[Hallicrafters] BBODs

Sun Mar 8 20:29:43 EDT 2015

Hi Chris,

Thanks for the response and depth of the note.  No bullets will fly.  That’s for the reflectors that allow nut cases to poison them.  

Your point is well taken and has merit.  I believe the conversation has been that the paper caps when new were better than Ceramic and had essentially the same positive attributes of the Polypropylene caps.

The problem is that so many paper capacitors had failed; some taking other parts out with them.  You have to admit that if you lump all of the paper caps of that era together you will see clearly a pattern of failure even though some are to this day just fine.  Kinda like if 80% of the red cars have break failure you likely will feel that red Chevies, Fords, BMW’s, and any other red car is suspicious especially if they take out another car when they fail.      

My concern is that a person will acquire a treasure and decide to restore it turning the radio over, replacing all of the paper caps with ceramic; one of the great tragedies of radio.  From a performance point of view, they would have been better off taking their chances with the paper.  

There’s an alternative, replace them with all Polypropylene.  Now performance will be the same as with paper but they won’t fail.

If I look at the statistical comparison of Paper or Polypropylene failure there cannot be any doubt that Polypropylene is 99.9 % safer.

Now comes the great debate.  Chris, it’s good and interesting to have these conversations regarding the mysteries of the technology.     

Do paper caps have some sort of property that sets them apart from all other capacitors where they develop a distinguishable difference in tone or quality for audio applications?

I do believe some people can distinguish something because my wife can hear these 40Kc rabbit chasers.  I brought one home last year to keep em out of the yard plugged it in outside came into the house and she said what the hell is that horrible noise I’m getting a migraine?  Both collies were sitting there wondering what she was talking about.  Went outside unplugged it and came in to my better half thanking me for turning it off.

I asked her what it sounded like and she said “I don’t know haven’t heard anything to compare it to”.  There is some substance to what people are able to hear as well as they hear what they want to.  Kind of confusing like “Go tell your mother she wants you”  

Some years ago we tried an experiment to determine whether paper or ceramic caps made a difference in audio applications.  We installed all ceramic caps in an audio amp in a recording studio owned by a retired audio engineer from Nashville and played a stored symphony track while recording it.  Then we did the same after installing paper caps and yes it was difficult to find caps that passed muster.  We played the two tracks through a mixer INVERTING one then synchronizing the tracks.  Yep, all kinds of flack on this comparison.  

Then to Polyethylene capacitors.  Synced them up with the paper track and it looked like there was nothing there.  

I find it very difficult to believe but do not discount the proposition that there is a distinguishable difference in audio performance between paper and film caps.  

I do believe some people are gifted and can actually hear the difference between Polyethylene and paper and I also believe some can hear exactly what they have come to believe they hear. 

Nothing said here is in any way meant to be offensive.  I will always wonder about this enigma.

Thanks again Chris --- these things stir a good deal of interest.

Kindest regards Jim K9AXN     

-----Original Message----- 
From: Chris Farley via Hallicrafters 
Sent: Sunday, March 08, 2015 3:00 PM 
To: Hallicrafters Reflector 
Subject: Re: [Hallicrafters] BBODs 

I'll throw throw in one kick before the horse is buried..   In lieu of the recent BBOD discussion, here's something I wrote up on the Collins reflector a year or so ago.  Enjoy, and let the bullets fly!:
To venture into dangerous territory, I will step out on a limb and counter your blanket statement- Paper caps were _not_ all junk when new. Paper dielectric capacitors are still available to this day, (at a justifiably high price!) in both metalized and non-metalized (foil instead of film) configurations for use not only in hi-fi equipment who want that paper/foil cap "sound", (Let's not get into that discussion, please), but for motor run and other various industrial and commercial settings. These are oil wetted/filled and capable of withstanding higher voltage and dissipating more heat without degradation, than a poly(x)ene film or foil caps. I'm sure Bill and others have Collins transmitters from the 30's with paper dielectric capacitors that still test just fine in the capacitance AND leakage department, even at full rated voltage. 

The main problem with the molded paper Sprague "Black Beauty Telecaps" and so-called "Bumble Bee capacitors" (both referred to as BBOD, Black Beauties Of Death) is how well they are sealed- Contrary to popular belief, the genuine Sprague "Black Beauty Telecaps" were very high quality components in their time.  The  end seals on these caps are actuallyquite good- however the molded bakelite phenolic body by unintended design, is vulnerable to cracking which allows contaminating air and moisture (oober bad) inside, and allows the oil to vent out. Ever wonder why all 600+V (and some lower voltage) Black Beauty caps have what looks like a solder ball on one end? These caps were molded DRY. The end with the solder blob is actually a very small tube/eylet which allowed mineral oil insertion under high vacuum AFTER the capacitor was rolled and molded. A lead was then slid inside this tube, and soldered in place. By molding the capacitor dry and wetting the paper later, a much lower contamination level was able to be reached during the manufacturing process. 
This is the same manor in which the much more expensive (and reliable) metal encased, glass "hermetically" sealed capacitors such as the Sprague "Vitamin Q" series were made. These caps are commonly found in the R-390A, and many other military radios from the mid 50's onward until plastic capacitors took over.  Of the ones I have removed, I have only tested ONE of these low value Vitamin Q caps to have under 500Mohm of leakage resistance, my "replacement threshold" being 200-500Mohm depending upon humidity, the phase of Mars, and just how lazy I'm feeling that day.  
To the same point, I recently rebuilt a Detrola manufactured broadcast radio from about 1932 for a friend. The cabinet had been refinished so the goal was long term reliability, not originality- So all capacitors were replaced. For kicks, I decided to check out a few of the old "guaranteed to be junk" caps.  All but one of those paper decoupling/bypass capacitors were original to the set, and made by Solar. They were metal cans with rubber end seals, dipped in wax, and had a rolled paper covering. Guess what? EVERY SINGLE ONE tested within 10% of their stated value, and had leakage greater than 1000Mohm, most approaching infinity. This from "junk when new" paper capacitors that are (almost!) older than the eldest CCA member according to the recent informal survey. 

I hope I work as well as those caps at 82....
A counter to all said above, is a personal theory...  The paper used in these old capacitors may very well not be acid free- additionally it could vary in pH from batch to batch, manufacturer to manufacturer.  This could indeed present an age alone failure, as <7pH acidic paper breaks down (At what speed? Additionally at what speed when oil impregnated??) in addition to very possibly reacting with the high purity aluminum foil. If someone has scientific analysis equipment available to them, this would make for a VERY interesting study. 

Moral of the story, not all paper caps are junk... The "shotgun replace 'em all" approach does regrettably have it's place- But should never be an automatic requirement for every piece of vintage gear- It should be done on an individual basis. Odds are if a cap passes the "life test" and still measures very good after the first 50 years, it may very well outlast you. 

Regards,
Chris kc9ieq
      From: Tom Dailey <radio at daileyservices.com>
To: hallicrafters at mailman.qth.net 
Sent: Saturday, March 7, 2015 9:14 AM
Subject: [Hallicrafters] BBODs

BBODs - Black Beauties of Death -  have been discussed ad nauseum here, but 
point of fact is that they're BAD.  Period.  I've seen 'em split, 
DEAD-shorted, leaky, and every other thing.  You may not see immediate 
improvement, but not changing them will result in DEATH of many things; not 
the least being the B+ windings on your pwr xfmr.  Yes, there are many 
differences in caps, and the explanation by Jim, was spot on. 

---
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