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How To Build A Vacuum Tube Tesla Coil (VTTC)by Xellers on June 7, 2009

Table of Contents

How To Build A Vacuum Tube Tesla Coil (VTTC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Intro:   How To Build A Vacuum Tube Tesla Coil (VTTC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Step 1:   Vacuum Tube? What's a Vacuum Tube? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Step 2:   The Triode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Step 3:   The Vacuum Tube Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Step 4:   Our Tesla Coil Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Step 5:   Parts! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Step 6:   Assembling the Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Step 7:   Winding the Secondary Coil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Step 8:   Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Step 9:   Sparks! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Step 10:   Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

http://www.instructables.com/id/How-To-Build-A-Vacuum-Tube-Tesla-Coil-VTTC/

Intro:  How To Build A Vacuum Tube Tesla Coil (VTTC)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 TeslaCoils, 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 builtduring the spring of my 8th grade year.

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 untilthen - 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 mysecondary 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 oscillatingabout 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 betterperformance 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 wasreplaced 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 primaryoscillator!

Thanks!

Image Notes1. 7" to 8" Sparks

http://www.instructables.com/id/How-To-Build-A-Vacuum-Tube-Tesla-Coil-VTTC/

Image Notes1. 5" long sparks using only one 811A tube, and the coil is about 100kHz out oftune! Results when coil is properly tuned (when I buy a new capacitor) should beamazing.

http://www.instructables.com/id/How-To-Build-A-Vacuum-Tube-Tesla-Coil-VTTC/

Step 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 Ibegin 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 analternating 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 lineabove 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 ofthis 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 positivelycharged. 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? Takea 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 heatsthe 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 arestil 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, thermionicemissions 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 aroundthe 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 attractsthem, 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 turnsthe diode on and off, to accomplish this, we use a triode. Read on the find out how it works.

Image Notes1. This is the filament2. This is the plate3. This picture was created by me using "Paint", it was not take off of theinternet.

Image Notes1. This picture was created by me using "Paint", it was not take off of theinternet.

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Image Notes1. This picture was created by me using "Paint", it was not take off of theinternet.

Image Notes1. This picture was created by me using "Paint", it was not take off of theinternet.

Step 2: The TriodeThe first true electronic amplifier was the vacuum tube triode. It works because like charges (in this case, electrons) repel each other. Take a look at picture 1. It lookssimilar to the symbol for a vacuum tube diode, but it has an extra part that looks like a grid between the plate and filament.

This grid normally allows electrons to pass through itself for diode operation, but as it grows more and more negatively charged, it allows less and less electrons to travelfrom the filament to the plate due to electrostatic repulsion. In this way, you can regulate the flow of a relatively large current by using a relatively small one.

Image Notes1. This picture was created by me using "Paint", it was not take off of the internet.

Step 3: The Vacuum Tube OscillatorA Tesla Coil is essentially a very large oscillator. When the primary side of the coil oscillates at the natural frequency of the secondary side, resonance is achieved. Thisis a fundamental concept that is used in all Tesla Coils and other resonant transformers (such as the ones found in many switch-mode power supplies, and CRTtelevision sets). The Vacuum Tube Tesla Coil that I detail here uses a configuration known as an Armstrong Oscillator.

In the standard model of a transformer, there are two coils, a primary and a secondary coil. Currents are usually induced from the primary coil to the secondary coil(although the opposite sometimes happens, usually with destructive results), this is a concept that we will not go over now, if you are unfamiliar with it, then this is a goodplace to become acquainted: http://en.wikipedia.org/wiki/Transformer. However, an Armstrong Oscillator works by introducing a third coil, called the feedback, orsometimes "tickler" coil.

Currents are not only induced from the primary coil into the secondary coil, but also into the feedback coil. This feedback is then used to turn off the oscillator by blockingcurrent from flowing into the primary coil. However, when the primary coil is turned off, current is no longer induced into the feedback coil, and it no longer blocks currentfrom flowing through the primary coil. In this way, the cycle repeats indefinitely, until it is interrupted, or the power is switched off.

