Can't find a neon sign transformer? Want to build your first Tesla Coil without facing the complexities of going solid state? Here's some good news: Vacuum tube Tesla Coils, which have been making a comeback in recent years, can be just as rewarding as any other type of coil without breaking the bank. This is one such coil that I built during the spring of my 8th grade year.
You can even use it to wirelessly transmit electricity to a lightbulb! (12/3/12)
Noteworthy:
While this project does work in its current form, I have detected some problems and and working to fix them. You would best be advised to postpone your building until then - it seems that theses tubes could operate more efficiently at higher frequencies and my primary RLC tank circuit's natural frequency is much higher than my secondary side RLC circuit's natural frequency; a new secondary coil with a frequency of approximately 1.5MHz is being designed and the primary circuit will be retuned. I expect a great leap in performance, with sparks possibly as long as 7" to 9".
3/10/10: I decided to try to estimate the resonant frequencies of my primary and secondary circuits using deepfriedneon's formulas, and I found that my coil is oscillating about 100kHz above my primary circuit. I don't have any parts to fix this now, but will add a capacitor or two to the primary circuit to lower its frequency soon. IMPORTANT: I found a 6.3V at 12A Hammond power transformer and replaced my 5V computer power supply - the results were truly impressive; I am getting better performance with one tube than I ever got with two, filament voltage really matters! Here is a quick video:
4/16/10: The MOT (plate transformer) burnt out because the secondary windings were damaged by previous experiments (SGTC,s, Jacob's Ladders, etc.). It was replaced with a larger one and the sparks are now almost 7" long - this coil performs as well as Steve's did, but with only one tube and with a poorly tuned primary oscillator!
Thanks!
You can even use it to wirelessly transmit electricity to a lightbulb! (12/3/12)
Noteworthy:
While this project does work in its current form, I have detected some problems and and working to fix them. You would best be advised to postpone your building until then - it seems that theses tubes could operate more efficiently at higher frequencies and my primary RLC tank circuit's natural frequency is much higher than my secondary side RLC circuit's natural frequency; a new secondary coil with a frequency of approximately 1.5MHz is being designed and the primary circuit will be retuned. I expect a great leap in performance, with sparks possibly as long as 7" to 9".
3/10/10: I decided to try to estimate the resonant frequencies of my primary and secondary circuits using deepfriedneon's formulas, and I found that my coil is oscillating about 100kHz above my primary circuit. I don't have any parts to fix this now, but will add a capacitor or two to the primary circuit to lower its frequency soon. IMPORTANT: I found a 6.3V at 12A Hammond power transformer and replaced my 5V computer power supply - the results were truly impressive; I am getting better performance with one tube than I ever got with two, filament voltage really matters! Here is a quick video:
4/16/10: The MOT (plate transformer) burnt out because the secondary windings were damaged by previous experiments (SGTC,s, Jacob's Ladders, etc.). It was replaced with a larger one and the sparks are now almost 7" long - this coil performs as well as Steve's did, but with only one tube and with a poorly tuned primary oscillator!
Thanks!
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Signing UpStep 1: Vacuum Tube? What's a Vacuum Tube?
In the early 21st century, many of us have never even heard of vacuum tubes, and the few who have only know that they were used in old electronics. Therefore, before I begin this project, I feel the need to explain how they work.
Lets take a look at picture 1. This is the standard symbol for a vacuum tube diode. A diode only conducts electricity in one direction. They can be used to turn an alternating current into a direct current. In the diagram, the bottom half hexagon is the filament. It is just like the filament inside of an incandescent lightbulb. The line above it is called the plate. The circle around the filament and plate represents the (usually glass, sometimes metal) envelope of the tube. Almost all of the air inside of this envelope has been evacuated, there is a vacuum. This will become important later.
Now, lets take a look at picture 2. Here we have applied a voltage between the filament and the plate. The filament is negatively charged, and the plate is positively charged. While the electrons in the filament are attracted to the plate, there is not enough voltage for them to do so on their own. So how can we get them to jump? Take a look at picture 3.
In picture 3, a few new things have appeared.First, we have a 10 volt power supply connected to each side of the filament. Just as in an incandescent lightbulb, this heats the filament up. The negative side of the power supply is still connected to the filament, but the positive side is not. Notice that now, the negatively charged electrons are stil flowing into the filament from the 100 volt power supply, but something is different. Why are they floating around the filament? As the filament heats up, thermionic emissions occur. Essentially, the electrons are shaken off of the filament by its thermal energy. This can happen because there is a vacuum. So now, the question is: What happens when we connect the positive side of the 100 volt power supply to the plate? Take a look at picture 4 to find out.
