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Depotting NSTs and getting out all the 'gunk'

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LAN_403

Plasma Lover

Fri Mar 13 2009, 07:28PM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

Hello Everyone,

I am planning on depotting two NSTs that belong to a friend of mine for him and removing shunts, as well as fixing them. I was wondering whether or not anybody on the forum knew how to get all of the 'gunk' tar out, after getting most of it. I have been told that all of the tar is impossible to get out, but I have read that you can get a great deal more if you let gasoline soak in. I, for one, do not want to put gasoline onto the inside of a high-voltage transformer, attempt to fix it, fail, have it arc in the secondary and burn up all of my work. I was wondering if there were any other solvents that are less volatile that will dissolve the tar.

Thank you,

Christopher

P.S. Should this have been in chemistry? I think that it should be in high voltage since I am rebuilding a high-voltage device(?).

Tigeris

Fri Mar 13 2009, 10:33PM

Registered Member #1656 Joined: Wed Aug 27 2008, 03:28PM
Location: Pittsburgh PA
Posts: 53

Epoxy strippers might work. Getting the potting out of those are such a pain. Take WAY to much time, too much messy, and pain in the back. Now i don't know if the stripper will mess with the coating on the coils, so be careful.

Arcstarter

Sat Mar 14 2009, 03:06AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

I have heard something that sound rediculous i think, that you could use gasoline. That sounds horribly dangerous, but maybe you can find something else that can eat the gunk away, and not the coils and will either evaporate easily or is not flammable.

aonomus

Sat Mar 14 2009, 03:47AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

First, try heating up the NST gently, perhaps boiling water or so, and try pouring out the majority. Be careful if you try to stick a object in to scoop things out as there maybe loose leads and fragile things inside. Be careful, do this in a ventilated area, and have a fire extinguisher handy.

Also, try google and the search function first.

Then some solvents you may consider are:

Harsh:
Dichloromethane
Acetone

Soft(er):
White spirit/Turpentine

Gentle (may not work):
Isopropyl alcohol

Plasma Lover

Sat Mar 14 2009, 06:25AM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

Thank you, aonomous, your reply helped me greatly. I look forward to you answering my questions in the future!

=)

By the way, getting the cover-plate off of an NST your first time is as hard as trying to get a DRSSTC to work without an oscilloscope. Okay, maybe not that hard, but still...it's difficult. I would use language...but that would be frowned upon...

Anyways, thank you for your help.

Now I need to know whether or not it will work to melt the tar in the oven and, if so, what temperature would be best. I know that you CAN melt it in the oven, but, since it's my parents' oven, should I do it on there, or should I try something else because it's going to make my house smell like burning tar? I don't want a dense tar smell and my dad would probably disapprove of it.

Thank you for your help.

Steve Conner

Sat Mar 14 2009, 11:27AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Try searching the TCML archives at pupman.com for more information, people there used to do this all the time.

Yes, the tar can be melted in the oven, and yes, it'll probably stink the place out. I've heard of people BBQing their faulty NSTs in the back yard.

Be careful with solvents, some of the ones suggested (like dichloromethane and maybe acetone) may eat the enamel off magnet wire. Diesel or kerosene might work, and they're certainly less volatile than gasoline.

Finally, make sure it really is tar! You sometimes see NSTs potted in epoxy resin, and that doesn't melt.

Gunboat

Sat Mar 14 2009, 11:49AM

Registered Member #338 Joined: Thu Mar 23 2006, 12:28PM
Location:
Posts: 41

I have used kerosene succesfully and had no problems,then I got rid of the "kero" with turpintine. Yes,you can put it in the oven at about 200 degree F,and yes it will stink to high heavens. Do not,repeat,DO NOT,put it back into the oven after you have put the kero and turp in it. They can possibly catch fire. Don't use acetone,it will more than lickly eat the enamel off the windings. After the two baths of kero and turp,you can wash again with gasoline,it will evaporate fast and leave you with just a slight smell,that will dissipate after a few days.

aonomus

Sat Mar 14 2009, 01:04PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

And this is why boiling water and steam are the best alternatives, much lower risk as the boiling water bath keeps the temperature locked at just above or below 100degC with the only hotspot being the bottom of the pot directly against the heating element of whatever is heating the water.

And I believe the first google result is a Terry Fritz post on pupman Conner -.-

Download

Sun Mar 15 2009, 09:07AM

Registered Member #561 Joined: Sat Mar 03 2007, 02:46AM
Location: Adelaide Australia
Posts: 230

Possibly acetone?

It would evaporate off pretty quickly so there shouldn't be a problem of your core catching fire

Plasma Lover

Mon Mar 16 2009, 07:48PM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

They were both potted in real tar. I was already sure of that. For some reason, one melted at a lower temperature than the other. I was able to get the ceramic insulators off of one of them (since my friend only wants the core and windings) and I now need to douse them in gasoline. I tried kerosene with dismal results. As a matter of fact, the results were not visible.

The Wire that connected the insulators to the windings broke off and, now, all I have is the hair-thin wires and remnants of said HV wire. What should I do? Solder new HV wire to the secondary wires? Then should I use some kind of glue, like super-glue (contains acetone ><) or polyurethane or epoxy to hold down the wire?

I will finish cleaning the core off, this afternoon, by applying a generous amount of gasoline to the core (via a small bucket).

Wish me luck, and thank you for the tips!

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