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Registered Member #1837
Joined: Tue Dec 02 2008, 02:20PM
Location: NYC
Posts: 65
Hello everyone. I'm running through some equations and I have a question. I'm looking at equations here, (credit to Jerry Gore). I started at equation 2 of the 4 equations at the top, since i already have a primary cap of 940pF.
My answers to top equations 3 and 4 are 3. reactance of primary cap is 2821.67Ohms 4. inductance in microhenries is 7484535.81, or 7.48 Henries
That brings me back to an answer of 60Hz for the next equation 3. (I know it's confusing, but there are two sets of equations 1-4, and 1-10)
Is this what i should see? It seems like it is bringing me in a circle. I thought I would see the desired frequency in KHz or MHz, but instead i just seemed to prove the line frequency.
The next equation for me is 5 (number of turns for a helical primary), and i don't know what to input for height. Do they mean height above lowest point of secondary? I get hung up here and dont know what to input. After this i think i can complete calculations but I'm stuck!
Any help appreciated. I'm not asking to double check all my math, but maybe you can see something that looks way off and i can investigate. Thanks for any help.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
In a VTTC you need to work with some different terms as Q factor and load impedance of the tube.
Use the math that Steve Ward have collected in the bottom of his faq:
Basicly decide on a Q factor of 10, decide on a resonant frequency you want to work at, then with the load impedance of your tube you can calculate the size of your capacitor. The its just designing a secondary + topload to fit that resonant frequency. Use calculators at and JAVATC at
Registered Member #1837
Joined: Tue Dec 02 2008, 02:20PM
Location: NYC
Posts: 65
Thanks again MK. I went through all the math on his page and feel a little more understanding of how this thing will work. I think all the other equations were for spark gap coils. Oops! No wonder I got stuck! Anyway, you've been very helpful and I appreciate it.
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VTTC mathematics
