Re: [TCML] 35 KVA Vacuum Tube Tesla Coil

["Carlos Van Camp" <carlos@xxxxxxxxxxxxxxxxxxxxxx>]

Hi Roger,
Fully agree about acting more like transformers.
My existing set up has 10 turns in the primary with a 0.0082uf cap.

FYI, the low power bench tests I did before building the BIG one yielded a 
2" brush of arc from a TB3/750 triode (this is while keeping the valve 
within its rated conditions).
I tried many different oscillator circuits (including steves example) and 
spent months of my spare time playing with values etc to improve it.
Most the circuits gave pretty much the same 2" brush, so I settled on a 
convienient circuit and went about building the BIG coil as previously 
described...

Since I feel there must be something I can do to improve the output of the 
big one, I went back to bench tests again with the TB3/750.
There was a circuit in my ARRL book that I had always avoided testing, 
because it had the tuned circuit in the grid, and no tank cap in the plate 
circuit.
Being a spark gap enthusiest, I could not see how it would work well with 
out the tank cap, but I decided to give it a try...
After fiddling with some turns and values, I was able to nearly double the 
output for the same power input.
The number of turns in the Plate coil is key to getting good efficiency, and 
it appears to be a balancing act between matching the output impedance of 
the valve and turns ratio of the primary/secondary.
EVERY test so far has yeilded best results with tighter coupling.

I am yet to try it on the BIG coil but I am hopeful to see similar increases 
in efficiency.

Hope there is something in there that helps...

Kind regards,

Carlos
> >
> Hi Carlos,   The circuit I used is basically the same as the circuit Steve 
> Ward has on his web site for his 833 VTTC.    I don't claim  to be an 
> expert on this stuff but my gut feeling is that since these VTTCs are so 
> tightly coupled they tend to act a little more like transformers than 
> Tesla coils so if you have too few turns in the primary,  that might be a 
> problem.  The objective here isn't to get the highest voltage 
> theoretically possible but rather to get the voltage and the current in 
> the right proportions to match the load of the spark.
>
>       It seems like a loosely coupled VTTC would be self matching but I 
> haven't had much luck with that approach.     Having said all this ,  I 
> think I have a long way to go to get my coil as efficient as it could be. 
> The 50" inch sparks are nice but 35 KVA is a hell of a lot of power.
>
>    Good luck with your endeavors,  Roger
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