Re: Solid State Tesla Coil - Mysterious Electrical Shocks

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Original poster: "S Gaeta by way of Terry Fritz <twftesla-at-qwest-dot-net>" <sgtporky-at-prodigy-dot-net>

Hi Ken,

That coil was easy to tune. It's a Hartley power oscillator. Once you get
the thing tuned correctly to oscillate at the secondary's resonant frequency
there is no problem. Even when I drew an arc, the plate current actually
dropped. I killed the tube when I did the same thing that Dan did to his
SSTC2. I said "lets see what this beastie can do!" and I cranked the variac
up to give 2500 volts on the plate. The plate current was only 500mA, and
the grid current only 50, but after a few seconds everything went dead, and
the fuse blew. I was left with a cathode to grid short. I tried blowing out
the short with a high powered battery but it only shorts out again after a
minute or so. I think the grid broke free from it's support structure.

So.. I put that one aside and built an 811A coil with a DC supply. This coil
was a pain in the neck to tune. I have to knock the oscillator onto the
correct frequency by drawing an arc off the secondary before I can bring the
variac up to full voltage. This is a mystery to me,  and the problem does
not exist when I run the thing on AC and let the tubes self rectify, but I
needed to modulate this coil for a special demo.

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Regards,
Sue

>
> I can agree with that.  I note that my mains current goes way down as
> soon as the sparks break out.  Prior to break-out, all that power is
> going somewhere:  Out!
>
> And Sue...I wonder if you might consider adapting your VT coil to
> self-tuning?  If you power the tube from some kind of amplifier, you
> should quite readily be able to use the secondary's return-current,
> suitably phase-shifted, as the excitation for that amplifier.  Think of
> it:  Always in tune!  No more wood-burning!!
>
> Ken Herrick
>
>