?? I absolutely agree with this. However, all paper caps tend to
become degraded with time. The Sprague caps seem to have had a
peculiar problem and short time failures but all old paper caps
should be suspect.
??? Old oil filled transmitting caps seem to have a longer life
than the wax filled kind. My understanding is that one function
of the oil is to eliminate air which can cause oxidation of the
paper. This may also have been the reason for using a plastic
impregnant. I thought I saw advertising from Sprague saying that
the Black Beauty caps were plastic impregated but was not later
able to find it. The paper looks like it has a coating of something.
??? I would certainly be interesting to know the manufacturing
process used for these. It may be buried in the literature
somewhere. In any case really old paper caps of any make or type
should probably be replaced.
On 11/6/2021 6:57 AM, Chuck Harris wrote:
> Hi Richard,
>
> I have never seen anything that would lead me to believe
> an end cap was glued onto the body of the capacitor, but
> maybe that is what they did?? Or, maybe the capacitor was
> built in halves, and the mold line is really a glue line?
>
> Capacitors of all types ultimately boil down to a pair of
> plates, with a dielectric fill between them.
>
> If the dielectric sheet does not fill the space fully, it
> greatly reduces the effect of the dielectric on the capacitance.
> The oil's greatest contribution is in making an intimate
> contact with both plates, and eliminating any air between
> the plates.? This both improves the capacitor's stability,
> and its dielectric strength.
>
> All of my speculation is secondary to the message both of
> us should be (are) giving:
>
> Replace oil filled BB capacitors on sight!
>
> I know that ASCII art doesn't work well on these lists, but
> if you consider this line below a single axial slice of the
> capacitor, it shows the important observable characteristics
> of BB capacitors:
>
>
> ==========O(|||..||...)==========
>
> The "O" is a solder blob that seals the oil filler tube.
> The "==" is the capacitor's leads.
> The "(" and ")" are the domed ends of the capacitor's body.
> The "|||" are the color bands on the body...
> And, the "..." is just the black body.
>
> -Chuck Harris
>
>
> On Fri, 5 Nov 2021 22:08:12 -0700 "Richard Knoppow"
> <
dickburk@...> wrote:
>>? ?? I may be wrong about the voltage value, I am going by memory
>> of the advertising.
>>? ?? I have wondered the same thing about the oil filling. Its
>> possible the casings were cast and the winding inserted in it. I
>> don't think the windings were deliberately misshapen? but that
>> might be. I wonder what effect squeezing them would have on the
>> value. If the spacing remained constant the shape would have
>> little effect. My own experience in manufacturing is with
>> precision resistors, I have little idea how capacitors were made.
>>? ?? BTW, the Micamold paper caps seem to have a terrible
>> reputation. Every one I've encountered was very leaky but they
>> look find inside. Same with the Solar flat paper caps.
>>? ?? Both of these companies vanished shortly after WW-2, I have
>> never been able to find out what happened. Solar had space
>> reserved in an early "Radio's Master" catalog but no entry and
>> the next issue just was not there.
>>? ?? I've never seen any Micamold caps in -hp- stuff but lots of
>> Sprague, they must have had something going for them.
>>
>> On 11/5/2021 9:11 PM, Chuck Harris wrote:
>>> Hi Richard,
>>>
>>> Bumble bee was a descriptive name based on the colorful
>>> bands used to indicate the capacitor's value and voltage
>>> rating.? It was certainly not a brand name.
>>>
>>> Tektronix used numerous 400V oil filled versions of this
>>> capacitor.? I replaced several dozen in my 513D, so I am
>>> certain that your statement about the 650V version being
>>> the only oil version is incorrect.? The 400V rating is one
>>> of the yellow bands that makes it look like a bumble bee.
>>>
>>> Every one that I replaced had the oil filler tube.
>>>
>>> I have observed that the capacitor "slug" is smaller than
>>> the cavity that it fits into.? It had to be, or they would
>>> not have been able to fill the capacitor with oil from the
>>> tube on the end.? How did they make that cavity?