In picture 4, the positive side of the 100 volt power supply is connected to the plate. We have zoomed back towards the tube. In the picture, the electrons floating around the filament are moving towards the plate! There are no air particles to hinder their passage, so after the thermionic emission occurs, the positively charged plate attracts them, and they accelerate towards it, hit it, and move along the wire back into the power supply. That's how a vacuum tube diode works.
The principle of operation is relatively simple, but a Tesla Coil such as the one that we are building is an oscillator. That means that there is a feedback system that turns the diode on and off, to accomplish this, we use a triode. Read on the find out how it works.
Lets take a look at picture 1. This is the standard symbol for a vacuum tube diode. A diode only conducts electricity in one direction. They can be used to turn an alternating current into a direct current. In the diagram, the bottom half hexagon is the filament. It is just like the filament inside of an incandescent lightbulb. The line above it is called the plate. The circle around the filament and plate represents the (usually glass, sometimes metal) envelope of the tube. Almost all of the air inside of this envelope has been evacuated, there is a vacuum. This will become important later.
Now, lets take a look at picture 2. Here we have applied a voltage between the filament and the plate. The filament is negatively charged, and the plate is positively charged. While the electrons in the filament are attracted to the plate, there is not enough voltage for them to do so on their own. So how can we get them to jump? Take a look at picture 3.
In picture 3, a few new things have appeared.First, we have a 10 volt power supply connected to each side of the filament. Just as in an incandescent lightbulb, this heats the filament up. The negative side of the power supply is still connected to the filament, but the positive side is not. Notice that now, the negatively charged electrons are stil flowing into the filament from the 100 volt power supply, but something is different. Why are they floating around the filament? As the filament heats up, thermionic emissions occur. Essentially, the electrons are shaken off of the filament by its thermal energy. This can happen because there is a vacuum. So now, the question is: What happens when we connect the positive side of the 100 volt power supply to the plate? Take a look at picture 4 to find out.
In picture 4, the positive side of the 100 volt power supply is connected to the plate. We have zoomed back towards the tube. In the picture, the electrons floating around the filament are moving towards the plate! There are no air particles to hinder their passage, so after the thermionic emission occurs, the positively charged plate attracts them, and they accelerate towards it, hit it, and move along the wire back into the power supply. That's how a vacuum tube diode works.
The principle of operation is relatively simple, but a Tesla Coil such as the one that we are building is an oscillator. That means that there is a feedback system that turns the diode on and off, to accomplish this, we use a triode. Read on the find out how it works.
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thanks
You'll need to pick a different tube; peak voltage from a single MOT is already pushing it, but when I run with a doubler I get arcs inside the tube. Is there any reason you're planning to wire two MOTs in series rather than use a doubler? (The diode and the capacitor you get from the microwave are all you need!)
Do the 811a need to be a matched pair?
Good luck!
At the moment, I would strongly recommend upgrading to a 572B tube - it's a drop-in replacement the 811A and solves the plate reddening problem.
Good luck!
Try local hamfests/electronics events - I got a few American-made 811A and 572B tubes at Swapfest in Cambridge MA near MIT.
You don't need a particularly complex staccato circuit to pull this off - just get an SCR rated for several amps at several hundred volts (dirt cheap on eBay), put it in between the filaments and ground, and add a simple 555 timer circuit - I used my 555 timer-based DRSSTC interrupter and it worked fine.
Good luck!
Note: 16A at 600V is extreme overkill for this application, so don't worry about using a weaker SCR.
http://www.youtube.com/watch?v=wpSBRJETQDg
http://teslacoil.ru/devices/fakelnik-na-gu-50/
(check out the other VTTCs on this website too)
thanks
paul
This is just a suggestion for the more advanced coilers, for beginners, you will want to just stick to the design as the calculations can get pretty crazy really fast!!!
nothing is happening wen i test it there was a loud hum sound and
that was it . the tubes are not heating up and the grid circuit
does not seem to be working but the continuity is ok. also
continuity is ok thou the rest of the Tesla coil please help
specs
1 k mot
1.85uf microwave oven cap
two 811a's
veritable resistor in gird with 0.0022uf cap
The easiest way for me to try to diagnose the problem is to look at what you built. If possible, can you upload and post some pictures of your coil from different angles so that I can see what you did (if you do, please make sure the photographs are detailed enough for me to see what's going on)? Also, if you have access to a video camera, can you post a video of yourself quickly demonstrating what happens when you turn the coil on?
Good luck!
Xellers