The basic schematic for an Armstrong Oscillator using a vacuum tube is given in the first picture. (This picture is from Steve Ward's site:http://www.stevehv.4hv.org/VTTCfaq.htm, you can read more about VTTC operation there)

http://www.instructables.com/id/How-To-Build-A-Vacuum-Tube-Tesla-Coil-VTTC/

Step 4: Our Tesla Coil SchematicHere is the particular schematic for the Tesla Coil that we will be building. I do not take credit for its creation - it was made by Steve Ward and you can find the full - sizedimage on his site here: www.stevehv.4hv.org/VTTC1/dual811Aschematic.JPG. A few things that you should note are that I have found that you should make the primarycoil (L1) slightly larger but allow for it to be tapped every other turn. Also, I've noticed that a slightly larger (~2nF) tank capacitor (C1) works better for my coil, but thiscould vary. Also, if you are adventurous enough, you might consider using a level shifter to double the voltage to the 811A tubes to 4000VAC RMS and then use astaccato circuit (something you should consider even without the level shifter) to keep the tubes running cool. However, since this is a slightly more advanced project I willnot cover it here (yet!).

Step 5: Parts!Here are the parts that I used, and the approximately how much each one cost:

~$30 (2) 811A Vacuum Tube Triodes~$0   (1) Microwave Oven Transformer~$10 (1) 30kV 1.0nF Polystyrene Capacitor (2 or 3nF will also work here, I found that larger capacitance increased the performance slightly)~$15 (1) Bundle of 1000 ft. of 28 AWG Magnet Wire~$10 (1) Bundle of 100ft. of 16 AWG Insulated Audio Wire (Can be purchased from Radio Shack)~$3   (2) Small Circuit Boards~$10 (1) 1' x 1' x 1" Wooden Board (This price is for about 10 of these boards)~$5   (1) Box of Nails~$0 (2) Ferrite Toroid Cores (Should be at least about 1/2" in inner diameter, these are not critical parts)~$2   (4) 3kV 1.8nF Ceramic Disk Capacitors~$10 (1) 50W 5k? Resistor (?  = Ohm Symbol)~$7   (2) 20W 30? Resistors~$0   (1) 6.3 VAC 10A Filament Transformer (You can use 5 volts from a modified computer power supply instead if you want to save some money, but the performancewill decrease)

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~$5   (1) Small Container of Epoxy Glue (This is for gluing the secondary coil down, if you want to experiment (like me) then you shouldn't glue the coil down)~$5  (1) 1' of 4" Diameter PVC Pipe (Primary Former)~$3  (1) 1' of 2" Diameter PVC Pipe (Secondary Former)

Total: ~$100

This is actually a very crude estimate, and shipping costs will differ depending upon where you buy from and where you live. The parts marked $0 were either salvaged(like the Microwave Oven Transformer) or they were free samples (like the Ferrite Toroid Cores) or were already owned (I used a computer power supply instead of acostly filament transformer).

http://www.instructables.com/id/How-To-Build-A-Vacuum-Tube-Tesla-Coil-VTTC/

http://www.instructables.com/id/How-To-Build-A-Vacuum-Tube-Tesla-Coil-VTTC/

Step 6: Assembling the BaseWhile there are no general guidelines on how to do this step properly, you should strive to fit everything on one board and keep connections as short and simple aspossible with as few overlapping and/or twisted wires as possible in order to minimize stray capacitance and inductance. Here, you can see my main board with all of themajor parts.

One thing you may have noticed is that some of my photos appear to show a coil with a different base - this was the original variant of the coil which did not work as wellbecause of the long hookup wires.

NOTE (4.5.11): This circuit layout is now obsolete - arcing between the top leg of the primary capacitor and the microwave oven transformer's iron case has becomeproblematic to the point where I completely reassembled the circuit and put the transformer on its own board. Hopefully, I'll get some pictures of this soon.

