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Old 10th May 2007, 02:05 PM   #21
bigwill is offline bigwill  United Kingdom
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Quote:
Originally posted by I_Forgot
I think you're getting ahead of yourself.

Graphite will not give a coating that is more than 50 Meg Ohms, especially if you "used too much". Graphite will typically read in the 100k-2 Megohm range. How did you do the measurement? How did you apply the graphite? Does the diaphragm look gray (it should). Are you sure you connected the right side of the diaphragm to the bias supply? Did you connect the other side of the bias supply to the center tap of the audio transformer(s)?

ESLs will play at very low volume with no bias supplied because the diaphragm will pick up charges just from being handled. The film may also retain some charge from the film manufacturing process.

I_F

I applied the graphite by sprinkling some on the diaphragm and rubbing it in relatively hard with cotton wool. I tried to get an even spread as I could. It looked grey and if I rubbed it it, I would get graphite deposited on my finger.

I attempted to measure the resistance by putting two copper pennies on various points of the diaphragm and putting the probes on them. I could not measure anything.

The bias supply is connected to the diaphragm via copper tape. I has a big surface area touching it


I've ordered some neon lamps (annoyingly in packs of 10) in order to build a leakage indicator!
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Old 11th May 2007, 04:54 PM   #22
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What sort of meter are you using and are you sure it is working properly? Are you sure that what you used is graphite? I have never seen a graphite coating that gives resistance >2 Megohms, especially not if it is a heavy coating as you have suggested.

Can you post a schematic of your system?

I_F
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Old 11th May 2007, 06:56 PM   #23
bigwill is offline bigwill  United Kingdom
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Here is the schematic
Attached Images
File Type: gif wiring.gif (5.7 KB, 441 views)
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Old 11th May 2007, 07:39 PM   #24
bigwill is offline bigwill  United Kingdom
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My neons arrived today and I wired up the schematic for the leakage detector, but it acted strangely. Sometimes it blinked as the bias supply was turned off, blinked about once as I connected the diaphragm wire, and the neon GLOWED IF IT TOUCHED IT?

Is my bias supply just making high voltage AC or something? Or at least pulsed DC?
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Old 11th May 2007, 10:37 PM   #25
bigwill is offline bigwill  United Kingdom
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Ok, with a bit of fiddling I got the indicator working. With just a sharp wire coming from it, not connected to the diaphragm, it works sanely. As I bring my hand to the end of the wire, it flashes faster. Bring a grounded object nearby and it flickers quickly.

If I connect my diaphragm to it, it just says on

My panel is obviously leaking massively. I think coating the stators with acrylic lacquer is the easiest way to solve this, am I right?
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Old 12th May 2007, 12:50 AM   #26
gvy is offline gvy  Belgium
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May be, while coating the membrane with the graphite, and not being carefull, you made a low resistive leakage path to the metal stators?

Geert
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Old 12th May 2007, 03:33 PM   #27
bigwill is offline bigwill  United Kingdom
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Quote:
Originally posted by gvy
May be, while coating the membrane with the graphite, and not being carefull, you made a low resistive leakage path to the metal stators?

Geert

Perhaps.

I just got a spare stator panel on its own and connected it to the EHT lead and the neon flashed about 5 times per second. There is no way this can work with these panels uncoated. They seem to have too many sharp edges to leak from.
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Old 12th May 2007, 06:59 PM   #28
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Default Welcome....

to the world of insulated wire stators where there are no sharp edges. There are of course ways around the troubles that you are experiencing because perf metal stators are made that work just perfectly. That said I believe that while wire stators are more fuss to make than are perf metal stators the end results are far more dependable/reliable (for the DIYer) than the kinds results that you are going through.
Buy the right wire wind your stators and glue the wire down. Done like dinner, they will work and keep working for a very long time. Do it right and you only have to do it once.
As an aside there are sources out ther where you can purchase professionally made insulated perf metal stators that look just like those that people like Martin Logan use. So if that is what you are after the money to buy them is well spent. The devil lives in the details and if they have sharp edges there is no amount of insulation of any kind that you can apply to fix that little detail. You will be better served to start over and deal with the issues at hand or find anothe method that simply circumvents those issues.
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Old 12th May 2007, 08:01 PM   #29
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I don't think your transformers have the correct turns ratio. 40:1 will not make enough voltage for your panels. Get some tube audio output transformers.
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Old 12th May 2007, 08:06 PM   #30
SY is offline SY  United States
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Well, a typical small tube output tranny with turns ratio on the high side will be able to match 8k to 4R. Impedance ratio of 2000, so turns ratio of 44. Not a big difference and it's tough to find higher impedance trannies than that.

40:1 isn't huge for an ESL (50 or 60:1 would be better), but it's not that far out of range. Figure that 30V out from a medium power amp will drive 1200V to the stators. Translating to peak, that's about 1700V.
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