Re: VTTC MOT doubler, is it safe?

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

Original poster: FutureT-at-aol-dot-com 

In a message dated 11/16/03 8:08:17 PM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:

>Hi,
>I recently completed my first VTTC, it uses an 813 tube and a MOT from a
>1200w microwave.  I am getting about 5-7" sparks from the breakout point
>during good conditions, and I was wondering would it be at all possible to
>overdrive this tube and use a doubler on my MOT?  The tube has a max 2200v
>plate, and I am afraid if I put doubled MOT power into it, it will form a
>fatal arc inside or somthing.  The tube has a graphite plate, so Im not too
>worried about it melting or anything, but I am afraid of arcs
>inside.  Also, I am not running the tube in optimum conditions, I have the
>screen and control grid tied together, and the beam plate tied to ground,
>should I change it so that the screen is tied to B+  by a resistor, will
>this increase my output noticalbly?  If not, I am going to spend some big
>bucks on a few 833's
>
>Regards - Jim Mitchell
>


Jim,

Most likely you can use the MOT doubler with the 813 tube, and
keep the grids tied together.   The system may want to draw
a terrificly high amount of power though.  You may need to
raise the grid leak resistance, and possibly use more turns
in the primary depending on your design.  If you have a proper
plate lead choke installed, this will protect the tube to a degree
if there's an internal arc.  You may need to use less grid feedback
also.  You probably want to run the system on a variac so you
can raise the power gradually.  You can sometimes see if small
arcs are occuring by peering into the tube while the coil is running,
but don't get electrocuted while doing this.  An 813 with MOT
doubler can give at least 19" sparks.  Assuming you're in perfect
tune now, you'll need to readjust the tuning as the sparks get
longer.  More tank capacitance (or more primary turns) will be
needed to account for the capacitance of the sparks).

John