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Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780
Hi all
Since I have encountered too much failings with my small TC ideas, I'm going to make a simple but reliable SGTC
I have everything needed but I'm sure there are some points which need some enlightenment you could provide
I'm going to use my 4kV 25mA NST with a 23nF capacitor (a bit overrated compared to the recommended 19nF but that's the better combination with my doorknobs) and a 2.5mm² helical primary
So far, here are my calculations
Primary inductance : 8.98µH (10 turns 2.5mm² on 90mm form, helical) Primary capacitor : 23.5nF Primary resonant frequency : 347kHz
Secondary turns : 1500 (0.3mm diameter magnet wire) Secondary inductance : 16.7mH Secondary capacitance : 6.135pF Topload : something between 8pF and 10pF Secondary resonant frequency : 347kHz depending on topload
The doorknobs to be used are 4700pF 20kV pulsed units (from a nitrogen laser cartridge)
The outer right part is a triggered spark gap, could be useful to control triggering speed
Finally, as a load I have two alternatives, either a small tire or a glass globe, or the two depending what is best
Latest picture is from the primary and secondary forms yet to be wired
After wiring those, I'll have to design a spark gap and was thinking of 3 sections of copper tube to have an uniform firing rate without too much heat to cope with
Do anyone think I'll need a safety gap for these ratings? I don't think it will be too powerful at only 100W of input power (transformer only draws 1.06 amperes from the line)
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780
simulation in ltspice gives me 300kVpp at topload with a 2p toroid and 400kVpp with a 10.4p combined sphere/toroid topload
I can't say if this is accurate so if anyone has a clue...
also I'm thinking of a special arrangement for my capacitors but fear parasitic inductance... should I put them in a range on copper bar or dispose them in circle with HV terminals in the middle?
I'm planning to wire the secondary in the next days, then form some copper bars out of piping, and screw everything on a wooden base
Registered Member #1316
Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365
Safety gaps are always good. They are inexpensive to add compared to the price of a new NST. Have you tested you capacitors for capacitors for standoff voltage and capacitance? The bottom left one and the top right one appear to be chipped....
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Shrad -
As Weston noted, two of your caps are damaged, perhaps fatally. You mention that they were removed from a nitrogen laser "cartridge". Can you describe this cartridge, and how the capacitors were removed? The damage doesn't look like "chips", it looks like the capacitors were somehow attacked with a grinding wheel or something similar. I wouldn't count on using them in your tank circuit.
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first SGTC, a little more planning than what I'm used to...
