On Thu, 02 Feb 2017 14:53:42 -0600, oldschool wrote:

Why should someone replace ALL the capacitors on old Tube equipment?

It seems that some people advocate that.

I understand that the electrolytic caps contain chemicals which decay
over time, from the chemicals corroding the metal parts. So,
electrolytic caps should always be replaced. But why replace the old
paper caps coated with wax? All they are, is metal foil and paper rolled
up, and as long as the wax is sealing them to keep out moisture, why
should they become defective?

And for that matter, what are the new ones made from? Aside from being
sealed inside of some sort of plastic (instead of wax), are they not the
exact same thing inside?

While this is not part of my original intent for this message, I want to
ask if anyone remembers the old oil filled electrolytic caps in the
1930's and 40's radios? I never understood what the oil did inside of
them. But what I do remember is having one of them "blow". *SCARY *****.
I plugged in some ancient chassis with those old oil filled caps, and
all of a sudden there was hot oil spraying all over me, from the tiny
hole in the top of it. After that, I always put a tin can over those
caps before plugging the device in. (or just replaced them). Those
seemed to almost always be bad. (Probably why they were not used to too
many years).

Actually, the electrolytic capacitors are more likely to be good than the
paper capacitors. Almost all of the paper capacitors I have from the
"old days" are bad, even if they were never used while a small number of
the electrolytics are still functional.

The paper capacitors were made of sheets of foil separated by paper,
"sealed" in wax. Unfortunately, wax isn't a very good seal; moisture can
penetrate it. These capacitors were a know failure point 10 years after
a set was made. There just wasn't anything better to replace them with
(at a reasonable price). Modern capacitors are made from plastic film
that is much less affected by moisture and is a better insulator in the
first place.

The old electrolytic capacitors you are talking about don't sound like
the oil filled variety. Indeed, if they are electrolytic, they aren't
oil filled. Oil filled capacitors aren't polarized and many of them are
good today. They were the high quality capacitors used in military and
premium industrial equipment; you seldom find them in consumer gear
unless someone has repaired it with surplus parts. The capacitors you
talk about are more likely wet electrolytics. They aren't filled with
oil but with an acid. They are indeed all bad; don't power a set that
has them. Sometimes they leak if you turn them upside down (the vent
hole you mentioned). And be careful not to puncture them while you are
removing them. If there is still any acid inside, it will corrode any
metal it gets on.

You can still get high quality electrolytic capacitors from authorized
distributors like Mouser or Digi-Key. No-name ones from Amazon or Ebay
are likely to be junk. Name brand ones from these latter sources may be
counterfeit.

While tube electronics may survive a nuclear war, it is irrelevant.
There won't be any electricity to run them. The power plants are
controlled by computers. Likewise, having your own generator won't help
either. Many of the new ones are also semiconductor based, and you won't
be able to get gas to run them since the pumps at the gas station are run
by electricity which won't be available. Solar cells are also
semiconductors and the inverters used with them also use semiconductors.
So, if there is a WW3, don't count on ANYTHING electrical working.

--
Jim Mueller

To get my real email address, replace wrongname with dadoheadman.
Then replace nospam with fastmail. Lastly, replace com with us.