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Jim Mueller Jim Mueller is offline
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Default What type of capacitor should I use?

On Wed, 09 Aug 2017 04:54:25 -0700, Big Bad Bob wrote:

On 03/09/17 17:01, wrote:
What type of capacitor would be the best match to replace the old
paper/wax caps in old tube gear?

I am not referring to the electrolytics, those I know need to be
electrolytic caps. I am referring to the inter stage caps, such as .01
.05 .1, .005 and so on.....

The object is to replace all the caps in an old tube radio, or any
other tube stuff.


well, if you must replace them with more modern components, a decent
ceramic capacitor should do fine. From what I have seen, ceramics were
common in gear made in the 50's and 60's because of their small relative
size and reasonable consistency in manufacturing.

You should be able to order them from companies like Digikey, Mouser,
etc.. Just make sure the voltage ratings are high enough, and you
should be ok.

I've seen on-line "photo piles" of before/after restoration efforts in
which modern components were "hidden" inside of hollowed-out components.
Maybe you can stash a modern ceramic inside of the paper/wax tube, and
seal it up with a bit of hot glue...


It will be tough to find good ceramics in the values listed with voltage
ratings high enough for tube gear. Polyester (Mylar) or Polypropylene
are better choices.

As for the quality of ceramic capacitors, it depends on what kind of
ceramic is used. C0G ceramics are about the best capacitors you can
easily get. They are very stable, have very low loss, and are excellent
in just about every other way. The one way they are not excellent is
that, except for low values (less than around 1000pF - depends on
manufacturer) they are large and expensive. Mid grade ceramics like X7R
are less stable and less expensive. They are suitable for most audio
frequency work. The really bad ceramics are the ones like Z5U. They are
truly horrible in most ways and are suitable only for non-critical
circuits like supply bypassing. They are, however, tiny and very cheap.
Go to the manufacturer's data sheet for the capacitors you want to use to
see if their characteristics match the application.



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Jim Mueller


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