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Re: Toroid's effect on Q of the secondary

Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>
I slitted up a toroid once (6 x 24 inch size) and noted that it worked fine at low levels atop the secondary, however, a solid surface toroid produced the exact same discharge when it was properly elevated. This was testing on a coil with a 60 inch long spark.
It's best to experiment with small blocks of wood to elevate the toroid until you are achieving max spark discharge possible ---- very much like experimenting with sec coil elevation until you are hitting your max.
We wind all of our "test" coils within 1 inch of the lower end and start elevating until we hit a max using a small 10 rpm DC motor on a flex drive. After hitting it then we just design for the proper start height on all of our sizes, 4", 6", 12" 18" and 24". The larger size 18" (ID) requires 6.75 inches of elevation above the primary and the 24 inch (ID) requires exactly 9 inch elevation. Sec elevation is absolutely linear right down to the 2 inch size so you can just make up a simple graph and get the 4", 6", 8", 10", etc. readings right off the graph ( I will email one to Terry F for posting) and, we you do all the testing, will get the exact same output as you will off my graph --- no exceptions with classic coils. This could change with DRSSTCs as I have not tested elevations on them. 


Dr. Resonance



Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Norman,
I have not heard of anyone using a slit toroid. You may be experimenting into a topic that hasn't been looked into deeply. I generally keep my toroid as high as possible (not allowing sparks to issue from the top winding, well, unless I'm in a lazy mode of operation). It's been stated on the list that a toroid low or partially covering the top windings may heat the top windings (I have not experienced this myself). It certainly appears the Q was definitely affected. Out of curiosity, how did you measure fo? 

Take care,
Bart

Tesla list wrote:


Original poster: norman@xxxxxxxxxxxxxxxxxxxxxxxxx
I just finished measuring the resonance frequency of my secondary by observing the null due to the series resonance of the 1/4 wavelength coil. The toroid on top of the coil was constructed out of 4", "semi-rigid flexible aluminum duct", bought in Home Depot. The ID is 3.5", OD 11.5" and the center of the toroid is hollow so that it slides over the PVC coil form. The coil is 9" x 3.5" wound 
with # 24 wire and resonates at 500kHz.

I noticed that when the toroid was about 3" above the top of the secondary
winding the resonance notch was very deep, but when the toroid was moved close 
to the top of the winding, the notch was not very steep.  Clearly the toroid
was affecting the Q of the coil, probably by acting as a shorted turn. I have not come across any information about how far the toroid should be placed from the top of the coil. Anybody have any information about this? Should I place 
a slit through the toroid?

Also the surface of the semi-rigid flexible duct looks like an accordion with
1/4" deep ridges spaced about 1/4" apart.  Will this surface effect the
streamers?  This is a low power Tesla coil that I hope will produce at least
10" streamers.