This is a blog style page documenting my Vacuum Tube tesla coil.

Vacuum Tube Tesla Coil

I recently came across a website documenting how vacuum tubes were used to make a Tesla Coil giving 28 inch arks! I decided I would give it a go and make my own Vacuum Tube tesla coil. I have never done any work with valves and this is my first project involving vacuum tubes.

Before I could really decide on building a VTTC I had to get some questions answered about the component values what they do and get a complete schematic. At this point I headed towards the TCBOUK and PUPMAN T.C mailing lists for advice. Please see the schematic here. The answers to my questions are below:

1.) C2 and the capacitor across the filament transformer these look like they are decupling capacitors. If I am correct pretty much any value will work here as long as it is up to the voltage?

Phil Perry replied with this : For decoupling/RF bypass I used 2.5nF 10kV disc ceramics from JPG (on ebay or www.jpgelectronics.com ) The value isn't critical so the 2.5nFs will work fine.

2.) C3 and L1 do these make up a tuned circuit (similar to a tank circuit in a regular circuit)?

Steve Ward replied with this: YOU BET THEY ARE! In a tube coil, the tank is the determining part of the
circuit. The tuned tank sends pulses to the grid which then controls the
tube. With an un-tuned tank, the coil won’t work very well ;) And tuning is rather sharp with VTTCs!

3.) Can the value of c5 be changed?

Phil Perry replied with this: This is your grid leak - another doorknob would be best here, and stick to the stated capacitance until you get the coil working (I assume you're using a published design).

Where I Started 1^st August 2003

I first started by finding a supplier of the 833a tubes used in the design. After hours of searching and 50 + emails sent to importers and valve suppliers and phone calls all over the uk.I found a supplier in America who was willing to allow me to import the valves. This meant that the project could finally start.

Construction Start 23^rd August 2003

28^th August 2003 – Staccato Controller Construction

I spent most of Friday evening coming up with a pcb layout for my staccato controller. I decided to use Dans design from spacecatligthing.com as it was a proven working design. After spending till 3am getting the layout perfect I decided to call it a night. There is a photo of my design on the left.

 

 

 

 

29^th August 2003 – PCB Etching

I got up early to get the PCB for my staccato controller etched. I decided to use the press and peel method as I didn’t have access to a UV light box. The press and peel method is basically a film you photocopy or laser print the layout onto and then iron onto the copper clad. The copper clad needs to be perfectly clean and free of all greasy prints. I usually clean the board first with wet and dry and wear latex gloves when handling. There is some photos below showing the process I used to make the PCB.

	The layout if first printed onto film. This film is then ironed onto the copper clad. As you can see this attempt was not too good and as I was in short supply of the film I decided to fix the tracks by handing using pcb transfers.
	After a few hours of running down tracks I finally got the PCB to look professional with no missing tracks. Time for etching!
	The complete PCB after etching, Tin plating and drilling.

 

After the pcb was etched and drilled it was time to start construction. There is a photo on the left of the PCB during construction. I decided to use a case that I had from a previous project and was not used, It’s a screen rf enclosure so will be well suited for my VTTC. 30thAugust 2003 – Wednesday 3rd September – Table Construction The next couple of days were dedicated to making the table that the valves, transformers, control electronics and coil would be mounted on. I decided to use softwood to make the base as this was the easiest to work with and was pretty cheap to buy at my local DIY store. The cost of the table was about £35.00 including the castors. After a few days of cutting sawing gluing and sanding I finally had a almost perfect table. The top was routed to give it a professional look.

During the evening I mounted all the electronics control gear in the case with the thyristor.

The large connector on the back brings a 12V supply out to the fans ac input from a low voltage transformer and thyristor output.

4^th September 2003 – Electronics Testing.

I returned to work today. I decided in my spare time to test the circuit and do some scope measurements. For safety I did these tests using a 50 Hz sine wave from a function generator. The bench setup is shown below.

