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Re: Solid State - air core driver??

Greetings.

Thanks Harri, Jim et all for the responses.

I'm going to abandon the traditional primary.
Unless the ends are clamped as in a full
bridge the secondary is always going to
induce high voltages back onto the primary
breaking down the FET's. So a pushpull
traditional primary is definately out. 
Jim wrote:
> watch out for voltage spikes!
>from the resonant rise of the TC (300-400 as measured by malcolm
>watts) divided only by your secondary/primary turns ratio 1500:18 =83.

>So if you put in 75 volts, multiply it by 300 (coil Q) and then divide
>that back down by 83 you will get 271 volts  across the coil (twice
>that if you use a push-pull).

540v will kill irf740's - at 150v single side operation has been very iffy.

A full bridge I will leave till later. Thanks for the transformer details
Harri - yes I I've enough information now to design one - that might
even work!!

I bought Babani's book "Coil Design and Construction Manual"
Not Tesla coils but RF coils, valve coils, HF chokes, power transformers.
Some useful formula's and wire tables - L3.95 at Maplin. 
(UK publisher)

I've got a ferrite transformer, and one side
completed of a pushpull driver. I will
complete the other side and then try it out.
I'll start witha 7:1 ratio and see how it goes.
 I haven't got bifular wire but I have
wound two 1.25mm wires carefully side by side.
20 turns.
I'll keep the current limiting though in case it
saturates.

I have at present got a number of 0.33 ohm 
resistors in //
for current limiting - at 1.4volts. but of course
this means at peak maybe a 2v rise - between
the FET and ground which must be transfered
to the gate via the internal FET capacitance.
Presumably this voltage rise makes it preferable
to measure the current using a current
transformer, and the same signal can be used
to drive a phase locked loop - thingy. OK that
can go in the next one too!

Right I shall start to build - will it be serious spark
or serious smoke wait for the next exciting 
installment......

Alan Sharp (UK).