Image Notes1. Secondary Coil2. Microwave Oven Transformer3. Alligator Clips for the Primary Taps4. Tank Capacitors5. Feedback Coil6. Primary Coil7. Vacuum Tube Protection Circuitry (Resistor and Inductor Circuits)8. Vacuum Tubes9. Filament Power From the Computer Power Supply10. Mains Power for the Microwave Oven Transformer11. RF Filter - Found Inside of an Old Microwave12. 5k 50W Resistor13. Connections to Feedback Coil14. All Ground Point Lead Here (To the Microwave Oven Transformer's Case)15. 1.8nF 6kV (Equivalent) Capacitors Connected Across the Resistor16. Helping Hands Holding Up a Grounded Discharge Rod17. This Wire Leads to the Bottom of the Secondary Coil - it is Connected to theMicrowave Oven Transformer's Case (Ground)

Step 7: Winding the Secondary CoilUnfortunately, I did not take pictures of this part of my construction - both of my hands were too busy winding and holding!

The ideas involved in winding an effective secondary coil are very simple, but some things are easier said than done. All that you are really doing is winding wire aroundyour 2" PVC pipe former. Here are a few general guidelines for winding your own coil:

DO NOT:

1) Break the wire - if the wire snaps half way through, it is better to buy a new roll (or buy are bigger one in the first place) than to solder the broken wires back together.This is not a good idea because you will risk serious damage to your coil - there will be problems with unwanted discharges (the secondary coil could potentially arc to theprimary coil and ruin the entire primary circuit; very bad) and the coil can also destroy itself by burning through the plastic form or by melting the solder you used to holdthe rip together, thus unwinding the secondary coil.

2) Drill Holes in the Secondary Coil Former - this is the most common mistake, and you will pay the price for it with this coil. If you drill holes in the secondary former,there will be a huge risk of the coil discharging through the inside of the pipe or discharging upwards though the secondary former (at the top) and damaging itself (not tomention that the impressive sparks won't be flying into the air, but rather melting through the secondary former).

3) Wind the Secondary Coil Haphazardly - If you cross windings or wind them on top of each other, the performance of your coil will suffer greatly and the secondary coilwill be at risk of damaging itself. While its okay to make one or two small mistakes (with emphasis on small!) near the bottom of the secondary coil, you will regret it if youdo not wind well.

DO:

1) Use relatively thick wire for winding the secondary coil - increasing the thickness of the wire you are using will make it easier for you to wind the secondary coil and willdecrease the chances of the wire snapping.

2) Wear gloves while working with your coil and/or wash your hands very well - some of the various molecules in your sweat and on your hands, if caught on thesecondary coil, can decrease performance. While you can wind the coil with sweaty hands, you will notice that the sparks will be shorter than if you had used dry, washed

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hands or worn gloves.

3) Work slowly and deliberately - its not a race, you will make fewer mistakes if you are willing to commit a few hours to winding the coil. Sometimes, if you make amistake earlier on, you might want to unwind and then rewind the coil entirely. For this particular coil, I wound the secondary half way through before I noticed somecrossed windings and rewound the whole thing.

4) Use shellac (I used the spray-on type) or polyurethane to cover your secondary coil - this will help to prevent the coil from unwinding and will hold everything togetherwell, it also looks and feels very nice. Give it a good day to dry off after the shellac (even if the can only says 15 minutes) as the secondary coil might erupt in flames if thecoating has not dried thoroughly.

Step 8: TestingWhen you're finally ready to turn your coil on, be sure that you have a large open area to work in where there is no danger of sparks from the coil setting anything on fire.I would recommend testing the coil at a lower voltage first (using a Variac - I would start by testing it around 30VAC input first and then working up to full power) instead ofplugging it in to see what happens. Also, a 10 ampere FAST safety fuse is REQUIRED in series with the mains electricity you are using in order to prevent electrical firesand other nasty scenarios in the event that your coil does not work properly.

Before you plug anything in, however, you should use a multimeter to make sure that your connections are all correct and that your vacuum tubes are not damaged (ie.burnt our filament, shorted grid and filament, etc. - all of these have happened to me when working with vacuum tubes)

On the first attempt, do not expect to immediately be rewarded with roaring sparks - be glad if your coil works at all. Once you have established that it does, then attach asmall topload to the top of the secondary coil (I like to use a filment lightbulb wrapped tightly in aluminum foil) and use the taps on the primary coil to tune your coil formaximal spark length. Note: you will need some sort of breakout point like a sharp nail if you use a topload of any sort).

