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Re: [TCML] Toroid Problems

Nicholas -
   
  A few areas of concern are revealed by your photos:
   
  1. It looks like your tank wiring to the MMC and spark gap is extremely small gage stranded wire (#16 AWG?). All the interconnects between primary coil, spark gap, and tank capacitor need to be fairly heavy gage (I recommend no smaller than #12 AWG for a small NST powered coil). The peak current in the tank circuit can be hundreds of amps when the spark gap fires and the tank capacitor dumps all of its energy, and #16 AWG is not adequate.
   
  2. All the wiring in the tank circuit needs to as short and direct as possible. You didn't post any photos of the overall coil and all the interconnects, but I suspect that your primary wiring may be longer than necessary. It appears that you have carefully calculated the inductance and resonant frequency of both primary and secondary coils, but I bet you did NOT include the length of the additional tank circuit wiring in your primary coil calculations. Measure the total length of your primary wiring, include this in the length of the primary coil, and re-calculate primary inductance and resonant frequency. It may be much lower than you thought. You may need to relocate the spark gap and the MMC to keep the primary wiring as short and direct as possible.
   
  3. I suspect that your solder joints where the primary wiring is connected to the copper tubes of your spark gaps are really "cold joints", and are not electrically sound. You simply cannot directly solder small gage wire to a large copper pipe with a small soldering iron. If you wiggle and pull on these joints, I suspect that the wires will just fall off. You either need to use a torch to get the copper pipe hot enough to "tin" it, and solder the wire while the pipe is hot, or connect your new, larger-gage wiring to the pipes using crimped ring terminals with screws & nuts.
   
  4. Again, have you verified that the NST is good, and that you can pull arcs of EQUAL LENGTH from each bushing to the NST case?
   
  5. Have you verified the resistance value of EACH ONE your bleeder resistors? In the past, several people have had problems with using the wrong resistor value (1 meg instead of 10 meg), or had one or two resistors of the wrong value. Wrong resistor values will burn up a large percentage of the meager 30ma NST output current.
   
  6. What type of bleeder resistors are you using in your MMC? Are they 1/4 watt, or 1/2 watt resistors?  Are they rated for the voltage they are actually being subjected to in your MMC? Standard 1/4 watt carbon-composition and metal-film resistors are typically rated for only 250 volts, and 1/2 watt resistors are rated for 350 volts. In your MMC, assuming you are using all twelve capacitors and running only 120 VAC input, your transformer's peak output voltage is about 12,750 volts. Each resistor will then have over 1KV across it. Check them carefully for any sign of arc-over, or discoloration from overheating. Vishay offers a line of special high voltage resistors (VR-37 series), and the 1/2 watt series is rated for 3500 volts. They only cost a few cents more per resistor than the standard 350 volts resistors, and I have never had one fail, even at considerably higher than 3500 volts. If there is any question about your resistors breaking down, a quick (temporary) fix is
 just to connect two or three resistors in series across each cap. The time constant to discharge the caps will increase, but it should reduce any arc-over problems and won't adversely affect coil performance.
   
  Regards,
  Herr Zapp
   
   
   
  4. 

"Nicholas J. Goble" <ngoble@xxxxxxx> wrote:
  I just posted a set of pictures of my coil on Flickr.com. By the way 
Neal, the Science and Surplus store that I was at was located at 5316 
N. Milwaukee Avenue, right where 90 merges with 94.

Here's the link to my set of pictures.

http://www.flickr.com/photos/28523883@N06/sets/72157606573696858/

Thanks for all your help

Nicholas Goble
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