Water Cooled Synchronous Triggered Spark Gap construction

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Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi All,

I have been working a bunch with Water Cooled Synchronous Triggered Spark
Gap (WCSTSG) construction.  These gaps will hopefully cool the tungsten
carbide electrode tips enough that they do not wear.  I would like to
report my results (finally :-)).

First I got some MIG welding wire electrode tips and pure (green band) 1/8
inch x 7 inch tungsten rods.  I cut the rods with a file and I drilled the
copper MIG tips a little undersize with a cheap drill bit and pressed the
tips into the MIG tips with a vise.  You could also drill and braze the
tungsten in place (see later).

http://hot-streamer-dot-com/temp/MarcGap/P8120002.JPG

This actually worked very well and was really darn cheap and easy :-))  I
then just soldered the assembly to some copper fittings for a nice water
cooled triggered gap.

http://hot-streamer-dot-com/temp/MarcGap/P8120004.JPG

Since tungsten carbide inserts are common.  

http://hot-streamer-dot-com/temp/CarbidTips.jpg

A way to solder the inserts to copper pipe was needed.  I thought that
plating the tungsten with copper and simply soft soldering them to copper
pipe would be good.  Although it worked fine, it was a LOT of work!!

http://hot-streamer-dot-com/temp/CopperPlateSolder.jpg

You "NEED" sulfuric acid for the plating.  For the small quantity, maybe
just borrow it from the car battery :-)  Since the tips are small, only
20mA of current was needed and I was in no hurry.  But unless you want to
learn or use copper plating anyway, this is probably the most complex way
to go.  One caution, don't use anything but plain 60/40 tin lead solder.
Other alloys like 96/4 Tin Silver leached the thin copper layer right off
the tungsten!  I had never done metal plating, so it was a load of fun
learning about this.  Many thanks to Mike and others for the many tips on
getting it to finally work :-))

Brazing - I usually try not to weld anything since I am really bad at
welding.  Everyone said brazing was best and I now agree.  If you need to
attach the tips to the copper (as opposed to press fit) then brazing is the
way to go.  You need a nice MAPP gas torch since it has to be pretty hot.
Those Benzomatic 4500/7000 series ($40) torch heads are super nice!

You then need 45% silver brazing wire and flux.  You can find these at the
welding shop in little kits made by J.W. Harris:

http://hot-streamer-dot-com/temp/BrazeStuff.jpg

They have these little kits of wire and flux all ready to go.  Be
forewarned the ~1 meter of silver alloy wire ran the kit's price to $20!
But it really is a wonderful thing and worth it!  The wire will last
years...  Many thank to Jon for pointing out this "right stuff" :-)  I had
no clue...

http://hot-streamer-dot-com/temp/P8150010.jpg
http://hot-streamer-dot-com/temp/P8150006.jpg

I tried the blue flux coated silver nickle rod from the hardware store and
it was just to large and the flux to uncontrolled to do this rather precise
work...

I also found some copper (alloy) plasma torch tips ($5 each) that were just
perfect so I got some of them too.  The welding shop has all the cool stuff
for this.

So I made the new set of brazed tip electrodes.

http://hot-streamer-dot-com/temp/BrazedStuff.jpg

You will need a stiff wire to "play" with the tip position as you are
brazing them on since they like to float to odd places.  But everything is
well controlled and the brazing works very well.  I cleaned all the
surfaces with oxide sand paper first.  Use plenty of flux with helps keep
the copper from getting a thick black oxide layer from the high heat.  I
did the tips first and then soldering them to the pipe (I drilled a hole
for the torch tips).  I wire brushed an polished the heck out of copper
later...

The tungsten carbide tips should last just about forever on a small coil
and the copper tubing filled with water will draw heat away extremely well.

So now onto the other work of getting this WCSTSG to work.  I have heard
that putting resistors in series with the 2uF caps going to the ignition
coil, and the use of 500pF isolation caps on the coil output, may help
stabilize the triggering...  Thus reducing the need for the big power
resistors...  Much work still to be done!!  

Many great thanks to Marc for getting all this started!!

Cheers,
	
	Terry