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Re: Spice simulation pictures
Hi Robert,
<snip>
> One important aspect characteristic of vacuum tube Tesla coils which
> is not often considered because it is not an issue with disruptive
> coils is the duty cycle of the circulating current in the secondary.
> Didn't someone (Bert?) recently post that the disruptive system has a duty
> cycle of some 0.03%? In a vacuum tube coil operating from a full
> wave filtered DC power supply the secondary circulating current is
> 100% CW RMS toaster watts power. At 100 kilovolts the resonator
> circulating current starts climbing rapidly as you add a little topload
> capacitance to your vacuum tube Tesla coil.
>
> I made a 100pF cap which sustained 150 KV before
> breakdown from a 50 US gal steel drum and a smaller metal cylinder
> with rounded ends suspended inside. I wound a secondary out of #14 AWG
> enamelled copper wire on a 6 inch PVC form that resonated with this 'topload'
> at 150 kHz and drove it with my 1000 watt vacuum tube oscillator
> (3 x 810 triodes).
>
> I was able to swing the 100 pF load to about 85 kilovolts RMS (120 kV
> peak). The secondary winding got so hot in just 120 seconds of operation that
> I shut the system down for fear of melting the PVC tube on which it was
> wound! My circulating current was 8 amps RMS according to the
> measured output voltage across a capacitive reactance of some 10.6 K
> ohms, but the heat produced in the wire felt more the equivalent of
> maybe 30 amps RMS. Can anyone explain where my figuring leads to
> such an error? The interconnect between the top of the secondary and
> the drum capacitor was #14 PVC covered solid wire. It got bloody hot
> too. If I had had one then, that's where I would have liked to place an RF
> thermocouple ammeter.
<more snip>
I think the answer is in the skin effect. The whole conductor is not
dissipating the energy - just the skin to a certain depth which
falls off exponentially. It's the only way I can explain it.
What thinx?
Malcolm