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Old 27th April 2009, 05:56 PM   #1
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Default Repairing paper in oil caps.

Hi all,

I have recently completed a new amp and have used some vintage paper in oil caps for the outputs. One is showing a bit of DC leakage (I had it connected up to a friends DC coupled solid state amp and it did some interesting things to his speaker cones).
I can just about live with it because my main amp has input transformers, but obviously I would like to sort it out. Unfortunately I haven't got any spares.
I understand that PIO are self healing, but I have been running these biased at about 180V for over a week and things haven't changed. There is absolutely no sign of leakage from the metal cans.

Does anyone have any ideas as to how to assist them to heal. I thought the Oil might have become a little stiff over time so was thinking that baking them in an oven for a bit might re-liquidize them and fill out the short. What does anyone think.

Shoog
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Old 27th April 2009, 06:45 PM   #2
pointy is offline pointy  United Kingdom
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Don't bake them as this will make all the oil wax

the only thing i can think of which may help is on the leak tl12 amp they have a cap block ie. multi caps soaked in a low viscosity car engine oil (by low viscosity i mean runny) so the electrolyte should hopefully be something of the like

may be vacuum the cap and feed in some oil but then you would need to reseal them afterwards.
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Old 27th April 2009, 06:49 PM   #3
pointy is offline pointy  United Kingdom
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PS....................I mean part vacuum
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Old 27th April 2009, 06:59 PM   #4
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The term self-healing is a much exaggerated phonemena that applies only to the latest capacitors. And then is limited to minor overloads of certain particular types. When an insulation is punctured by arc over, it is damaged and has a permanent weak spot. I'm of the strong opinion that "vintage" capacitors, especially the old paper jobs, are useless once they become leaky. The internal paper insulation has aged out and they should be replaced. Salvage is futile.

I also fail to fully understand the love affair with PIOs. Paper has the worst dielectric properties of any insulation material used today. It's absorption rating is high and it's release rate is poor making it a comparatively slow capacitor. Musically this translates to poor high frequency response producing a rolled off characteristic sound. Is this what people like? I would think the better plastics or teflon dielectrics should perform better, especially where transformers are in the signal path. But to each their own ears I guess.
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Old 27th April 2009, 07:01 PM   #5
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Thanks,
The oil in these is more like sticky grease so it doesn't flow well. Its that nasty PCB stuff which gives you liver cancer if your stupid enough to suck on it, so I don't really want to go opening them up.


Shoog
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Old 27th April 2009, 07:07 PM   #6
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Quote:
The term self-healing is a much exaggerated phonemena that applies only to the latest capacitors. And then is limited to minor overloads of certain particular types. When an insulation is punctured by arc over, it is damaged and has a permanent weak spot. I'm of the strong opinion that "vintage" capacitors, especially the old paper jobs, are useless once they become leaky. The internal paper insulation has aged out and they should be replaced. Salvage is futile. I also fail to fully understand the love affair with PIOs. Paper has the worst diaelectric properties of any insulation material used today. It's absorption rating is high and it's release rate is poor making it a comparatively slow capacitor. Musically this translates to poor high frequency response producing a rolled off characteristic sound. Is this what people like? I would think the better plastics or teflon diaelectrics should perform better, especially where transformers are in the signal path. But to each their own ears I guess.
Interestingly its exactly that sound which is quite appealing. Having said that, run solo they do have a rolled off sound. I had them bypassed with some 500pf silver mica caps and that made things a bit zingy. I now have them bypassed with some plastic caps which a friend gave me. My prefered option is PIO bypassed with polystyrene which seems to give a very neutral sound overall.

Its effecting the input transformers on my Headphone amp so it will have to be sorted. Unfortunately the case is drilled and mounted so cosmetically ditching them will be a disaster.

Shoog
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Old 27th April 2009, 07:51 PM   #7
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Quote:
One is showing a bit of DC leakage (I had it connected up to a friends DC coupled solid state amp and it did some interesting things to his speaker cones).
Why risk damage to other components when modern caps are so much more reliable? I'll have to agree with HollowState here. And Film/Foil types are really cheap these days....just about any poly cap will sound better than those dinosaurs!
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Old 27th April 2009, 08:49 PM   #8
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Isn't the idea of repairing caps a bit childish? Russian PIOs are available for peanuts, sound great and will probably outlast most films.
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Old 27th April 2009, 10:34 PM   #9
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Quote:
Originally posted by HollowState
I also fail to fully understand the love affair with PIOs. ... Musically this translates to poor high frequency response producing a rolled off characteristic sound.
It's a strange thing -- people who don't like PIO caps and thus who don't use them often say the reason for this is that the highs are rolled off. However, people who do like them often note the reason for this is due to the the sparkle and extension in the high frequencies.

My experience is that Vitamin Q's have good high frequency response (as do the Jupiters -- the other cap you see the same dichotomy about). The Russian stuff does too, though I dislike them for other reasons. On the other hand, many of the audiophile film caps have comparatively terrible high frequency response.

As for repairing toxic leaky antique caps? Dispose of them, but please do so in a responsible way.
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Old 27th April 2009, 10:50 PM   #10
DHT112A is offline DHT112A  United States
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Whether or not you like PIO why even attempt to repair a cap??????
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