For what reason would a ceramic cap be used instead of a paper cap assuming same value was available? Can ceramic caps be replaced with our usual generic replacements (orange drops, yellow etc.)?
thanks,
Sandy

Depends greatly on the era and application. When ceramic discs first came out they were more expensive than a paper cap. That only held true for a year or two and the ceramics took over quickly for bypassing applications.
Our 'yellowcaps' could easily replace ceramics on older radios but the ceramics aren't typically bad to start with! I'd prefer to stay with a ceramic rather than working backwards to a 'rolled' cap that might add undesired inductance to a circuit.

99% does not matter. RF and close dress are exceptions. Proceed with caution.

Ceramics, like micas, are at their best in situations where stability and low loss are the primary considerations. That typically means the RF range, and the higher in that range you go, the more important stability and low loss become.

Larry

Discs take up a lot less room and provide a clean look compared to paper or those ugly orange excrement droppings

Carl

Although ceramic are good for bypass most shouldn't be used where values are critical. Try measuring a .1 mf ceramic cap while heating it. I found at first the value increases and then greatly decreases to around .01 mf using a heat gun or soldering iron.

This all makes sense. What about the tubular appearing ones? Some I've seen about 7/16" diameter maybe 1 1/2" long.
thanks,
Sandy

Tubular ceramic caps, you mean?

They were the original style, if memory serves. Temperature-compensating caps were built in tubular style for years. I don't know if they dramatically change value (or get ruined) if they get too hot during soldering, but I expect they would, since most other parts are adversely affected by excessive heat.

Some tubular ceramics resemble the notorious "bumblebee" paper caps with axial leads; most, especially the smallest, have radial leads like dogbone resistors.

Larry

7/16" diameter by 1-1/2" long and tubular in shape are probably metalized paper or film inside. The ceramic tube is only a shell or casing; it plays no part in the operation of the capacitor. 1960s television sets were often full of them. The ceramic tubes were claimed to be more moisture and heat resistant, and more flameproof than plastic or cardboard dipped in wax. They also exploded with a real vengence when something went wrong with them!

That all depends upon the class of construction but for tube radios a .05 is about the limit Id use, after that a film is better and often still cheaper.

Discs are not designed to be run with a heat source on them anyway, its an interesting example of a rather meaningless experiment unless a circuit is being designed that will require attention to that detail. OTOH those caps do have frequency and current ratings that should not be exceeded.....no worry in a tube radio but critical in transmitters and amplifiers.

http://en.wikipedia.org/wiki/Ceramic_capacitor

Carl

That's a bit misleading. It really depends on the dielectric.
There is a big difference between a Z5U dielectric, used in larger
values, vs. the NP0 dielectrics in smaller value caps for use in tuned
circuits.

Pete

Hollow tubular ceramics are not all temperature compensating, the color code has to be interpeted. I have many NOS tubulars here from a generic 10% to N-1500 and find the non-TC type in many 50's era equipment.

Carl

Leigh Bassett incarnate.........

I'm relatively new at this and I think what Norm said makes perfect sense--heat can affect capacitance. Nothing meaningless there.

Wasn't Sprague based somewhere in New England ?

North Adams, MA and later in VT where the new owners concentrate on custom values and have the run of the mill stuff made in China.

Thanks for all the replies. I'm glad I didn't ask this a couple of years ago. Ignorance can be bliss. I've definitely reached the point now though where "just re-cap it" doesn't do it for me anymore.
regards,
Sandy

I never use ceramic capacitors unless I know their pedigree. NPO and XR7 dielectrics are pretty temperature stable, and the XR7 comes in larger values. There are a lot of cheap ceramic caps that have come in or are coming in from Asia, and they should be avoided like the plague. Tube radios get plenty hot, so if the sound quality changes during the turn on cycle a cheap ceramic might be changing value.

Yet another invasion of cheap parts from that part of the world? Devil knows where or how this will end.

Larry