High voltage driver for AB2 operation GU81m tubes - Page 27 - diyAudio
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Old 13th August 2012, 09:50 AM   #261
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before potting you can test the opt.....then when everything works out good, you can start potting those OPT's.....your traffo maker should be able to do that for you...
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Old 13th August 2012, 09:54 AM   #262
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Quote:
Originally Posted by Tony View Post
your traffo maker should be able to do that for you...
testing the opt or potting it?

either way it can't be done realiably. I must test the opt in action with the gu81m and it would be very expensive to have the toroidals sent back for potting.

installation in my chassis is difficult to so I will have to work with the opt "outside" the amp before final installation.

what would be a good way to dessicate the amp? airtight storage with silicagel for a few days?
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Old 13th August 2012, 10:05 AM   #263
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i mean potting it......

in that case you will have to pot it yourself....if you can find a suitable container and epoxy compounds, you can diy....
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Old 13th August 2012, 12:12 PM   #264
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epoxy I have plenty (I used to make my own carbon fiber parts for my motorcycle)

Container, will a plastic toroidal container suffice?

I have a picture of some testing on the driver.

Click the image to open in full size.

I need a x100 probe to proceed further. The scope at 50v/div clips.

The 6bl7 can really take a beating. I made all sorts of mistake working on it and it is still kicking!
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Old 13th August 2012, 12:15 PM   #265
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looking good.....

so you have experience with carbon fibre, that will even make a good encapsulant for your opt'S....
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Old 13th August 2012, 12:34 PM   #266
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really? do you think a carbon fiber encapsulation is worth exploring? I can easily make one with a stamp of the container as template.
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Old 13th August 2012, 12:39 PM   #267
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you have everything.....go ahead and do it...
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Old 13th August 2012, 12:40 PM   #268
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ok. I will.

I can either wrap an existing container in CF or make an entire new container. What do you think?
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Old 13th August 2012, 12:43 PM   #269
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I will install 4kv GDTs in clear glass tube envelopes
I'm not so sure that is the answer. I worked with lower voltage GDT's about 20 years ago to protect line powered radio equipment mounted in remote locations where the power source was less than ideal and lightning strikes were guaranteed.

We used devices made by CP Claire and Siemens. The GDT functions much like a neon bulb or a 0B2 regulator tube. It has a speciallized gas mixture inside so that once the strike voltage is reached an arc will occur causing the voltage across the device to drop. The ones made to operate directly across the power lines can carry a huge amount of current for one half cycle, about 16mS on 60 Hz. The arc should extinguish when the line voltage crosses through zero.

We were getting field failures where the GDT had melted and in some cases the arc continued after the GDT ceased to exist destroying the PC board and most of the device. I could not duplicate this destruction in the lab.....until I duplicated the field conditions where the device could be powered by several hundred feet of wire between the device and the power company distribution transformer. The same power source was also operating several kilowatts of sodium vapor lamps.

After a consultation with the GDT vendors engineers, we learned that the GDT must experience a zero crossing of its supply voltage in order to extinguish. This must come before the critical temperature is reached where the device will auto-strike on the next half cycle. In our case the sodium vapor lamps and their solid state ballasts were poluting the power source such that there was no clear zero crossing, and the GDT never extinguished.

I believe that you may be in the same situation with a constant DC voltage across the GDT. Maybe the devices have improved in the past 20 years, I don't know. I would check with the vendor, or perform some experiments before risking a possible catastrophic event.
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Old 13th August 2012, 12:44 PM   #270
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ok. I will.

I can either wrap an existing container in CF or make an entire new container. What do you think?
good plan...
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