I was thinking about making a tesla coil of sorts, and thinking over various possibilities. One of them being a design that's basically a push-pull tube amp.
For your tesla primary, you could perhaps have an untuned centre tapped coil, just like the primary of an output transformer. Each phase could be driven by the anode of something like an 807 or GU50.
Driving the grids of these valves could be a relatively fast phase splitter (something capable of around 500Khz), LTP pentodes would work nicely here. The input could be a sig get running at the resonant frequency of the tesla secondary, or even an antenna or pickup winding so it's self oscillating.
I have little RF experience so this may not work but it seems like a neat way to do it - a fair pit of power from push pull finals, and the flexibility of being fed with an arbitrary input signal (or feedback from itself).
I don't want to make a huge coil, just something with CW output that doesn't buzz horribly
Do any of these design ideas make sense for a tesla coil?
For your tesla primary, you could perhaps have an untuned centre tapped coil, just like the primary of an output transformer. Each phase could be driven by the anode of something like an 807 or GU50.
Driving the grids of these valves could be a relatively fast phase splitter (something capable of around 500Khz), LTP pentodes would work nicely here. The input could be a sig get running at the resonant frequency of the tesla secondary, or even an antenna or pickup winding so it's self oscillating.
I have little RF experience so this may not work but it seems like a neat way to do it - a fair pit of power from push pull finals, and the flexibility of being fed with an arbitrary input signal (or feedback from itself).
I don't want to make a huge coil, just something with CW output that doesn't buzz horribly
Do any of these design ideas make sense for a tesla coil?
These output RF tubes operates at Class C, meaning that in the most part of a cycle, the tube is cut off, and only conduct over a small % of the cycle. Usually, the bias is generated itself by simply rectifying the signal input of a couple thousand volt RF (200V or so peak), so the -200V at grid becomes it cut off. Yuo can try any low power pentode oscillator, classical is a 6V6 as a Hartley, and a 6L6 driving the 807´s. At this low frequency, they will perform OK. Be careful with the high voltages inside the equipment, and with MW radio interferences.
Good luck.
I´m ham radio from 1987.
Good luck.
I´m ham radio from 1987.
My favourite:
Tesla-Generator mit PL504
use Russian line pentodes when PL504s are out-of-stock...
..
Tesla-Generator mit PL504
use Russian line pentodes when PL504s are out-of-stock...
..
A tesla coil is a resonant transformer The resonant frequency is something like 1/4 of the electrical length of the secondary, which is 1/transmission line delay.
Whether the primary is a tuned circuit of uses an oscillator, it is driven at approximately the resonant frequency of the secondary. The classic tesla coil uses a spark gap as an impulse generator and the primary circuit is tuned to resonate. These operate oin a repetitive burst mode. Modern coils often use an oscillator that is tuned through feedback from the coil or manually tuned to peak the coil output. The load on the coil changes the resonant frequency a little. The driver should be quite efficient in that the tubes are either on or off, which will minimize the plate dissipation compared with a sine wave as used to characterize audio amps.
There is good power transfer from primary to secondary, so the load on the tubes depends on the load on the secondary. Typically a coil is sized for a particular VA or wattage, and there are a few websites that show how to calculate the variables.
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Hey Bigwill
I have built 7 Tesla coils and one of them was a VTTC, you can see it here Kaizer VTTC I | Kaizer Power Electronics and I will gladly answer any questions you have.
I have built 7 Tesla coils and one of them was a VTTC, you can see it here Kaizer VTTC I | Kaizer Power Electronics and I will gladly answer any questions you have.
I must admit I'm fond of that sweet ozone smell
Thanks, that is brilliant
This is what I'm still struggling with - the primary coil is generally on the order of 30-100μH, and the secondary resonance is usually in the hundreds of Khz range. The reactance of the primary will be pretty low at these frequencies, tens to hundreds of ohms - certainly not something a tube is happy driving. Will the coupling to the resonant secondary increase this, or must I add a tank capacitor in parallel so the impedance peaks around where you want? (Q could be adjusted to give you a usable range of tuning)
What gets me is I've seen a VTTC design WITHOUT an anode tank capacitor here: Miniature Vacuum Tube Tesla Coil
There is one in the grid circuit, but presumably that's just to set the oscillation freq, not energy storage?
I must admit I'm fond of that sweet ozone smell
Thanks, that is brilliant
This is what I'm still struggling with - the primary coil is generally on the order of 30-100μH, and the secondary resonance is usually in the hundreds of Khz range. The reactance of the primary will be pretty low at these frequencies, tens to hundreds of ohms - certainly not something a tube is happy driving. Will the coupling to the resonant secondary increase this, or must I add a tank capacitor in parallel so the impedance peaks around where you want? (Q could be adjusted to give you a usable range of tuning)
What gets me is I've seen a VTTC design WITHOUT an anode tank capacitor here: Miniature Vacuum Tube Tesla Coil
There is one in the grid circuit, but presumably that's just to set the oscillation freq, not energy storage?
You are right about the grid circuit, its only feedback and not a energy storage.
To explain it simple, running a Tesla coil without a tank capacitor will make you able to produce sparks, but not very big ones. With these it is important to have a feedback locked on the secondary frequency.
With a tank capacitor you get much higher peak currents in the primary circuit and you deliver a greater amount of energy to the secondary in shorter time and thus get longer sparks.
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