Yes it was wasn't it.
However the scenario I had in mind [and my experience] both allow for
'probably' OK.
The mil capacitors of post-war gear have been good for treatment if just
lousy due to storage time.
The capacitors in old commercial radios any era depend on manufacturer. I
don't collect them but had re-furbished two with sentimental value - hence
the caps are disconnected and new types 'temporarily' fitted. This is to
protect the mains transformer as much as anything else. Added thermal fuse
to transformers as insurance -weak as it may be.
WWII caps are hit and miss.
The capacitors that you mention "a hostile-ish environment (near tubes and
other sources of heat)," are in a category that I call Faulty or worn out. I
am/was talking about OK caps that were stored for ages - they can be
revitalised [generally] and I hear such comments from WWII Rx collectors eg
WS19 which is much in vogue over your way.
I have had more trouble with 'modern' caps. Even the manufacturers specs
don't give you much confidence in commercial quality electros. I can
remember the probs we [a gov dept] experienced at inwards goods - eg the
Philips electros came in different 'life' categories. They were marked the
same; only difference was the physical size. Some suppliers were either
trying it on or were as ignorant as some of our inspectors !
With 'modern' gear I replace instead of mucking about; and some collector
will rant and rave about it in 50 years :-))
Speaking of modern - a capacitor characteristic often overlooked in current
times is the manufacturer specified operating voltage RANGE. Using a cap
well below the marked voltage causes it to do two things; lose capacitance
and also become resistive [ie leaky, but not liquid if you follow me]. In
the 90s I was trouble-shooter at a largish [>2000 employee] local company
and there were product recalls due to acceptance of electro caps of higher
than specified voltage. eg 50V instead of 6V. The circuit already worked at
a non-optimum <2.5V across the cap and that was acknowledged in the design.
I guess I was motivated by my hate of needless destruction of old gear.
Attempt a reform - replace if required.
John K.
[PS The very old electros that slosh when you move them are better
'temporarily' replaced as I have done in my old Airzone. An explosion of
those is a real mess and dangerous. The explosion of a typical WWII and
later type just results in a bit of paste splatter and tons of paper and
foil. (says I who had just moved his unprotetced eyes to the other side of
my home-made 6 x 807 surplus parts guitar amp. As a schoolboy I just
purchased the WWII surplus caps and wired them up. 800V parts and used at
650V. )]
[PPS. I suppose this is one of those topics you mentioned that moved
off-topic is it?]
----- Original Message -----
From: "Nick" <n...@desmith.net>
On Jun 30, 8:53 am, "JohnK" <yend...@internode.on.net> wrote:
Generally, old electrolytic caps that have just been allowed to sit can be
re-formed and henceforth operate properly.
From: "Nick" <n...@desmith.net>
That's a bit of a sweeping statement. Of the kit I've rebuilt, the
electrolytics have typically dried out, and thus cannot be reformed.
Many were not sealed well and as they were operating is a hostile-ish
environment (near tubes and other sources of heat), they often dry
completely.
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