Here are some pictures of my Tesla Coil's first light:

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Step 9: Sparks!If you're satisfied with the way your tests are looking, then you can plug everything in and enjoy the plasma! Interesting experiments you can try include observingdischarges inside of an argon filled lightbulb, inside of a vacuum tube (be careful some tubes might produce small amounts of X-Ray radiation if you do this by way ofBremsstrahlung), and you can light up fluorescent tubes at a distance. Also, if you remove the breakout point and tune a nearby radio (and sometimes a faraway radiotoo) to the resonant frequency of your coil (Usually somewhere on the AM band) you will be able to hear the 60Hz buzz of the coil.

Image Notes1. 5" long sparks using only one 811A tube, and the coil is about 100kHz out oftune! Results when coil is properly tuned (when I buy a new capacitor) should beamazing.

Image Notes1. 7" to 8" Sparks

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Step 10: ConclusionThis is a page where I will answer general (and sometimes specific) questions that you have and will try to help to explain some of the deeper operating principlesprinciples of the Tesla Coil.

On a different note, the 811A also makes a great audio output tube!

Image Notes1. 811A in Class A22. 5AQ5 (Equivalent to 6V6GT) driving the 811A in Class A2.3. 12AX7 Preamplifier - Made from a dead Heathkit HD-11 Q-Multiplier.4. A 12V power transformer being used as an audio output transformer, will be upgraded soon!

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5. Filament Transformer (Same as the one used in the VTTC).6. Power Transformer - A lucky find from an HP Nixie Tube Voltage Meter.

Related Instructables

My 811aVacuum TubeTesla Coil(video) bygigavolt

Jiffycoil's TeslaCoil projects(Photos) byjiffycoil

How To Build ASpark Gap TeslaCoil (SGTC) byXellers

Step By StepPlans toBuilding a250,000 VoltTesla Coil.(REVISEDVERSION) byTesla Coiler

my tesla coil(video) byTheTeslaWarrior

Step By StepPlans ToBuilding A250,000 VoltTesla Coil byTesla Coiler

Comments

50 comments Add Comment view all 124 comments

 everyday im shuffling, except fridays, i got to get down on friday says:  Aug 8, 2011. 6:10 PM  REPLYamazing!!

 Xellers says:  Aug 8, 2011. 6:56 PM  REPLYThanks! :)

 ZachFejes says:  Jul 19, 2011. 12:19 PM  REPLYTrue, it won't burn you, but you still shouldn't touch it. You may not feel it, but it is can burn out (permanently) your nerves, which you do NOT want.

 gigavolt says:  Apr 14, 2011. 5:32 PM  REPLYI just got my coil working, and I'm wondering if I would be able to add a voltage doubler circuit to the plate voltage. It's a 2k mot, and 2 811a's. Do you thinkthe tubes would arc over or would they survive???

 Xellers says:  Jun 23, 2011. 3:44 PM  REPLYI tried adding a voltage doubler to this coil, but my tube started arcing after a short period of time, so I took it out. I was using a staccato circuit, so if youtry this, I would recommend the same. My tube is the cheapest Chinese variant available, so if you're using NOS American-made 811As, you mightencounter more success than I did.

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 oneBay), 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!

 gigavolt says:  Jun 23, 2011. 3:54 PM  REPLYThanks for the advice! Looking for an SCR now!!!

 Xellers says:  Jun 23, 2011. 4:31 PM  REPLYJust in case you were wondering, the SCR I used was a BTA16-600B (600V, 16A) -http://www.datasheetcatalog.org/datasheet/SGSThomsonMicroelectronics/mXywxqt.pdf

Note: 16A at 600V is extreme overkill for this application, so don't worry about using a weaker SCR.

 gigavolt says:  Jun 23, 2011. 4:37 PM  REPLYOk, thanks!

 gigavolt says:  Apr 4, 2011. 6:29 PM  REPLYStupid 12ax7a's!!! They cut out for the most part at 50khz!!! I need 1.5 Mhz for my super-mini-plasma globe-ish vttc!!!

