[cpollock]

I was wondering if there is any reason to choose a plastic film type capacitor, like the "orange drop", over a ceramic capacitor.  I've got a collection of each for 0.015 uf.  The ceramic caps are much smaller, at even higher voltages. I got the ceramics to replace the caps in the "bathtub" connector for the power line input, and when they arrived I was impressed by the difference in size from the orange drops I'm putting in for coupling.
I'm actually an electrical engineer and probably should know this, but to me, so long as it is non-polarized, it seems they should all be equivalent.  However, there is art in electronics, especially in tube electronics,  so I am curious if there is some reason to choose one over the other.  
Thanks!
Clif

[cpollock]

I just did a web search and found a lot of info on this. The ceramic cap displays some microphonics, and is allegedly more nonlinear than the plastic film, so it is not typically used for audio coupling. The plastic caps do not couple mechanical energy into a voltage, and have less nonlinearity, so they are preferred for audio coupling applications.
I had no idea. I always though ceramic would be the most stable, but clearly I was wrong. Anyway, it sounds like the best coupling caps are film caps, and for power line filtering it probably doesn't matter either way because any microphonics that might appear will be completely shorted by the low impedance of the power line.
Sorry to add this noise to the forum. Other than my input I'm really enjoying reading the stories posted here.

[Arran]

You can use either type for a power line cap, though many prefer to use the x or y rated safety types as they are designed to fail as open rather then shorted, I believe that most of the safety caps are some sort of ceramic cap as the package appears that way. You can probably get away with using ceramics in audio circuits, they used to do that in some later model tube radios in the late 1950s and 60s and I've never noticed a difference, where you can get into trouble with ceramic caps in in the vertical circuits in TV sets, you also can't use them in the HV power supplies in electrostatic TV sets and scopes.
Regards
Arran

[Radioroslyn]

Ceramics don't like RF current. They tend to get hot and change value. Have tried to use them in some of my ham transmitters in the RF amp matching circuit. That could be the same situation that you could have in the hor and ver deflection amps. On the other micas work fine in the RF amps and mylars seem to work fine it the small screen tv's.

GL
N3GTE

[morzh]

As an EE (same here) you should know the differences.
Caps have

- different dielectrics, that dictate
- different tolerances
- different temperature drifts
- different kinds of dielectric losses

Also not directly related to dielectric but somewhat affected by it indirectly (dielectric dictates assembly technique, size etc)
- frequency and resonance characteristics
- ripple rating
- ESR/ESL.

some other stuff.

Ceramic caps are naturally low in ESL.
They are also more susceptible to microphonics.

Basically, datasheet is your friend.

[Arran]

Mike;
  You have forgotten two overriding considerations given the choice of what capacitor with which type of dielectric to choose, at least with manufacturers, one is space, and the other is cost.
You could probably come up with an 8 mf mica cap to use a filter condenser in the power supply of a model 90, but it would probably be larger then the power transformer, and it would be cost prohibitive, if you could even find such a thing. But nobody needs that level of precision in an old radio power supply filter cap, usually a tolerance of + or - 20% is good enough, so long as the voltage rating is high enough for the surge current. In the rest of the radio, outside of the front end or the IF transformers, you can pretty much use anything that's the same value, other then an electrolytic, though you can use those as a bypass cap sometimes, and many sets did.
 As you know from your own collection the earliest AC radios used large paper capacitors for filter caps, but the materials and manufacturing techniques available at the time limited their practical size to 2 maybe 3 mf, to compensate for this they used a series of filter chokes, and neither was inexpensive to use. Of course with the advent of the wet electrolytic capacitor they could build AC radios much less expensively, and more compact, they could use a single choke on the speaker field coil, and make up for having a single choke with larger value input and output filter capacitors, and make an AC set half the size and weight. Now that relatively inexpensive large value, and high voltage, film caps are available, we've come full circle, you can actually use them as substitutes for some of the smaller wet electrolytic caps, at least up to 8 mf, 10 is probably pushing it.
Regards
Arran

[morzh]

Cost I did not list indeed; space I did when talking about geometry.

Indeed, for line filtering I do not need an NPO capacitor, although some electrolytics used to (and still do) come as -20/+80% and this is way to loose a tolerance.

[cpollock]

Thanks for all the input, it has been educational. I did some searching on ESL and ESR (equivalent series inductance and resistance) for the various types of capacitor, and they are different and must be accounted for in design. As Morzh said, when in doubt, pull up the spec sheet.
But fortunately these parasitics become issues mostly at higher frequencies. My take-away is that for the audio coupling (not DC filtering, not RF) , the parasitic effects are negligible, and thus there is not much impact on the specific choice of cap. For the RF and IF sections, however, one is clearly getting into the regimes where the parasitics become non-negligible, and cap choice is more critical. Clearly the designers back in the 30's understood this well and hence chose mica caps for the small values.

[morzh]

>>My take-away is that for the audio coupling (not DC filtering, not RF) , the parasitic effects are negligible

tell that to the people on on Audiokarma or other audiofile forums; they will shred you apart.
They can hear parasitics on audio frequencies. They can even hear the characteristic impedance of an audio cable.
We should seriously think of using them instead of capacitor testers, or even TDRs for that matter.

