[TCML] hybrid coil

["Carlos Van Camp" <carlos@xxxxxxxxxxxxxxxxxxxxxx>]

Hi Guys,
Following on from my problem of trying to get longer arcs from my 50kw valve coil, I have had an idea that I would like to run by you all...

I have thought about the many suggestions made, and aggree that the key differences in the way the arcs are generated, between SGTC and VTTC is the slower rise time that the secondary coil sees, and the size of the tank capacitor.

Even with a stacato controller pulsing the cathode of the valve, it still means that the tank capacitor is starting from "empty" , meaning the oscillations start small (as the tank gains momentum) and build up to there peak...
With a spark gap coil, the opposite occurs.
The tank capacitor charges up to the full break down voltage so when the gap breaks over, the oscillations are at a maximum and then ring down to zero...

Because I want the coil to be sound modulated (at the least it needs to be break rate modulated) I am wondering if a hybrid system may be workable.

I could build a spark gap (Could even be a rotary gap with a high break rate, but may need to be a quenched gap or at least a static gap) and place it in the circuit between the primary coil and Capacitor, as you would a standard spark gap coil.

I would use an interface circuit to trigger the valve to turn on and off at the Audio frequency in pulses. Stacatto...
This would cause the Tank capacitor to charge up until the spark gap breaks down and then the valve would shut off, effectively disconnecting the supply from the tank circuit...

The valve would only be conducting the 4-5 amps required to charge the capacitor, and would not have any RF feedback like a normal valve coil. It would just be acting as a switch between the 10kvDC power supply and the tank cap.
Also I would be using a much bigger capacitor in the tank. (like a standard spark gap coil).

The Idea is that the spark gap would give me the fast rise time required to get the long arcs, but the valve would be there to "commutate" the pulse rate to music and disconnect the power supply from the tank circuit. (one of the problems with spark gaps at higher power levels is that the power supply is shorted out by the spark when it fires, and causes it to "arc" which destroys the HF oscillations...)

What do you think?
Comments?

Carlos
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