Home » Audio » Thermionic Emissions » Air Dialectric caps
References [message #8965 is a reply to message #8964] Mon, 16 May 2005 01:19 Go to previous messageGo to next message
muman is currently offline  muman
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or rubbish

Re: References [message #8966 is a reply to message #8965] Mon, 16 May 2005 05:48 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
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Well; I guess the only way to find out is build it.

Re: Dielectric Constant (of water?) [message #8967 is a reply to message #8962] Mon, 16 May 2005 05:51 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
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I'm sorry; I am quoting another source who apparently uses these to do low level circuits. I would ordinarily not offer a fact that I did not check but this seemed harmless. Should the study not appear you have my apology.

Re: Reference - "Valve Amplifiers 3" [message #8968 is a reply to message #8965] Mon, 16 May 2005 05:54 Go to previous messageGo to next message
Damir is currently offline  Damir
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See "Valve amplifiers 3" by M. Jones, pages 211-229, especially Fig. 4.4 - various capacitors types, and the quality of them. The air plate caps are the more nearly perfect, with electrolytic Al-foil/bipolar at the "other side".
Then citation: "Possible audio uses (of air dielectric, metal plate) include:
- ~300pF variable capacitor across the input of a MM RIAA stage to allow cartridges to be optimally loaded by the pre-amplifier
- ~50 pF for trimming equalization capacitors to their exact value"

And later, author uses just that - 40 pF variable cap for "trimming" the exact value of RIAA EQ cap in his EC8010 RIAA preamp, Fig. 7.37, page 568.
And please, calm down your agressive tone, one of the reasons why are all here is to avoid "rubbish" from some other forums...

"Electrical breakdown is not always associated with high voltage" [message #8970 is a reply to message #8968] Mon, 16 May 2005 21:12 Go to previous messageGo to next message
muman is currently offline  muman
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Thank you for the reference. I looked and found Morgan Jones book. I don't agree that air is a better dielectric or that it sounds better, but at least this reference is something. At the microvolt level of a moving magnet cartridge, if the air is clean and humidity controlled, it would work.

I work in power systems, and we always consider air to be a problem. The dielectric properties of other insulators are much better. Even an air bubble in an insulator can be catastrophic. Advances in materials have made air gap insulators obsolete, IMO. The fact they aren't used in most good radios anymore says something too.

Quoting John J. O’Dwyer, "Breakdown voltage is directly related to the dielectric thickness. Its counterpart, dielectric strength, indicates the relationship between thickness and breakdown voltage, and is expressed as a ratio of voltage to thickness. Thermal effects due to local Joule heating can cause thermal breakdown at sufficiently high temperatures. This correlates to electrical conductivity through an exponentially increasing function of the temperature. Other factors that contribute to breakdown include particlates, material contamination and water vapor. Each can influence breakdown; actions must be taken to eliminate their contribution to breakdown voltage measurements. Humidity, for example, reduces the resistance of most dielectrics, thus increasing the return current (the current that opposes a charge build-up). Contamination can contribute to leakage currents and charge mobility across isolation areas."

Two plates separated by a 1mm air gap will arc with 3000 volts, and can as low as 300 volts. Air is a fluid mixture and unless controlled, it is a nonspecific gas. Water vapor is a big factor in reducing the dielectric strength of air (or any other dielectric, for that matter) and other contaminations also contribute to modify dielectric properties. It's a crap shoot with air so I don't think an open capacitor is the best way to go.


Air Caps, Right Here, Get 'em While they're Hot!!! [message #8971 is a reply to message #8970] Tue, 17 May 2005 00:39 Go to previous messageGo to next message
Triode_Kingdom is currently offline  Triode_Kingdom
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Note that I have no personal or professional relationship with any person at this company.


MODERATOR [message #8972 is a reply to message #8940] Tue, 17 May 2005 16:13 Go to previous messageGo to next message
akhilesh is currently offline  akhilesh
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PLease check some posts below in this thread. I believe they go against the spirit of ART. Just FYI: a heads up.
-akhilesh

Re: MODERATOR [message #8973 is a reply to message #8972] Tue, 17 May 2005 18:30 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
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AK; Hey, E-mail me off line.

Re: Get 'em While they're Hot!!! [message #8974 is a reply to message #8971] Tue, 17 May 2005 22:25 Go to previous messageGo to next message
muman is currently offline  muman
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I would not use those past 10% voltage listed, if even that. You don't have to melt the plates for corona discharge to adversely affect quality.

Bolivars [message #8978 is a reply to message #8963] Fri, 20 May 2005 18:05 Go to previous message
PakProtector is currently offline  PakProtector
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Illuminati (2nd Degree)
fron the Island...

if your screen is brown, imagine what your lungs must look like, or for that matter how they function. A good friend of mine just got a 4x bypass from a few decades of smoaking. 9 hrs with his chest split open...no thanks.
regards,
Douglas



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