HFVTTC V1

So I have finally decided to build some sort of a Tesla coil, starting with an HFVTTC.

Whether or not this was a good starting point, I have no idea, but the schematic is rather straightforward.

My design was based on this one by uzzors2k:

The difference was mainly that I used a different tube, and handled the g2 power differently.

I am for now using GU50 Soviet pentode, while he used a way more powerful GK-71.

As for the G2 supply, I am currently using rectified mains (filtered) which is put across g2 and the cathode instead of a large resistor which just connects G2 anode potential.

This leads to a low G2 voltage of only about 110V. I plan to fix this by using a CW voltage multiplier in the future.

Note: In a further iteration, this was no longer an issue since the circuit was driven with way higher voltage anyway.

For another change, I also used a different capacitor in the feedback which is only about 5kV and its capacity is way too large. This should not be much of an issue unless I short out the jar lid™ capacitor while running at high powers, but I do plan to replace it.

I also think that I should up the number of turns on the L1 (first) inductor, as that seems to have worked better for others.

Updates¹

Both the resonator coil and the choke have been rewound:

• Resonator: ~23 turns
• Choke: ??? I don’t know, I eyeballed it.

I have also split them off so they are no longer on the same coil form. I specifically 3D printed a 5cm wide 7cm high form for the choke.

I have also pushed way higher voltage into the setup which helped the initial arc to stay ignited.

Some Results

For now, I haven’t been able to get much, but I plan to improve the output with the aforementioned ideas. Resolved in the section above.

Here are some arcs produced by this setup, from what I’d guess they are maybe 10cm+ at best and the tube only starts redplating at very high powers. Since this run I somehow managed to “kill” the setup, it still works but the arc doesn’t grow as much with the voltage.

I will probably try rebuilding it for it to be a bit cleaner and handle the high voltages a bit better, but for now I’m a bit clueless about what happened since the setup didn’t change at all. I am still quite happy with the results I was able to get. Here is a video of the coil running

I was also able to get some neat images of what is seemingly a neon bulb being excited in an interesting way.

Despite being filled with neon (for the most part) giving a deep orange color in the EMF of my standard SSTC, it gives off a blue glow here. This could be caused by some mixed-in argon or mercury vapor (no droplets seem to be forming inside the glass).

Here’s a picture with the tube being somewhat spaced from the “antenna”:

And here it is placed right next to the “antenna” where you can see some of the neon orange starting to show at the contact point:

This causes lots of interference; a radio far away across the house is unusable.!

Hopefully, I can get some more arcs (over several cm) out of this circuit soon™ and post some updates here.

Sidenote

A fun way to start a project is to realize some of your components are unusable.

For me, I found out one of my MOT has died and that my microwave diode is dead as well.

This led me to make an abomination of a diode (which somehow didn’t explode yet) out of 1N4007 diodes.

As for the MOT, I just used a different one after realizing trying to save it is futile.