Re: strange vttc

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi Steve,

On 30 Mar 2004, at 11:17, Tesla list wrote:

 > Original poster: "Steven Ward" <srward16-at-hotmail-dot-com>
 >
 > I think VTTCs have this magic instability in their operation that
 > makes the idea of fine tuning go out the window for a moment.  I once
 > substituted a 3nf tank cap in for my 2nf cap, and i figured i would
 > tune at several fewer turns.  Well, when all was said and done, i
 > ended up only 1 turn less than before! even though my tank cap was 50%
 > larger!  Whats the deal with that???

How many turns did you end up with? Inductance does vary with the
square of the number of turns to a crude approximation (for less than
ideally lumped coils). The tolerance of the cap may also have played
a prominent part in the result.

   I think also that the Q of the
 > tank will play a large roll in how things work out and how close you
 > must get the tuning.  Some of my VTTCs will tune to a very wide
 > variety of tap points, others will not.  I think part of it has to do
 > with the feedback and its RC circuit getting in with the mix of
 > things.

And probably also the degree of coupling between primary and
secondary.

Malcolm

   At the moment i havent thought about it enough to really give
 > any good answers, just some thoughts i had...
 >
 > Steve
 >
 >
 > >From: "Tesla list" <tesla-at-pupman-dot-com>
 > >To: tesla-at-pupman-dot-com
 > >Subject: Re: strange vttc
 > >Date: Mon, 29 Mar 2004 22:23:15 -0700
 > >
 > >Original poster: "Jim Mitchell" <electrontube-at-sbcglobal-dot-net>
 > >
 > >I don't think this is all that strange.  For one,  with a VTTC,  it
 > >is not a self resonant system.  So the VTTC will be running at the
 > >frequency of the tank LC circuit,  which may not be the EXACT
 > >resonance of the secondary. Therefore, you reading a different
 > >frequency output on your scope is probably due to the coil not being
 > >in exact resonance.  Just like on an oscillator driven SSTC, you have
 > >to retune sometimes when the output grows because of it's
 > >capacitance.
 > >
 > >Regards - Jim Mitchell
 > >
 > >----- Original Message -----
 > >From: "Tesla list" <tesla-at-pupman-dot-com>
 > >To: <tesla-at-pupman-dot-com>
 > >Sent: Monday, March 29, 2004 6:42 PM
 > >Subject: Re: strange vttc
 > >
 > >
 > > > Original poster: Mike Poulton <mpoulton-at-mtptech-dot-com>
 > > >
 > > > Tesla list Wrote:
 > > >  > Original poster: "claude masetto" <claudmas-at-optusnet-dot-com.au>
 > > >
 > > >  > Hello all,
 > > >  > I have been playing around with my vttc and have been taking
 > > >  > some observations with my scope and have noticed something
 > > >  > strange. The res frequency of the resonator as calculated by
 > > >  > Java TC is 342khz. When I measured it with a signal generator
 > > >  > and a scope the result was 360khz.
 > >Close
 > > >  > enough for me.
 > > >  > I then setup an antenna with a scope probe attached to it and
 > > >  > measured
 > >the
 > > >  > resonator frequency with the the coil running and noticed it
 > > >  > was
 > >255khz. The
 > > >  > coil is in tune, as best as I can get it because it performs
 > > >  > great.
 > >Twin
 > > >  > 304tl tubes with 30" spark on a good day.
 > > >  > I can't understand the difference in the two measurements. I
 > > >  > have
 > >checked
 > > >  > the results over and over.
 > > >
 > > > Is that the frequency when producing a 30" discharge? Does it
 > > > increase when you turn the power down until the discharge
 > > > disappears? If so, then the additional capacitance of the
 > > > discharge is pulling the frequency down (as expected). That is a
 > > > very large change, though -- much more than I would have
 > > > anticipated. Do you have a topload of any kind on the secondary?
 > > > ------------------------------------------------- Mike Poulton MTP
 > > > Technologies mpoulton-at-mtptech-dot-com KC0LLX (70cm AM ATV, 33cm/12cm
 > > > FM ATV, Omaha, NE)
 > > >
 > > >
 >
 >
 >