>>>
>>> It is my impression that if the slug was misshapen, it most
>>> probably was built that way.? Perhaps to keep it from rattling
>>> about in the larger cavity that it fit into.
>>>
>>> Excepting where the solder sealed filler tube was damaged during
>>> the capacitor's installation, oil filled BB's lasted a very long
>>> time... easily more than 10 years.? The ordinary beeswax dipped
>>> paper capacitors became leaky after a year or two.
>>>
>>> -Chuck Harris
>>>
>>>
>>> On Fri, 5 Nov 2021 15:50:59 -0700 "Richard Knoppow"
>>> <
dickburk@...> wrote:
>>>>? ? ??? I want to respond to a couple of things in this thread.
>>>> First of all, there were other brands of molded paper caps. None
>>>> of these had the consistent problems of the Sprague caps of
>>>> cracking and actually breaking. Also, I have disected number of
>>>> failed plastic caps but don't see the distorted windings in
>>>> others. Something went very wrong with these. The early caps were
>>>> coded with the JAN striped coding, hence the name "Bumble Bee".
>>>> The actual brand name was Black Beauty. The 650V versions were
>>>> the oil filled ones, lower voltage were not oil filled. The oil
>>>> filled caps are often found with the oil leaked out. The failure
>>>> seems to be the seal of the filler tube. The tube was also the
>>>> lead on one side having a wire soldered (maybe welded) into it.
>>>> If the seal is disturbed by, for instance, excessive soldering
>>>> temperature, the oil will leak out. The SP-600 seems to have had
>>>> an especial problem with this.
>>>>? ? ?? Also, the property of dielectric absorption, which causes a
>>>> capacitor to retain some charge after being discharged, can be a
>>>> problem with timing and low frequency circuits. One of the few
>>>> virtues of paper capacitors is low dielectric absorption. They
>>>> are a better choice than mica and much better than HI-K ceramic
>>>> caps. Plastic film caps, particularly of certain types have
>>>> practically no DA and are the best choice. I don't think the
>>>> Black Beauty caps were particularly low in DA but all paper caps
>>>> are pretty good.
>>>>? ? ?? The Black Beauty line was advertised as a long life, high
>>>> quality brand. I think Sprague may have fixed the problems with
>>>> them eventually but they got a bad reputation quickly. Hammarlund
>>>> went to all ceramic caps and at least military SP-600's were
>>>> modified to replace all of the paper caps with ceramic ones.
>>>> Those are pretty much trouble free.
>>>>? ? ?? Whatever happened it caused physical distortion of the
>>>> windings of the caps. That could have come from shrinkage of the
>>>> case material as it cooled. It seems to be in both the oil filled
>>>> and non filled versions, at least the ones I've dissected.
>>>> On 11/5/2021 7:25 AM, greenboxmaven via wrote:
>>>>> Thanks for this very good explanation. In addition to the
>>>>> points you made, I have read the oil fill was often complete,
>>>>> and hydrostatic force would test the integrety of the plastic.
>>>>> Shrinkage and loss of resilience of the case would increase the
>>>>> chance of cracks and leaks. The late 1940s is a fascinating
>>>>> time in history for me. There was a great deal of technological
>>>>> progress made, often with over confidence in new materials? and
>>>>> techniques inspired by wartime successes that performed very
>>>>> well in the short term but lacked long term reliability. The
>>>>> "Bumble Bee" condensers were excellent in one regard- they had
>>>>> very little residual charge in the dielectric after being fully
>>>>> discharged. When used as a coupling condenser, that can make a
>>>>> difference.
>>>>>
>>>>>? ??? Bruce Gentry, KA2IVY
>>>>>
>>>>>
>>>>>
>>>>> On 11/5/21 9:38, Chuck Harris wrote:
>>>>>> BB capacitors were molded as well as the technology of the day
>>>>>> would allow... That is not why they cracked.
