[Milsurplus] Fwd: Re: BC-348-R Paper Capacitors

[AKLDGUY .]

What have you got to lose by trying it?
Perhaps a little extra noise as the capacitors dry out.

73 de Neil ZL1ANM


On 2/27/16, Bruce Gentry <ka2ivy at verizon.net> wrote:
> Slow cooking to drive out moisture doesn't always work. The foil
> windings in the condenser corrode from the moisture, and the products of
> the corrosion impregnate the paper and make it conductive. Also, the
> paper may contain acids  that do the same. Once this happens, drying the
> paper out will not eliminate the leakage completely.
>
>        Bruce Gentry. KA2IVY
>
> On 2/26/16 5:04 PM, AKLDGUY . wrote:
>> Should be a lot better than 1 Meg, even by 1940's standards. Paper is
>> absorbent. The fact that moisture got in means that it can be driven
>> out. What has happened is that old sets don't get turned on, in some
>> cases for decades. Retain those old caps but run the set more often.
>> The heat in the set will drive out the moisture, slowly but surely.
>>
>> 73 de Neil ZL1ANM
>>
>> On 2/27/16, Bruce Gentry <ka2ivy at verizon.net> wrote:
>>>
>>>
>>> -------- Forwarded Message --------
>>> Subject: 	Re: [Milsurplus] BC-348-R Paper Capacitors
>>> Date: 	Fri, 26 Feb 2016 15:51:33 -0500
>>> From: 	Bruce Gentry <ka2ivy at verizon.net>
>>> To: 	k2cby <k2cby at optonline.net>
>>>
>>>
>>>
>>> The leakage you are seeing is very excessive even by the standards of 70
>>> years ago. Paper condensers are not junk, but they don't age well. For a
>>> radio that could easily be destroyed within a year or so of manufacture,
>>> using less expensive condensors made of more plentiful materials made
>>> sense.  AudioPhools actually search for good ones, and they are also
>>> made today for specialized applications. There was a brand of condenser
>>> called Micamold, it was a paper condenser in a molded plastic case to
>>> look like a mica and make the buyer think they were getting a mica at a
>>> bargain price. Other manufacturers also made them. I always get rid of
>>> them because they may be good now, but can fail without warning.
>>>
>>>
>>>         Bruce Gentry, KA2IVY
>>>
>>> On 2/26/16 2:56 PM, k2cby wrote:
>>>> The BC-348-R uses two varieties of .01 uF postage stamp capacitors.
>>>>
>>>> Part numbers beginning 12- are micas and seem to be in good shape.
>>>>
>>>> Part numbers beginning 11- are rectangular black paper capacitors are
>>>> .01 uF 10% capacitors rated at 500 volts and used in non-critical
>>>> plate and bypass applications. I discovered that one of these had
>>>> shorted and taken out the dropping resistor associated with it. This
>>>> prompted me to pull out one of the other paper caps.
>>>>
>>>> My Heathkit capacitor checker showed “bad” with any voltage above 50
>>>> or so applied. In the bridge mode I could not get a null, but my
>>>> digital capacitor meter showed .01 uF – right on the money.
>>>>
>>>> I then decided to see “just how bad” and connected the cap to a
>>>> variable dc supply. With 250 volts applied (the BC-348 uses just a bit
>>>> over 220 volts B+) the cap drew 220 uA, corresponding to a resistance
>>>> of about 1.16 Meg.
>>>>
>>>> I checked a couple of other “11-series” capacitors with the same result.
>>>>
>>>> In today’s world a capacitor with these specs wouldn’t pass muster.
>>>> Before I yank out and replace all of them, I wonder whether these were
>>>> passable values for a bypass capacitor in the 1940s with “a war on.”
>>>>
>>>> Any thoughts?
>>>>
>>>> Miles B. Anderson, K2CBY
>>>> 16 Round Pond Ln.
>>>> Sag Harbor, NY 11963
>>>>
>>>> k2cby at optonline.net
>>>>
>>>>
>>>>
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>>>
>>>
>>>
>
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