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RE: [TCML] vttc primary capacitance
hi steve
my desighn at the moment is just a basic rig up kinda just getting the feel for it
i have the primary secondary coupling loose at the moment as the tube its on is well , its all i have
there is a video on youtube that shows a vttc running at a low frequency like mine is
he gives some detail but not much and his output is massive
its a pole pig powered beast runningt a 3cx3000 tube
i got most of my desighn ideas from him
the looser coupling and the low frequency
the video in question is here
http://www.youtube.com/watch?v=7Ky4a9KPlVY
when i started i was using a much tighter coupling but i was getting flash overs between primary and secondary so i used the the next size of tube that i had which was the 9.75 inch you see in my video and then i used the larger secondary to get my low frequency
basicly copying him
thanks for your advice
earl
> Date: Tue, 27 Jul 2010 09:57:33 -0500
> Subject: Re: [TCML] vttc primary capacitance
> From: steve.ward@xxxxxxxxx
> To: tesla@xxxxxxxxxx
>
> Earl,
>
> It appears you are operating at a pretty low frequency compared to other
> VTTCs, and this means you can afford to use a larger tank capacitance and
> still maintain a "high" tank impedance. I dont see why 4nF would be too
> much, typically one just watches for plate redness or other signs that they
> might be stressing the tube too far, and often the solution is to increase
> tank impedance (smaller tank cap, more primary turns)
>
> There are some things that could be improved in your design, but mainly the
> primary to secondary coupling looks very sub-optimal, and this alone can
> cause excessive primary currents and additional tube heating. Basically, in
> a CW machine, tight coupling is desirable because there is no real need to
> store energy in the primary, you want to transfer it to the secondary as
> fast as possible. In a CW situation, this means that the ratio of primary
> current to secondary current will be smaller with higher coupling (this is
> good!). If the coupling was really loose, you'd run a bunch of primary
> current and only get a little bit of secondary excitation. Again, this has
> to do with the physics of energy transfer, and because its a CW system,
> there is no benefit to energy storage like there is in a SGTC, where low
> coupling is acceptable because it all eventually can get transferred to the
> secondary.
>
> I'd be interested in hearing any counter-examples, but in general i think
> most experimenters find that the highest coupling you can manage without
> flashover, typically works the best. Of course, there could be subtle
> tuning issues that might suggest a slightly lower coupling worked better for
> someone, but id have to guess that if they were to finely re-tune the tank,
> that higher k would almost always be better, probably until you get to
> around k=0.5.
>
> Steve
>
> On Mon, Jul 26, 2010 at 5:11 PM, earl rhodes <earl_1975@xxxxxxxxxxxxx>wrote:
>
> >
> > hi guys
> > im building a large vttc using a gu5b tube rated a minumum of 3.5kw
> > i was wondering what is the max capacitance somebody could use for the tank
> > circuit
> > at the moment i am using 4nf or there abouts anyway thing is i cant find
> > any other examples using this much capacitor
> > i dont want to wreck my tube there are videos of my progress on my youtube
> > channel
> > thanks
> > earl
> > aka teslaspigeon
> > http://www.youtube.com/user/teslaspigeon
> >
> >
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