I have found a source of glass capacitors in my area in a large range of values (.5pf - 1.5nf) and tolerances (sometimes +-1% sometimes +-10%). Most of them are Corning or Vitramon but there are a few noname brand. None of them are particularly expensive in the $1-$5 range. I was wondering if they were any good for audio or do they produce any nasty distortions like ceramic caps?
You should have said "...like high-K ceramic". NPO ceramic is an excellent, linear dielectric, as is glass.
So I take it they're good for audio. I was going to use them to get more exact values on a phono-preamp.
Are you sure glass = NPO? The AVX line of glass caps, for example, spec a DA in the polystyrene range and are listed separately from the Ceramics. I'ld love to find some.
I've measured some glass capacitors, Corning and AVX I think. You'd think glass would have some great properties, and it's not bad, but it's no better than some films, and probably worse than styrene or propylene. I think the military likes 'em, either for radiation resistance, temperature, space apps, or some other not-really-audio reason.
Conrad! You were the one who reminded of the National capacitor soakage paper from which I culled representative 'styrene DA numbers for comparison with AVX's claim. ~0.015 vs. 0.012. I feel so betrayed....
I know a physicist who only gets excited about things that are "an order of magnitude" different. I think he's on to something. Be it THD, power output, or component measurements, a lot of the things we worry about are probably down in a region of uncertainty that just keeps a discussion going, but without ever resolving anything. 
My high school physics teacher was like that. To quote:
I think hes teaching at a Taiwan University now. His wife was not happy about the move until she realized how well teachers are treated over there compared to RI (she was an english teacher or something).
I think hes teaching at a Taiwan University now. His wife was not happy about the move until she realized how well teachers are treated over there compared to RI (she was an english teacher or something).
I actually have a large stash of these type of CGW capacitors I just came across. NOS military overstock. This is a long dead post, but I'll give it a shot anyhow 🙂
I have a broken CY15C CGW cap in Brüel&Kjær preamplifier (fragile glass is so fragile) so look for a decent alternative/replacement. A comparison of http://www.avx.com/docs/techinfo/GlassCapacitors/perform_gl.pdf and http://datasheet.octopart.com/04025A120JAT2A-AVX-datasheet-5039.pdf yields:
glass NP0/C0G
TC: 140±25ppm 0 ±30ppm
life change: ≤0.5% or 0.5 pF ≤±3.0% or ± .3 pF (whichever is greater)
Dissipation factor <0.001 0.1% max.
Dielectric Absorption 0.05% 0.6%
Looks like NP0 is a good candidate (considering nuclear radiation hardness isn't the case). Hope someone could corroborate this assumption with practical experience.
glass NP0/C0G
TC: 140±25ppm 0 ±30ppm
life change: ≤0.5% or 0.5 pF ≤±3.0% or ± .3 pF (whichever is greater)
Dissipation factor <0.001 0.1% max.
Dielectric Absorption 0.05% 0.6%
Looks like NP0 is a good candidate (considering nuclear radiation hardness isn't the case). Hope someone could corroborate this assumption with practical experience.
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