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Old 6th April 2011, 01:25 PM   #1
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Default how can test the stator insulation and mylar coating?

first to build a complete esl i would test if the mylar coating and stator insulation are good. For the mylar i diluited 8gr elvamide in 100cc ethanol but the document on audiocircuit say it have to be further diluited with equal volume of "anhydrous A.R. or L.R. grade methanol",
that i haven't, can i use ethanol again?. About the stators i would use a perforated metal sheet but im not sure of the perfect insulation. It's possible to make some electric test with a little piece of it and a little sheet of coated mylar to see if the sistem work good?
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Old 6th April 2011, 02:11 PM   #2
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I use my bais supply connect between a screw driver and the stator.

Scanning the the surface area of the stator with the screwdriver will show any leaks evident in the stator coating.

Make sure that you use at least a 1 megohm resistor in series with the bais supply and the screwdriver.
The resistor will limit the curent draw and save the diodes in the bias supply from shorting due to excess current draw from an arc when a leak is discovered. jer
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Old 6th April 2011, 02:17 PM   #3
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Once you get that far you can use the same method to test if the diagrpham coating works.
By touching the diagphram with the screwdriver the diagphram should suck into the stator. jer
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Old 6th April 2011, 02:41 PM   #4
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thanks gerald, i'll try as soon as possible
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Old 6th April 2011, 04:50 PM   #5
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Making your own coating material isn't easy. A lot of times you'll end up with unsatisfactory results. I would suggest you look into purchasing the right stuffs. I have been using a permanent antistatic solution with great successes.

Wachara C.
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Old 6th April 2011, 06:26 PM   #6
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Quote:
Originally Posted by chinsettawong View Post
Making your own coating material isn't easy. A lot of times you'll end up with unsatisfactory results. I would suggest you look into purchasing the right stuffs. I have been using a permanent antistatic solution with great successes.

Wachara C.
hi wachara, i'm interested. This will not add mass to the diagphram?
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Old 7th April 2011, 07:09 AM   #7
Calvin is offline Calvin  Germany
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Hi,

You could use a piece of household Aluminum-foil. Connect the HV-supply to the stator at one end and the foil to the other end. The foilswill be sucked towards the stator. Raise voltage of the HV-Supply and listen and look where flashovers occur. Itīll start with tickling noise all over and eventually single clean flashovers pop up. If the flashover is strong enough it pounds small pickles into the foil surface. So You can easily detect where a spark flew and the insulation fails.

jauu
Calvin
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Old 7th April 2011, 07:57 AM   #8
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Quote:
Originally Posted by lutherblisset View Post
hi wachara, i'm interested. This will not add mass to the diagphram?

Any coating adds mass, most of the time you don't know how much because this information is not provided I(while it should). Check out the previous discussions about coatings on this forum, you will also see there is much better to get than elvamide.
Using a wire stator instead of perforated sheet seems to be the best way to make a reliable esl.
Also look for a neonoscillator at the output stage of the HV-supply as it indicates the amount of charge supplied to the membrane
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drs M.J. Dijkstra
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Old 7th April 2011, 03:39 PM   #9
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Over here in the states some of us have have been using a product called licron and licron crystal.

I first discovered "LICRON" in 2003 and "LICRON CRYSTAL" hit the market in about March of last year.

I don't know if it is avaiable in your area but I'm sure that a suitable equivalent can be found.

On my original diagphrams I had used licron.
Its thickness was about .1mil to .3mil depending on how many coats were applied to my .25 mil mylar.

It worked great and still worked after 7 years of deliberate extreme environmental torture.
Upon disassembley of the panel there was no evidence peeling of the coating just a bunch of dirt, sand and salt stuck to the diagphram.

So, I then cleaned the diagphram with denatured alcohol and reassembled the panel and it worked with out any problems at all.

Due to the cleaning, The detail of the high end was restored that was lost becuase of the added mass of the dirt and sand.

Then I replaced one of the diagphrams and tried the licron crystal formula to do a comparison against the old formula.

