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Re: tubes

Jason,
 
Try to find an 810 triode (175 watt) or use a single or pair of paralleled
805 (~100 watt) triodes. Their plate voltage rating is just right for a
straight MOT without voltage doubler.  Stay away from 811A, too marginal
and easily melted here.  872B would be a good one singly or paralleled as
well.  I had an enormous amount of fun using a single 810 in a coil I built
in electronics class at hi-school.  
 
If you click on the Tesla coil button on our website www.area31-dot-org  you
can see a couple of vac tube TC's I've built in operation.  One has four
811A's on a MOT and produces an 11 inch brush.  Don't go that route as I
mentioned above, I melted several 811A's trying to find 4 that would survive.  
 
One 'trick' that you can employ is to wind several turns of solid, PVC
covered 'house wire' inside the primary core window if there is enough
space over the primary winding of the MOT and use this as your filament
supply. This saves having to use a second transformer for the filaments.
You will get almost 1 volt per turn, so adjust the number of turns until
you get the correct voltage for the tube you choose.  You should center tap
this filament winding and use the tap as the cathode return connection for
the tube circuit, rather than one or the other side of the filament which
places undue wear on a portion of the emitting surface of the heater,
lessening tube performance and lifetime.
 
Be careful, the plate supply you will be working with is highly lethal. 
 
Robert W. Stephens
Director
AREA31 Research Facility
www.area31-dot-org
----- Original Message ----- 
From: Tesla List 
To: tesla-at-pupman-dot-com 
Sent: Thursday, March 02, 2000 19:12
Subject: tubes

Original Poster: "Jason R. Johnson" <hvjjohnson13-at-xoommail-dot-com> 

Does anyone know a good fair sized ~200 watt tube that will 
work well with an MOT? I've done some stuff in small 
disruptive coils but I would like a small tabletop coil that 
won't generate large (potentially dangerous -at- school) sparks 
but considerable RF to use at science fairs for lighting up 
bulbs etc. and was thinking that a vac toob tc would be 
nice.

Always learning,
Jason Johnson

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