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Old October 10th 18, 08:02 PM posted to rec.radio.amateur.boatanchors
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Default capacitor replacement




When restoring the old tube equipment (tube receivers ) does it make any
difference if the old paper capacitors are replaced with the ceramic
disk or should another type be used ?

I know for RF one needs to use capacitors that are rated for rf but in
the audio stages does it really matter what kind of capacitor is used as
long as it is the correct value ?


Reason for asking is that I bought an old receiver that someone has
replaced many of the capacitors. The book says pape capacitors for some
but they have been replaced by the ceramic disk type.

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Old October 10th 18, 10:32 PM posted to rec.radio.amateur.boatanchors
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Default capacitor replacement

Ralph Mowery wrote:

When restoring the old tube equipment (tube receivers ) does it make any
difference if the old paper capacitors are replaced with the ceramic
disk or should another type be used ?


You are better off replacing them with plastic film capacitors, because
many of them are going to be of larger values where C0G ceramic disc capacitors
that can handle the voltage will be expensive and rare.

For smaller ones, such as in an IF strip, you would be fine replacing them
with C0G ceramics.

You don't want to be using high density ceramics.

I know for RF one needs to use capacitors that are rated for rf but in
the audio stages does it really matter what kind of capacitor is used as
long as it is the correct value ?


It does, because it has to fit and be stable and not fail. And in the case
of high density ceramics like Z3U types, they are very nonlinear which is
okay for supply decoupling but bad news for IF strips.

Reason for asking is that I bought an old receiver that someone has
replaced many of the capacitors. The book says pape capacitors for some
but they have been replaced by the ceramic disk type.


When was it done? If it was done sixty years ago, likely ceramics were the
only alternative you could get. And back then, high voltage NP0s were
available at your local tv repair supplier.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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Old October 10th 18, 11:09 PM posted to rec.radio.amateur.boatanchors
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Default capacitor replacement

In article , says...

Reason for asking is that I bought an old receiver that someone has
replaced many of the capacitors. The book says pape capacitors for some
but they have been replaced by the ceramic disk type.


When was it done? If it was done sixty years ago, likely ceramics were the
only alternative you could get. And back then, high voltage NP0s were
available at your local tv repair supplier.
--


This is a hq140 receiver built around 1955.

I have no idea when the capacitors were replaced. I just obtained that
receiver a few months ago and started looking into it. The paper ones
were around .02 and .05 which plenty of ceramic disc were around with
that value during the years. I just thought if the manufactor used paper
instead of ceramic there may be a reason.

I did find the electrolytics were replaced, but I replaced them with the
correct values as instead of the origional 10 and 20 uF values some 100
uF capacitors were used. Some tubes are not recommended to use very
large values for the filters.

Most of my work is with more modern and mostly solid state equipment so
that is the reason for asking about the paper vers ceramic disc. I know
enough about the tubes to do the simple repairs but not from an
engineering point. I have a good assortment of the more modern tublar
type capacitors and could replace the already replaced capacitors if
needed. To me at frequencies of audio and lower unless dealing with
critical frequency circuits , a capacitor is a capacitor if the UF and
voltage is in range, but I could be educated on that. Now, RF and
critical frequency circuits are totally different.

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Old October 12th 18, 11:38 PM posted to rec.radio.amateur.boatanchors
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First recorded activity by RadioBanter: Jun 2018
Posts: 25
Default capacitor replacement

On Wed, 10 Oct 2018, Ralph Mowery wrote:




When restoring the old tube equipment (tube receivers ) does it make any
difference if the old paper capacitors are replaced with the ceramic
disk or should another type be used ?

I know for RF one needs to use capacitors that are rated for rf but in
the audio stages does it really matter what kind of capacitor is used as
long as it is the correct value ?


Reason for asking is that I bought an old receiver that someone has
replaced many of the capacitors. The book says pape capacitors for some
but they have been replaced by the ceramic disk type.

Paper capacitors were never that good, just what was available. They can
pick up noise (which is why they are often marked so you know which side
should go to ground), they are inductive, they are big. But that's all
there were until better capacitors came along.

It's no different from electrolytics, I can't think of any application
where a polarized capacitor is needed. But in order to get higher
capacitance, in a reasonable size package, electrolytics (and
tantalum) make them practical. But it confuses people, they see the
polarization and think that's the needed factor.

So paper capacitors were used, and there's absolutely no reason (unless
someone is finicky with making everything "original") to use them still,
if you could get them. And a lot of old equipment suffers, paper
capacitors gone bad because they had a life span.

I came along after ceramic capacitors became viable in values useful for
RF bypascc capacitors, so that's what I'd use, but others seme to want
something newer. They won't have the inductance of paper capacitors,
otehr than long leads. Recapping decades ago would see paper capacitors
replaced with ceramic.

Michael



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