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Re: [TCML] VTTC geometries, opinions needed

Hi Jim
I didn't tap the primary. The secondary coil resonates about 250 KHz and I set the tank circuit around that. Fine tuning was done by adjusting the tank capacitance and toroid top load. I slowly acquired a stack of toroids that starts at 30" and goes to two inches so I had plenty to work with.
The top load is size is sufficient to put the coil in or out of tune. The VTTC are really touchy that way, but when you learn how to dial them in, it just becomes a final task. There is no reason why you can't tap the primary, I was just following my old radio habits by tuning with capacitance with the L C tank circuit and found that adjusting the secondary C was easy (in bounds) 
with enough toroids. Just technique with existing equipment.
John

John W. Gudenas, Ph.D.
Professor of Computer Science

On Sep 8, 2009, at 3:34 AM, Jim Mora wrote:


Say Doc,
Great advice. I will plan on using phenolic for my standoffs off the acrylic (1" stringers). Most of the tubing will be in open air which should help keep it cool. HDPE melts at a low temp I believe so that's now out!! Out of 
curiosity, how many turns do you have at your tap point? First design
change!
Also keep in mind that 12awg is .0808". The tubing will be slightly more 
than twice the diameter of 12awg at .1875" Though I will be running 4
tubes...

Thanks Much,
Jim

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf 
Of Dr. John W. Gudenas
Sent: Monday, September 07, 2009 8:42 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] VTTC geometries, opinions needed

Jim
You are going to have a huge current in your primary.  With my dual
833A VTTC and a 12awg primary that was
initially on a .125 acrylic form, I developed a problem. I melted the
primary acrylic form. Now, I did have long runs of 5 minutes or longer
while I took a lot of discharge pictures. Just be aware that many
acrylics have a very low melting temperature and your primary can get
hot.
Obviously heavier gauge wire will not get as hot, but it really wasn't
"that" hot. The acrylic just melted easy.

I did not run staccato but the 60 Hz continuous duty cycle and this
certainly will cause greater heat. I finally had a high temp. phenolic 
form with a .5" wall fabricated for my primary to accommodate my long
runs and duty cycle.

I don't know what type of acrylic you have, but just be aware it can
have a very low melting point and your primary can get hot.
I really don't know if this is a problem for you, but it can't hurt to
keep it in mind.
John


John W. Gudenas, Ph.D.
Professor of Computer Science


On Sep 7, 2009, at 2:12 AM, Jim Mora wrote:






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