On 05 Feb 2017 00:21:42 GMT, Jim Mueller wrote:

I think that there is a misunderstanding here. The statement to replace
all the capacitors actually means all the electrolytic and paper
capacitors. Usually ceramic and mica capacitors are still good and
nobody replaces those unless they are proven to be bad.

The paper capacitors in the IF and RF stages need to be replaced even if
the radio "works". Leaky capacitors change the voltages on the tubes
causing them to work at less than their best performance. Also, these
capacitors are used as supply bypasses and AVC filter capacitors. They
do not affect the alignment of the set; the ceramic and mica capacitors
may. Their value is not particularly critical; pick the closest modern
value.

I hear you.....

Consider the value issue. If the radio has a .05 uF, 20% capacitor in
it, its actual value can be anywhere from 0.04 uF to 0.06 uF. A modern
0.047 uF 10% capacitor can be between .0423 uF and 0.0517 uF. So the
0.047 uF capacitor can be closer to 0.05 uF than the old one marked with
that value.

OK. That makes sense...

As for life expectancy, there was a time in the late '50s and early '60s
when both paper and plastic film capacitors were used. The paper
capacitors I have from that period are universally bad while the plastic
film ones are almost always good. Plastic film has passed the test of
time.

As for what type of plastic film to use, polyester (AKA Mylar) is the
cheapest and has the poorest performance. But it is still better than
the paper capacitors of old so it is suitable for use just about anywhere
a paper capacitor was formerly used. Polycarbonate (no longer made) and
polypropylene are better but more expensive. Polystyrene capacitors are
also very good and inexpensive but are usually seen only in small values

I see where this can get confusing. I'll consider the polyester (AKA
Mylar), but for the small cost difference, I'd probably prefer the best.
It looks like polypropylene would be that choice.

Do you have any brand names to recommend for these types?
(I will be buying online, there are no electronics stores around here).

and are frequently not seen at all. They also have the problem that they
melt at lower temperatures than other plastic capacitors and solvents
dissolve them. Still, within their limitations, they are excellent.


Dont you mean they melt at a *HIGHER* temperature? I cant imagine how
something could melt at a low temp?

Upon reading a URL that somone posted on here, I see where the
audiophliles say that some caps have better sound quality, than others.
On a SW radio, I'm not really looking for "precision sound", but more so
for best performance from the signal coming from the antenna to the
speaker. And while some (or most) of these newer types of caps are made
to be used with modern gear, containing semiconductors, which are the
best choice for old tube stuff. I would think that the caps should mimic
the old paper caps, because that is what these circuits were designed to
use. I know the values of caps are the capcitance (in MF or MMF) and the
voltage. But I know there are other factors that I know nothing about.
Someone mentioned tempco (is that what I read?) in another message in
this thread. What the heck is that?

Either way, I do believe the caps should be similar to the original ones
to work properly. Just made from better materials.


--
Jim Mueller