>>>>>>
>>>>>> The problem is the plastic they used, like most plastics, shrinks
>>>>>> slowly over time, and the wire leads, and especially the solder
>>>>>> sealed oil filler tube, that penetrate the plastic, don't.
>>>>>>
>>>>>> This can cause a crack to form at the weakest point, which is
>>>>>> usually at the mold line formed by slight misalignment of the
>>>>>> mold halves.
>>>>>>
>>>>>> When you injection mold plastic, the plastic's internal bonds
>>>>>> stretch out to fill the mold.? When the plastic cools, it is
>>>>>> frozen into a state where those bonds are stretched.
>>>>>>
>>>>>> Over time, under the continuous stress of these stretched bonds,
>>>>>> the plastic will cold flow into a more relaxed state... becoming
>>>>>> slightly smaller.
>>>>>>
>>>>>> The problem is if the plastic is constrained by something inside
>>>>>> of it that cannot shrink.... such as the wire leads, a gear's
>>>>>> hub, or an oil filler tube, something has to give.
>>>>>>
>>>>>> If the plastic shrinks around a metal tube, the thickest parts of
>>>>>> the plastic will break the thinest parts forming a crack, and a
>>>>>> leak.
>>>>>>
>>>>>> I was told by Deane Kidd, that in the early days, Tektronix
>>>>>> created a situation, ripe for failure with BB capacitors, by
>>>>>> putting them tightly fitted into ceramic or bakelite terminal
>>>>>> strips.? When the capacitor's leads were soldered, the heat
>>>>>> traveling down the very short leads would melt the capacitor's
>>>>>> solder seal, allowing the oil to mix with the solder, and make a
>>>>>> leak.? In the worst cases, the oil would drool out leaving the
>>>>>> capacitor incapable of withstanding its rated voltage.
>>>>>>
>>>>>> Not to mention it made a greasy dirty mess in their otherwise
>>>>>> very nice looking scopes.
>>>>>>
>>>>>> -Chuck Harris
>>>>>>
>>>>>> On Thu, 4 Nov 2021 14:40:42 -0400 "greenboxmaven via "
>>>>>> <ka2ivy=
[email protected]>? wrote:
>>>>>>> Sprague "Bumble Bee" and "Black Beauty" condensers were molded
>>>>>>> improperly, and they will crack, especially the oil filled ones,
>>>>>>> and let in moisture. That seems to react with the oil and make
>>>>>>> it conductive as well as corrosive. Once this happens, leakage
>>>>>>> gets very bad, especially when the condenser is heated by
>>>>>>> surrounding components. Many efforts have been made to bake
>>>>>>> and otherwise restore them, but once the problem begins it can
>>>>>>> not be reversed. The dielectric charicteristic? is perported to
>>>>>>> be superb for audio circuits, and AudioPhools will freak out if
>>>>>>> these condensers are replaced, that is until the power
>>>>>>> transformer, rectifer, output tubes, and filter choke in their
>>>>>>> amplifiers are all incinerated. Not only did Hammarlund use
>>>>>>> them in receivers, Collins and National did as well. Tektronix
>>>>>>> used them in their equipment, and too many consumer electronics
>>>>>>> companies to recall all of them.
>>>>>>>
>>>>>>>? ? ?? Bruce Gentry, KA2IVY
>>>>>>>
>>>>>>> On 11/4/21 13:45, Richard Knoppow wrote:
>>>>>>>> Who made those? Some early advertising for Sprague Black Beauty
>>>>>>>> caps said they were plasticized paper. The main problem with
>>>>>>>> these is some sort of production problem they had. I have
>>>>>>>> dissected a number of "bumble bee" caps, these are actually
>>>>>>>> Sprague Black Beauty caps with striped value markigns. I found
>>>>>>>> the windings were distorted. I suspect this happened during the
>>>>>>>> encapsulation but don't know. Some of these caps, the higher
>>>>>>>> voltage ones, were oil impregnated. The oil was introduced
>>>>>>>> through a tube which formed one of the leads. It is common for
>>>>>>>> all the oil to have leaked out due to a lack of sealing at the
>>>>>>>> solder joint between the tube and the lead. That may have been
>>>>>>>> due to excessive heat when the caps were installed. The most
>>>>>>>> notorious of the BB caps are those in the Hammarlund SP-600,
>>>>>>>> however, they were very widely used including in a lot of -hp-
>>>>>>>> gear. However, in the receiver it is common to find cracked or
>>>>>>>> split caps or even caps where part of the casing has come off.
