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

["Jim Mora" <wavetuner@xxxxxxxxx>]

-----Original Message-----
From: Jim Mora [mailto:wavetuner@xxxxxxxxx] 
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

New comments and corrections added.

-----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 (**** and
saturation****)?

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 **** actually the filaments are all paralleled ( acts as the
cathodes) so current sinked when switched on is 4*550ma=~ 2.2 amps at >5kv
with a 833C *****and the floating voltage is 4-5.6KV which is then clamped
to ground when the device is triggered for conduction. So we are saturating
a switch and then removing the signal or go low for the off time (cathode
opened to ground). A power mosfet is probably not a good enough candidate do
to voltage constraints so I need some IGBT education. FYI a SCR once
triggered in the classic setup can't be shut off with a fullwave, filtered
power supply. This is one of the reasons the MOT level shifter is liked (not
acceptable for modulation).

The staccato circuit output is positive leading for on time (saturation) and
goes low for cutoff. The signal level in 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 with modern silicon. 

This will be a interesting hybrid of WWII big triodes and modern
electronics.

Thanks Much,
Jim Mora


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