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Old 11th Jul 2017, 4:15 pm   #1
greenstar
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Default Rejuvenating condensers

I came across this interesting wrinkle in a 1935 Practical Wireless. It might not be practical for the smaller cylindrical jobs, but I'm wondering if it might be worthwhile for the larger sort in tins, including the multiple capacitors. I have heard of people drying out waxies, this seems a further process. I would guess it would be done if there was much value in it.
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Old 11th Jul 2017, 4:37 pm   #2
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Default Re: Rejuvenating condensers

Fascinating...! Just goes to see that the "make-do-and-mend" attitude predates WWII.

Must admit, I've wondered whether there could be a market to sell old "Vacuum-reclaimed" waxies back into the hardcore audiophile community.

Sticking them [the waxies, not the audiophiles that is] into a vacuum-chamber and using a turbomolecular pump to wind them down to 100 nanoPascals for a day or so should get any absorbed/adsorbed dampness out of the paper dielectric and bring about a several-hundred-fold increase in their resale value!
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Old 11th Jul 2017, 5:06 pm   #3
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Default Re: Rejuvenating condensers

Now that's what I call a proper repair!
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Old 11th Jul 2017, 5:25 pm   #4
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Default Re: Rejuvenating condensers

Quote:
"Vacuum-reclaimed"
Better still, do it with the capacitor in a bath of molten wax, when the vacuum is let down wax will fill the gaps.
 
Old 11th Jul 2017, 5:47 pm   #5
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Default Re: Rejuvenating condensers

I am wondering what chemical raction could occur between aluminum plates and wax to create bubbles of a gas?

I am thinking about one that cannot be spotted during long term testing, maybe hydroxides in the wax ?
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Old 11th Jul 2017, 6:12 pm   #6
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Default Re: Rejuvenating condensers

If you drop anything - such as wooden or cardboard coil formers - into hot molten wax, the moisture boils off as a gas and bubbles up and away. I don't know how permanent this is, but would guess it could be as 'good as new'. Maybe a decade or two? I suppose this isn't as good for reliability as replacement with a modern component, but it does preserve the original more completely and could possibly be repeated!
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Old 11th Jul 2017, 6:21 pm   #7
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Default Re: Rejuvenating condensers

It's not just the effect of moisture ingress: Waxes can degrade with age and their conductive/dielectric properties change: I've had plenty of trouble in times past with the "wax" that Japanese radio-manufacturers slathered over the RF tuned-circuits in VHF/FM tuners and amateur-radio gear in the 1970s and 1980s. It degrades and can cause sufficient loss-of-Q in tuned-circuits to stop VFOs and crystal-oscillators from oscillating, and cause enough damping to mean you lose tens-of-dB of sensitivity if this stuff's still on the RF front-end circuits.

I don't like wax, or waxies.
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Old 11th Jul 2017, 6:27 pm   #8
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Default Re: Rejuvenating condensers

Just moisture absorbed by wax ? OK, I thought there was some small gas bubbles on the plates.
I would apply the same HV to both terminals to separate the plates evenly (when hot).

Thank you,

Jacek

PS :Sounds like a good idea for a good valve amp bussiness : original waxies, carbon resistors, transformers, high voltage, valves, lots of heat (I don't care, got AirCon, because there is too much heat from my oil rigs)
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Old 11th Jul 2017, 6:44 pm   #9
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Originally Posted by G6Tanuki View Post
Sticking them [the waxies, not the audiophiles that is] into a vacuum-chamber and using a turbomolecular pump to wind them down to 100 nanoPascals for a day or so should get any absorbed/adsorbed dampness out of the paper dielectric and bring about a several-hundred-fold increase in their resale value!
In case anybody else likes equivalents, 100 nPa is about one ounce per square mile .....
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Old 11th Jul 2017, 6:58 pm   #10
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Default Re: Rejuvenating condensers

I guess the thing is to try and see how well it works. I am thinking of the often green rectangular tin things found in early 30's sets. When I have chance I will do so!
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Old 11th Jul 2017, 7:24 pm   #11
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Lovely Julie, I like mad units too!
 