http://www.instructables.com/id/How-To-Build-A-Vacuum-Tube-Tesla-Coil-VTTC/

 Xellers says:  Apr 4, 2011. 8:01 PM  REPLY12AX7s are designed as low power preamplifier tubes - they only have 1 watt of plate dissipation, so I don't think they'd stand up to much VTTC use. Abetter tube for your purposes would probably be the Russian-made GU50. It can run right off of a MOT and I've seen some people get pretty impressiveresults for a tube of its size:

http://www.youtube.com/watch?v=wpSBRJETQDg

http://teslacoil.ru/devices/fakelnik-na-gu-50/(check out the other VTTCs on this website too)

 gigavolt says:  Apr 5, 2011. 5:29 PM  REPLYI know its not meant for vttc use...I was bored last night and i had a few 12ax7a's laying around, so i got out the signal gen, scope, and powersupply.It's looking horrible for 12ax7as but i dont really care :D

 electricfan says:  Apr 20, 2010. 5:07 PM  REPLYin the plan are all grounds commen ? all the tubes and transformers are grounded so doesn't that te primary and seccondary share ground correct me if imwrong.thanks

paul

 gigavolt says:  Apr 4, 2011. 6:25 PM  REPLYThey would share the same ground. For (small)Solid State coils and most Vacuum Tube coils, this is quite common.

 gigavolt says:  Apr 4, 2011. 12:34 PM  REPLYIf you vary from the design, you may want to run some calculations(if you are up for it)!!! It will seriously help, trust me!!! If you change the top load size, orthe secondary size, or the capcitor value, etc. It will throw the tuning off. I found that if you calculate the resonance of the secondary coil, then tune theprimary coil and feedback coil accordingly.

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 reallyfast!!!

 jp333 says:  Mar 11, 2011. 4:22 PM  REPLYi have built a vttc i have found the plans on your web site andnothing is happening wen i test it there was a loud hum sound andthat was it . the tubes are not heating up and the grid circuitdoes not seem to be working but the continuity is ok. alsocontinuity is ok thou the rest of the Tesla coil please help

specs1 k mot1.85uf microwave oven captwo 811a'sveritable resistor in gird with 0.0022uf cap

 jp333 says:  Mar 14, 2011. 9:48 PM  REPLYhello i am still having problems with my coil. i have done some readjusting to my coil and also remove 1.85uf microwave oven cap as the tank cap andreplace it with an a new one but still no success . it seems like to me feedback coil isn't picking any thing up at all and i don't know y . i hope these photoscan help.

http://www.instructables.com/id/How-To-Build-A-Vacuum-Tube-Tesla-Coil-VTTC/

 Xellers says:  Mar 14, 2011. 10:15 PM  REPLYWhat are the dimensions of your feedback coil? From what I see, it looks like only 1 turn of wire! One things you should consider is that the LC circuitformed by L1 and C1 is a tuned circuit that should resonate with the secondary coil and topload! You MUST make sure these are tuned properly, orelse you will get little or no output - I would suggest making a completely new primary circuit (new primary coil and new capacitor) with thespecifications I give in the instructable, that way, you know that everything is already approximately tuned. You CANNOT use a microwave ovencapacitor in your primary circuit because the voltage rating is a bit low and its capacitance is way too high!

 Xellers says:  Mar 11, 2011. 5:49 PM  REPLYHello, I'm quite glad that someone actually went and tried this instructable out! As for your coil not oscillating, one possible culprit is the feedback coil. Inany circuit involving an Armstrong oscillator, I always try reversing the feedback coil connections if it doesn't start up. As for the parts you listed, whatwhat do you mean when you say a "1 k mot"? What parameter is " 1 k" describing? Also, where did you use the microwave oven capacitor? There is noplace in this circuit for one and if you inserted it somewhere, it might be causing problems. What sort of grid resistor are you using? If it's not a highenough wattage resistor, it will quickly die and if it's too big or too small, the coil might not oscillate properly. When you say that the tubes are not heatingup, do you mean that the filaments are not lighting? If so, there's something wrong with the filament transformer circuit (for example, if you inserted themicrowave capacitor across the tubes' filaments, then that would cause the filament power supply to short circuit). Finally, what do you mean when yousay the "continuity is ok"? What exactly were you testing?

