....
When I see metalpacks or their smaller friends metalmites in always remove them and replace with some of mr. Vishay's nice yellow goodness. Doing this turned a Pye C12 transceiver from a deaf underachieving lump into a much more usable beast.
Yes the Vishay are perfect for this as they fit nice and snug.
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Old 30th Sep 2021, 12:11 am   #13
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Default Re: Capacitor leakage.

As well as agreeing with the wisdom of replacing those PIO caps on sight, I'd also counsel NOT dismantling and restuffing them but to dispose of them in a hazardous waste repository as as far as I am aware the "oil" in them is a PCB and that's not good for you at all.
Is it worth risking your health for a cosmetic result?
regards.

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Old 30th Sep 2021, 9:59 am   #14
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Default Re: Capacitor leakage.

Quote:
Originally Posted by bikerhifinut View Post
as as far as I am aware the "oil" in them is a PCB and that's not good for you at all.
Is it worth risking your health for a cosmetic result?
regards.

Andy
You could be right about that. I have some PIO caps but they are labelled 'No PCB oil'....They are 1970's vintage and I've used a few in non-critical items but I've also had a couple leak and make a mess in the storage tray so likely the rest will be binned.
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Old 30th Sep 2021, 11:21 am   #15
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Default Re: Capacitor leakage.

Quote:
Originally Posted by bikerhifinut View Post
As well as agreeing with the wisdom of replacing those PIO caps on sight, I'd also counsel NOT dismantling and restuffing them but to dispose of them in a hazardous waste repository as as far as I am aware the "oil" in them is a PCB and that's not good for you at all.
Is it worth risking your health for a cosmetic result?
regards.

Andy
hi yes I was under the impression that the metal pack were non PCB but there is so much conflicting information out there that it seems best to assume old caps like this are PCB. I will definitely avoid opening up the smoothing caps which appear to not have reformed that well and result in a low hum on the audio out. Leakage clearly visible around one of the 15uF
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