Old 11th Jul 2017, 8:45 pm   #12
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Thought you might, seeing your 32nHz frequency for the Sun

I've probably mentioned this before, but the kinetic energy imparted by a ten-ton truck stopping from 60 mph is scarily close to 1kWh. (60 * 1609.344 metres in 3600 sec. = 26.8224 m/s.; 0.5 * 10000 * 26.8224 * 26.8224 = 3597205.709 J. 1 kWh. = 1000J/s. for 3600s. = 3600000J.)
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Old 11th Jul 2017, 10:10 pm   #13
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Default Re: Rejuvenating condensers

Speaking of green rectangular tin things; were these condensers oil filled in the 1930's? What record of continence/incontinence do they have please?
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Old 11th Jul 2017, 10:34 pm   #14
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Default Re: Rejuvenating condensers

General consensus from previous threads is leakage may be caused by chemical decomposition in the oiled paper as the failure occurs just as commonly in well sealed capacitors. It would still be interesting to see if this works although not wildly practical. I may have some 1930's paper caps in tin somewhere that I have not yet pulled apart.
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Old 11th Jul 2017, 10:48 pm   #15
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Default Re: Rejuvenating condensers

Quote:
Originally Posted by G6Tanuki View Post
Fascinating...! Just goes to see that the "make-do-and-mend" attitude predates WWII.

Must admit, I've wondered whether there could be a market to sell old "Vacuum-reclaimed" waxies back into the hardcore audiophile community.

Sticking them [the waxies, not the audiophiles that is] into a vacuum-chamber and using a turbomolecular pump to wind them down to 100 nanoPascals for a day or so should get any absorbed/adsorbed dampness out of the paper dielectric and bring about a several-hundred-fold increase in their resale value!
You could even claim this as some novel new treatment like cryogenicly treating cable and even valves, I see a whole new market for genuine old super audio capacitors!.
greg.
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Old 12th Jul 2017, 10:39 am   #16
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Default Re: Rejuvenating condensers

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Originally Posted by The Philpott View Post
Speaking of green rectangular tin things; were these condensers oil filled in the 1930's? What record of continence/incontinence do they have please?
In my limited experience the green ones - or possibly grey - were usually wax filled, TCC, plus brown bakelite Dublier but there were certainly oil filled caps by the 40's in military sets, BC312 etc. Oil said to be rather toxic. They can leak.
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Old 12th Jul 2017, 1:31 pm   #17
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Default Re: Rejuvenating condensers

Paper exposed to air slowly carbonises at room temperature. If that contributes to the leakiness of waxed paper caps, it's not reversible.
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Old 12th Jul 2017, 3:20 pm   #18
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Default Re: Rejuvenating condensers

Forum member GMB has done some similar research:http://www.vintage-radio.net/forum/s...ad.php?t=48730
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Old 12th Jul 2017, 8:08 pm   #19
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Default Re: Rejuvenating condensers

The one I was mindful of is inside an early Avometer, it is a TCC in green, 2 1/4" x 2" x 5/8".
There was a stripe of a slightly oily deposit on the inside of the glass and I wondered if it derived from this component.

I am not brave enough to test it in-situ as I don't think it has seen any action for a very long time! I also doubt I would be confident enough to try and reanimate it if it failed to hold charge.
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Old 9th Aug 2017, 12:05 pm   #20
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Default Re: Rejuvenating condensers

Last weekend I found nearly half a kilo of assorted unused wax paper capacitors (Ducon and UCC) at a garage sale, so I've been experimenting with the simmer in paraffin wax method. It works very well, but it takes around three hours to fix medium sized capacitors. These capacitors have wax-coated cardboard tube cases plugged at the ends with plastic. I'm using a mixture of paraffin and brown model making wax for resealing. I think the modelling wax is mostly carnauba, and it acts to reduce the brittleness of the paraffin.
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