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Re: site update + filter question

Tesla List wrote:

> Original Poster: "Jan Florian Wagner" <jwagner-at-cc.hut.fi>
>
> Hi all,
>
> snip

> Other thing, I'd like to ask about RC filter design. I've a 3kV
> 50mA NST for that tiny twin TC. The tank cap is 8.5nF.
>
> The current filter looks like this
>
> NST side         tank side
> ---/\/\/\---+---/\/\/\----
>             |
>            === 470pF 6kV max (ceramic)
>             |
> ---/\/\/\---+---/\/\/\----
>  15kOhm power resistors
>
>
> Those 60 kOhm total at 3kVAC (=>50mA) shouldn't be a problem, as it is
> 50mA max from the NST anyway? Or?
>

>
> The filter should now be a low-pass below 10kHz. Is that ok, or should
> the freq be even lower?
>
> The problem now is that once the filter is connected, there's a dramatic
> performance drop (about half of streamer length), so there's probably
> something wrong with that filter design?

The thing you didn't say was how much current  you were actually pushing
through  the 60 K resistance.
The current of 0.05 A. through 60,000 ohms would give a  3000 volt drop.
That figure is only
accurate if we were talking about a d.c.. circuit.  However, it is within
reasonable limits for this application.

The resistance/ capacitance filter has some advantages because of component
cost, but it doesn't seem to
me to be a good choice for this application just because of the voltage
drop.  The only good use for RC
filters I can think of is for audio filters and tone controls in tape decks
and such.  I have seen them used in cheap  AC/DC radios,
but only the very cheapest.  The kind of set you could use to keep your
coffee hot!

 This could very well be why your performance drops. A more conservative
design, from the standpoint of
TC performance, would use inductance rather than resistance.  The objective
is to keep the voltage drop
as low as possible.  The internal resistance of inductors aka. choke coils,
can be very low depending on the size of
the wire used to wind them.  I suggest you look in the Tesla Coil Archives.
I seem to remember some design
data there.

Best

Ray