I spent more time fooling around with the spark gap of my first TC than I did with the rest of the system put together. It was an ignition powered coil, and until I got the gap right, I couldn't get it to actually break out, although it would draw nice 4" arcs to a screwdriver.

I hate to admit it, but I would tune it by sticking my finger up to it and seeing how much it hurt! When the coil was properly tuned it didn't hurt at all, it just felt weird. DON"T do this, it's really stupid. Anyway, once I got the gap right, I got a nice 3-4" brush discharge from the coil.

The gap that did the trick was a 5 gap washer style. The washers were 5/8" brass screwed down on to a piece of plastic cutting board spaced away from the board with fiber washers of smaller diameter. I don't have a picture, unfortunately. A fan placed next to the gap blowing over it improved performance further. This gap worked OK for OBIT power levels as well.

Here is a picture of a gap I made that failed miserably. It lasted seconds.

You can't really see it in the picture, but carbon tracks formed on the perf-board, shorting out the whole affair. I'm surprised I still had it laying around, I guess I was too disgusted to even disassemble it and salvage the parts.

When I progressed to NST power levels, I wasn't getting the sparks I should, or anywhere close. With my previous experiences, I assumed it was the gap that was limiting my performance. It was true. No multi style gap I made seemed to perform adequately. Then I saw Gary Lau's vacuum static gap and decided to give it a try. It took me less than $20 and two hours to make. I used a shop vac to supply the vacuum. I think this piece of equipment has the highest dollar to improvement ratio of all my Tesla stuff, and that's including the 15kV/120mA NST I got for $20! When I tried it for the first time, spark length doubled!

    

As you can see, construction is exceedingly easy. I used all 2" PVC fittings. The copper pipe is 1/2". I could have made the unit more compact, but I wanted a big copper heat sink which turned out not to be necessary. This thing runs cool, no matter how long you run it. The yellowing you see is NOT due to heat! It must be from UV damage.

In order to be able to easily adjust the gap, I made the electrode fittings of 1/2" pipe, then used a long repair coupler to slide them into. Brass nuts were soldered over holes in the repair sleeve to hold the electrodes. The picture below explains it better than I can.

All of the pictures so far show the new tungsten bullet electrodes I got from Marc M. on the Pupman list. As you can see, I drilled holes all around the bullets to allow air flow. I haven't used the new electrodes much. Previously, I used hardware store brass bushing for the electrodes, and they seemed to run fine. I have noticed some wear on the tungsten electrodes, which was never a problem with the brass ones, all they ever needed was an occasional cleaning. However, I think the problem is not with the tungsten, but that the system I was trying them with was power arcing. Here is a close up of the tungsten electrodes.

The vacuum motor was wrested from an old Eureka. I pried the housing apart and screwed on a 2" PVC slip fitting and then replaced the housing. I have found that more vac power isn't better. I get max spark length applying around 40vac to the motor. Another interesting thing is that low power systems don't seem to like this gap, as I get better performance with an IC or OBIT using a fan cooled multi gap.