From mrbarton@ix.netcom.comWed Sep 20 03:37:27 1995
Date: Sun, 25 Jun 1995 11:44:14 -0600
From: Mark Barton <mrbarton@ix.netcom.com>
Reply to: usa-tesla@usa.net
To: billbeskimo.com
Subject: Re: Vacuum Tube Driven Tesla Coils

You wrote: 

>The idea of making an offline switchmode power supply driver for a TC
>primary (using IRF840 FETs in a full h-bridge configuration) occurred
>to me a while back while I was designing a supply for a European
>Customer. You could put at least 500VA into the primary with such a
>setup and probably get a nasty RF burn, to boot, if you were careless.
>This is a piece of cake with modern PWM control and CMOS power FET
>driver IC's. Anybody out there try this yet?? Certainly not as
>mad-scientist-looking as a rotary spark gap but the potential for EMI
>control is certainly there and would make for a much happier
>neighborhood.
>

Geoff,

I have posted info on this system before, but will tell you it briefly. 
A friend and I have built a VFET H-bridge driver that operates at 10KW 
CW and about 40KW in burst mode (carrier bursts at about 100Hz rep 
rate).  The carrier frequency is 80KHz.  The effects are startling.  CW 
operation yields a 4 foot SHEET of electrical flame that sprays from 
the discharge electrode with hisses and crackles.  Burst mode gives the 
familiar tendrils of a classic TC along with that rrraaaaaaattt sound 
we all love.

Power supply: rectified and power factor corrected 240VAC yielding 
400VDC.  Large bank of electrolytics to support burst mode operation.

I believe the FETs are IRF540 type, 4 per leg.

Mark