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 fromdifferent 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, ifyou 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

 jp333 says:  Mar 5, 2011. 11:57 AM (removed by author or community request)

 Xellers says:  Mar 5, 2011. 12:07 PM  REPLYUnfortunately, as much as I would like to help, I'm afraid I can't do that because I don't understand what your comment means. If you want to audio-modulate your VTTC, the easiest way to do this would probably be to add a full wave rectifier and filter capacitor to your power supply and then to use aTL494 PWM interrupter to switch an SCR or MOSFET that control whether the filament of your tube is grounded or not. Basically, the idea is to build astaccato-like circuit onto a CW VTTC, but to interrupt the semiconductor via a PWM audio signal instead of a 555 timer.

 Jimmy Proton says:  Aug 16, 2010. 12:41 PM  REPLYwhere did you get the vacuum tubes? i cant find any as cheap as you got

 gigavolt says:  Aug 29, 2010. 11:44 AM  REPLYI got my tubes from ebay, they were $40 for a matched pair from K5SVC. K5SVC is a great seller of all sorts of high quality tubes.

 Jimmy Proton says:  Aug 29, 2010. 6:14 PM  REPLYwell, i was looking for less than that but iv'e decided not to build this one 'cuz it cost to much money

 savka says:  Jan 19, 2011. 2:21 AM  REPLYYou could find old tv. It is a real treasurechest for vacuum tubes. You can also find HV capacitors in there.

 Jimmy Proton says:  Jan 19, 2011. 12:33 PM  REPLYThe problem is, I don't know where to get one, but I've always wanted one!

 savka says:  Feb 1, 2011. 2:59 AM  REPLYdo you have any recicling centre nearby?

 Jimmy Proton says:  Feb 1, 2011. 7:36 PM  REPLYyeah but i never get to go

 Xellers says:  Feb 1, 2011. 2:25 PM  REPLYSomehow, I doubt that an old TV would contain many useful parts - in a VTTC, one usually pushes all the parts (especially the tube)as far as they go, and this could easily lead to catastrophic failure with an old tube or with other old parts. Given that you can buy asmall VTTC-worthy tube like a GU50 for several dollars on ebay, and given that it's probably better than anything you could find in anold TV, I think it's worth the investment. If you're not looking for maximum efficiency and just want to build a small coil that works, I'msure you could find the rest of the parts you need for very little money.

http://www.instructables.com/id/How-To-Build-A-Vacuum-Tube-Tesla-Coil-VTTC/

 304TL says:  Jan 12, 2011. 5:24 AM  REPLYI would kindly submit that the reason you burned out the first MOT is that the design you copied is fundamentally flawed. Using a larger transformer maymake it last a bit longer, but the key problems from the original schematic still persist. Identifying what the problems are, is left as an exercise for theinterested reader wishing to copy the design.

Never mind that this contraption will instantly kill you, if you have a spark flowing to your hand (as shown in one of the photos) and you then accidentally getthe other hand near the oscillator coil or the top of the tubes.

But the colors in the photos are pretty (being positive here.)

 Xellers says:  Jan 12, 2011. 10:23 AM  REPLYOK, I certainly agree with the second part of your comment, but I think you're quite dead if your hands wander in that direction at any point during the"contraption's" operation. As for the first part, can you elaborate? From what I can tell, this "fundamentally flawed" design is what almost any ArmstrongOscillator-based VTTC would use - what's missing? I'm not trying to be defensive here, I just want to improve the design because I think you're right -I've already killed another MOT with this thing and I want it to stop!

 asustec001 says:  Sep 23, 2010. 10:31 PM  REPLYthank very good

 -max- says:  Jun 28, 2010. 1:55 PM  REPLYthat looks SUPER dangerous to touch!!! did it burn you?

 electricfan says:  Jul 9, 2010. 8:14 AM  REPLYThe answer is= IT WILL NOT BURN YOU!!!!!!! iF YOUR CAREFUL!!!

 -max- says:  Jun 29, 2010. 5:07 PM  REPLYcan you tell me the values of all the parts? I'm planing to make an table top version of this... also, i will tweak it so that is an AM transmitter!

