Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx> Hi Victor,Interesting. This is actually a post where I can advice opening up the gap. But later on that.
First, the coil should resonate at about 386 kHz with topload mounted just above coil. Typically a 1/4" copper tube primary is used and commonly with the same spacing. Secondary to inner primary distance is typically 1.5". If your primary is near this, then likely the coil will tune in at 9.25 turns. If your primary differs, then of course the tuning changes.
In any event, it's good you started with a narrow gap. Usually, coilers will begin opening the gap. Eventually, their NST dies and then they ask why. You started opening, but you started with a very narrow gap.
To set the spark gap distance, take the NST and gap aside and connect the transformer to fire directly across the gap. Set the gap spacing until the NST is no longer capable of arcing across the gap by itself. Then begin narrowing up the total gap spacing so the NST fires consistently across the spark gap. Then your gap is set. Don't play with it anymore. Don't try to open it up further to get longer sparks. You'll only kill your NST if you do.
Take care, Bart Tesla list wrote:
Original poster: "Victor Valencia" <victor_valencia2@xxxxxxxxxx> Hi Everyone, What a great list. Lot's of interesting topics. I just finished building my first TC. Here are the specs: Transco NST 12Kv, 30mA (marked as 200w) Spark Gap: copper tube-based, 9 gaps with 20 mils/gap Tank Capacitor: 77x GE 42L 3kv, (7 strings of 11 caps) (.0066 uF total) Secondary Coil - 3.25" diameter, 801 turns 24 awg wire Top Load: 4.5" diameter aluminum ducting. total dia = 15" It worked the first time although it did not create sparks that were very long. The most I got was about 12". Should I be getting more?? I tried tuning it by first adjusting the primary coil tap point between 10 and 12 turns and then varied the spark gap by varying the total gap 140 mils total to 180 mils. Nothing seemed to get it any better than the 12". In most cases it made it worse. I don't have a scope to tune it. I was thinking that maybe I should try increasing the spark gap since that would increase the charge voltage on the tank caps (unless it's already at the max). Any suggestions? I want to make sure I am getting the most out of this first one before I embark on making a "bigger" one :) Victor