How small can a VTTC be? / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

How small can a VTTC be?

first previous 6 7 8 9 next

Move Thread

LAN_403

Steve Conner

Thu May 31 2007, 11:40AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Hi edy19,

That worked better than I'd have expected!

You'll know you are running the tube too hard if you see the plate start to glow a dull red, then it's time to back off. Tubes are nice that way, if a MOSFET is unhappy the only way it can tell you is by exploding :(

Switching the cathode with a MOSFET works. The cathode will rise to whatever grid voltage the tube curves show as corresponding to zero cathode current: typically about 100V. The cathode current should be a couple hundred milliamps at most, so you don't need a large MOSFET at all.

What did you connect the screen grid to? You may be able to get a staccato type effect by connecting it to one of the nodes in your quadrupler that carries pulsating DC. Say the positive end of the capacitor whose negative end connects to the 120V line input. That pulsates between 0 and 360V, which will modulate the tube with 60Hz and make the arc buzz.

You shouldn't need any current limiting on the line BTW, though a fuse may be a good idea in case the tube decides to arc or short out.

EDY19

Thu May 31 2007, 02:07PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

screen grid is connected to the other side of the capacitor that is connected directly to the neutral line- ~330V or so, I would guess. I'll get that resistor out of there, too. Hmmm, audio modulation eventually?

ShawnLG

Mon Jun 04 2007, 01:58AM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399

Just got my coil running! I will not give any details until I have move the vttc from protoboards to etched ones and get everything super compact. I wonder who will be the first to stuff their tube in their secondary.

1180922694 286 FT1630 Vttc Testarc

Filament:

EDY19

Mon Jun 04 2007, 09:59PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

I'm not sure if this will disqualify me from the competition or not, but its for the sake of larger sparks, so I really don't care

I think I may add another tube to my coil- making for a dual 6146 tube coil- after a while running, the plate on my single tube gets a little bit red, so I'm going to pick up a new filament transformer to get the required current, and put the two tubes in parallel- after that, another capacitor is definatly in order for the tank

Updates to come once i get some stuff sorted out.

EDY19

Tue Jun 05 2007, 08:16PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

Have the coil running on 2 tubes, and no more plate reddening

I'm having a brain fart here- when I add a capacitor in parallel to the primary of the VTTC, do I need to decrease the number of turns? - If that is the case, how can I increase the number of turns while adding capacitance? I could use another tap for the tube anodes, correct? In this case, I believe that I would put the capacitance where the coil is tuned, and then move the anode connection of the tube up a couple more turns, correct? I guess I just would feel more comfortable with more turns on the primary, ~7 or so seems like a little too few. Oh, and lastly- I put a 10 ohm 40W resistor in series with the input of the quadrupler just to limit the startup current required to initially charge the capacitors-I also put a switch in parallel with the resistors so once initially charged, I can short them out. However, when the resistors are shorted, the output drops to near nothing- I'm thinking that the capacitors don't have enough capacitance to supply the kind of current that the 2 tubes want. Would this be a reasonable assumption?

EDY19

Tue Jun 12 2007, 12:04AM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

Heres a picture of the coil with the two tubes in place- no major modifications really required- I bought a new filament transformer because mine was rated at 1.25 amps, and each tube requires that much current. I just added another socket and wired the two sockets in parallel. Next up- interrupter and more tank capacitance! There's been a lot of time since the last post- how are any of the other coils coming along? Progress?

ShawnLG

Tue Jun 12 2007, 12:31AM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399

My progress is cumming along good except that I had a primery and secondary short causing a burn on the secondary, this causing a short between two secondary winding. If I can not repair it, I would need to wind a new one.

EDY19, is that an inductor connected in series with your plates?

EDY19

Tue Jun 12 2007, 12:52AM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

That inductor is wound over a 100 ohm resistor in order to "kill oscillations that can be set up in the event of a tube arc" in the words of steve

- and yes, it is in series with the plates. I think I need to get the thing running off from a transformer though, as i believe the voltage quadrupler is not able to supply enough current- i suppose i could just interrupt it, and give the caps time to charge between each "shot"

Vaxian

Thu Jun 14 2007, 04:21AM

Registered Member #635 Joined: Tue Apr 10 2007, 01:56AM
Location:
Posts: 85

Wow, some action!

I am back home now, going to start working on my coil very soon.
Need to wind a new secondary and find the "sweet Cap"

More pix soon!

Also going to start on the award / trophy.

Dr. Drone

Thu Jun 14 2007, 10:26PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

first previous 6 7 8 9 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob