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

[Dennis DuVall]

Results not predictable or reliable and not worth the risk of failures that can destroy other hard to replace components down the way.

Dennis DuVall, W7QHO 
Glendale, CA

******************
> On Feb 26, 2016, at 7:34 PM, AKLDGUY . <neilb0627 at gmail.com> wrote:
> 
> 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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