Original poster: "Gerry Reynolds" <gerryreynolds@xxxxxxxxxxxxx> Hi Victor,The value of your tank cap is mains resonant. This means that the effective inductance within your NST and the tank capacitance will series resonate at the mains frequency. If you open your gap too much, very high voltages could develope that will kill your NST. With no spark gap limiting the voltage, you could easily get over 80000 volts. Being mains resonant at your current gap setting, the BPS will be high and gap losses will be high.
I would recommend increasing your Cp to 10.6 nf (this will give you around 120BPS). I would also recommend the addition of a safety gap if you dont already have one and make sure to have it properly set. Disconnect the TC from the NST to run the NST unloaded, and then increase the safety gap setting in small increments until it stops firing. Of course, any adjustments are made with POWER OFF. When properly set, the safety gap width will be just sufficient to not arc and not be any wider. In this way, if you increase your main gap too far, the safety gap will take over and prevent overvoltage of your NST. You may also want to build a "Terry Filter" if you havent already done so to help protect the NST from RF.
With your power source and a static gap, you should be getting 20 to 30 inches. Tuning your coil can be done for the longest spark to an strike target that's grounded to the base of your sec coil (RF ground). Try to fine tune it to within a 1/4 turn after you course tune it. In general, a coil system should be course tuned at low power variac settings before fine tuning it at full power. Again, all adjustments are made with POWER OFF. You probably know this, but I just want to make sure.
Gerry R.
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