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Re: HP200CD oscillator
¿ªÔÆÌåÓýSprague "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. |