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but they have been replaced by the ceramic disk type.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