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RE: [TCML] VTTC geometries, opinions needed, Fo calc wanted, sword sparks, turning off a SCR in staccato mode
Hi Dr. John, et al,
I do have a big variable cap under oil which measures 35-260pf.I thought I
would set it in the center point, tap the primary, and tweak the variable
cap for fine tuning. My main cap bank will be .004uf
Fo calc wanted. I used a micrometer on my wire and the insulation is ~
.002244" or slightly less. This gives me 944 turns or so at 32" long. The
top load is very small namely 7"x.25. I am trying to stay in the 350Mhz ball
park. The wire is 21awg. I know that ain't happening. Even reducing to 30"
self res is 309Mhz with 885 turns. I think I'll wind all 32 inches.
In CW operation, I don't care if the sparks are brush like. There will be a
hell of a lot of RF energy! I should be able to burn a screw driver and
light big lamps @ near breakout.
So here is the last question: when I run staccato mode, can I get the
coveted swords? John seemed to think so and we know his vast experience with
this! Anyone else have experience with this to verify the outcome?
I have yet to figure how to turn off the Staccato SCR with FW >4KV @ >4KW
in.
Ant help or suggestions welcomed!
Thanks,
Jim Mora
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Dr. John W. Gudenas
Sent: Tuesday, September 08, 2009 7:19 AM
To: Tesla Coil Mailing List
Subject: 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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