The coating dried absolutely clear and the thickness was unmeasurable with my micrometer.

In the comparison test I did notice a slight increase in high end detail aswell.

This was only barley noticeable in an a/b comparison with the other panel of exact size made of the same material and construction only using the old formula as a coating that was 7 years old.
That had no degradation of performance since the day it was built after the cleaning.

I will find and post the links where I showed this procsess with lots of pictures and closeups of the surface of the diagphram as well.

Also the one ones where Charlie had redone his panels with the new formula too.

My little panels turned out to be pretty efficient and get exteremly loud usiing a 1:200 to 1:400 stepup ratio and diagphram size of 3.25" X 9.75" and a d/s around .075" (75mil).

I am able to get down to around 100hz or lower without excursion clipping with this setting while not sacrificing efficiency.
This type of clipping was only witnessed using a microphone and an o-scope when the panel was driven very hard and the clipping was very slight at that.

The stator coating I used was a double layer of powder coating.
This process has some bugs that need to be worked out and were the last panels that I made and the only ones that used powder coating.

Later on I had discover that had some leaks but nothing major, but, they wouldn't hold the 7.5kv bias that I was applying.
A few coats (6) of clear acrylic took care of that.

On my last test I used my Crown dc300a to power them at full power and a full 5kv to 7kv bias with an estimated 27kv p-p across the the stators.
This was a very extreme condition and was so loud the average joe would have vacated the room instantly.

They survived this condtion thru many cyclings of amplifier shutdown due to overheating.
In other words they brought that Crown to its knees.
But, It kept on going and still works perfectly to this day.
It is one heavy duty amplifier with unadequate heatsinks, IMO.

This went on for a good 1 1/2 hours until a leak devoloped along the edge of the screen and arced over to a sandwhiching bolt to the other side or to/or near the charge ring.

So, I then ran them in this condition for a while to see if any thing else would develop while I blew out the flames of the burning acrylic spacer material.
No other problems occured.

Upon disassemebly of the panel had found no damage to the diagphram, aswell as, no pinholes burned in the diagphram.

The leak was caused from a sharp end of the stator wire not buried deep enough in the insulating material used to seal the cut edges of the screen stator and it just happend to be near a bolt.

Originaly I used clear silcone as an insulating seal but during the refurbishment process I discovered that the clear acrylic spray did not bond the the silicone.

So questioning this as being unadequate in this area, I spent endless hours taking off the silicone and resealing the preimeter with clear nail polish.

I did have A hard time sealing that exact spot from leakage and I wasn't going to put that bolt back in, but I did, and figured that a problem would eventualy arise and it did.

This was the only flaw in the design I have found so far and is an easy fix for the next build.

I had also delibreately built the diagphram frame with an inside deminision of an 1/8" smaller than that of the stator to protect against such an occurence.
It worked, As the flashover went the other way to the bolt which is much farther away instead of going through the diagphram.

So, I merely cleaned off the burnt material and carbon residue resealed the bad spot and retested it for leakage and arc through and it is now ready to be reassembled for another go around.

That is were I had left off last summer as I had to rearange my equipment to solve some noise and ground loop issues and I still have to build two more variable bias supply prototypes that I had designed and put them in a proper enclosure.

As not to cause any risk of HV getting back into my equipment like last year.
I was lucky that nothing happend to any of it.

If you do a search on licron in the forum you will find two pages of threads on various ESL builds many of which I have never seen or read before.

So I guess I have some catching up to do aswell from 2006 when I was MIA due to my stupid mistakes in life (ha,ha,ha, live and learn the hard way). jer

Last edited by geraldfryjr; 7th April 2011 at 03:55 PM.
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Old 7th April 2011, 04:13 PM   #10
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Here those links.
This is an excelent thread and should be read from beginning to end.

Opps there was one diagphram where that coating came off I suspect it was due to improper cleaning and handling during the coating process and had occured when I cleaned the diagphram after 7 years of abuse. jer


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