[Boatanchors] 2013 myth

[Richard Knoppow]

----- Original Message ----- 
From: "KA4INM" <ka4inm at gmail.com>
To: <boatanchors at mailman.qth.net>
Sent: Sunday, July 07, 2013 1:21 PM
Subject: Re: [Boatanchors] 2013 myth


>   On 07/07/13 12:48, Bill Cromwell wrote:
>
>> To be more clear...
>>
>> I have no doubt that old paper caps are bad news. I DO 
>> replace them all
>> if I replace one while have the radio apart. The real 
>> question is
>> whether black beauties are particularly worse than any 
>> other paper caps.
>> The caps (and all other parts) in our toys are getting 
>> very old now. I
>> have some idea of how they feel (evil grin).
>
>   In my experiences and understanding, the BB capacitors 
> were paper capacitors that were encased in Bakelite which 
> was thought to be a good moisture proofing.
> That turned out to be incorrect.  Nothing special was done 
> to seal the wire entrances, (like the wire going through a 
> rubber plug) so almost if not all have incurred moisture 
> damage.
>   As it turns out the cheap capacitors that were encased 
> in wax frequently out last capacitors that were encased in 
> Bakelite by a large margin.  Many "bathtub" (soldered into 
> metal cans) capacitors have also enjoyed long lives.
>   In this world the obvious is frequently NOT the case.
> The currently used epoxy dipped capacitors seem to be well 
> sealed.
>
>   A friend of mine working on (and in between) military 
> bases in desert countries, of the far east, servicing 
> communications equipment built in the early 1960's with 
> large quantities of BB had a record of none had gone bad.
> -- 
>   Ron  KA4INM - Youvan's corollary:
>                 Every action results in unwanted side 
> effects.
> ______________________________________________________________

     Black Beauty caps used plastic impregnated paper 
dielectric and were saturated with oil.  One problem was the 
seal at the leads. The oil was injected through a tube at 
one end, the tube was sealed by soldering one of the leads 
into it. If too much heat was applied when installed the 
solder would melt and the oil would leak out.  Another 
series of caps was made by the same company under the name 
Telecaps. These had similar specs but not the oil. Both were 
sold as high quality caps capable of operating under high 
temperature conditions.  Apparently, the problems with the 
Black Beauties became evident early on as witness the 
modification work orders for military SP-600-JX receivers 
within a few years of manufacture.  Black Beauty caps were 
used in a lot of high quality equipment including 
Hewlett-Packard instruments.  Not all of them went bad 
quickly.  There were many other capacitors of similar 
construction, that is plastic impregnated paper dielectric 
in molded Bakelite cases, and most had normal lifetimes for 
the type.  Micamold and Solar made flat package paper 
capacitors using a similar impregnated paper but folded flat 
rather than being wound into a spiral.  These caps also were 
in Bakelite cases that eventually had mechanical problems 
but not for decades.  Sprague also made a series of 
capacitors with the same dielectric as the BB but with 
dipped epoxy cases under the name Orange Drop. These seem to 
have very long life and don't suffer from the mechanical 
problems of the molded case type.
     I am not sure what the plastic used to impregnate the 
paper was but it was supplosed to improve the 
characteristics of the cap.  Proabaly all of these caps 
should be replaced today because of their age.
     I saved the caps I replaced in an RCA AR-88 built 
around 1945. The bathtub type oil filled paper caps had bad 
seals and the oil had leaked out all over the bottom cover. 
It also had Micamold paper caps in the RF and elsewhere and 
a few Solar paper caps of similar type. Curiously enough the 
oil filled paper caps have less electrical leakage than the 
Micamold caps despite having lose most of their oil filling. 
All the caps I pulled out were bad.
     I found the same thing with old wax filled paper caps, 
the leakage is high.  Some of these caps will check OK on a 
bridge although the dissipation factor may be a bit high. 
The real problems show up when DC is put across them, they 
have low parallel resistance AKA high leakage.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com