Re: Tube coil related questions

["David Sharpe" <sccr4us-at-erols-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Carl

Suggest placing a capacitor across MOT secondary, in series
with doubler capacitor.  When a kickback occurs, energy is
passed through capacitor(s) to ground.  Typical values seen in literature
range from 0.1 to 1.0 uF at 2.5X MOT pk output.
Also in all new high power VTTC's I plan to build, I'm putting
a 50ohm, 200W power resistor in series between level shift
power supply and tank of VT oscillator. This will likewise limit
impulse currents with kickback or tube flashover.

Regards
Dave Sharpe, TCBOR
Chesterfield, VA. USA

Tesla list wrote:

> Original poster: cwillis-at-guilford.edu
>
> Hello fellow tube coilers,
>
> I have an 833A coil that has given great performance with one small
> problem:  the microwave-oven diode that I use in my "level-shifted (or
> doubler)" supply gets toasted now and then.  I believe John Freau has
> suggested, and probably correctly, that this is due to large RF kickback.
> Anyway, I wanted to eliminate this issue, and was thinking about other
> rectifier options. By getting all the weak spots out of my coil (all the
> silicon) I will be able to do demos and carry it around without having to
> be surprised by killed parts.
>
> Perhaps a magnetron with the magnets removed could serve as a nice
> high-voltage rectifier tube for the doubler.  The only disadvantage would
> be the requirement for filament power- but this is supplied in MOT's from a
> HV-insulated winding.  Any thoughts about this approach before I go ahead
> and try it?
>
> One especially useful piece of info for me now would be the difference in
> resistance between the "maggie" and a oven-type rectifier.  I think they
> might be similar, but I have nothing to conveniently measure the rectifier
> resistance.  Has anyone done this?
>
> And finally, a more general question.  Does someone have a good idea of how
> to estimate the inductance of flat spiral coils that are stacked and linked
> in series?  Of course it's not just going to be the sum of the individual
> inductances but will include the mutual inductance as well, and that's the
> part that I really don't have a practical clue about.  Suppose two coils
> have the same dimensions, same # of turns, are coaxial and are spaced a
> distance X.  How much will the mutual inductance add on to the sum of the
> individual inductances?
>
> Thanks for any help!
>
> Carl