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Thread: Cornell Dubilier "greenie" capacitors

  1. #1
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    Cornell Dubilier "greenie" capacitors

    I've noticed that all of the CDE capacitors from the late 1960s in those light-green tubular plastic cases I've run across tested pretty much like new (very close to nominal value and low dissipation factor). I've replaced them, at times, for the sake of reliability, based on advice I've received, but I was still curious as to why they seemed to last so long with little observable degradation of performance compared to other capacitors from that time period (e.g., Sprague Black Beauties). Now I have a better idea.

    Not being able to find a CDE catalog from those years online, I e-mailed Cornell Dubilier, and, within a day, I got a response with a scan of a 1965 catalog. Unlike many popular capacitors from the 1960s, these have a Mylar film dielectric only; they're not a hybrid of paper and Mylar. The engineer who responded to my e-mail pointed out that these tend to last a long time for two reasons:

    The key to this series' longevity is the molded case (moisture resistant) and CDE's "Dykanol Y" impregnation (stopped using it because it contains PCBs).

    PCBs were good at controlling capacitor aging and stabilizing dissipation factor, but I wouldn't recommend cutting one open and ingesting the contents.

    Here's the scan for anyone interested. It also contains data on the "Budroc" capacitors you find in some vintage equipment.

    CDE Type PM.pdf

  2. #2
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    Cool. So it appears the green ones are more likely to still be good. Thanks for sharing the datasheet! FWIW the CDE PKM ("Black Cat"--similar appearance but black cased) are AFAIK are polyester film + kraft paper, and some of the ones I've tested were usually a bit leaky (IIRC I also encountered a shorted .68uF).

  3. #3
    Old Timer Tom Phillips's Avatar
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    Very interesting. I wonder if the blue molded caps used by Fender in the early to mid 1960's were made using the same process as the CDE greenies or were actually manufactured by CDE. The blue molded caps hold up very well. The yellow molded Astron caps used before the blues, on the other hand, virtually all went bad by the 1980s.

  4. #4
    Senior Member Mars Amp Repair's Avatar
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    Well,
    I obtained a whole bag of those green cornell dublier caps & have been using them very frugally in amps that 'deserve' them ;-]

  5. #5
    Old Timer km6xz's Avatar
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    The main reason tubular caps from that era went bad was leaks, more than stability of the electrolyte, although each had its some differences. The Black Beauties were made a little differently, they were filled through little brass tubes in the end of the cap that were sealed with solder or crimped after filling(over their production life Sprague tried a couple closure methods but with limited success). All those caps that had the little solder ball on the lead right next to the molded casing were filled that way and should be suspect. The same composition was used for some industrial and military caps that, if large values, could be refilled by design.
    I remember buying some new back in the late 50s and one had leaked in before I got it home. I never made anything using them after that. They were found in a lot of TV sets of the period and often there was an oily coating on the metal chassis from leaking caps.

  6. #6
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    Quote Originally Posted by Mars Amp Repair View Post
    Well,
    I obtained a whole bag of those green cornell dublier caps & have been using them very frugally in amps that 'deserve' them ;-]
    I'm curious as to how the Greenies sound in your amps, and what portion of the circuit have you used them in? I've got a very few good Yellow Astrons (rare) and, like many, am trying to find something a cap relatively close to those in Tweeds. Thanks, Dale

  7. #7
    Supporting Member Jazz P Bass's Avatar
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    So does this sound the death nell for Bumblebee caps.
    (as the market price collapses)
    Oh, it is so difficult being an audiofool.

  8. #8
    Senior Member Mars Amp Repair's Avatar
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    Ya know, I had a tech who used them just because of all the mojo chatter on the web about them. Frankly, I'm not entirely convinced that any caps of quality in the proper application wouldn't provide the same sound quality as these vintage ones would. you could always buy those had wrapped 'Musicap' caps that CE Dist is offering for $$$$$ ea. glen.

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