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GU5B VTTC project

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vasil

Sun Aug 23 2009, 07:29PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

I think it is a missunderstanding. I got the best results on my anterior VTTC (with GU81 tube) by reducing the primary cap from 2 nF at 700 pF.

The GU5B VTTC is in tune and is using a 1.35 nF cap.

I added 500 pF more on the primary cap in my experiments and didn't notice longer sparks, but hoter, with important warming of the primary windings.

Have to figure a feedback design to protect it from the arcs. Maibe a strike ring above the feedback would protect it a bit.

Dr. H.

Sun Aug 23 2009, 09:29PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Hi there

on the cap - YES you have to experiment but changing the cap value will mean that you have to retune the primary. And YES - there are systems in wich smaller capacitors work better than big ones.

I don't think putting a strike ring is a particularly a good idea because grounding it will create a perfect target for the sparks (will "attract them"). I've withnessed how a spark missed two strike rings and went directly for the primary (on a DRSSTC) 3-4sm bellow the strike ring, so I woudn't use one on a tickler coil. A better idea are the "Hooper" rings. Look at Dr. Spark's work - the re are some great ideas on it how to make it properly. One of the most importan things - use insulated wire ( not Enamelled Magent Wire). And after that cover it with epoxy and put the rings.

Cheers

teravolt

Mon Aug 24 2009, 02:16AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I have seen a youtube video "big vttc" and he has the tickler on the bottom

vasil

Mon Aug 24 2009, 05:09AM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

Mine also is on the bottom.
I was thinking about the things to do next time:

-rebuilding the source
-increasing the primary cap to 2 nF
-winding a new primary with lower AWG wire (decrease primary resistence)
-a new feedback

It will take some time to do it, so have patience.

vasil

Sat Oct 24 2009, 04:46PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

YYupii, a new little vacance started.

Shortly:

-redone the primary with heavier solid copper wire, less coupling:

-increased the primary cap at 2.96 nF (I used all the caps found):

-rebuilt the HV source with new 4 identical output MOTs and a new 50 nF filter cap:

-the system is ready to fire. Added later a bigger toroid:

At the first try I had some RF interference problems with staccato. Though the sparks are longer 94-95 cm with rare hits at 102-103 cm:

http://www.youtube.com/user/teslina#p/a/u/1/jPZDqgVUosM

Resolved the staccato problems (alu foil and ferrite beds on the input and output wires), so now GU5B-zilla can make its big sparks:

http://www.youtube.com/user/teslina#p/a/u/0/jv6Syp-BlEg

Unfortunately I didnt found higher voltage MOTs. I am confident that with some new modifications the sparks can be even longer but I stop here. These russian tubes are really wonderful.

My next project will be a classical spark gap coil. I bought from the internet these nice NSTs (7 kV@25mA each):

Believe or not, they are the first NSTs I have in my hands since I begun coiling. The coil will have a spherical topload in an attempt to aquire spontanously formation of a swirling streamer, like in one of my old movies:

http://www.youtube.com/user/teslina#p/u/56/nj0ARi5JTgc

...but at higher power.

Enjoy

vasil

Mads Barnkob

Mon Oct 26 2009, 09:20PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Good looking sparks and wonderful that you are hitting 100 cm+

This makes me want to get going with my next VTTC sooner than planned :)

Got a nice 5kV 3kW plate dissipation tetrode tube at hand, filament transformer, ceramic caps for tank and lots of mots, but would like a power supply that is less power hungry and smaller :)

darkspeed

Sat Jul 03 2010, 02:46AM

Registered Member #2958 Joined: Sat Jul 03 2010, 02:36AM
Location:
Posts: 8

Vasil do you have a schematic for the GU5B circuit? I would really like to build a GU5B VTTC

Thank you!
darkspeed

vasil

Sat Jul 03 2010, 09:33AM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

Hi
I dont have a schema on paper but I will give you some details:

Power source:

2 strings in parallel of 2 MOTs in serie (for 4200 V @ 1 A)
doubler made with a 44 pieces of 1N5408 diodes (44 kV @ 3 A) and a 2.3 microF cap
filter cap: 50 nF @ 20 kV

fillament transformer: a big 350 W toroidal xfrm (I added a few turns to get the right voltage under load)
5.4 nF cap filter on fillament connections
big 56 ohms @ 160 W resistor in the primary circuit of the fillament xfrm to feed the fillament gradually, in two steps.
Rgrid: 150 W light bulb
Cgrid: 1.3 nF @ 10 kV polietilene cap
Cprimary: 2.96 nF @ 18 kV (made with different size ceramic russian caps)
20 cm diameter PVC pipe for primary, 34 turns
grid coil 20 turns, under the primary coil
11 cm diameter PVC pipe for secondary, 1200 turns with 0.4 mm wire
little toroid on top made with a wheelbarrow tire
Steve Ward staccato circuit

The schema is just usual VTTC schema.

Happy coiling!

vasil

-------------------------------- -------------------------------------------------- ------------------

Oct 16 2020

Hi forum

I made a few grid network modifications preparing the setup for full CW (I collecting parts for a new power source). I am runing now with a 0.56 Kohm high power grid resistor (made with different size high watage resistor).

Grid setup:

Whole system ready to fire:

Over 80 cm hot streamers:

and a MOVIE

I hope to finish the new source maibe in a week (just currious how it behaves in CW).

Enjoy

vasil
>
>

Oct 18 2010

The new source is ready.

I was lucky enough to get these nice HV diodes (75 kV @ 100 mA):

The new PSU is a Greinacher cascade. The voltage from the 4 MOTs is doubled. The cascade capacitors and the filter caps reduce ripple. I used ferite beads as RF suppressors on the output HV cables:

The pics of the PSU:

and the final results: HOT discharges

YOUTUBE LINK

After playing with the new toy, my little variac was a bit toasted:

....but I will find another one.

So, an important thing for the VTTCs is the HV power source. They need a dedicated HV source. More power = better spark. With a weak power source (1-2 MOTs), the coil would need higher current than provided by the HV setup, so the MOTs will run hot. Just give enough current to the tube, it will take what it needs. My experiments just illustrate the old tesla concept that the lenght of the spark is proportional with the power input of the tesla coil. And this principle is very importanty, especially for VTTCs with big toobs and high catode current.

Enjoy

vasil

darkspeed

Sat Jul 03 2010, 08:00PM

Registered Member #2958 Joined: Sat Jul 03 2010, 02:36AM
Location:
Posts: 8

Thank you vasil!!

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