Re: [TCML] A New Kind of Valve Coil

[Steve Ward <steve.ward@xxxxxxxxx>]

I'd like to point out that the issue of "feedback" is not trivial.  There
are many ways to obtain a self-oscillating system, but you can end up
operating in subtle different modes, particularly with double-resonant
systems like a VTTC or DRSSTC.

John Gudenas suggests using essentially, primary feedback.  This works fine
for power oscillators, it may or may not deliver power at the best phase
angle to the secondary coil, however, does make sparks of good size.

Phillip is positioning his feedback coil to where the coupling is much
stronger with the secondary flux than the primary, this difference seemed to
give his original VTTC quite a performance edge over any other VTTCs (before
the HV modulated supply was developed).  I suspect that the operating mode
is more efficient in Phillips case than Johns case, in terms of providing
power at the right phase to the secondary.

Im not claiming to fully understand these modes (yet) and how to force the
system to operate at each of them, but i would encourage you at least do a
AC sweep of the system in SPICE or otherwise, and look at where the poles
and zeroes (peaks and dips) are in the response, and you will see there are
indeed many frequencies where the system should theoretically be a good
oscillator and treat the tube kindly, but i think some mode will have better
performance than others.  And its *not* just an issue of tuning, its an
issue of how the feedback is derived.  You can play with turn count, grid
leak networks, and primary tuning until you've exhausted every combination,
and you will not see the operation difference that you do by changing the
feedback coil location.

Steve

On Thu, Jun 23, 2011 at 9:58 AM, Dr. John W. Gudenas <
comsciprof@xxxxxxxxxxxxx> wrote:

> Phillip,
> as you know I have been following your progress with your coil as well as
> Steve's work.
> I solved the grid coil issue a few years ago and there should be some
> posting in the archives.
> Instead of using the secondary as the major feedback source, I put a flat
> spiral pancake coil under the primary with the inner diameter about the size
> of the primary. It is also covered by a circular piece of phenolic so no one
> can see it.
> I have always used a high wattage adjustable grid leak resistor set for the
> sweet spot. This system is sound, never any flash over. I used 14 awg
>  insulated wire because it was easier to make the pancake.
>
> Now, there is no reason why you can't pick up the current from a primary
> lead with a current transformer, but then you need to get that to control a
> high voltage with proper timing for the grid. I am not really sure if this
> solves problems or adds to them.
> But, I guess you will find out. However, if you can, give the pancake grid
> coil a try.
>
> John W. Gudenas, Ph.D.
> Professor Emeritus of Computer Science
>
>
>
>
>
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla