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RE: [TCML] VTTC HP gate help Igbt?, was grid coil help



Jim,

Might I suggest building the coil first and get it running good in CW
mode. During construction I would leave removable links on the cathode
and grid so you can experiment with different modulation configurations.
This is precisely what I did when I was building my twin 833c. Chris's
"Quadzilla" is set up similarly. The experimental staccato and audio
modulators were built separately in a hybrid box, as one never really
knows what the evil RF monster will slap you up side the head with. You
may find more mods required than you first thought or even dreamed
possible. My multimode coil featured at:
http://www.youtube.com/watch?v=AvMJBcx55Eg&feature=related has all the
different modules separate for experimental purposes. This coil uses
both an SCR and an IGBT in the cathode, as well as a 100W/30~500khz grid
drive amplifier, transformer coupled. At the moment I am not concerned
so much with length of arc; but rather what I can do with them. Here you
can see the coil in it's "exploded view" form, prior to me building the
rack. It is playing music low-level grid modulated at 300khz from a CD
player through one 833a
http://www.youtube.com/watch?v=idGc6hDE_7k&feature=related Hope this
give you some good ideas.

Regards,
Hank 




-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Jim Mora
Sent: Saturday, July 04, 2009 12:10 AM
To: 'Tesla Coil Mailing List'
Subject: RE: [TCML] VTTC HP gate help Igbt?, was grid coil help



-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf
Of futuret@xxxxxxx
Sent: Friday, July 03, 2009 6:01 PM
To: tesla@xxxxxxxxxx
Subject: Re: [TCML] VTTC grig coil help

Hi Jim,

You mentioned the grid coil is 11" dia, but the primary is
8" dia.  Is this correct?  I would think they'd be about the
same diameter.

<snip>

No, sorry John, that is the height of the primary form. The primary and
grid
coils are on it. I suspect it will be long enough. If the primary is at
the
bottom, the height is about 5-6 inches. So the grid can slid away from
the
primary. I can make it longer if needed by decommissioning  a spark gap
demo
coil I made and fusing another 11" 8" acrylic form piece.
<snip>

I'm cogitating your well informed information. The voltage level = raw
is no
problem if I can get the staccato to work somehow. Is there is another
gate
type that can take that kind of power (2W) (not a triac clearly)? Much
of
new power technology is new to me since I worked with signal transistors
and
FET's and darlington power transistors. I suspect the silicon is out
there
now for this application.

To get the grid type staccato to work, does the tube need to be biased
in
the middle of the family of curves then driven into cutoff?

Maybe I need to learn about IGBT's sooner then expected. Someone that
has an
idea please jump in. All we are doing is trying to turn the cathode on
and
off to ground to vary the duty cycle of conduction to control the heat
on
the tube's plate and change the spark output profiles. The current per
tube
may be 550ma with an 833C and the floating voltage is 4-5.6KV which is
clamped to ground for conduction. So we are saturating a switch and then
removing the signal for the off time (cathode opened to ground). FYI a
SCR
once triggered in the classic setup can't be shut off with a fullwave,
filtered power supply.

The staccato is positive leading for on time (saturation) I believe, and
goes low for cutoff. The signal level is out of a 555 pin 3 and probably
will need to be tweaked. How about it power folks, there should be a
simple
thus elegant solution to this. 

Thanks Much,
Jim Mora


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