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First Sparks: 9/6/98

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Well here it is...The first sparks.  I finally got tired of jacking around with the poly cap.  My frustration peaked when I went to rebuild the cap in the new container I bought.  I went to lay in one of the 16" x 16" poly sheets and it didn't even come close to fitting.  I began to wonder if the advertized dimensions were a poor english-metric conversion or if the label should have read [ 17"  (in your dreams) x not even close to 24" x
nearly 4".]  I was so mad!  I had to go inside and have a beer to cool down.  So there I sat enjoying the brew watching the shiny beads of sweat rolling down the bottle...and a moment of inspiration hit!  I ran back out to the garage and started digging through the storage room... down in the corner was my dusty old 10 gallon fish tank.  I drug it out.  This just might work...I finished my beer and the other two in the refrigerator, dumped out the year old mayonaise, finished off the last of the grape jelly, and scrounged any other glass bottles I could find.  One quick trip to the store to get a few pounds of salt, and my salt water cap was born!

I topped the whole arrangement off with the corn oil I had removed from the poly cap (about 2" of oil total).  I slapped the meter on this little jewel and measured a respectable .013 uF capacitance.  Respectable for some old beer and mayonaise jars...yes, but only about half of the capacitance the coil was designed for.  Still I was determined to have a go.  I took a quick run out the garage door trailing a ribbon of aluminum foil behind, tied this off to the water meter near the street (about 40 feet) and the radio frequency ground was done!

Back inside, I made the final connections, adjusted the RQ spark gap to 4 gaps @ 0.030 per gap and ramped up the power.  At about 50 VAC input, the spark gap fired to life, but no sparks off the toroid.  I spent about 10 minutes checking connections adjusting coupling, tuning primary inductance...all to no avail.  Then I began thinking about the small cap...I guess this has raised the resonant frequency significantly, and since no other corresponding changes were made in the secondary, it still wanted to resonate with a .026 uF cap.  I figured the easiest way to raise the secondary resonant freq was to dump the top off came the toroid.

Back at the variac, the spark gap once again came to life, but this time it was accompanied by thin purple streamers off of the top of the toroid support!  I spent the next 10 minutes jumping around, celebrating, and saying to myself "this thing actually works".   I went back and played with the tuning for about 15 more minutes.  The coil seemed to be happiest with no top load, 11-5/8 turns in the primary, and 5 gaps @ 0.030".  Any more gap and the 'ol cap would start to arc out of some of the wide mouth, short neck jars.  Phenomenal...I spent the rest of the evening taking pictures and setting up the point to point discharge tests.  I maxed out at about 13 inch arcs point to point with about 8 inch streamers into air.  I felt the coil had a lot more, but this cheesy cap and the change in resonant frequency were holding it back.

The next day dawned hot and humid, but I did notice that the water and oil in the cap were considerable clearer than the day before.  I began to wonder what effect this clarification would have on the performance.  I put two more gaps in and ran up the power.  No arcs in the cap!  I dialed in the last gap, now running
8 @ .030".  I reassembled the point to point set-up and tried the same 13 inches as yesterday.  Nailed it!  Moved out to 16" nailed it too, moved to 18" still regularly hitting, went to 20"  made a couble of good hits before the cap erupted in arcs.  Boy, was I glad I had a couple of good photos at 18".  Later examination revealed a cracked bottle in the cap, so I'll call the max. sustained discharge at this time 18" in about 70% relative humidity.