 Xellers says:  Jul 2, 2010. 7:17 PM  REPLYThe values of the parts are all specified within the instructions, and you can visit Steve's site (there's a link) if you need some more information. Also, this*is* a tabletop coil! Regarding the AM transmitter, this is probably not the best way to go about building one, the 811A is better suited for building a linearamplifier or a modulator than it is for making an oscillator. I would use something like a 6146A (or B) tube as an oscillator and a pair of 811A tubes in a500W RF amplifier for an AM transmitter. If you do build a transmitter, then please post some pictures and tell us how you did it!

 -max- says:  Jul 3, 2010. 9:22 AM  REPLYalso, if you want to answer my question,how to build a table top VTTC (vacuum tube tesla coilyour more than welcome!

 -max- says:  Jul 3, 2010. 9:13 AM  REPLYit will be a while before i build it as a gather info on it, but i think this schematic is useful... i took your schematic, (the second pic) and took out all thestatic, moved some components around, and then added a audio transformer and ac-to-dc converter. the third schematic is similar to the firstschematic without modification.

 savka says:  Feb 23, 2011. 3:33 AM  REPLYI have 2 nice new EI-niš PL-519 tubes. It is a penthode rated at 7Kv. I also have new mot. I don't want to use schematic with transformer T3 foraudio-modulation, but because I have a penthode I would apply audio-input to some of the grids. What grid should I use? Should I apply audio-input to both tubes, or just one?

http://www.instructables.com/id/How-To-Build-A-Vacuum-Tube-Tesla-Coil-VTTC/

 Xellers says:  Jul 3, 2010. 4:19 PM  REPLYYou can follow the link in step 4 to the complete schematic. The parts are listed in the schematic, as well as in step 5. A cost estimate is alsogiven in step 5. In order to modulate the coil, you need steady DC power supply; in this particular schematic, the oscillator is only active duringthe positive half cycles of the current provided by the MOT. This means that you are already modulating a 60Hz signal into the coil, and this isreflected by the loud buzzing noise it makes when it is turned on. To modulate audio, you would need a full wave rectifier and a filter capacitor inthe power supply (I can already see a half wave rectifier in your second schematic, but this will still cause some hum, use a full wave rectifier).However, if you continued to use the MOT in this configuration, it would destroy the tube almost immediately - you would need to significantlyreduce the power supply voltage, which would in turn reduce the spark size. Also, this would add about $50 to the cost of the project becauseMOTs are relatively easy to come by and you can find one for next to nothing (if you can't find one for free inside of a broken microwave oven),while other high voltage plate transformers are rare nowadays and would probably have to come out of vintage radio gear. (I have also postedthis comment an answer to your question)

 -max- says:  Jul 5, 2010. 3:33 PM  REPLYi'm now using this schematic but i don't know if it will work. i have many new questions on my question "how to build a table top VTTC(vacuum tube tesla coil)" will this schematic work?

 -max- says:  Jul 4, 2010. 7:39 PM  REPLYcan you give me some info on the tubes why they will break? and do i have to use a MOT, cant i use another transformer like a BIG wall-wart(wall adapter) or a bunch of batteries?

 Xellers says:  Jul 4, 2010. 9:30 PM  REPLY1) Vacuum tubes will arc over, resulting in catastrophic failure and destruction. 2) I'm sorry, but if you do not know why you need to beusing a microwave oven transformer, then you probably shouldn't be using one in the first place. I do not want to give you information thatcould be potentially harmful; the "hobbyist approach" (learning by doing, rather than by understanding) works well in some cases, but I donot believe that it is wise to be building Tesla Coils without some proper foundations in electrical engineering. Find a book or website thatexplains vacuum tube operation, and then read the article on Steve Ward's site about designing VTTCs.

 -max- says:  Jul 6, 2010. 7:00 AM  REPLYi just want a safer transformer. don't vacuum tubes work at low voltages? not a lethal 2.5KV @ 100ma+ ?

