It could explain why the windings of the caps I took apart were so
distorted. Steam pressure. Why did they do this? Perhaps to leave a void
for the oil. By eyelet I think they mean the hollow tube at one end.
This is connected to the foil on one end and allows both the moisture to
escape and the oil to enter. It is sealed by soldering a lead into it. I
always thought that the caps failed because too much heat was applied to
the lead on that end allowing the solder to melt out and the oil to
escape. However, that does not explain the mutilated windings. The
process of creating pressure during molding to create a void for the oil
could well explain it. I am sure the answer was in the engineering
records at Sprague but the chances they have survived is virtually zero.
I have dissected other failed caps but never saw any others with the
mashed up windings in the BB's.
I wonder how the world these escaped the QC at Sprague. Mashing the
winding must have affected the value if nothing else. Very strange, I
think we don't know the whole story yet.
I was also involved with audio professionally when my hearing was
still good. It is a great frustration to me that I am now deaf and can
no longer judge audio quality. There is probably more misinformation and
myth in audio than anywhere else beyond politics.
BTW, I may have mentioned that I have recently had surgery to place
a cochlear implant. Its too soon to know if it is going to work. If it
restores my hearing enough so that I can carry out a conversation and
use the telephone again I will be satisfied. It takes months and many
adjustments to make it work. At the moment I am no further ahead than I
was before the surgery. Well, I go in again on Friday and hope for the
best.
FWIW, the guitar amp folks WANT distortion, I was always working to
eliminate it. Its the difference between being a sound _producer_ and a
_reproducer_.
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On 4/30/2024 8:20 PM, Jacques_VE2JFE wrote:
Hi all,
Following the address provided by Richard, I read, then downloaded the
article and edited it before conversion in a .pdf.
See attached.
What scares me the most in it is the description of the manufacturing
process for the ¡°Bumblebees¡±:
/Construction Details (eyelet variation):///
/Eyelet was soldered to a wound foil and left sticking out of the
Bakelite phenolic case during the molding process./
/_Paper and foil slug is soaked with water_//before casing in the
Bakelite to give the slug extra body and prevent the high pressure of
the casting process from distorting the capacitor./
/_After the slug is encased in Bakelite, it is placed in a vacuum oven
where moisture is allowed to escape through the eyelet_//./
/Oil is then introduced into the vacuum chamber and pressure is applied
to force it into the capacitor through the eyelet./
/Capacitor is then removed from the chamber and the wire lead is
soldered onto the eyelet./
I never figured that WATER SOAKING can be used as a part of the
manufacturing process for a PIO capacitor.
I also understand that this water, once that the external envelope was
cast, was evacuated thru the use of vacuum.
This means that the water within the envelope was forced to _boil_ when
the pressure was lowered.
What was the time allowed for the water vapor to escape ?
What if some water (or some oxidation on the aluminum plates) remained
inside the capacitor before the ¡°oil¡± was forced inside the envelope and
the ¡°tip¡± sealed ??
Can it ultimately explain why they failed so bad ??
It remembers me the failure mechanism described in the article about the
BBoD failures on a SX-88 by this guy in Germany we read some time ago.
Not that those BBoDs will have stayed good forever without the use of
water during their manufacturing process: all the PIO we know are
failing sooner or later (except the ones in gas-tight enclosures) but
can it be that the Sprague BBoDs failed earlier because of this
manufacturing process ?
Related to the reference (and the doubts of Richard) about the
capacitors ¡°sound¡±:
At an earlier age, I was bitten by two bugs: Radio was the first, but
Audio was the second, to the point that I earned my living for some time
with audio amplifier design (tube based variants).
From a lot of testing and listening sessions, I can testify that no
capacitor ¡°sound¡± the same and certainly not like no capacitor at all
for most.
All the capacitor variants changes the sound reconstruction, like adding
a different color to the picture if I can compare the effect with a
visual equivalent.
Pleasant or not, good or bad, all those ¡°colorations¡± are judged by the
ears of the listeners, but they can definitively be heard.
There is no simple explanations for these effects, and sometime they
defies electronic laws, like some people that states that they prefer
the ¡°sound¡± of a leaking PIO.
*73, Jacques, VE2JFE in Montreal*
_._,_._,_
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
