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need help with VTTC primary

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LAN_403

teravolt

Tue May 19 2009, 04:10AM

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

I am building a VTTC primary using the tube in my avatar and the secondary in the picture. I have 8awg and 5awg wire available for the primary. the secondry is about 1 by 3 Ft. I think about 40 turns should do. my question is what gauge to pick

Cesiumsponge

Tue May 19 2009, 04:30AM

Registered Member #397 Joined: Wed Apr 19 2006, 12:56AM
Location: Western Washington
Posts: 125

What power levels? I think 8awg should be more than sufficient and will give a primary coil that is shorter overall given the same turns, giving you more axial room on the coilform to slide your feedback coil for tuning.

I personally am not aware of any VTTCs that required 5awg on the primary side. I think that doorknob and smaller mica caps typically used in tank circuits would probably fail before you run into unacceptable heating/resistance issues of 8awg wiring on your primary. I remember a thread where some folks were having issues with doorknob caps that were getting uncomfortably warm and that was only the 1-2kW power level (though I think they weren't for RF purposes and more snubbing)

The best bet is to not make any permanent attachments, cuts, or holes in your primary coilform...leave it at full length and get it tuned first with the primary using your 8awg and whatever for the feedback coil. If 8awg is insufficient, then apply 5awg. 40 turns is simple enough that it wouldn't require a great deal of work to make the change.

Dr. Drone

Tue May 19 2009, 04:48AM

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

teravolt

Tue May 19 2009, 08:00PM

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

hello Cesiumsponge and Dr. Spark, the power levles should be around 10-15kw for now. I will be using mica caps or Russian door knobs. I don't know yet.

can you guys tell me how come tube teslas have many primary turns vrs other teslas. I am thinking that it's because the tank Q is higher or the primary tank impedance is higher for the tube because tubes are for the moast part high impedance devices

Tonskulus

Wed May 20 2009, 09:00AM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

Yes, Load impedance has to match with tube. Thats why there is usually lots of turns because tube is high impedance device, usually. However, once I made VTTC using just 2 turn primary but there was separate matching network to convert high impedance/low current to low imp/high current. Matching network was actual tank circuit consisting 3nF tank capacitor and 18turn tankcoil, 100mm diameter. 8mm coppertube was used there and it still gets burning hot! Teslacoils primary was connected to GND and tappingpoint on tankcoil. I think it was 3th turn that worked best.

Spark pics:
http://www.elisanet.fi/tonskulus/sparks4.jpg
http://www.elisanet.fi/tonskulus/ih_vttc.jpg

Oscillator section:
http://www.elisanet.fi/tonskulus/ih/ih_osc.jpg

schema:
http://www.elisanet.fi/tonskulus/putkiskm.GIF

teravolt

Wed May 20 2009, 08:03PM

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

thanks Tonskulus, I have been thinking about this and i have a set of 1500pf 10kv adjustible caps and inductors that i could use for this purpace they were for a 3cx3000 setup. can you relist your scematic because the lower part of it is scambled. that must have taken a bit to tune it. i like how your plate tank coil is like a auto transformer the cirulating current must be high. do you know how to calculate the primary paralell tank impedance. one of things to work out is matching the tube to the tesla.

Tonskulus

Thu May 21 2009, 08:22AM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

Oh, sorry about bad picture. Anyway, the circuit is this:
http://www.elisanet.fi/tonskulus/ih_schem.JPG

Where final coil acts as tesla primary. It is actually my induction heater circuit but however it can feed teslacoil as well.
And its easily adjustable also to match different kinds of load.

For calculating LC impedance etc. i have been using this calculator:
http://www.pronine.ca/lcf.htm

Its very useful!

teravolt

Thu May 21 2009, 04:52PM

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

when you set it up did you have to tune it to the secondary. it is bacicaly still an armstrong oscillator but with no pickup or tickler coil arould the secondary. insted the grid leak is disconneced set up as a pure oscillator. so what role does the tickler coil play other than feedback for the tube. in this vttc the tickler is on the bottom

.

is it pausible that the sward like sparks are because the tesla is being fed by a pure signwave insted of a pulse or square wave witch are ritch in harmonics?

thereticaly you could use a plain oscillator, an rf power amp and a matching network and treat the tesla as antena. there are many examples of this on youtube

I found a link for matching networks here

that may be usefull.

my plan is to seperate the power supply from the tesla but I am debating wether to put the tube at tesla end or put it with the power supply and match it to the tesla primary and secondary

Tonskulus

Thu May 21 2009, 05:24PM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

Its basic grid coupled oscillator. Tickler coil is inside of tankcoil. It can be also outside of tankcoil as in common VTTC's..

I knew that my primary res.freq was around 700kHz so I took one of my teslacoil secondaries with Fres of 1MHz. Then I added topload to tune it to about 700kHz. And thats it. Teslacoil secondary just adds some load (R) for tank circuit.

Dr. Drone

Thu May 21 2009, 09:10PM

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

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