The top PSU supplies 15V to the 12V Reggie on the PCB and the bottom PSU is unused. The function genie s to the far left and supplies a 50 Hz sine wave to the zero crossing circuit. I got a Fluke meter for voltage measuring on the right and a Gold digital storage oscilloscope.

	This is the input to the zero crossing circuit at the top and output from the zero crossing circuit. The 555 only sees the negative part of the cycle and ignores the positive going part of the cycle. The 555 is triggered in sync with the mains 50 Hz cycle.
	Output to thyristor and IC2.
	As you can see the circuit looks like it is working. I won’t know any more until Its connected to my VTTC. I’ve decided to spend some more time on the table and mount components to that. When I got home from work I finished mounting the circuit in the case and tested it with a mains transformer (12V – 0 – 12V).In the photo you can see the thyristor on the right near the front of the case. Its a 25A 700v unit.

6^th September 2003 – 7^th September 2003 – Secondary Coil Winding

This weekend I dedicated to winding me secondary for the coil. The coil is wound on 4inch drain pipe using 27SWG enamelled wire. I made a quick lash up winder using some old wood, a circular saw, an old electric drill and a huge variac. I got my mate to feed me the wire while I wound it on the pipe keeping it flat using an off cut of laminate floor. Took about 3 hours to wind and took a day to put on 17 layers of polyuthrane varnish to make it strong.

11^th September 2003 – 833a Power Triodes Arrive

At last my valves arrived! After paying £37.24 in import tax they are finally mine. They are brand new from rf parts in the state (www.rfparts.com) Very good people, fast shipping and excellent communication.

 

 

 

 

 

 

13^th – 14^th September 2003 – Transformers and Mains Wiring.

 

I ordered the filament transformers for my project from RS components.  They cost me £20 each. These took 3 hours to wire up and are connected in the base and run up the back of the coil in 22mm plastic pipe (I small of cut was given to me) The oaks blocks are now routed and varnished and secured to the top of the table and these will be used to mount the valves. The photos shows oak blocks for the 833a sockets. It’s really starting to look like a coil now!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The filimant transformers are mounted on the bottom. All mians wireing is done inside the base.

16th September 2003 – Soak Testing

Using a 20A bulb I decide to test the filament transformers. These are standard 10V – 0 – 10V transformers, 5A per winding transformers wired in parallel to give 10V 20A. The photo shows the transformers pulling a 10V 20A load for 1hour constant use.

 

 

 

 

 

 

 

 

 

20th - 21th September 2003 - The Valve Sockets

After been given a quote for £40.00 for a valve socket for a 833a power triode I sat down in shock. I looked around the net for a home made solution and found that Steve ward had a homemade solution. He used some large aluminium electrical connectors drilled out to fit the valve legs and some angle iron to mount them to the base. There is a photo and diagram of Steve’s design on the left. I could not find any of these large electrical connectors so decided to make my own out of a large piece of aluminium block cut to size drilled and tapped. This is exactly what I decided to do. I got some 1 inch square bar cut it into an L shape and drilled on the pillar drill at work. I needed one 4 of these one for each leg of the valve. In total they cost about £9.00 to make. My design is shown below.

 

 

 

 

 

 

 

After about 2 lunchtimes at worked and a day of cutting I made the sockets. Below are some photos of the valve holders.

2nd October 2003 - Capacitors Arrive

After my plea on TCBOUK for mivrowave capacitors Colin Heath replied and said he would donate some towards the project. Thanks Colin!

3rd October 2003 – FIRST LIGHT – WELL Almost

Well I spent all of today wiring up the high voltage transformer (ok so it’s a microwave over transformer) and all of the high voltage cable associated with it. I even finished the holders, At about

12:00am I decided to put some voltage through the filaments and see them glow. The photo on the left shows one of the valves with a filament supply.

 

 

 

 

 

 

 

 

 

Sunday 5th October 2003 - First Light - FIRST ARKS

My coil works. I got arks. I have not attempted any tuning yet with the circuit to et longer arks. During this run my control electronics decided to self destruct so I will have to fix this. Below are some photos of this run.I only managed to get 8 inchs from the coil during this run