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Is there a way to tune a tesla coil without an oscilloscope?

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LAN_403

magnet18

Thu Sept 08 2011, 01:32AM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

Hey, I'm finishing the construction of my SGTC, (just finished actually, first power up tomorrow night, damn rain

)
And all the methods of tuning I see involve an oscilloscope, which is great, but I don't have one that can go over 20 volts. So, is there any way to tune it without one? Or is it just guess and check with the primary tap?

Dr. ISOTOP

Thu Sept 08 2011, 01:39AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Tune for maximum spark length is generally good enough.

lightlinked

Thu Sept 08 2011, 06:52AM

Registered Member #2087 Joined: Tue Apr 21 2009, 08:32AM
Location:
Posts: 115

you can have the scope near and just have the probe uncconected acting as an antenna. the scope will act like an am radio and show you a signal proportional to the output and you can adjust your tap untill the trace seems to be at its peak. you can use other indicators such as a fluorescent tube at a fixed distance

magnet18

Thu Sept 08 2011, 03:04PM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

Right, so just move the primary tap around until I get the longest sparks.
I'll post some pics tonight :)

Dr. Brownout

Tue Sept 13 2011, 02:48AM

Registered Member #2405 Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140

Using Flourescent bulbs can work, however they will most likey be at their brightest before the spark breaks out, I have checked with an EMF meter and lights, once the spark breaks out the meter drops and the bulbs dim down some, however before the spark breaks out the meter pegs at 8 feet away from the coil and the flourecents are at their brightest.

The quick and dirty way is to adjust for longest spark length, tune it using low voltage to start with and apply the same voltage each time you move the tap position and when you get the longest spark length using the same input voltage each time then you should be set.

There are other ways but knowing how much your putting into the coil each time gives you a good base starting point for tuning.

One thing for sure using the bulbs is a good way to tell if you dumping anything into the primary because it does not take much to light them up, and once they light you know you have something going into the coil.

Herr Zapp

Tue Sept 13 2011, 03:28AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

M18 -

The point of preliminary tuning is to verify that the primary and secondary circuits CAN actually be brought into resonance (no hours of fruitless "tuning" that never yields any results), and to minimize the risk of damaging components by powering up a seriously out-of-tune coil.

If you don't have an oscilloscope and RF signal generator, then build Terry Fritz' cheap, simple Tesl Coil Tuner to determine the resonant frequency of both primary and secondary circuits, and find a preliminary tap point for the primary:

Herr Zapp

Tetris

Wed Sept 14 2011, 11:59PM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

Trial and error. run it on low power, take a giant stick (I used a meter stick because max outut was one inch at the max XD) but if yors is powerful I suggest a 11 foot pole, and connect the wire from the spark gap to the end of the pole, and move it along the primary. :p

Herr Zapp

Thu Sept 15 2011, 07:08AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

M18 -

The problem with all the "just change the tap point until you get the longest sparks" suggestions is what do you do if you sweep the entire length of your primary, and still don't get any output? Or you do get some meager corona, but it doesn't seem to change regardless of where you tap the primary. This is an all-to-commmon situation especially with a "first coil", when the builder doesn't first "design" the coil to determine the EXACT parameters that will be needed to achieve resonance, or doesn't construct the coil EXACTLY to the design specifications.

When assisting a first-time coil builder in troubleshooting a "no output" coil, far too often you hear a dialog like this: QUESTION: "OK, tell me EXACTLY how many turns are on your secondary." ANSWER: "Well, I don't know exactly, I kinda lost count .....maybe 800 or 1,000 turns. I don't know, probably somewhere around that many, it seems like a lot". Etc, etc.

That's why an oscilloscope and RF signal generator (or even a Tesla Coil Tuner) are so valuable in determining the resonant frequency of both the primary and secondary circuits, and determining the "almost optimum" primary tap point before the coil is ever powered up.

If you did your homework, designed the coil on paper first, and then meticulously built the coil per the design, you should have no trouble in getting it running and achieving a satisfactory initial tune by the "trial and error" method. It's when your design was a bit off, or your construction deviated from the design, that having some test equipment becomes so valuable.

If you can't get the coil running quickly and easily, spend a few dollars to build Terry Fritz' Tesla Coil Tuner and find the actual resonant frequency of your primary and secondary circuits, and adjust/modify as needed to get both circuits resonating at the same frequency.

(by the way, what exactly is a SGCT?)

Herr Zapp

magnet18

Thu Sept 15 2011, 11:43AM

Registered Member #3766 Joined: Sun Mar 20 2011, 05:39AM
Location:

Posts: 624

Thanks, I got about a foot and a half output by using a TCT

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