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In Reply to: Anybody try air variable caps for RIAA networks? posted by DrM on October 31, 2001 at 08:20:53:
just a note here... as capacitors go...depending how you look at it air can be considered a very poor dielectric in that its DC is 1.. replace that air with say teflon with a dc (dielectric constant) of 2 and you get double the capacitence for a given plate size and spacing...the whole reason we want our trannies to have low DC materials is to reduce capacitences, but if its a capacitor we are trying to build...
i am looking at it from the capacitence vs size issues and not linearity......so maybe bigass air caps are the best??? what could be better.. well maybe vacuum caps... but like air their values are so tiny...
so i guess it goes back to that whole quality vs. quantity compromisees, but i suspect the air caps should be quite good anybody have a reason why they should suck??? i see no reason why not to give it a try, when you get it all dialed in.. then try swapping it out for matched values of different constructions and report back on the sound.
looking at the tables... i have always wanted to do a water capacitor... its DC is up around 70 so you could get some pretty impressive values by just sinking a few metal plates into a vat of water...
i almost went and bought one of those developing tanks for 4X5 film and got some 4X5 sheets of copper cut and filled the whole thing with distilled water to just see what values i got... of course the problem is water is very instable and impractical in this situation, but... it would be a goof to try.
someday :-)
dave
Follow Ups:
Dave,Pure water is a bad conductor of electricity. The problems start because of dissolved minerals. Use either high quality distilled or demineralized water.
Eli D.
dammit eli... don't make me try this... the whole thing was a joke... the copper plates would tarnish and contaminate the water too... maybe silver plates :-) possibly gold plated :-) i'm not worried about the breakdown... just want to get a clue if the whole thing is actually possible... and maybe get my ears on it for a day or two if it actually works... think of the threads... evian is smooth... pelligrino has a bubbly edge... and if you hav the $$$ cristal is the way to go... fwiw alcool has a lesser DC than water, but it is more stable wrt impurities... this is the diy fourum... so why not diy caps??? some sort of sealed system would be needed for anything liquid... hmmm batteries use plates and liquids... how different are they than caps... maybe they could be adapted...dave
dave
dave
Go on try it Dave, I've been bored to death lately we need a filip!!
well dan M could dunk that variable air capacitor in a glass of water and see what happens to the values... leseee assuming air = 1 and water = 70..... 750pf * 70 gives us a .5mfd varaible cap :-)just looked at the dielectric constant table... water is closer to 80... but get this... hydrogen peroxide is a whopping 121, anybody know how stable this is, and how it might respond to voltage potentials??? and for those of you whio had to know, cocaine is a mere 3.1, so save it for insulating your transformers.
dave
I ain't gonna stick no capacitor in no stinnkin water! :) I've got enough project brewing without some wacky thing like that. I just want to know if these sound at all good before I plunk down some $$Dan
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sissy... use them for cathode bypasses or for filament supplies... don't go tossing the plates out with the bathwater...dave
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Looking down your list dave I suppose bath water comes somewhere between urea and h2o, about 2 then!
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