 Xellers says:  Jul 6, 2010. 8:30 AM  REPLYYou are correct, many vacuum tubes work with relatively low voltages on their plates. In fact, some types of later "space charge"tubes (like the 12DZ6, for example) were even designed to work with only 12 volts on their plates. Some smaller space chargetubes have been run with only 3 - 6 volts on their plates! However, these types of tubes are usually not capable of any significantpower output (most of them can't handle more than a watt or so of output power in class A), usually they were designed for use asRF amplifiers in the first stages of a radio circuit. Some other types of "subminiature" tubes and small 7 pin tubes can work withrelatively low voltages of several dozen volts on their plates, but these too suffer from weak power handling abilities. The smallesttype of tube that can be used in a VTTC is a strong RF amplifier from a radio receiver, or a weak RF oscillator (or amplifier) from aradio transmitter (when I talk about "strong" and "weak" here, I am talking about how the particular tube compares in terms of platedissipation power with other similar tubes). The smallest VTTCs can run with only about 200 or so volts on the plates of theirtubes, but they only produce sparks a few millimeters long. I'm sure you've already seen this, but this is more or less what youshould expect if you plan on building a small VTTC: http://www.youtube.com/watch?v=dYJ2U0IHJ00. Another popular tubes forsmall VTTCs is the PL504. However, the voltages on the plates of even the smallest VTTCs are still lethal. The minimum voltagerequired to operate a tube like the 811A is only a few hundred volts, but don't even expect it to be able to oscillate.

 -max- says:  Jul 8, 2010. 4:47 PM  REPLYwill a NST work for it?

 Xellers says:  Jul 8, 2010. 5:54 PM  REPLYThis question has already been answered, and the answer is no, unfortunately, it will not.

 Plasmana says:  Jun 1, 2010. 4:02 PM  REPLYI thought people are making VTTC with tubes they have kept from the past and didn't really bother reading about them until now... I am really surprised thatmanufactures still makes vacuum tubes now days! Now I am interested in making a VTTC as it seems simpler than making a SSTC, :)

One question, I read somewhere that 811A tubes can overheat quite quickly when used in VTTC, just how do I tell if they are overheated? I really don't wantto melt my brand new pair of 811A's...

http://www.instructables.com/id/How-To-Build-A-Vacuum-Tube-Tesla-Coil-VTTC/

 Xellers says:  Jun 1, 2010. 4:23 PM  REPLYNowadays, most tubes are manufactured for HiFi audio or for radio transmitters, the 811A falls under the second category, although there are a few goodHiFi amps out there that use 811As. One thing you should watch out for are people selling 811As as HiFi tubes, they'll cost you twice as much!

In most cases, VTTCs push tubes far outside their safe operating zones, and can only be operated for short periods of time. Right now, my primary RLCis out of tune with my secondary, so this adds to the overheating effect. Determining whether a tube is dying really depends upon which model you areusing. Some types of tubes are designed to run with their plates red, others are not. In most cases, you can run your VTTC until the plate becomesorange or yellow, at which point you must immediately turn the coil off to prevent arcing and tube destruction. Also, always use the exact (or slightlyunder the exact) filament voltage specified, too low and the coil will hardly work (this coil now makes 6" long sparks with the filaments at 6.3 volts and1.5" long sparks with the filaments at 5 volts). I know it will be tempting, but never run the voltage any higher, that's why I only have one tube now when Istarted out with two - most filaments can handle many volts more than they are rated for, but the rest of the tube will melt (in my case, the grid meltedand is now electrically connected to the filament).

Btw, I was trying to use the same CD4046 driver schematic as is contained that PLL SSTC you linked me too, I got everything right, I think, but thatCD4046 just wouldn't oscillate....

Good luck!

 Plasmana says:  Jun 3, 2010. 6:23 PM  REPLYWow, thanks for this information, I just only started learning about tubes. Also, does the grid glow as well?

I will start off my VTTC at 5v just to test to see if everything works then Ill use 6.3v for the filaments.

 electricfan says:  Jun 4, 2010. 2:03 PM  REPLYDON'T DO THAT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! THAT WILL RUIN THE THORIDE ON THE FILLAMENT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! IT IS BETTER YORUN THE TUBE SLIGHTLY OVER THE VOLTAGE THAN UNDER IT. i KNOW WHAT I'M TALKING ABOUT, I HAVE TALKED TO 10S OF 4HVMENBERS, ANTUQUE RADIOS MEMBERS. SO NEVER USE 5 VOLTS FOR A 6.3 VOLT FILLAMENT thanks, Paul

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