My first VTTM (Vaccum tube tesla magnifier) WIP

[kaboooom2000uk]

Hello Ladies and Gentlemen, I present my VTTM which I believe may be a first as I haven't seen any circulating the internet, seen plenty of classic spark gap derived machines, but none where they employ a tube oscillator. Mine uses a little 830B tube which seems to perform well and provides about 6" arcs.

here I use a simple schematic from an induction heater but I have modified the work coil to work at the same Fres as my secondary (which I established using the signal generator and scope method as I find it simpler to do this) and built it using parts around the shack. As you can see the circuit itself is very simple. Only real changes I made to it are making both the feedback and the primary resonant at the same freq as the resonator coil


Basic setup, but instead of spark gap I am driving it with an oscillator.


In my version I use a tightly coupled "driver" coil made from about 100 turns of litz wire wound on a borosilicate glass lantern chimney, which serves as a former, the primary is about 20 or so turns of thicker litz wire I made using some magnet wire and a drill which sits on its own former.

The feedback winding is about 5 turns of more litz wire. I wound that on a acrylic tube which sits over the other coils for simple removal and modification.


Power input was conceived using a pair of 650-115 transformers, I hooked them up backwards, to step up and the 115V windings were wired in series and fed with my 8A 240V variac. so I had about 1400V or so to play with at about 1KVA which is the limit of the transformers. This AC is then fed into a simple level shifter composed of a dual diode package and a 220uf 2500V capacitor, and 4700pf ceramic decoupler cap.


From the footage I took it appears to be working, I would say this because it appears the input voltage to the resonating coil is very low but then gains voltage the further up the coil I go.

I hope to get some more refinements done on this at some point but its been put on the hiatus while I play with solid state stuff. Namely my half-bridge universal driver.

[Duane B]

I know this is an old post, and I don't know if Adam visits this site anymore, but I thought I would add some info here on the VTTC base drive setup. First, I think you get more "bang for your watts" by not using a full-wave rectifier for your plate voltage supply. Don't even use a half-wave rectifier for that matter. Put the AC from the plate transformer right on the tube. The tube itself will rectify the AC. It's a simple way to get 60 BPS, or PRF (Pulse Repetition Frequency).

Also, you need more voltage out of the RF transformer that drives the base of the resonator. However, you have a tube, and if you are getting all the power out of it for it's rating then you're ok. You can only get as much power out as your tube will supply.

You are not the first to do a VTTC with base driven resonator, but the only other one I have seen besides the one I built in 1989. Below are some photos of it.



This is the driver portion with the power supply and the RF output transformer. Sorry I don't have a better photo. It uses a pair of Eimac TL-250 tubes in parallel. There is a meter to measure plate current and a meter to measure grid voltage. The output transformer is kind of unique. The plate tank coil is on the outside and consists of maybe 20 turns of #12 wire with taps about every 5 turns. This is a rough frequency adjustment. I could also change tank capacitors, and I think there was a variable cap there too. The grid feedback coil was mounted inside the primary on a small form that could be rotated. This way the grid feedback voltage could be controlled just by turning a knob. The output coil was on a similar form that would rotate inside the tank coil, allowing output power to be controlled with the twist of a knob. The output coil had two different sections; one side had about 4 layers of teflon covered wire and the other side had a like coil with about 4 layers. This gave me several choices on output connections. I could use the entire output on one resonator (or multiple resonators), or I could ground the center tap between the two half's and drive two resonators 180 degrees apart.



The above photo shows the complete output of the output coil driving two resonators in parallel. This produces output voltages that are in the same phase and the sparks therefore repel each other.



The above photo shows half of the output coil driving one resonator and the other half of the output coil driving another resonator. The output voltages are 180 degrees out of phase so the sparks are attracted to each other.

[NerdlabsMadScience]

Wow those arcs look nice   btw VTTCs tend to run better with a shorter but thicker secondary coil.