>>>>>>>> I have not seen that in any other make of equipment. Perhaps
>>>>>>>> just a bad lot or perhaps some difference in installation.
>>>>>>>> Nonetheless, ALL paper caps become degraded with age. The usual
>>>>>>>> symptom is an increase in series resistance. Leakage, which is
>>>>>>>> another term for parallel resistance, is sometimes a problem
>>>>>>>> but not as often. I don't think any of these caps, even the
>>>>>>>> real oil filled transmitting caps, was intended to have a
>>>>>>>> lifetime of over about ten years. The life problem was known
>>>>>>>> and described in some engineering texts. It was dependent
>>>>>>>> partly on voltage; the closer the voltage to the rated voltage
>>>>>>>> the shorter the life of the cap. Likely it was some sort of
>>>>>>>> electrolytic degradation of the paper. In any case, paper caps
>>>>>>>> should be replaced with modern plastic film caps. These for
>>>>>>>> the most part will last forever and generally will improve
>>>>>>>> performance perhaps beyond the original. There is a good
>>>>>>>> amount of information on the web about the relative merits of
>>>>>>>> various kinds of plastic dielectrics. Polypropylene seems to
>>>>>>>> be about the best especially for RF use.
>>>>>>>>
>>>>>>>> On 11/4/2021 9:33 AM, Dave Wise wrote:
>>>>>>>>> Even the later plasticized-paper ¡°Prokar¡± and ¡°DiFilm¡±
>>>>>>>>> versions can cause trouble in some applications ¨C they may
>>>>>>>>> not be leaky, but their Dielectric Absorption and Dissipation
>>>>>>>>> Factor are ¡°through the roof¡±.
>>>>>>>>>
>>>>>>>>> Dave Wise
>>>>>>>>>
>>>>>>>>> *From:*
[email protected]>>>>>>>>> [mailto:
[email protected]] *On Behalf Of
>>>>>>>>> *greenboxmaven via
>>>>>>>>> *Sent:* Thursday, November 04, 2021 6:25 AM
>>>>>>>>> *To:*
[email protected]>>>>>>>>> *Subject:* Re: [HP-Agilent-Keysight-equipment] HP200CD
>>>>>>>>> oscillator
>>>>>>>>>
>>>>>>>>> ALL Sprague "Black Cat", "Black Beauty" and? color striped
>>>>>>>>> "Bumble Bee" condensers should be considered bad on sight.
>>>>>>>>> Unfortunately, they are common in older equipment of all makes
>>>>>>>>> and models. The 630V. polyester condensers are a fine
>>>>>>>>> replacement. The only condensers that are polarized are
>>>>>>>>> electrolytics, poyester condensers are not polarized.
>>>>>>>>>
>>>>>>>>>? ? ??? Bruce Gentry, KA2IVY
>>>>>>>>>
>>>>>>>>> On 11/4/21 8:51, Richard Merifield wrote:
>>>>>>>>>
>>>>>>>>>? ? ??? My unit has Black Cat 0.5MFD 400v axial capacitors for
>>>>>>>>> C8 and C9. Would 630v polyester unpolarised caps be ok
>>>>>>>>>? ? ??? replacements?
>>>>>>>>>
>>>>>>>>>? ? ?
>>>>>>>? ? ?
>>>>>>? ? ?
>>>>>? ? ?
>>>
>>>
>>>
>>>?
>
>
>
>
>
--
Richard Knoppow
dickburk@...WB6KBL
