Re: VTTC MOT doubler, is it safe?

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

Original poster: "Steven Ward" <srward16-at-hotmail-dot-com> 

I would agree with John here.  Its a bit of a trick, but ive pushed my 810 
tube with a MOT and doubler.  The 810 is rated to 2500v i think.  At one 
point it did arc and you can hear it in the output.  I think the fix was 
less grid feedback.  But, i was only using 2500ohms of resistance on the 
gridleak circuit, this seemed to make the tube happier.  Anyway, i think 
higher gridleak resistance would promote tube arcs since the load on the 
power supply is lower thus allowing the voltage to get excessively high.
Though im sure the amound of grid leak resistance you want would also 
depend on the tanks impedance. I guess just try stuff out and see how it 
goes.  Its all a balancing act...

Steve Ward


>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: VTTC MOT doubler, is it safe?
>Date: Sun, 16 Nov 2003 20:36:07 -0700
>
>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
>