Re: K and tube coils, loss gain factors...

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 7/20/03 1:53:56 PM Eastern Daylight Time, 
tesla-at-pupman-dot-com writes:

>Hello all,
>
>I am wondering what is the "ideal" coupling coefficient for a 3 Vtube 833a
>coil would be, pushing things a bit, and using low loss High insulation
>factor  materials around the secondary. I have a 4" polystyrene coil form
>which will be wound with triple insulated #28 AWG. to 22 inches, PE end caps
>and topped with a Freau 6 x1.75" terminal top load (and whatever else is
>needed added for additional tuning).


Jim,

I usually use a coupling of about 0.18 to 0.22.  Small changes don't seem
to make much difference.

>I plan to use the classic half wave MOV doubler initially but would also
>like to experiment with a 4200v, 1.5a plate transformer in full wave, and
>modulate the grid.
>
>Classically, everyone seems to use PVC as the primary  (6 or 8"??) and move
>the grid feedback up or down... this NAGS me somehow. Perhaps these would be
>better serve on a separate coil forms, of less lossey material? And the
>primary wire itself....I have thoughts of using small cu tubing with Teflon
>tubing, wound on PE.(that be tricky)


I generally use polystyrene or plexiglas for my tube coil forms.  I place
the grid feedback coil onto a separate form that slides over the top (or 
bottom)
portion of the primary form (above or below the primary winding), so I can
adjust both the main coupling and grid feedback independently.

If you use copper tubing, it could form a stand-alone coil with lexan supports
at 3 or 4 places around the circumference of the coil.


>I plan to use a .003 Sangamo, if it can handle the tank oscillation voltage.
>It is rated at 12A at 400KC, but only 8KV peak working voltage. I would not
>like to be near this big cap if it let go:)


That cap can handle the MOV doubler voltage, but it's getting near the edge.
I blew out a nice 0.006uF, 8kV rated mica cap when I ran at 5.5kV or so.


>Since I am new to the VTTC world (except a wimpy candle stick one I made a
>long time ago that didn't spark doodley squat), your suggestions would be
>honored and much appreciated..


I'm sure you'll get a nice result.  The key with VTTC's is they often need
a *lot* of tweaking to get the best results.  Getting longest sparks is not
the key.  Getting longest sparks without the tube getting too red is the key.

To get 24" sparks, you'll most likely need to remove the shunts from
the MOT.

John


>Warm Regards,
>Jim Mora
>Ojai, Ca.
>