[cpollock]

Yes, I've encountered a few of those people, it is always amusing. They truly and passionately believe in their systems. My favorite product that was being hawked for the ultra-audiophile was a coaxial speaker cable (gold plated, of course) which had an arrow indicating which way the current was supposed to flow. Apparently some "experts" don't appreciate that sound in a speaker comes from an ac current.

[morzh]

---AC curent---

Yes, but there's PERMANENT MAGNET there!!!! Are you people blind or something! The cable direction has to be aligned with the magnetic field!!!


Oh, and speaking of unidirectional cables, have you heard that cables need breaking-in and ONLY THEN they develop their full sound.

Go write an equation for that, Maxwell!

[Arran]

I've read a few of the forums over at Audiokarma, and indeed some are quite nauseating. One involved some China made tube amplifier, which some had bought and tried out. It seemed that they were much more obsessed with what tubes were used in the China amp then either on what circuitry it used, or in the quality of the output transformers. They were debating whether it needed the Chinese tubes replaced with American made or European made tubes to improve the audio quality, odd that only one suggested maybe trying some Russian/Soviet made ones. What annoys me are the sellers on fleabay that list RF tubes and rectifiers as being in "matched pairs" which only ever applied to audio output tubes, and even then it isn't that precise as long as one tube isn't running at 30% and the other at 80% emission, and using fixed bias.
 One of the testers of this amp was using a Carver made using for a pre-amp, from what I heard about Carver products is that the only thing special about them is the price. I can recall watching a series of videos a You Tuber made regarding the repair of a Carver power amp, what a headache he had getting it going again, everything had to be just so thanks to some stupidly and unnecessarily complex circuits. One of the comments someone made about them is that not only are they stupidly complex but they don't even sound that great, so clearly when it comes to Audiophools if they pay enough they will convince themselves that it's a great sounding amp even if it sounds like mud, but if something is reasonably priced then there must be something wrong with it. If you think that the speaker cable thing is bad some even think that they need to use a special power cord, which has 120 v 60 cps AC running through it, and I don't mean that the cord has a shield over it  I mean that it has to be made out of special wire, or at least that's what the slicksters who market the things tell them so that they will pay $200 for the privilege.
Regards
Arran

[morzh]

Well...Carvers have to be complex, after all theirs was the famous amp with configurable transfer function that could match the sound of any tube hi-end amp being solid state itself. Built in a hotel room at that.

[WallaceRoger]

I've read a few of the forums over at Audiokarma, and indeed some are quite nauseating. One involved some China made tube amplifier, which some had bought and tried out. It seemed that they were much more obsessed with what tubes were used in the China amp then either on what circuitry it used, or in the quality of the output transformers. They were debating whether it needed the Chinese tubes replaced with American made or European made tubes to improve the audio quality, odd that only one suggested maybe trying some Russian/Soviet made ones. What annoys me are the sellers on fleabay that list RF tubes and rectifiers as being in "matched pairs" which only ever applied to audio output tubes, and even then it isn't that precise as long as one tube isn't running at 30% and the other at 80% emission, and using fixed bias.
 One of the testers of this amp was using a Carver made using for a pre-amp, from what I heard about Carver products is that the only thing special about them is the price. I can recall watching a series of videos a You Tuber made regarding the repair of a Carver power amp, what a headache he had getting it going again, everything had to be just so thanks to some stupidly and unnecessarily complex circuits. One of the comments someone made about them is that not only are they stupidly complex but they don't even sound that great, so clearly when it comes to Audiophools if they pay enough they will convince themselves that it's a great sounding amp even if it sounds like mud, but if something is reasonably priced then there must be something wrong with it. If you think that the speaker cable thing is bad some even think that they need to use a special power cord, which has 120 v 60 cps AC running through it, and I don't mean that the cord has a shield over it  I mean that it has to be made out of special wire, or at least that's what the slicksters who market the things tell them so that they will pay $200 for the privilege.
Regards
Arran

This reminds me of my year working in inventory/receiving at a Best Buy. Part of my job was scanning new shipments into inventory, which was an eye opener because the system showed both our retail price and the price we paid the manufacturer for the item. One of the items sales was instructed to push relentlessly with every TV and stereo system sold was Monster cables. Monster cables (just the regular RCA audio) retailed for around $20. Our cost per piece? $2.35. We used to sit back there and laugh at this stuff. The funny thing was that all of the floor demo models were using the OEM video and audio cables from the manufacturer, so if Monster cables were so great, why didn't our demos use them? Haha

[morzh]

When I bought my SONY home theater ($500 everywhere; my friends paid that much; Amazon was selling it for $250 but one had to wait....2 weeks. I thought two weeks were worth $250) it came without HDMI cable. I went to BB and found that the cheapest HDMI that was selling there was some Monster variety at $35 or so.
So I went on eBay, and for $6 (I decided not to buy $1.50 ones, though I have no proof they were not bottled from the same barrel) bought me a cable which is working fine (it's been about......8 or 9 years or so).

I am sure the true connoisseurs could discern them; I can't.